Phenylketonuria screening

What it is

Phenylketonuria (PKU) is the most common IEM of amino acid metabolism. Inheritance is autosomal recessive and the defective enzyme is phenylalanine hydroxylase (PAH), so the phenylalanine level rises and phenylalanine, phenylpyruvate and phenylacetate accumulate.

How it presents

Symptoms are often absent at birth, so the diagnosis is made by screening rather than by the picture. Where features do appear they are:

• Intellectual disability
• Seizures
• Fair skin and hair, and hair loss
• Eczema
• A musty urine odor, which comes from phenylacetate

Brain damage follows the rise in phenylalanine.