What genetic disorder prevents the metabolism of phenylalanine?

What genetic disorder prevents the metabolism of phenylalanine? Phenylketonuria, or PKU, is the inherited disorder in which phenylalanine cannot be properly broken down.

Most PKU cases result from mutations in the PAH gene, which provides instructions for phenylalanine hydroxylase. That enzyme normally converts phenylalanine into tyrosine. When enzyme activity is absent or greatly reduced, phenylalanine accumulates in the blood and can damage the developing brain.

PKU is autosomal recessive, so an affected child usually inherits a changed copy of the gene from each parent. Babies may appear healthy at birth, which is why newborn screening is crucial. Early treatment typically combines a carefully controlled low-phenylalanine diet with specialized medical nutrition; some patients also benefit from medicines such as sapropterin or pegvaliase.

The condition was identified by Norwegian physician Ivar Følling in 1934, after he connected an unusual urine chemical with intellectual disability. A major treatment breakthrough followed in 1954, when researchers showed that a low-phenylalanine diet could improve outcomes. People with PKU must also avoid aspartame, which contains phenylalanine.