timer Asked: Dec 16th, 2017
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Question description

A female baby was born after a non--‐eventful normal pregnancy.

For the first few days she was healthy but then started to vomit frequently.

Her mother noted that her urine had apeculiar ‘mousy’ smell.

When the infant was a month old she was admitted to hospital where they realised that the genetic screening test after her birth was deficient.

Her blood tests showed that the level of Phenylalanine Was (1.6 Mmol dm--‐3) reference value <0.1 Mmol dm--‐3.

Questions to be considered

1. What is the diagnosis for this baby?

2. Describe why this disease occurs and the mode of inheritance.

3. Explain why her urine smells differently from normal urine.

4. What are the clinical features you would expect to see?

5. How should she be treated?

6. What would happen if this child is not treated?

Filiano JJ. Neurometabolic diseases in the newborn. Clin Perinatol. Jun 2006; 33(2): 411-79.

Gassio R. School performance in early and continuously treated phenylketonuria. Pediatr Neurol. Oct 2005; 33(4): 267-71.

Tutor Answer

School: University of Virginia


Is a disease caused by a defect in the gene responsible for synthesis of the enzyme
phenylalanine hydroxylase. This enzyme is the first in the catabolism pathway of phenylalanine
and it is responsible for converting phenylalanine to tyrosine. As a result an inefficient secondary
pathway of phenylalanine metabolism is activated and phenylalanine undergoes transamination
with pyruvate leading to the formation of phenylpyruvate (phenyl ketone). Phenylalanine and
phenylpyruvate end up accumulating in tissue and blood and end up being excreted in urine.
Another cause though rare can be as a result of exposure to high levels of phenylalanine mostly
dietary or environmental.
The mode of inheritance of the gene defect is autosomal recessive. This means that two
copies of the abnormal gene must be present in order for the disease to develop. In other words
for an infant to develop phenylketonuria, both parents must have the defective gene and if the
child inherits only one defective gene he will only be a carrier and the disease will not develop.
Carriers do not show any signs or symptoms of the disease and if both parents are carrying the
faulty copy of PAH gene, the chan...

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Outstanding Job!!!!

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