Curriculum · Metabolic and Endocrine and Diabetes Mellitus
Phenylketonuria
What it is
Phenylketonuria is the most common IEM of amino acid metabolism. Inheritance is autosomal recessive and the defective enzyme is phenylalanine hydroxylase, PAH, so phenylalanine rises in the body. The metabolites that accumulate are phenylalanine, phenylpyruvate and phenylacetate.
How it presents
Symptoms are often absent at birth, which is why it is detected by screening. When it does show, the features are intellectual disability, seizures, a musty odor, and fair skin and hair, with hair loss and eczema. The musty odor is due to phenylacetate. The problems that follow the rise in phenylalanine are seizure, brain damage, musty odour and intellectual disability. The urine odor is what tells it apart from maple syrup urine, where the odor is maple syrup-like instead.