Enzyme deficiency

Phenylketonuria

What is missing: Phenylalanine hydroxylase.

Presentation

Intellectual disability, seizures, fair skin and hair, and a musty body odor

Why the signs follow

Phenylalanine cannot become tyrosine, so it accumulates and spills over into phenylketones. Tyrosine becomes conditionally essential, which is why melanin, and therefore pigmentation, is reduced.

Written for exam preparation, not for diagnosis.

Amino acids All control points