Overview
Phenylketonuria (PKU) is an autosomal recessive condition and is the most common inborn error of amino acid metabolism due to reduced or absent phenylalanine hydroxylase (PAH) enzyme activity. This converts dietary phenylalanine into tyrosine which is important for the genesis of neurotransmitters and melanin. The affected gene is on chromosome 12.
High levels of serum phenylalanine lead to the production of neurotoxic byproducts.
PKU is screened for by the heel-prick blood test in all babies in the UK and avoiding dietary phenylalanine treats the condition and reduces the risk of neurological damage.
Epidemiology
- Phenylketonuria can affect up to 1 in 10,000 live births
Presentation
- Children may be pale with blue eyes and fair hair compared to other family members – due to reduced melanin production
- Developmental delays and learning difficulties
- Musty or ‘mousey’ odour in urine and sweat due to the production of phenylacetate
- Recurrent vomiting
- Seizures
Investigations
Overview
All newborns in the UK are screened using the heel-prick test which screens for PKU and other metabolic disorders. Other investigations include:
- Serum phenylalanine:
- Elevated
- Urinalysis:
- May show phenylpyruvic acid
- Genetic testing:
- May identify the specific mutation
