Phenylketonuria

Question 1

INhertiance

Answer 1

autosomal recessive

Question 2

Enzyme defect

Answer 2

defect in phenylalanine hydroxylase
- this converts phenylalanine to tyrosine

Question 3

High levels of phenylalanine lead to what problems?

Answer 3

learning difficulties and seizures.

Question 4

Gene encoding for phenylalanine hydroxylase is found on what chromosome?

Answer 4

12

Question 5

Clinical features of PKU

Answer 5

child classically has fair hair and blue eyes
learning difficulties
seizures, typically infantile spasms
eczema
‘musty’ odour to urine and sweat*

Question 5

what is the incidence of PKU?

Answer 5

1 in 10,000 live births.

Question 6

When does PKU typically present

Answer 6

usually presents by 6 months e.g. with developmental delay

Question 7

Tests for diagnosis

Answer 7

Guthrie test: the ‘heel-prick’ test done at 5-9 days of life
hyperphenylalaninaemia
phenylpyruvic acid in urine

Question 8

Management of PKU

Answer 8

non-specific ?dietary modification

dietary restrictions are important during pregnancy as genetically normal fetuses may be affected by high maternal phenylalanine levels