Select the best answer for the following questions:

Question 01:

The most likely consequence for untreated PKU is:
Significant mental retardation
Heamolytic anaemia
Sensorineural Deafness
Mild learning disorder
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Explanation

PKU, if left untreated, can result in severe mental retardation. Other features of untreated PKU include growth failure, spasticity, seizures and a form of eczema. If treatment is instituted within the first 2-3 weeks of life then normal growth and development is expected.

Question 02:

What are the likely physical features of a child with untreated PKU?
Short stature
Hyperpigmented skin
Macrocephaly
Tremor and unsteady gait
Hepatomegaly
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Explanation

Children with PKU commonly have a very fair complexion, a movement disorder, e.g. tremor, Parkinson-like features, abnormalities of gait, hyperactivity, destructiveness, self-injurious behaviour and autistic features.

Question 03:

Phenylketonuria due to phenylalanine hydroxylase deficiency has an autosomal recessive pattern of inheritance. This means that:
Carriers often show mild clinical features of the disorder
Males are usually more severely affected than females
It is allelic to phenylketonuria caused by tetrahydrobiopterin deficiency
Siblings of a child with PKU that have a normal phenotype have a 2 in 3 chance of being carriers
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Explanation

In Autosomal recessive disorders it is very unusual for carriers to manifest any clinical features. Males and females are affected with equal severity. There is a 2 in 3 chance that a sibling will be a carrier. Different genes are defective in phenylalanine hydroxylase deficiency and tetrahydrobiopterin deficiency, and are therefore NOT allelic.

Question 04:

What is the characteristic odour of children with untreated PKU?
Sweaty feet
Maple syrup
Swimming pool/chlorine
Boiled cabbage
Mousy
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Explanation

The characteristic smell of PKU is a mousy odour. Sweaty feet is characteristic of Glutaric academia; Swimming pool of Hawkinsinuria; boiled cabbage of Tyrosinemia; maple syrup of Maple syrup urine disease.
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