There are 15 questions in this prequiz. Feedback will be given as you proceed through the questions.

Question 01:

PKU is a disorder of neurotransmitter metabolism.
True
False
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Explanation

It is a disorder of phenylalanine hydroxylation. The effects on brain are secondary.

Question 02:

In phenylketonuria, phenylalanine levels are high in the blood, but low in the brain.

True
False
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Explanation

Phenylalanine levels are increased in blood and are also greatly increased in cerebrospinal fluid of untreated patients. In two studies, levels of phenylalanine measured in post-mortem brain were also elevated.

Question 03:

Phenylalanine levels need to be kept within the normal range to ensure normal growth and development in PKU children.
True
False
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Explanation

Children whose plasma phenylalanine levels are maintained above the normal range but lower than 400 umol/l have normal growth and development.

Question 04:

In humans, phenylalanine can be metabolised to form the neurotransmitter acetylcholine.
True
False
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Explanation

It is metabolised to the neurotrasmitters dopamine, noradrenaline, and adrenaline.

Question 05:

In the fed state, plasma phenylalanine is principally derived from endogenous biosynthesis.

True
False
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Explanation

Phenylalanine, being an essential amino acid, is derived primarily from the diet. In the fed state, this is the usual source, but it can also be released from endogenous protein stores during catabolic states.

Question 06:

Phenylalanine can be metabolized to dopamine.
True
False
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Explanation

Phenylalanine is converted to dopamine through a series of linked reactions: phenylalanine - tyrosine - L-dopa - dopamine.

Question 07:

Phenylalanine hydroxylase is the most important factor regulating phenylalanine homeostasis.
True
False
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Explanation

Phenylalanine hydroxylase is the rate-limiting step in phenylalanine catabolism.

Question 08:

Phenylketonuria is most commonly inherited in an autosomal recessive manner.
True
False
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Question 09:

The normal gene for phenylalanine hydroxylase (PAH) occurs once in the haploid genome.
True
False
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Explanation

The haploid genome is that which is present in the germ cells where there is one copy of each chromosome. There is one gene for PAH in the haploid genome. PAH is therefore called a single-copy gene.

Question 10:

Phenylketonuria (PKU) is frequently associated with compound heterozygosity.
True
False
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Explanation

Any disease of this type is frequently associated with compound heterozygosity i.e. the mutation on one copy of chromosome 12 is different from the mutation on the other.

Question 11:

PKU is generally associated with deletion of the phenylalanine hydroxylase (PAH) gene.
True
False
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Explanation

Some genetic disorders are caused by deletion of the entire gene e.g. alpha thalassemia. PKU is not one of these.

Question 12:

PKU is generally associated with reduced levels of phenylpyruvate, phenyllactate and phenylacetate.
True
False
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Explanation

The function of the enzyme is such that in situations where the concentration of phenylalanine is high, there is increased production of phenylpyruvate, phenyllactate and phenylacetate since they are products of the transamination of phenylalanine (a minor metabolic pathway).

Question 13:

PKU infants can be breastfed.
True
False
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Explanation

Partial breastfeeding is recommended for infants with PKU. Breastfeeds may be used for the phe allowance. In addition a special low phe formula is given to provide non-phe protein, calories, vitamins and minerals.

Question 14:

Children with PKU are more susceptible than other children to liver disease.
True
False
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Explanation

Children with PKU are no more or less likely to get liver disease. Most medications are suitable, except those containing aspartame because aspartame is metabolised to phenylalanine.

Question 15:

The normal child first smiles at 3 months.
True
False
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Explanation

A normal child should have smiled socially by 6 weeks.

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