Library · Disease
Phenylketonuria
Make it clearer
Phenylalanine is an amino acid, one of the building blocks that proteins are made from. Phenylketonuria is the most common of the disorders that arise from an inborn error of amino acid metabolism, that is, from a defect present from birth in the way the body processes amino acids.
It is inherited in an autosomal recessive pattern, meaning that the altered gene has to come from both parents. The PAH gene variants that cause the disease reduce or abolish the activity of an enzyme found mainly in the liver that converts phenylalanine into another amino acid, tyrosine. The result is a stalled assembly line: what comes in piles up and what should come out is missing. In the blood, phenylalanine rises and tyrosine runs low.
Babies usually look normal at birth, and that is the trap. Without treatment, seizures, microcephaly, meaning a head smaller than expected, and neurocognitive impairment can gradually appear. And because tyrosine is a precursor of melanin, the pigment that gives skin its color, the lack of tyrosine lightens the skin.
In brief
Phenylketonuria is the most common disorder caused by an inborn error of amino acid metabolism.
It is inherited in an autosomal recessive pattern, and pathogenic PAH gene variants reduce or abolish the activity of a largely hepatic enzyme that converts phenylalanine to tyrosine: phenylalanine rises and tyrosine runs low.
An assembly line stalled: what comes in piles up and what should come out is missing.
Newborns usually look normal; without treatment, seizures, microcephaly and neurocognitive impairment can develop, and the skin lightens because tyrosine, a melanin precursor, is lacking.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhenylketonuria (PKU), StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated