Name: Reference (APA Format) Theoretical Basis Hypothesis Independent Variables Dependent Variables Control Groups Data Analysis & Statistical Methods Discussion Summary Recommendations for Future Research Article 1 Date: Name: Article 1 Date: I am relating the article to Chapter ____ and ___________________ disorder. Relating the Article (13 points) On this page please relate the findings of the article you reviewed to the text and classroom discussions on the appropriate chapter (5, 6, or a combination). This part of the write-up should be Double Spaced, Times New Roman, 12pt font, two to three pages (2-3), APA writing style. Be sure to also place your name in the header and indicate the chapter and disorder you are writing about. Remember to Bold terms from the textbook the first time they are used and denote the relevant Chapter (Example Prognosis-Chapter 4). Class Date Week 1 Jan 13 Due Jan 22 Intro to Normal and Abnormal Behavior in Children and Adolescents Ch. 1 cont. Ch 2 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Theories and Causes Research Assessment, Diagnosis and Treatment Feb 12 Feb 19 watch online video and complete Virtual Classroom – Discussion Board Test 1 (Ch. 1-4) Ch 5 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Intellectual Disability (Intellectual Developmental Disorder) Chapter 5 Review Test 1 Ch. 5 cont. Ch 6 Quiz (Opens Mon 4:30 – Closes Wed 2:30) Week 8 Mar 2 Mar 4 Week 9 Mar 8-15 Week 10 Mar 16 Mar 18 Chapter 4 Ch. 4 cont. Review for Test 1 Week 7 Feb 24 Feb 26 Chapter 3 Ch. 3 cont. Ch 4 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Week 5 Feb 10 Week 6 Feb 17 Chapter 2 Ch. 2 cont. Ch 3 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Week 4 Feb 3 Feb 5 Chapter 1 MLK – No classes Week 3 Jan 27 Jan 29 Reading Assignments Classes begin Introductions, Syllabus Ch 1 Quiz (Opens Mon 4:30 – Closes Wed 2:30) Jan 15 Week 2 Jan 20 PGS 443 Abnormal Child Psychology M/W 3:05-4:20 Spring 2020 Topic Autism Spectrum and Childhood Schizophrenia Chapter 6 Article Review 1 (from Ch. 5 or 6) Ch. 6 cont. Ch 7 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Spring Break No classes Communication and Learning Disorders Ch. 7 cont. Ch 8 Quiz (Opens Wed 4:30 – Closes Mon 2:30) Chapter 7 Week 11 Mar 23 Mar 25 Week 12 Mar 30 Attention-Deficit/ Hyperactivity Disorder (ADHD) Interview 1 (from Ch. 5, 6 or 7) Conduct Problems Review Test 1 Depressive and Bipolar Disorders Anxiety and Obsessive-Compulsive Disorders April 29 Chapter 11 Article Review 2 Ch. 11 cont. (from Ch. 7-11) Ch 14 Quiz (Opens Mon 4:30 – Closes Wed 2:30) April 22 Week 16 April 27 Chapter 10 Ch. 10 cont. Ch 11 Quiz (Opens Mon 4:30 – Closes Wed 2:30) April 15 Week 15 April 20 Chapter 9 Ch. 9 cont. Ch 10 Quiz (Opens Mon 4:30 – Closes Wed 2:30) April 8 Week 14 April 13 Ch. 8 cont. review for Test 2 Test 2 (Ch. 5-8) Ch 9 Quiz (Opens Mon 4:30 – Closes Wed 2:30) April 1 Week 13 April 6 Chapter 8 Eating Disorders and Related conditions Interview 2 Ch. 14 cont. (from Ch. 8-11 or 14) review for exam 3 Complete Course Evaluation (bring computer, tablet or phone) Test 3 (Ch. 9-11 & 14) Last class May 1 May 2 - 3 All classes end Study Days Week 17 May 4 - 9 May 4 Finals Week FINAL Online (comprehensive) Monday, May 4th Chapter 14 5 Intellectual Disability (Intellectual Developmental Disorder) Everybody is a genius. But if you judge a fsh by its ability to climb a tree, it will live its whole life believing that it is stupid. —Albert Einstein CHAPTER PREVIEW IntellIgence and Intellectual dIsabIlIty Genetic and Constitutional Factors The Eugenics Scare Motivation Neurobiological Infuences Defning and Measuring Children’s Intelligence and Adaptive Behavior Changes in Abilities Social and Psychological Dimensions The Controversial IQ Features oF Intellectual dIsabIlItIes Clinical Description Severity Levels Prevalence 124 developmental course and adult outcomes Language and Social Behavior Emotional and Behavioral Problems Other Physical and Health Disabilities causes Inheritance and the Role of the Environment preventIon, educatIon, and treatment Prenatal Education and Screening Psychosocial Treatments dren and adults who today would be diagnosed as having an intellectual disability were labeled “idiots” and often were lumped together with persons suffering from mental disorders or medical conditions. They typically were ignored or feared, even by the medical profession, because their differences in appearance and ability were so little understood. Although age-old fears, resentment, and scorn continue to overshadow many important discoveries about subnormal intelligence, the feld of intellectual disability has experienced monumental gains over the past century in determining causes and providing services. Advances in understanding the development of children with intellectual disability, along with research in genetics, psychopathology, and other areas, have dramatically changed the face of this feld. The term intellectual disability has replaced the previous term mental retardation in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), based on consensus among professionals, advocacy groups, and the lay public. Intellectual disability is a neurodevelopmental disorder, a group of conditions with onset in the developmental period that produce impairments of social, personal, academic or occupational functioning (APA, 2013). Intellectual disability (ID) is characterized by signifcant limitations in mental abilities (such as reasoning, planning, and judgment) that result in impairments in adaptive functioning, such as conceptual, social, and practical skills needed to fulfll aspects of everyday life (Tassé et al., 2012). Although the name has changed, the three essential elements defning this condition have remained the same for the past 50 years: intellectual limitations, defcits in adaptive skills, and early onset. Importantly, modern defnitions of intellectual disability take into account a person’s intellectual functioning within the context of what is typical for that individual’s peers and culture. Cultural and linguistic diversity, as well as differences in communication, sensory, motor, and behavioral factors, must be carefully considered in determining a defcit or disability (American Association on Intellectual and Developmental Disabilities [AAIDD], 2010). Understanding improvements in knowledge about and treatment of intellectual disability, as well as understanding the prejudice and ignorance that had to be overcome, can be gained by looking at how the disorder has been viewed over the years. INTELLIGENCE AND INTELLECTUAL DISABILITY Throughout recorded history, persons with intellectual and other disabilities have suffered scorn and rejection from others, largely because of fear and ignorance. The prevailing misunderstanding and mistreatment of children with intellectual disabilities changed very little until the end of the eighteenth century, fueled by the discovery of feral children such as Victor, the “wild boy of Aveyron” (discussed in Chapter 1), and by the expansion of humanitarian efforts to assist other oppressed or neglected groups, such as slaves, prisoners, the mentally ill, and persons with physical disabilities. By the mid-nineteenth century, the concept of mental retardation had spread from France and Switzerland to much of Europe and North America. During the same period, Dr. Samuel G. Howe convinced his contemporaries that training and educating the “feebleminded” was a public responsibility, and he opened the frst humanitarian institution in North America for persons with intellectual disability—the Massachusetts School for Idiotic and Feeble-Minded Youth. Parents of children with ID can be credited with advancing a perspective and response to the need for long-term care that was completely different from the prevailing public and professional opinions. By the 1940s, parents began to meet in groups and create local diagnostic and guidance centers to increase the availability of humane care. These groups organized in 1950 to form the National Association for Retarded Children (now known as The Arc), which quickly established a scientifc board made up of representatives from every specialty possible to study, prevent, and care for persons with intellectual disability (Kanner, 1964). These efforts gained momentum when President John F. Kennedy, who had a sister with intellectual disability, formed the President’s Panel on Mental Retardation in 1962 and called for a national program to combat intellectual disability. Soon thereafter, exposés in the media of the use of solitary confnement and restraints ©iStockphoto.com/Moodboard_Images U NTIL THE MID-NINETEENTH CENTURY, chil- Ignorance resulted in the segregation of children with intellectual disabilities, who were subjected to inhumane treatment. Today, most children with ID are integrated into regular classrooms. C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 125 for persons with ID increased public awareness of and outrage at the treatment of these individuals. the eugenics scare Three generations of imbeciles are enough. —Justice Oliver Wendell Holmes Jr., commenting on the Supreme Court’s 1927 decision to uphold eugenics sterilization laws Evolutionary degeneracy theory, a pervasive nineteenthcentury phenomenon, attributed the intellectual and social problems of children with intellectual disability to regression to an earlier period in human evolution (Bowler, 1989). In fact, mental defciency experts in the nineteenth century believed they had found the “missing link” between humans and lower species (Gelb, 1995). J. Langdon H. Down, best known for the clinical description of the genetic syndrome that bears his name, interpreted the “strange anomalies” among his medical sample of persons with intellectual disability as an evolutionary throwback to the Mongol race (Down, 1866). Down believed that parents in one racial group might give birth to a child with intellectual disability who was a “retrogression” to another group. While grounded in speculation and misinformed conclusions, evolutionary degeneracy theory and its notion of inferiority received growing support by the late-nineteenth century as an explanation for insanity, mental defciency, and social deviance. A Closer Look 5.1 depicts how this popular theory was conveniently used to explain undesirable human characteristics. By 1910, the eugenics movement was gaining momentum. Eugenics was frst defned by Sir Francis Galton (Charles Darwin’s cousin) in 1883 as “the science which deals with all infuences that improve the inborn qualities of a race” (cited in Kanner, 1964, p. 128). Public and professional emphasis shifted away from the needs of persons with intellectual disability toward a consideration of the needs of society; society was to be protected from the presumable harm done by the presence of these persons in the community. Consequently, persons with intellectual disability often were blamed for the social ills of the time, which is a powerful example of how labeling a problem can quickly become an explanation for it.A Closer Look 5.2, in fact, shows a 1912 New York Times article refecting this public sentiment. The appearance, ability, and behavior of persons with intellectual disability were considered evidence of their lack of moral fber, a belief that led to the diagnostic term moral imbecile, or moron, used to describe and explain their differences. This concept became a straightforward explanation for acts of deviance and justifed wide-ranging attempts to identify and control such individuals. Morons, considered the least intellectually impaired (roughly comparable to mild intellectual disability today) were seen as a threat to society because, unlike the insane, they could easily pass for normal (Gelb, 1995). The intellectually impaired and other “undesirables” were seen as a public menace, to be feared and ostracized. defning and measuring children’s Intelligence and adaptive behavior Around 1900, the pioneering work of two French educators, Alfred Binet and Theophile Simon, led to some of the frst major advancements in the feld of children’s intellectual functioning. Binet and Simon were asked to develop a way to identify schoolchildren who might need special help in school. They approached this monumental task by developing the frst intelligence tests to measure judgment and reasoning, which they believed were basic A CLOSER LOOK 5.1 the Infamous Kallikaks Psychologist Henry Goddard, who began one of the largest training schools for intellectual disability in the early twentieth century, was also a proponent of the popular degeneracy theory and eugenics movement. In his book The Kallikak Family: A Study in the Heredity of Feeble-Mindedness (1912), Goddard traced two lines of descendants from a Revolutionary War soldier, Martin Kallikak, who fathered a child by a “feebleminded barmaid” during the war, which began the first line, and then fathered other children by a “respectable girl” he married after the war. The name “Kallikak” was invented by Goddard from a combination of two Greek words: kalos, meaning “attractive, pleasing,” and kakos, meaning “bad, evil.” 126 P a r t 2 Neurodevelopmental Disorders Goddard reported that many descendants of the first union were feebleminded, delinquent, poor, and alcoholic, whereas those of the second union were of good reputation. He claimed this outcome was evidence for the inheritance of intelligence, although he overlooked the two families’ obvious environmental differences (Achenbach, 1982). A closer look at the disclaimer from the preface to the book is telling: “It is true that we have made rather dogmatic statements and have drawn conclusions that do not seem scientifically warranted by the data.” (Based on authors’ case material.) A CLOSER LOOK 5.2 early-twentieth-century perspectives on mental retardation WEAK-MINDED FILL RANKS OF CRIMINALS DR. HENRY GODDARD SAYS SOCIAL PROBLEMS CAN BE SOLVED BY SEGREGATING THEM WOULD NOT LET THEM MARRY THIS POLICY WOULD IN TIME LARGELY REDUCE CRIMES, DISEASE, AND DRUNKENNESS, HE BELIEVES From the army of 300,000 feeble-minded persons in the United States come the recruits that swell the ranks of the drunkards, criminals, paupers, and other social outcasts. Twenty-five per cent of the girls and boys in our reformatories are lacking in mental fibre and are unable to discern the difference between right and wrong or are too weak in character to do right whenever there is any inducement to do wrong. Sixty-five per cent of the children have a mother or a father, or both, who are feeble-minded. This country has so far taken no steps to segregate these irresponsible persons, so the number of them is constantly increasing…. This army furnishes the ranks of the criminals, paupers, drunkards, the ne’er-do-wells, and others who are social misfits. Their incapacity would be a priori cause of believing that they eventually will become public charges in one form or another, and investigation, in fact, proves that the groups of criminals, paupers, etc., actually do contain large percentages of people mentally irresponsible. Source: The New York Times, March 10, 1912. processes of higher thought. These early test questions asked children to manipulate unfamiliar objects such as blocks or fgures and to solve puzzles and match familiar parts of objects. The test later became the Stanford–Binet scale, which remains one of the most widely used intelligence tests. From these beginnings in intellectual testing, general intellectual functioning is now defned by an intelligence quotient (IQ or equivalent) that is based on assessment with one or more of the standardized, individually administered intelligence tests, such as the Wechsler Intelligence Scales for Children, 4th edition (WISC-IV), the Stanford–Binet, 5th edition (SB5), and the Kaufman Assessment Battery for Children, 2nd edition (KABC-II). These tests assess various verbal and visual–spatial skills (such as knowledge of the world, reasoning, and similarities and differences) and mathematical concepts, which together are presumed to constitute the general construct known as “intelligence.” By convention, IQ scores (with a mean of 100 and a standard deviation of 15) are derived from a standardized table based on a person’s age and test score. Because intelligence is defned along a normal distribution, approximately 95% of the population has scores within 2 standard deviations of the mean (i.e., between 70 and 130). Subaverage intellectual functioning is defned, accordingly, as an IQ of about 70 or below (approximately 2 standard deviations below the mean). As we will discuss later in this chapter, the defnition of intellectual disability includes not only subaverage intellectual functioning, but also a subaverage level of adaptive functioning. Adaptive functioning refers to how effectively individuals cope with ordinary life demands, and how capable they are of living independently and abiding by community standards (Hodapp et al., 2011). Note that some children and adolescents may learn to adapt quite well to their environment despite their lower intelligence as measured by an IQ test; therefore, they would not be considered to have an intellectual disability. Table 5.1 gives examples of the three major categories of adaptive behavior (conceptual, social, and practical adaptive skills). Similar to IQ, these skills are typically TABLE 5.1 | Specific Examples of Adaptive Behavior Skills Conceptual Skills Receptive and expressive language Reading and writing Money concepts Self-directions Social Skills Interpersonal Responsibility Self-esteem Gullibility (likelihood of being tricked or manipulated) Naiveté Follows rules Obeys laws Avoids victimization Practical Skills Personal activities of daily living such as eating, dressing, mobility, and toileting Instrumental activities of daily living such as preparing meals, taking medication, using the telephone, managing money, using transportation and doing housekeeping activities Occupational Skills Maintaining a safe environment Source: From the American Association on Intellectual and Developmental Disabilities(AAIDD). C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 127 assessed using standardized instruments such as the Adaptive Behavior Assessment System—Second Edition (ABAS-II; Harrison & Oakland, 2003) or the Vineland Adaptive Behavior Scales—Second Edition (VABS-II; Sparrow, Cicchetti, & Balla, 2005). the controversial IQ If a person’s intelligence is relatively stable over time, it would be tempting to conclude that it is largely innate and fxed. On the other hand, if intellectual and cognitive development is signifcantly shaped by environment, perhaps cognitive growth can be stimulated at an early age and the level of intellectual disability decreased. Because intelligence is measured in relation to agemates, IQ generally is stable from childhood through adulthood (Carr, 2005; Whitaker, 2008). One exception to this general rule is IQ that is measured during early infancy, when considerable fuctuation can still occur. For typically developing children, IQ measured prior to the frst birthday has virtually no correlation with the IQ score achieved at age 12; however, by the time children are 4 years old, the correlation with IQ 12 years later is high (r 5 0.77) (Neisser et al., 1996). The picture is dramatically different, however, for infants and children with developmental delays or intellectual disability. At the lower IQ levels (say, below 50), even the youngest infants show IQ stability over time, with correlations between infant and childhood test scores ranging from 0.50 to 0.97 (Sattler, 2006). Researchers have discovered a similar pattern of IQ stability from middle childhood to young adulthood among children with mild to moderate intellectual delays (Mortensen et al., 2003; Toth & King, 2010). Even though the IQ of cognitively delayed infants and young children is unlikely to change, proper environmental circumstances will help children reach their fullest potential. Since the early 1960s, researchers in child development and intellectual disability have been investigating ways to provide early stimulation programs that will help children with developmental delays to build on their existing strengths. Despite its strong genetic component, mental ability is always modifed by experience. Not surprisingly, infancy through early childhood offer the most signifcant opportunity for infuencing intellectual ability because of the young child’s rapid brain development and response to environmental stimulation (Campbell & Ramey, 2010; Pungello et al., 2010). The importance of genetic makeup not with standing, for some individuals IQ can and does change by 10 to 20 points between childhood and adolescence 128 P a r t 2 Neurodevelopmental Disorders (Simonoff, Bolton, & Rutter, 1996). Differences in outcome vary widely in relation to opportunities for each child to learn and develop. Children who live in healthy environments, where caregivers provide appropriate levels of stimulation and help them manage ambient levels of stress, are most likely to reach their full potential. Moreover, tests can sample only a limited spectrum of intellectual ability, and are incapable of accounting for each individual’s unique learning history (Sattler, 2006). Are We Really Getting Smarter? Scores have risen sharply since the beginning of IQ testing, ranging from a 5- to a 25-point increase in a single generation (Kanaya, Scullin, & Ceci, 2003). When James Flynn brought this phenomenon of rising IQ scores to the attention of scientists in 1987, it became known as the “Flynn effect.” The gain has averaged about 3 IQ points per decade, adding up to more than a full standard deviation since the 1940s. Once a test is re-normed (about every 15 to 20 years) the mean is reset to 100, resulting in a brief reversal of this gain in IQ scores. In attempting to explain the Flynn effect, scientists have considered the rising standards of living, better schooling, better nutrition, medical advances, more stimulating environments, even the infuence of computer games and complex toys (Flynn, 2007; 2012). IQ tests themselves have once again come under scrutiny, as have children’s exposure to problems similar to those on the tests—like the mazes and puzzles they see on their cereal boxes and fast-food bags. Yet the consistent IQ gains are too large to be the result simply of increased familiarity with testing methods. Although the exact cause of the effect remains unknown, experts on children’s intelligence suspect that the gains refect a meaningful aspect of intellectual growth and development. A relatively permissive and child-focused parenting style has emerged during recent decades, which may have given children greater facility with language and stronger overall cognitive capacity. Moreover, there are unprecedented cultural differences between successive generations—daily life and occupational experiences are far more complex today than in the past. There is a possible downside to the Flynn effect, however. Test scores drop an average of 5.6 points among persons with borderline and mild intellectual disability after a test is re-normed, which can have a signifcant impact on a child’s eligibility for proper educational placement and other related services (Kanaya et al., 2003). Are IQ Tests Biased or Unfair? Many express concern over the relatively lower mean of the distribution of intelligence test scores of African Americans, typically about 1 standard deviation (about 15 IQ points) below that of whites (Jencks & Phillips, 1998). Although recent estimates suggest that African Americans have gained 4 to 7 IQ points on nonHispanic whites since 1972 (Dickens & Flynn, 2006), considerable concern remains as to why differences in test results exist at all. The controversy in IQ score differences is fueled by researchers who argue that IQ is 80% heritable and therefore largely genetically determined (Rushton & Jensen, 2006). Other researchers argue that economic and social inequality—not test bias or racial differences—are the simplest explanations for existing group differences in test performance between African Americans and whites (Brooks-Gunn, Klebanov et al., 2003; Nisbett et al., 2012). For example, when personal and family background characteristics are statistically controlled for, African American and white children achieve similar test scores. However, once these students enter school, the gap between white and African American children grows, which researchers believe may be due to lower-quality schools in the lowerincome neighborhoods where some African-Americans live (Levitt & Fryer, 2004; Nisbett, 2009). A much higher proportion of African Americans and children from other ethnic minority groups in the United States as well as in other countries are poor and have fewer opportunities for advancement as compared with their white counterparts. Poverty and inequality are linked to poor nutrition, inadequate prenatal care, fewer intellectual resources, and similar realities that can have negative effects on children’s developing intelligence (Christian et al., 2013; Sternberg, 2010). Section Summary Intelligence and Intellectual Disability ● ● ● ● The early history of intellectual disability was plagued by ignorance and blame. By the mid-twentieth century, progress toward understanding intellectual disability moved more rapidly, as parents, researchers, politicians, and the public sought better answers regarding its causes and better ways to assist both children and adults with ID. Intellectual disability refers to limitations in both intelligence and adaptive behavior. However, many persons with this disorder are capable of learning and of leading fulflling lives. Despite its drawbacks, the IQ has become a principal standard for diagnosing intellectual disability, combined with other skills and abilities of the child. FEATURES OF INTELLECTUAL DISABILITIES M AT T H E W Gaining at His Own Pace Matthew was almost 6 years old when he was referred for a psychological assessment. His brief school record described him as “developmentally delayed,” and the school was concerned that his speech and social skills were very limited. He also had temper tantrums at home, and his new frst-grade teacher had expressed concerns about his aggressive behavior toward other children in his class. I frst met with Matt in his home. “Show me some of your favorite toys or games,” I suggested, unsure of how comfortable he was with a stranger at his home. He was a thin boy, with curly hair and a cautious, reserved expression. He looked me over for what must have been several minutes while I spoke with his mother and father. Although he said “OK,” I wasn’t sure he meant it—he stayed put and seemed uninterested in my request. Matt had turned 6 a few months ago, but I noticed that his clothes, games, and vocabulary were closer to those of my 3-year-old daughter. “I don’t want to talk about school stuff!” he exclaimed, quite loudly, when I asked about his favorite subjects. “I only like recess and lunchtime—the stuff they won’t let you do till the bell rings!” There was a certain degree of truth, and humor, to his statement, although I don’t think he intended it as such. Matt became a bit more interested when I brought out some testing materials. He completed with ease a puzzle designed for toddlers and was able to make the sounds of animals in the puzzle. But his emotional expression remained subdued, with little spontaneous laughter or joy. He seemed watchful and cautious. “Tell me about this story,” I said to Matt, holding up a card showing some animals arguing over a ball. “What do you think is going on in this picture, and what are the characters, like the elephant and the zebra, thinking and feeling?” Matt started right in: “He’s mad ’cuz the zebra grabbed the ball and ran away with it into the woods. That’s all I see.” My attempts to elicit more detail were met with only an inquisitive look. After a few minutes of this, we took a break and brought out his toys. “Do you like Harry Potter?” he asked. We found some common ground among the characters in the book, and under these “ideal” conditions, Matt’s communication became more at ease and spontaneous. He expressed a wide range of emotion throughout the interview, and settled in to his own comfortable level of relating. Gradually, his language production increased as we continued with the more relaxed play sessions. (continues) C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 129 (continued) In private, Matt’s mother told me about his behavior problems around other children, such as hitting, biting, throwing objects, and demanding attention. I saw a brief episode of it myself when his 3-year-old sister came into the room: “Get out! This man is here to play with me!” Overall, Matt behaved like a much younger child—for example, by shouting or pushing when he couldn’t get his way immediately. When we met for the second time, in my offce, Matt’s WISC-IV full-scale IQ was assessed at 64, and his adaptive abilities score was 68, based on his mother’s report on the Vineland Adaptive Behavior Scales. Despite his mild intellectual disability, however, Matt has been gaining over the past year in school, and he is showing a healthy gain in his developmental milestones as well. (Based on authors’ case material.) You judge a person by how they look or how they talk or what the tests show, but you can never really tell what is inside the person. —Ed, 27 years old, who was labeled mentally retarded and placed in a state institution at age 15 (Bogdan & Taylor, 1982) Intellectual disabilities encompass perhaps the widest variation in cognitive and behavioral abilities of any childhood disorder. Some of these children function quite well in school and the community, whereas others with signifcant physical and cognitive impairments require daily supervision and assistance. The situations of Matthew, age 6, and Vanessa, age 8, illustrate some of the unique challenges children with intellectual disability face every day. Matthew was diagnosed as having mild intellectual disability. Although his speech and language development were delayed, he was developing effective verbal skills and was capable of attending a regular classroom. Establishing friendships with children at school was sometimes problematic because he was often slow at understanding the rules of games and was teased by some children because of his slowness. Vanessa was diagnosed as having moderate intellectual disability. She could feed and dress herself with minimum assistance, and she communicated in short sentences, although her speech was not always discernible to people outside her family. Vanessa required daily assistance to complete her routines, but she too was able to attend a local school during part of the day. As these cases show, the special needs of both children were sometimes overshadowed by economic and educational limitations, which required creativity and coordinated assistance on the part of parents, teachers, and other professionals. 130 P a r t 2 Neurodevelopmental Disorders VA N E S S A Gaining at Home Vanessa is an 8-year-old girl with moderate intellectual disability (IQ 5 52) and limited communication skills. She was diagnosed prior to her fourth birthday, after medical and psychological examinations were undertaken to determine why she was not making many speech sounds or learning basic self-help skills. Vanessa’s mother told us about how her daughter’s special needs were poorly met while she was a resident in a special school for children with intellectual disabilities, and how this led to her parents’ decision to raise Vanessa at home with the help of their community: When our family moved here we were told that we would receive $75 per month to care for her at home, or she could live at the Children’s Training Center. Vanessa had been diagnosed with moderate intellectual disability prior to her fourth birthday, and we knew that we could not care for her daily needs at home with the limited assistance being offered. So we made the diffcult decision to place her at the training center. But, even though Vanessa came home every weekend, we felt there was something missing from her life; something beyond staff care and attention was needed to foster her growth. About 2 years later, things changed dramatically. Vanessa was injured by another resident, and we decided that she should return home once and for all. We made every effort to fnd services she needed for her training and education in our own community. She now attends an integrated classroom at the same school as her older brother, and her teachers have noticed strong gains in her behavior and language. She participates in recreational programs, and has become an accomplished swimmer and basketball player. (Based on authors’ case material.) clinical description When the psychiatrist interviewed me he had my records in front of him—so he already knew I was mentally retarded. It’s the same with everyone. If you are considered mentally retarded there is no way you can win. There is no way they give you a favorable report. —Ed, describing part of his intake interview at the state institution (Bogdan & Taylor, 1982) Children with intellectual disability show a considerable range of abilities and interpersonal qualities. With proper assistance, children with mild intellectual impairments, such as Matthew, can carry out their daily routines much like other children. They can attend a regular classroom, adjust to the demands of physical and intellectual challenges, and develop meaningful and lasting relationships with peers and adults. Many show normal physical development and can learn the physical coordination required to ride a bike. Others, like Vanessa, who have more severe impairments, will require greater daily supervision and care throughout their childhood and sometimes into early adulthood, at which time they may have developed the necessary skills to live more independently. Both Matthew and Vanessa, however, experience limitations that involve most areas of daily living. Their most obvious diffculties are learning to communicate effectively, due to their limited speech and language skills. Although Matthew eventually learned effective verbal communication, for several years Vanessa had to rely on sign language and nonverbal expressions or gestures to express her needs. Both children had problems developing friendships with other children because of their limited ability to comprehend what other children were expressing, especially during games and social activities that require stamina and formal rules. Many cognitive abilities, such as language and problem solving, are affected; therefore, most children with ID have diffculty with some aspect of learning. The degree of diffculty depends on the extent of cognitive impairment, which is the primary reason current defnitions of intellectual disability emphasize this aspect. Table 5.2 summarizes the DSM-5 diagnostic criteria for intellectual disability (also known as intellectual developmental disorder). These criteria consist of three core features that describe this disorder in both children and adults. First, such individuals must have defcits in the intellectual functions of reasoning, problem-solving, planning, abstract thinking, judgment, academic learning, and learning from experience. Such defcits are typically determined by clinical assessment and intelligence testing. But note that the DSM-5 does not provide specifc IQ cutoff limits for meeting diagnostic criteria, as was the case in previous editions. The second criterion for diagnosing intellectual disability requires defcits in adaptive functioning, which result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. In effect, a subnormal IQ score is not suffcient to warrant a diagnosis of intellectual disability. A person also must show signifcant limitations in adaptive behavior, such as communication, self-care, social/interpersonal skills, or functional academic or work skills (Lancioni et al., 2009). This aspect of the defnition is important because it specifcally excludes persons who may function well in their own surroundings, yet for various reasons they may not perform well on standard IQ tests. Importantly, TABLE 5.2 | Diagnostic Criteria for Intellectual Disability (Intellectual Developmental Disorder) Intellectual disability (intellectual developDSM-5 mental disorder) is a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains. The following three criteria must be met: (A) Deficits in intellectual functions, such as reasoning, problem-solving, planning, abstract thinking, judgment, academic learning and learning from experience, confirmed by both clinical assessment and individualized, standardized intelligence testing. (B) Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the adaptive deficits limit functioning in one or more activities of daily life, such as communication, social participation, and independent living, across multiple environments, such as home, school, work, and community. (C) Onset of intellectual and adaptive deficits during the developmental period. Note: The diagnostic term intellectual disability is the equivalent term for the ICD-11 diagnosis of intellectual developmental disorders. Specify current severity (see Table 5.3): Mild, Moderate, Severe, or Profound Source: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, American Psychiatric Association. whether a child or adolescent exhibits these various adaptive skills is related not only to ability, but also to experience and opportunity. Using public transportation, walking to a neighborhood store, and making simple purchases all can be affected by the individual’s place of residence (urban versus rural, for example), or their concerns about neighborhood safety. Clinicians and educators must make educated guesses regarding a person’s potential for performing a certain task if the person has not had experience with a particular skill on the test. The third and fnal criterion for intellectual disability stipulates that the child’s intellectual and adaptive defcits must have begun during the developmental period (generally considered to be before age 18). The purpose of establishing this upper limit for the age of onset is twofold. First, it acknowledges that intellectual disability is a developmental disorder that is evident during childhood and adolescence. Problems in learning and comprehension typically occur during this time of rapid brain development. Second, this age criterion rules out persons who may show mental defciencies caused by adult-onset degenerative diseases, such as Alzheimer’s disease, or by head trauma. C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 131 A diagnosis of intellectual disability specifes the level of impairment—mild, moderate, severe, or profound—similar to other disorders in the DSM-5. Although these four levels of impairment remain the same as in previous editions, they are specifed in considerably more detail, as described below. Similarly, as mentioned above, the DSM-5 does not provide specifc IQ cutoffs for meeting diagnostic criteria, to allow greater focus on adaptive functioning and levels of support that may be required. However, individuals with ID generally have an IQ score 2 standard deviations or more below the population mean (e.g., 70 points or below, allowing for a margin of error of 5 points). Changes in DSM-5 criteria for ID have sought to focus more on the nature or qualities of the person rather than on the IQ score, based on years of controversy over IQ measurement and social infuences (Toth & King, 2010). These criteria are not likely to result in a major shift in the numbers of people diagnosed with ID—as before, the majority of people diagnosed with intellectual disability fall into the mild range. However, because the ramifcations of diagnosing someone with intellectual disability can be serious, every attempt is made to consider other factors that may limit one’s mental abilities. As Ed described so well, a careful bal- ance must be struck between identifying the special needs of persons with intellectual disabilities and labeling them as having a disability on the basis of somewhat arbitrary criteria (Schalock et al., 2007). In addition, the defnition and identifcation of intellectual disability depend somewhat on our social institutions. When children enter the school system, it is a signifcant point at which their abilities are compared and defciencies are most likely to be detected. If children are placed in a poorly matched learning environment, their developmental progress can be disrupted. Following their school years, persons with mild intellectual disability often blend into the larger population, and their “diagnosis” no longer has as much meaning (Hodapp et al., 2011). severity levels The four levels of severity noted in Table 5.3 are defned on the basis of adaptive functioning in three primary domains: conceptual, social, and practical. These defnitions refect a major shift in focus away from IQ scores and more toward needed supports. This shift emphasizes the resources and strategies necessary to promote the overall adjustment and well-being of a person with intellectual disability. Specifc needs of T A B L E 5 . 3 | Severity levels for Intellectual Disability (Intellectual Developmental Disorder) Severity Level Mild Conceptual Domain ● ● ● For preschool children: no obvious conceptual differences. For school-aged children and adults: learning difficulties in academic skills involving reading, writing, arithmetic, time, or money, the support needed in one or more areas to meet age-related expectations. In adults: impaired abstract thinking, executive function, short-term memory, and functional use of academic skills. There is a somewhat concrete approach to problems and solutions as compared with age-mates. Social Domain Practical Domains Children: Children: ● ● ● ● ● ● ● Show immaturity in social interactions. Have difficulty in perceiving peers’ social cues. Show immature or more concrete communication, conversation, and language for age. Show difficulty regulating ageinappropriate emotion and behavior; may be noticed by peers. Have limited understanding of risk in social situations. Display immature social judgment for age. Are at risk of being manipulated by others (gullibility). ● ● May function age-appropriately and maintain personal care. May need some support with complex daily living tasks as compared with peers. Adults: ● ● ● ● ● Typically need support with shopping, transportation, home and child care, organizing, cooking, and money management. Participate in recreational skills similar to age-mates, but need support with well-being and organization. May hold jobs that do not emphasize conceptual skills. Need support with health care and legal decisions and with learning a vocation. Often need support raising a family. (continues) 132 P a r t 2 Neurodevelopmental Disorders T A B L E 5 . 3 | Severity levels for Intellectual Disability (Intellectual Developmental Disorder) (continued) Severity Level Moderate Conceptual Domain Social Domain Practical Domains Conceptual skills lag markedly behind those of peers. Individual: Adults: ● ● ● ● ● Severe For preschoolers, language and pre-academic skills develop slowly. For school-aged children, academic skill develops slowly and are limited as compared with those of peers. For adults, academic skill development is typically at an elementary level, and support is required for all use of academic skills and work and personal life. Adults need daily assistance with conceptual tasks of dayto-day life. Individual: ● ● ● Attains few conceptual skills. Has little understanding of written language or of concepts involving numbers. Needs caretakers to provide problem-solving support throughout life. ● ● ● ● ● ● ● Individual: ● ● ● ● ● ● Profound Shows marked differences from peers in social and communicative behavior across development. Uses less complex spoken language as primary tool for social communication. Shows capacity for relationships in lifelong ties to family and friends. May inaccurately perceive or interpret social cues. Shows limited social judgment and decision-making abilities. Needs caretakers to assist with life decisions. Has friendships with typically developing peers that are often affected by communication or social limitations. Needs social and communicative support in work settings. Exhibits limited spoken language in terms of vocabulary and grammar. Speaks using single words or phrases and may be supplemented through augmentative means. Exhibits speech and communication focused on the present. Uses language for social communication more than for explication. Understands simple speech and gestural communication. Has relationships with family members and familiar others for pleasure and help. Individual: Conceptual skills generally involve the physical world Has very limited understanding of rather than symbolic processes. symbolic communication in speech or gestures. Individual: May understand some simple instrucMay use objects in goaltions or gestures. directed fashion for self-care, Nonverbally, nonsymbolically expresses work, and recreation. most desires and emotions. Uses visuospatial skills, such Enjoys relationships with well-known as matching and sorting family members, caretakers, and familiar based on physical characterothers. istics. However, co-occurring Initiates a response to social interactions motor and sensory impairthrough gestural and emotional cues. ments may prevent funcMay have co-occurring sensory and tional use of objects. physical impairments, which may prevent many social activities. ● ● ● ● ● ● Individual: ● ● ● ● ● ● ● ● ● Needs support for daily living (e.g., eating, dressing, bathing, elimination). Needs supervision at all times. Unable to make responsible decisions regarding well-being of self or others. Needs long-term teaching and ongoing support in all domains to acquire skills. Maladaptive behavior, including self-injury, is present in a significant minority. Individual: ● ● Eat, dress, eliminate, and practice hygiene age-appropriately after extended teaching, time practicing, and reminders. Participate in all typical household tasks after extended period of teaching and ongoing. May achieve independent employment in jobs that require limited conceptual communication skills, but need considerable support from co-workers/supervisors. Develop a variety of recreational skills, but will need additional, extended supports and learning opportunities. Maladaptive behaviors present in a significant minority and cause social problems. ● ● ● ● ● ● ● Is dependent on others for all aspects of daily physical care, health, and safety, but may participate in some of these activities. Without severe physical impairments may assist with some daily work tasks at home. May perform simple actions with objects, with extended support, related to vocational activities. Enjoys recreational activities with the support of others. May have physical and sensory impairments that prevent participation (beyond watching) in home, recreational, and vocational activities. May exhibit maladaptive behaviors (only a significant minority.) Source: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, American Psychiatric Association. C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 133 the individual are evaluated and strategies and services are developed to optimize individual functioning. Concrete examples of support areas and support activities are shown in Table 5.4. Children with intellectual disability vary widely in their degree of disability. Some show cognitive impairments from early infancy, such as limited vocalizations or poor self-regulation, whereas other impairments may go relatively unnoticed throughout the elementary school years. Because of the wide variation in cognitive functioning and impairment, classifcation systems for intellectual disability have always attempted to delineate various degrees of cognitive impairment. The DSM-5 has continued the tradition by specifying disability as mild, moderate, severe, or profound; however, these designations are based primarily on ability and needed supports rather than on IQ scores, as in the past. Children and adolescents with mild intellectual disability constitute the largest group; it is estimated that as many as 85% of people with ID have the mild form of the disorder (King et al., 2009). Children with mild intellectual disability often show small delays in development during the preschool years, but typically are not identifed until academic or behavior problems emerge during the early elementary years. This category also has an overrepresentation of minority group members, most likely due to the social and economic disparities noted previously. As a group, children with mild intellectual disability typically develop social and communication skills during the preschool years (ages 0–5 years), perhaps with modest delays in expressive language. They usually have minimal or no sensorimotor impairment and engage with peers readily (although peers may see them as immature). Like Matthew, some children with mild ID may fnd school and peer relationships to be challenging. By their late teens, these children can acquire academic skills up to approximately the sixth-grade level. During their adult years, they usually achieve social and vocational skills adequate for minimum self-support, but may need supervision, guidance, and assistance, especially when under unusual social or economic stress. With appropriate supports, individuals with mild intellectual disability usually live successfully in the community, either independently or in supervised settings. Persons with moderate intellectual disability constitute about 10% of individuals with ID. Children and adolescents at this level of impairment are more intellectually and adaptively impaired than someone with mild intellectual disability, and usually they are identifed during the preschool years, when they show delays in reaching early developmental milestones. By 134 P a r t 2 Neurodevelopmental Disorders TABLE 5.4 | Examples of Support Areas and Support Activities Teaching and Education Activities: ● ● ● ● Interacting with trainers and teachers and fellow trainees and students Learning and using problem-solving strategies Using technology for learning Learning and using functional academics (reading signs, counting change, etc.) Home Living Activities: ● ● ● ● Preparing and eating food Housekeeping and cleaning Dressing Bathing and taking care of personal hygiene and grooming needs Community Living Activities: ● ● ● ● Using transportation Participating in recreation and leisure activities Visiting friends and family Shopping and purchasing goods Employment Activities: ● ● ● ● Learning and using specific job skills Interacting with co-workers Completing work-related tasks with speed and quality Accessing and obtaining crisis intervention and assistance Health and Safety Activities: ● ● ● ● Accessing and obtaining therapy services Avoiding health and safety hazards Accessing emergency services Maintaining mental health/emotional well-being Behavioral Activities: ● ● ● ● Learning and making appropriate decisions Incorporating personal preferences into daily activities Maintaining socially appropriate behavior in public Controlling anger and aggression Social Activities: ● ● ● ● Participating in recreation and leisure activities Making appropriate sexual decisions Making and keeping friends Engaging in loving and intimate relationships Protection and Advocacy Activities: ● ● ● ● Managing money and personal finances Protecting self from exploitation Exercising legal rights and responsibilities Using banks and cashing checks Source: Frequently Asked Questions on Intellectual Disability and the AAIDD Definition, by American Association on Intellectual and Developmental Disabilities (AAIDD), 2010. the time they enter school, these children may communicate through a combination of single words and gestures, and show self-care and motor skills similar to an average 2- to 3-year-old. Many persons with Down syndrome function at the moderate level of impairment. Because their social judgment and decision-making abilities are limited, children and youth with moderate ID often require supportive services to function on a daily basis. Like Vanessa, most individuals with this level of intellectual disability acquire limited communication skills during their early years, and by age 12 they may be using practical communication skills. They beneft from vocational training and, with moderate supervision, can attend to their personal care. They also can beneft from training in social and occupational skills, but they are unlikely to progress beyond the second-grade level in academic subjects. Adolescents with moderate intellectual disability often have diffculty recognizing social conventions, such as appropriate dress or humor, which interferes with peer relationships. By adulthood, persons with moderate intellectual disability typically adapt well to living in the community and can perform unskilled or semiskilled work under supervision in sheltered workshops (specialized manufacturing facilities that train and supervise persons with intellectual disability) or in the general workforce. Those with severe intellectual disability constitute approximately 4% of persons with ID. Most of these individuals suffer one or more organic causes of impairment, such as genetic defects, and are identifed at a very young age because they have substantial delays in development and visible physical features or anomalies. Milestones such as standing, walking, and toilet training may be markedly delayed, and basic self-care skills are usually acquired by about age 9. In addition to intellectual impairment, they may have problems with physical mobility or other health-related problems, such as respiratory, heart, or physical complications. Most persons functioning at the severe level of intellectual disability require some special assistance throughout their lives. During early childhood they acquire little or no communicative speech; by age 12, they may use some two- to three-word phrases. Between 13 and 15 years of age, their academic and adaptive abilities are similar to those of an average 4- to 6-year-old. They proft to a limited extent from instruction in pre-academic subjects, such as familiarity with the alphabet and simple counting, and can master skills such as sight reading “survival” words such as “hot,” “danger,” and “stop.” During their adult years, they may be able to perform simple tasks in closely supervised settings. Most adapt well to life in the community, in group homes or with their families, unless they have an associated disability that requires specialized nursing or other care (Toth & King, 2010). Persons with profound intellectual disability constitute approximately 2% of those with ID. Such individuals typically are identifed in infancy because of marked delays in development and biological anomalies such as asymmetrical facial features. During early childhood they show considerable impairments in sensorimotor functioning; by the age of 4 years, for example, their responsiveness is similar to that of a typical 1-year-old. They are able to learn only the rudiments of communication skills, and they require intensive training to learn basic eating, grooming, toileting, and dressing behaviors. Persons with profound intellectual disability require lifelong care and assistance. Almost all of these individuals show organic causes for their ID, and many have severe co-occurring medical conditions, such as congenital heart defect or epilepsy, that sometimes lead to death during childhood or early adulthood. Most of these individuals live in supervised group homes or small, specialized facilities. Optimal development may occur in a highly structured environment with constant aid and supervision and an individualized relationship with a caregiver. Motor development, as well as self-care and communication skills, may improve if appropriate training is provided. For example, persons with profound intellectual disability usually can perform simple tasks, such as washing their hands and changing their clothes, provided they have close supervision. The DSM-5 criteria for ID focuses on needed supports, which refects the consensus that determining the level of functioning of an individual with intellectual disability should be based on the interaction between the person and the environment (AAIDD, 2010). The criteria also remove specifc IQ cutoff scores or ranges, which acknowledges that IQ scores are approximations of a person’s mental abilities that require additional knowledge of their actual abilities. With a DSM-5 diagnosis of intellectual disability (moderate severity), Vanessa would likely also receive the following descriptive diagnosis: “Vanessa is a child with intellectual disability who needs limited supports in home living, academic skills, and development of self-help skills.” Matthew’s diagnosis of intellectual disability (mild severity) might also clarify: “Matt is a child with intellectual disability who requires support on an as-needed basis, especially during stressful or demanding times—for example, during the transition to school, when making new friends, and when faced with new academic challenges.” C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 135 Based on available evidence and estimates, the total number of children and adults with intellectual disability is approximately 1% of the general population (Maulik et al., 2011). However, each person applies his or her own cognitive abilities in unique ways that may be more or less adaptive in her or his own environment. Thus, prevalence estimates vary across time and across countries as a result of IQ measurement problems, different defnitions of ID, and varying study designs (Witwer, Lawton, & Aman, in press). Sex Ratio Among children with mild intellectual disability (by far the most common diagnosis), males outnumber females at a ratio of 1.6:1. Males outnumber females among the other levels of severity as well, but these ratios are inconsistent across studies and tend to be small. Similar to racial differences in the diagnosis of intellectual disability, gender differences in ID may be an artifact of identifcation and referral patterns rather than true differences in prevalence (Einfeld et al., 2010). If a true male excess of intellectual disability does exist, researchers suspect this may be due to the occurrence of X-linked genetic disorders such as fragile-X syndrome (discussed later in the chapter), which affect males more often than females (Handen, 2007). Socioeconomic and Cultural Infuences It is a well-established fnding that intellectual disability is more prevalent among children of lower socioeconomic status (SES) and children from minority groups (Witwer et al., in press). This link is found primarily among children in the mild intellectual disability range; children with more severe levels are identifed almost equally in different racial and economic groups. Whether or not signs of organic etiology are present, diagnoses of mild intellectual disability increase sharply from near zero among children from higher SES categories to about 2.5% in the lowest SES category (APA, 2000). These fgures indicate that SES factors play a suspected role both in the cause of intellectual disability and in the identifcation and labeling of persons with intellectual disability (Maulik et al., 2011). The overrepresentation of minority and low-SES children in the group with mild intellectual disability is a complicated and unresolved issue. As we noted, average IQ levels for the African American population are lower than IQ levels found in the white population, resulting in more African American children among samples of children with mild intellectual disability. What specifc environmental circumstances might create such an imbalance in IQ fndings? To answer this 136 P a r t 2 Neurodevelopmental Disorders Black-White IQ differences (by points) prevalence 220 218 216 214 212 210 28 Child characteristics Family income Maternal Home characteristics environment ● F I G U R E 5 . 1 | Factors accounting for differences in IQ scores between white and African American children at 5 years of age. Based on data from Brooks-Gunn, J., Klebanov, P. K., Smith, J., Duncan, G. J., & Lee, K. (2003). The Black-White test score gap in young children: Contributions of test and family characteristics. Applied Developmental Science, 7(4), pp. 239–252 question, Brooks-Gunn et al. (2003) tested the theory that the differences can be partially explained based on social and economic disadvantage. They accounted for initial IQ differences of over 17 points in African American versus white children by the independent effects of economic deprivation, home environment, and maternal characteristics. As shown in ● Figure 5.1, initial IQ differences were almost 18 points between a sample of African American and white children at 5 years of age, controlling for gender and birth weight. However, these differences were reduced by about 71% after adjusting for differences in poverty and home environment. Similar gains in IQ performance are found when children are adopted from working-class into middle-class homes, reinforcing the signifcant role of the environment in shaping one’s intellectual and adaptive abilities (Nisbett et al., 2012). These data remind us that the likelihood of a diagnosis of intellectual disability is shaped and infuenced by social and cultural forces such as racial discrimination, poverty, and cultural insensitivity (Emerson, 2012). Section Summary Features of Intellectual Disabilities ● ● The DSM-5 criteria for intellectual disability consist of defcits in intellectual functioning (confrmed by IQ testing and clinical assessment), defcits in adaptive functioning, and onset of intellectual and adaptive defcits during the developmental period. Children with intellectual disability vary widely in their degree of disability and level of functioning. ● ● ● IQ scores are no longer used to determine level of impairment. Rather, DSM-5 describes four levels of severity— mild, moderate, severe, or profound—based on adaptive functioning that determines a person’s level of needed supports. Intellectual disability occurs in an estimated 1% of the population, more often among males than females. Intellectual disability occurs more often among children from lower socioeconomic and minority groups. Economic disadvantage and discrimination practices often account for these fndings. DEVELOPMENTAL COURSE AND ADULT OUTCOMES To appreciate the manner in and extent to which children with intellectual disabilities achieve various developmental milestones, consider how typically developing children express themselves. An infant exploring his or her world relies on primitive sensorimotor functions— touching, tasting, and manipulating objects—to learn about the environment. At this stage of development everything is new, and the brain is establishing literally millions of new connections each day. Then, between 18 and 24 months of age, the toddler begins to acquire language and to draw on memories of past experience to aid in understanding the present. For an intellectually normal child, it is during this stage that the child’s environmental conditions and opportunities are known to play a crucial role in fostering enthusiasm for learning and in establishing the roots of intellectual sophistication. Although the majority of children with ID progress through each developmental milestone in roughly the same manner as other children, important differences in their developmental accomplishments are evident. Much of the knowledge about other issues involved in the developmental course and adult outcomes for children with intellectual disability is derived from studies of children with Down syndrome. Chromosome abnormalities are the single most common cause of moderate to severe intellectual disability. Down syndrome is the most common disorder resulting from these abnormalities. children with Down syndrome, along with their parents, have frequently participated in studies comparing their development with that of their normally developing peers. Dan, a 15-year-old with Down syndrome, describes how his early development was similar to, but much slower than, that of his younger brother. Dan, with moderate intellectual disability, is describing how his younger brother Brian, with normal DAN With His Brother’s Help When I was almost 3 and my sister was 5, we had a baby brother. I helped feed him and take care of him until he was almost 3. I was 5 by then, and could do most of the things he could do, but about that time he caught up to me. I could still do some things he couldn’t, but not many. He could do some things I had trouble with. We became good friends. Every time he learned a new skill, I would either learn it with him, or he would teach me later. I was really little for my age, so we were pretty close in size. We shared a bunk bed, toys, and clothes. We learned to do a lot of things together. When he learned to ride a bike, and I wasn’t ready to learn yet, mom and dad got me a Powerwheel motorized bike so I could ride, too. When he learned to read, he taught me how, too. When he played baseball and football, he took me with him. In those days, I still went to school in another district, so most of my friends were his friends. Now that we go to the same school it is sometimes hard for him to remember that I have my own friends, too. I have to tell him I am the big brother. He sometimes gets teased at school because he is my brother, but he is learning to explain instead of fght. Mostly, the kids are all nice to us. (Based on authors’ case material.) intelligence, caught up with him by the time Brian was 2 years old, and progressed through developmental milestones at a faster pace. Does Dan’s development follow the same organized sequence as Brian’s? Will his development show specifc defcits in certain intellectual abilities such as language? Or will he eventually catch up? This case illustrates the developmental-versus-difference controversy (Weiss, Weisz, & Bromfeld, 1986), an issue that has intrigued those in the feld of child development and intellectual disability for some time. Simply stated, the developmental-versus-difference controversy is this: Do all children—regardless of intellectual impairments— progress through the same developmental milestones in a similar sequence, but at different rates? Or do children with intellectual disability develop in a different, less sequential, and less organized fashion? The developmental position, which applies primarily to individuals not suffering from organic impairment, consists of two primary hypotheses: First, the similar sequence hypothesis argues that all children, with or without intellectual disability, pass through stages of cognitive development in an identical (invariant) order; they differ only in their rate and C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 137 138 P a r t 2 Neurodevelopmental Disorders same developmental sequences as his younger brother, but at a slower pace. motivation Many children who fall within the range of mild intellectual disability are bright enough to learn and to attend regular schools and classrooms. However, they are more susceptible to a sense of helplessness and frustration, which places additional burdens on their social and cognitive development. As a consequence, they begin to expect failure, even for tasks they can master; in the absence of proper instruction, their motivation to tackle new demands decreases (Harris, 2006). Ed, describing his memory of comments made by his teacher in elementary school, expresses this phenomenon well: Her negative picture of me stood out like a sore thumb. That’s the problem with people like me—the schools and teachers fnd out we have problems, they notice them, and then we are abandoned. That one teacher was very annoyed that I was in her class. She had to put up with me. (Bogdan & Taylor, 1982) Children with intellectual disability, consequently, expect little success, set lower goals for themselves, and settle for minimal success when they are able to do better, as compared with typically developing children of their same mental age (Weisz, 1999). This learned helplessness may be unwittingly condoned by adults. When they are told a child is “retarded,” adults are less likely to urge that child to persist after failure than they are to urge a normal child at the same level of cognitive development. On the other hand, young children with mild intellectual disability improve in their ability to remain on task and they develop goal-directed behavior when ©Denis Kuvaev/Shutterstock.com upper limit of development (Bennett-Gates & Zigler, 1998). Second, the similar structure hypothesis suggests that children with intellectual disability demonstrate the same behaviors and underlying processes as typically developing children at the same level of cognitive functioning (such as Dan and his younger brother were at ages 5 and 2). That is, if children with intellectual disability are matched to typically developing children by their mental age, then the children with intellectual disability will show equivalent performance on cognitive tasks, such as problem solving, spelling, and moral reasoning. The developmental position rejects the notion of a specifc defcit or difference among children with intellectual disability and instead emphasizes how these children traverse the stages more slowly and attain a lower developmental ceiling than typically developing children (BennettGates & Zigler, 1998). In contrast, the difference viewpoint argues that cognitive development of children with intellectual disability differs from that of children without intellectual disability in more than developmental rate and upper limit. According to this position, even when his mental age is matched to his younger brother’s, Dan will show qualitatively different reasoning and problem-solving strategies, and he may never be able to accomplish some tasks beyond a certain level. Evidence supports the developmental hypothesis for children with familial, not organic, types of intellectual disability, but this issue has not yet been resolved. Children with familial intellectual disability generally follow developmental stages in an invariant order, the same as children with normal intellectual abilities, with the possible exception of some children with co-occurring brain abnormalities or autism (Bennett-Gates & Zigler, 1998). The similar structure hypothesis has also been supported for children with familial intellectual disability, with some exceptions. Children with familial intellectual disability show slight defcits in memory and information processing as compared with mental-age–matched children without intellectual disability (Schuchardt, Gebhardt, & Mäehler, 2010), which may be due to the children’s diffculty in staying motivated to perform repetitive, boring tasks (Weisz, 1999). The picture for children with organically based intellectual disability (such as Dan, who has Down syndrome) is more straightforward. They often have one or more specifc defcit areas that cause them to perform more poorly than mental-age–matched children without intellectual disability. Thus, Dan is likely to show some differences in his performance in certain areas of development, including his expressive language. Nevertheless, he will likely pass through the “Acknowledge our children’s differences but respect their uniqueness.” —Parent of a child with Down syndrome provided with stimulating environments and caregiver support (Wilkins & Matson, 2009). changes in abilities Intellectual disability is not necessarily a lifelong disorder. Although it is a relatively stable condition from childhood into adulthood, the IQ score can fuctuate in relation to the level of impairment and type of intellectual disability. Children such as Matthew who have mild intellectual disability may, with appropriate training and opportunities, develop good adaptive skills in other domains and may exceed the level of impairment required for a diagnosis of intellectual disability. The major cause of a child’s intellectual disability certainly affects the degree to which his or her IQ and adaptive abilities may change. The IQ of children with Down syndrome, who are not representative of the course of intellectual disability in general, may plateau during the middle childhood years and then decrease over time. For example, from 1 to 6 years of age, children with Down syndrome often show signifcant age-related gains in adaptive functioning, but as they grow older, their pace of development levels off or even declines (Margallo-Lana et al., 2007). A similar deceleration is often seen in the rate of social development of these children as they grow older (Hazlett et al., 2011). This observation has been termed the slowing and stability hypothesis (Hodapp et al., 2011), and it affrms that children with Down syndrome may alternate between periods of gain in functioning and periods of little or no advance. Although these children continue to develop in intelligence, they do so at progressively slower rates throughout the childhood years. language and social behavior Research on language development and social functioning among children and adolescents with Down syndrome suggests that their development follows a largely predictable and organized course (Filippi & Karmiloff-Smith, 2013). Because their cognitive development, play, self-knowledge, and knowledge of others are interrelated in organized and meaningful ways, the underlying symbolic abilities in children with Down syndrome are believed to be largely intact. However, important differences in language development exist between children with Down syndrome and their typically developing age-mates. Perhaps the most striking difference for children with Down syndrome is the considerable delay in the expressive language development that is necessary to establish independent living skills. Their expressive language is often much weaker than their receptive language, especially as they attain communication abilities beyond the 24-month level (Filippi & Karmiloff-Smith, 2013). Another major milestone of infancy and early childhood development is the ability to form secure attachments with caregivers. Although their attachments form more slowly than usual, many children with Down syndrome form secure attachment relationships with their caregivers by 12 to 24 months of developmental age (Dykens, Hodapp, & Evans, 2006). Still, a signifcant number of these children may have problems in developing a secure attachment because they express less emotion than other children. In one study, children with Down syndrome were not picked up and held by either the mother or the stranger in the strange situation to the same extent as non-delayed children. (See Table 2.2 for a description of the “strange situation” method of assessing child–caregiver attachment.) Even when these children made approaches with appropriate signals for contact, mothers and strangers rarely completed the contact, presumably because the children did not show the distress signals of crying, reaching, or holding on that typically tell the parent “I want to be picked up!” (Vaughn, Contreras, & Seifer, 1994). This fnding has important implications for parents of young children with Down syndrome: Even though they may show few signals of distress or desire for contact, these infants and toddlers need to be held and nurtured just as others do. Following the attachment period, the next important developmental milestones relate to the emergence of a sense of self, which establishes the early foundations of personality. Like other children, toddlers with Down syndrome begin to delight at recognizing themselves in mirrors and photos, although this milestone is often delayed. The experience of self-recognition in most infants is immediately met by smiles and laughter, and this experience is also found among toddlers with Down syndrome (Mans, Cicchetti, & Sroufe, 1978). This positive affect accompanying their visual self-recognition suggests that these children feel good about themselves. However, as toddlers and preschoolers, children with Down syndrome show delayed and aberrant functioning in their internal state language, the language that refects the emergent sense of self and others (through the use of words such as “mad” and “happy”). Because internal state language is critical to regulating social interaction and providing a foundation for early self–other understanding, these children may be at increased risk for subsequent problems in the development of the self-system (Huck, Kemp, & Carter, 2010). C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 139 Children with intellectual disability, especially those with moderate to mild impairments, learn symbolic play—games, puppets, and sports—in much the same manner as do other children. Nevertheless, they often fail to gain their peers’ acceptance in regular education settings, because they may have defcits in social skills and social–cognitive abilities (Cook & Oliver, 2011). Concerns about the social development of children with intellectual disability are increasing as a result of the movement to include children with different levels of ability in regular classrooms and schools, rather than only placing them in institutions or specialized facilities. Typically developing children seem to prefer playing with other typically developing children, and as a result, children with intellectual disability are more socially isolated from other children their age (Guralnick, Connor, & Johnson, 2011). These integrated classrooms allow children with intellectual disabilities, despite their limited social skills, to interact with typically developing peers, which in turn has a positive impact on their social status (Leffert, Siperstein, & Widaman, 2010; Siperstein, Glick, & Parker, 2009). emotional and behavioral problems PAT T I E Disturbed or Disturbing? Pattie was labeled mentally retarded and lived in over 20 homes and institutions before being committed to a state school at age 10. At the age of 20, she discussed some of her experiences and feelings: “I guess I was very disturbed. I call it disturbed, but it was when I was very upset. A lot of people at (the institution) … told me I was disturbed—that I was disturbed and that I was retarded— so I fgure that all through my life I was disturbed. Looking at the things I done, I must have been disturbed. … Upset and disturbed are the same in my mind. Crazy to me is something else. It is somebody that is really gone. I mean really out. Just deliberately kill somebody just to do it. That is what I call crazy. I guess what I was was emotionally disturbed—yeah. Emotionally disturbed is a time when too many things are bothering me. They just build up till I get too nervous or upset. My mind just goes through all these changes and different things. So many things inside that were bothering me.” (Based on Bogdan & Taylor, 1982.) Pattie’s description of her feelings while living in various institutions illuminates how “disturbing” her behavior could be. But are her feelings a function of her 140 P a r t 2 Neurodevelopmental Disorders environment and personal limitations? Many children and adolescents with intellectual disability have to face many obstacles related to their intellectual, physical, and social impairments, and often they have little control over their own lives. In the early 1970s, a major study was conducted to gain some understanding of the extent of psychiatric disorders among children and adults with and without intellectual disability (Rutter et al., 1976). Ratings by both parents and teachers revealed that about one-third of the children with mild intellectual disability and one-half of the children with more severe forms of intellectual disability showed major signs of emotional disturbance, suggesting that these problems are common. Since then, research has estimated that the risk of emotional and behavioral disturbances among children with intellectual disabilities is approximately three to fve times greater than among typically developing children (Einfeld, Ellis, & Emerson, 2011). These problems are due largely to limited communication skills, additional stressors, and more neurological defcits faced by these children and youths (Adams & Oliver, 2011). The nature and course of psychiatric disorders in children and adolescents with and without intellectual disabilities is likely very similar. Problem behaviors of youths with mild and moderate disabilities are similarly stable and persistent over the course of their development (de Ruiter et al., 2008; Einfeld et al., 2011). Impulse control disorders, anxiety disorders, and mood disorders are the most commonly diagnosed psychiatric diagnoses for children with intellectual disability. Although these problems are sometimes severe and often require intervention, they are considered to be part of the spectrum of problems that coexist with intellectual disability, and as not indicators of other psychiatric illnesses (Hodapp et al., 2006). By early adulthood, persons with intellectual disabilities continue to show a greater risk for psychopathology than the general population, although problems in attention and aggression show a signifcant decline from childhood rates (Buckles, Luckasson, & Keefe, 2013). Adjustments usually are needed in how DSM-5 diagnostic criteria for other mental disorders are applied, however. The frequency of temper tantrums, hyperactivity, and mood disorders among these children requires consideration of what is normal or typical for other children with similar levels of intellectual disability. For example, the diagnosis of attention-defcit/hyperactivity disorder (ADHD) requires the presence of behavioral disturbance that is inappropriate for an individual’s developmental level. Attention spans, distractibility, and on-task behaviors vary considerably among individuals with profound intellectual disability. An individual with profound intellectual disability must be compared with other children with profound intellectual disability for the purpose of diagnosing any other psychiatric disturbance (APA, 2013). Internalizing Problems Adolescence is a developmental period of increased risk for mood disorders and other internalizing symptoms, which is especially true for those with intellectual disability (Hodapp & Dykens, 2009). Like their normally developing peers, adolescents with Down syndrome and other forms of intellectual disability may show a decline in their previously sociable and cheerful behaviors, and in some cases they may suffer from signifcant symptoms of depression and social withdrawal. ADHD-Related Symptoms Teachers and parents of children and adolescents with intellectual disability commonly report ADHD-related symptoms that require adjustments in instruction and child-management strategies (Neece et al., 2013). When a teacher is present to prompt the appropriate behavior and participate in the activity, children with intellectual disability with and without ADHD generally will remain on task. However, when instructed to work without teacher assistance, differences between those with and without ADHD emerge (Handen et al., 1998). When children with intellectual disability and ADHD are placed on stimulant medication, they are able to remain on task for longer periods and their accuracy on cognitive tasks improves, similar to the responses of children with normal IQs (Simonoff et al., 2013). Other Symptoms Children and adults with intellectual disability may show additional symptoms that can be particularly troublesome. Pica (discussed in Chapter 14), which can result in the ingestion of caustic and dangerous substances, is seen in its more serious forms among children and adults with intellectual disability. Self-injurious behavior (SIB) is a serious and sometimes life-threatening problem that affects about one in fve young children with ID (MacLean & Dornbush, 2012). Some common forms of SIB include head banging, eye gouging, severe scratching, rumination, some types of pica, and inserting objects under the skin. The long-term prognoses for pica and SIBs are not favorable. Emotional withdrawal, stereotypies (frequent repetition of the same posture, movement, or form of speech—e.g., head banging, hand or body movements), and avoidance of eye contact are often still evident more than 20 years later among persons with more severe forms of intellectual disability (Taylor, Oliver, & Murphy, 2011). Thus, children with intellectual disability may show emotional and behavioral problems that require special recognition and learning strategies. In general, these problems do not constitute major psychiatric disorders, but they do refect the greater challenges these children may have in learning to express their needs and in adapting to their surroundings. A 7-yearold girl with mild intellectual disability, for instance, may be at a developmental level comparable to that of a typically developing 4-year-old. In the classroom, therefore, she may have diffculty sitting in her seat and remaining on task. She may not always control her emotions or her behavior as well as other 7-yearolds in the class, leading to occasional outbursts of laughter or anger. It is important to keep these problems within a developmental perspective. We would not expect a 4-year-old to behave as well in the classroom as an older child, and expectations and teaching methods have to be adjusted accordingly. As expressed so well by Ed and Pattie, labeling a child with a diagnostic term that implies pathology or inability is often ill-conceived and counterproductive. Such terms must be used sparingly—only in circumstances, such as self-injurious behaviors, for which special attention is warranted. other physical and Health disabilities Children with intellectual disabilities may also suffer other physical and developmental disabilities that can affect their health and development in pervasive ways. Such disabilities are usually related to the degree of intellectual impairment. Based on a meta-analysis of 31 studies, the prevalence of chronic health conditions in this population is much higher than in the general population (Oeseburg et al., 2011). ● Figure 5.2 shows some of the more common developmental disabilities found among children with intellectual disabilities. Despite major co-occurring physical and intellectual disabilities, children and adults with Down syndrome now have a life expectancy approaching 60 years, largely as a result of better medical treatments for respiratory infections and congenital heart disorders (Dykens, 2013). However, most individuals with Down syndrome who live beyond the age of 40 demonstrate cognitive decline (much like Alzheimer’s disease) due to gene damage on chromosome 21 (Torr et al., 2010). C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 141 30 20 10 Prevalence per 100 children 0 tic r tis rde Au iso d e n om ow r D nd l er sy ona ord iti is os t d pp an O vi de y et r xi de r An iso d l ra eb er y C ls pa y ps Ep ile F I G U R E 5 . 2 | Chronic health conditions among children with intellectual disabilities. ● Based on Data from Oeseburg et al. (2011) Section Summary Developmental Course and Adult Outcomes ● ● ● ● Children with intellectual disability follow developmental stages in the same order as do typically developing children. However, their goals and motivation are reduced over time because of feelings of frustration, which often lead to expectations of failure. Adaptive skills and level of impairment may improve over time, especially for children with mild intellectual disability, if appropriate training and opportunities are provided. Developmental disabilities, such as speech and language problems and behavioral disturbances, are common. Emotional and behavioral problems are considered part of the spectrum of problems coexisting with intellectual disability, rather than indicators of mental disorder. Children with intellectual disability have a greater chance of having other physical and developmental disabilities, such as cerebral palsy, epilepsy, and emotional and behavioral disorders that can afect their health and development in pervasive ways. CAUSES It is astounding to consider that there are over 1,000 genetic disorders associated with intellectual disability, in addition to other organic causes (Hodapp & Dykens, 2009). Yet, despite the number of known causes, scientists are unsure of the causes of the majority of intellectual disability, especially mild ID. A genetic or environmental cause is known for almost two-thirds of individuals with moderate to profound intellectual disability, whereas the causes are known for only about 142 P a r t 2 Neurodevelopmental Disorders one-quarter of the individuals with mild intellectual disability (McDermott et al., 2007; van Bokhoven, 2011). Some causes happen before birth (prenatal), as is the case with all genetic disorders and accidents in the womb. Other causes are birth-related (perinatal) insults, such as prematurity or a lack of oxygen (anoxia) at birth. Still other causes are an infammation of the brain lining (meningitis), head trauma, and other factors that occur after birth (postnatal). Historically, causes of intellectual disabilities were divided into two fairly distinct groups—an organic group and the cultural–familial group (Hodapp & Dykens, 2003). The causes in the organic group have a clear biological basis and are usually associated with severe and profound intellectual disability, whereas causes in the cultural–familial group have no clear organic basis and are usually associated with mild intellectual disability (Hodapp et al., 2006). Four major categories of risk factors contribute to intellectual disabilities: biomedical, social, behavioral, and educational. These four risk factors interact across time and even across generations from parent to child and provide a more comprehensive explanation of the interacting causes of problems associated with intellectual impairments (AAIDD, 2010; Chapman, Scott, & Stanton-Chapman, 2008). The defnitions, characteristics, and causes of intellectual disability on the basis of these four risk factors are summed up in Table 5.5. Although a distinction between organic and nonorganic risk factors clarifes the underlying causes of intellectual disability, keep in mind that the distinctions are less clear in milder forms of intellectual disability than they are in more severe forms. For example, the large majority of persons at more severe levels of intellectual impairment (96%) show a clear etiology for the disorder, whereas a sizable percentage (32%) of those with mild impairments does not (Simonoff et al., 1996). Considerable knowledge exists about organic intellectual disability because of the strong biological factors involved. Also, the increased ability to diagnose organic problems has led to increased estimates of this type of intellectual disability relative to cultural–familial causes—about one-third to one-half of all persons with intellectual disability show a clear organic cause (Hodapp et al., 2006). In stark contrast, the cultural–familial group remains somewhat of a mystery, although it comprises one-half to two-thirds of all persons with intellectual disability (Witwer et al., in press). As noted in Table 5.5, the prime suspects are environmental and situational factors such as poverty, inadequate child care, poor nutrition, and parental psychopathology, which mostly affect the psychological, and not the biological, development of the child. However, more T A B L E 5 . 5 | Risk Factors for Intellectual Disability Timing Biomedical Social Behavioral Educational Prenatal 1. 2. 3. 4. 5. 6. 7. 1. 2. 3. 4. 1. 2. 3. 4. 1. Parental cognitive disability without supports 2. Lack of preparation for parenthood Perinatal 1. Prematurity 2. Birth injury 3. Neonatal disorders 1. Lack of access to prenatal care 1. Parental rejection of caretaking 2. Parental abandonment of child 1. Lack of medical referral for intervention services at discharge Postnatal 1. 2. 3. 4. 5. 1. Impaired child–caregiver interaction 2. Lack of adequate stimulation 3. Family poverty 4. Chronic illness in the family 5. Institutionalization 1. Child abuse and neglect 2. Domestic violence 3. Inadequate safety measures 4. Social deprivation 5. Difficult child behaviors 1. Impaired parenting 2. Delayed diagnosis 3. Inadequate early intervention services 4. Inadequate special education services 5. Inadequate family support Chromosomal disorders Single-gene disorders Syndromes Metabolic disorders Cerebral dysgenesis Maternal illness Parental age Traumatic brain injury Malnutrition Meningoencephalitis Seizure disorders Degenerative disorders Poverty Maternal malnutrition Domestic violence Lack of access to prenatal care Parental drug use Parental alcohol use Parental smoking Parental immaturity © Cengage Learning ® specifc cause-and-effect relationships have not been Inheritance and the role of the determined. Accordingly, both genetic and environenvironment mental factors are implicated in milder forms of intellectual disability, but in a manner as yet to be The study of human intelligence has received the determined (Toth & King, 2010). lion’s share of attention in terms of the underlying The relative importance of the environment also processes involved in genetic makeup and the envistands out in the two-group distinction. The socioecoronmental factors that infuence genetic expression. nomic background of the organic group is about the Still, the long-standing debate concerning the relative same as that for the general population, which fts with contributions of genes and environment is far from the notion that severe forms of intellectual disability can being fully resolved (McDermott et al., 2007). Conaffect anyone, regardless of SES. The familial group is ceivably, genetic infuences on development are pooverrepresented by those of lower SES and social disadtentially modifable by environmental input, although vantage and is signifcantly related to a family history of the practicality of the modifcations is another matintellectual disability. This fts with the assertion that an ter. Similarly, environmental infuences on developimpoverished social environment can infuence intellecment involve the genes or structures to which the tual growth and ability in subtle, yet crucial, ways. genes have contributed (Neisser et al., 1996). Simply In most cases, the risk factors for intellectual disstated, children do not inherit an IQ—they inherit a abilities have been supported empirically, with some genotype, which is a collection of genes that pertain adjustments as noted earlier in terms of nonorganic to intelligence. The expression of the genotype in the risk factors. First, the percentage of individuals with environment—the gene–environment interaction—is a clear organic cause has increased over the past few decades because of the greater knowledge of genetic and organic causes. Also, the original assumption that mild intellectual disability is not due to biomedical (organic) causes had to be tempered by fndings that epilepsy, cerebral palsy, and other organic disorders are found more often among persons with mild intellectual disability than among those without intellectual disabilities (Hodapp et al., 2011). © 2011 Greg Cravens, Reprinted with permission of Universal Uclick. All rights reserved. C h a p t e r 5 Intellectual Disability (Intellectual Developmental Disorder) 143 referred to as the phenotype. The heritability of a trait describes the proportion of the variation of a trait attributable to genetic infuences in the population (Neisser et al., 1996). Heritability of any given trait, therefore, can range from none (0%) to 100% genetically determined. Is it possible to estimate the heritability of intelligence and, by implication, the heritability of intellectual disability? This intriguing question can now be answered with some degree of confdence, but little fanfare. The overwhelming evidence points to a heritability of intelligence of approximately 50%; that is, both genetic and nongenetic factors play powerful roles in the makeup and expression of intelligence (Davis, Arden, & Plomin, 2008). There are so many specifc genetic causes of intellectual disability that some skepticism about the importance of environmental effects still remains. The diffculty of identifying, pinpointing, and measuring specifc, nongenetic variables certainly adds to this dilemma. However, considerable evidence has demonstrated that major environmental variations do affect cognitive performance and social adjustment in children from disadvantaged backgrounds (Ramey, Ramey, & Lanzi, 2007). For example, children born to socially disadvantaged parents and then adopted into more privileged homes have higher IQ scores, stronger self-esteem, and fewer acts of delinquency than siblings reared by their disadvantaged, biological parents (Juffer & van IJzendoorn, 2007; van der Voort et al., 2013). The prenatal environment may infuence IQ to a greater extent than was previously appreciated. A review of studies of twins and nontwin siblings revealed that a shared prenatal environment (i.e., all children shared the same mother) accounted for 20% of IQ similarity...
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