Description
presentation on sickle cell anemia
Explanation & Answer
Attached.
SICKLE CELL DISEASE
kibaru
OUTLINE
Describe
the genetics of sickle cell
disease
Outline
the crises associated with
sickle cell disease
What
are organ involvement in
sickle cell disease
EPIDEMIOLOGY
Incidence
Sickle hemoglobin is the most common abnormal
hemoglobin found in the United States
approximately 8% of the African-American
population has sickle cell trait.
The expected incidence of sickle cell disease
(SCD) at birth is 1 in 625.
NORMAL VS. SICKLE RED CELLS
Sickle
Normal
Disc-Shaped
Deformable
Life span of 120 days
Sickle-Shaped
Rigid
Lives for 20 days or
less
GENETICS
Sickle cell disease is transmitted as an
autosomal recessive trait.
Homozygotes (two abnormal genes) do not
synthesize hemoglobin A (HbA)
red cells contain 90–100% hemoglobin S (HbS).
Heterozygotes (one abnormal gene) have red cells
containing 20–40% HbS
SICKLE CELL PEDIGREE
Parents
with sickle cell trait: hemoglobin AS
Probability of child with hemoglobin AA: 25%
Probability of child with sickle cell trait AS: 50%
Probability of child with sickle cell disease SS:
25%
HbS arises as a result of spontaneous mutation
and deletion of the β-globin gene on chromosome
11
which results in selective advantage against
Plasmodium falciparum malaria in carriers
(balanced polymorphism).
CO-INHERITANCE
. α-Thalassemia (frequency of 1–3% in African
Americans) may be co-inherited with sickle cell
trait or disease.
Individuals who have both α-thalassemia and
sickle cell anemia are less anemic than those who
have sickle cell anemia alone.
However, α-thalassemia trait does not appear to
prevent frequency or severity of vaso-occlusive
complications.
CLASSIFICATION
Results of DNA polymorphism linked to the βs
gene suggest that it arose from three independent
mutations in tropical Africa:
1. Benin–Central West African haplotype (the most
common haplotype)
2. Senegal–African West Coast haplotype
3. Bantu–Central African Republic (CAR) haplotypen
southwest Saudi Arabia.
In Caribbean and North American patients of African
heritage
with SCD,
50–70% of chromosomes are Benin
▪ 15–30% are Bantu-CAR
▪ 5–15% are Senegal.
▪
The Benin and Senegalese patients have higher
levels of fetal hemoglobin (HbF) and fewer dense
cells compared with Bantu-CAR patients.
Patients with Senegal haplotype have the least
severe disease, whereas patients with BantuCAR haplotype have most severe disease.
PREVALENCE/I...
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