Question 01:

When a young woman with PKU becomes pregnant:
Her baby will have a 1 in 2 chance of having PKU
Breast feeding is likely to be contra-indicated
There is no risk of mental retardation in her offspring
The baby has an increased risk of cardiac malformations
Check answer

Explanation

Assuming the woman’s partner is not known to be a carrier for PKU, the risk that her offspring will have PKU is 1 in 100. This figure is based on the empiric carrier rate of PKU [1/50] multiplied by the risk of the mother passing on the mutant allele [1] multiplied by the risk of the partner passing on the mutant allele if he were a carrier [1/2].

Because high maternal plasma phenylalanine levels are teratogenic, a woman with PKU whose plasma phenylalanine is not well controlled before conception and during pregnancy, is at very high risk of having an infant born with growth failure, microcephaly, congenital heart disease and intellectual disability, which is independent of whether the baby has PKU or not (the so-called maternal PKU syndrome).

Breastfeeding is not contra-indicated in the infants of women with PKU, even if the infant has PKU.

Question 02:

In a child with PKU blood phenylalanine levels are likely to become elevated:

During periods of rapid growth
If the diet is high in carbohydrate
During an episode of the ‘flu
If fat intake is excessive
Check answer

Explanation

Phenylalanine will become elevated during catabolic illnesses or as a consequence of excessive protein intake. Non-protein sources of calories (ie. fat or carbohydrate) would have an anabolic (phenylalanine lowering) effect.

Question 03:

What is the most appropriate diet for a child with classic PKU ?
Low in phenylalanine
Supplemented with phenylalanine
High in aspartame
Low in fat
Low in carbohydrate
Check answer

Explanation

The correct diet includes one which is low in phenylalanine. However, as phenylalanine is an essential amino acid, it cannot be completely eliminated from the diet. It is a lifelong diet. Excessive protein intake must be avoided.

Non-protein sources of calories, such as fat and carbohydrate, have an anabolic effect that is phenylalanine lowering. Artificial sweeteners such as aspartame should be avoided as they are a non-natural form of phenylalanine.
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