Phenylketonuria

Question 1

What level of PHE in the serum diagnoses PKU?

Answer 1

> 700mmol/L, normal range is 100mmol/L

Question 2

What is PKU and how is it caused?

Answer 2

It is caused by the deficiency of the enzyme phenylalanine hydroxylase, leading to increased PHE concentration in the body. If it is left untreated it can cause severe developmental delay, causing an inhibition of neurotransmitter release

Question 3

How is PKU treated following a positive screening after birth?

Answer 3

Treated with a low protein diet and supplemented with amino acid mixture from which PHE has been removed, must ensure adequate tyrosine levels

Question 4

For a female with PKU when must they resume their strict diet?

Answer 4

Pre-conceptually and during pregnancy, if not controlled during pregnancy it causes high risk of foetal abnormalities such as microcephaly, congenital, heart disease and learning difficulties

Question 5

Sometimes a newborn screened positive for PKU do not respond to low PHE diets. Why is this?

Answer 5

They have defects in dihydropteridine reductase or biopterin synthesis, both of these causes defective PHE function

Question 6

How would you treat an individual with biopterin deficiency causing PKU?

Answer 6

These patients require supplementation of neurotransmitters as well as a low PHE diet. This is due biopterin deficiency affecting hydroxylases like tyrosine and tryptophan leading to a deficiency of neurotransmitters

Question 7

How is PKU acquired?

Answer 7

It is inherited autosomal recessively. In the UK affects about 1:10,000 births

Question 8

What are features of PKU (hyperphenylalanaemia)?

Answer 8

Fair hair, pale skin, blue eyes, mental retardation, eczema, poor feeding, irritability, vomiting