Phenylketonuria, also known as PKU, is an error in metabolism, an inherited disease present from birth resulting from the absence, or near absence, of phenylalanine hydroxylase (PAH) enzyme activity. If left untreated, PKU can lead to intellectual disability, seizures, or other serious medical conditions. The best-known treatment for phenylketonuria is a strict phenylalanine restricted diet, combined with adding amino acids.
Restricted foods, those high in phenylalanine (Phe) which should be avoided, include soybeans, egg whites, shrimp, chicken breast, fish, nuts, lobster, tuna, turkey and low fat cottage cheese. Since PKU is not a digestive disorder, eating any of these foods will not cause an immediate reaction. However, the buildup of Phe in the body may cause mood problems, difficulty in concentration, or even eczema. Individuals with phenylketonuria are advised to maintain this strict diet throughout their life, as PKU is not curable, merely treatable.
PKU is a genetic disorder that requires two PKU alleles in order to develop the disease. If both parents are carriers for PKU, a child will have a 25% change of being born with the disorder, and a 50% chance of being a carrier. Screening for PKU is generally done during routine newborn testing, performed within hours or days of birth in developed nations. If left untreated, infants with PKU will fail to reach early developmental milestones, including progressive cerebral impairment.