Phenylketonuria is a metabolic genetic disorder characterized by the mutation in the gene for hepatic enzyme making it non functional. Thisis necessary to metabolize the amino acid phenylalanine (Phe) to the amino acid tyrosine. When PAH activity is reduced this amino acid (phenylalanine) accumulates and is converted into phenylpyruvate.Although phenylalanine is an essential protein building block, abnormally high levels lead to severe and irreversible brain damage; If the Phe level gets too high, it can damage the brain and cause severe mental retardation. PKU is inherited in a recessive manner, meaning that only a child who receives two mutated copies of the PAH gene (one from each parent) will get the disease. The severity of the condition, and what measures are needed to manage it, depend on the specific mutations inherited.A person must inherit a mutated copy of PAH from each parent in order to have PKU. If two parents are carriers of a mutation, there is a 25% chance their child will be born with the disorder. There is a 50% chance that their child will be an unaffected carrier for PKU. Each unaffected sibling of an affected child has a two in three chance of being a carrier. Hundreds of mutations in the PAH gene have been identified. Most people with PKU have two different mutations. The exact combination of mutations determines to some extent how severe the manifestations will be. But, even in siblings with identical mutations, there can be variability. This is most likely due to other factors, both genetic and non-genetic.

A benefit from PKU is that all babies born in U.S. hospitals must now have a screeningtest for PKU. This makes it easier to diagnose and treat the problem early. Decisions about the details of dietary management for PKU are made based on blood tests that measure phenylalanine levels, not genetic tests. But information on which mutations a person carries can help guide treatment decisions. This knowledge can also be used to identify family members who are carriers for PAH mutations.
PKU is one of the most common inborn errors of metabolism, but the incidence of affected newborns and the carrier rate for PAH mutations, varies between different populations. Nowadays, thanks to widespread newborn screening followed by early treatment, fewer than one in a million children in developed nations develop intellectual disability as a result of inheriting two PAH mutations.


  • You will have to live all your life on a low PHE diet.
  • If the Phe level gets too high, it can damage the brain and cause severe mental retardation.


The phenylketonuria genetic disorder affects one socially because of the need to always be under a strict diet, which impedes you to eat with your friends and be socially active. Also this genetic disorder hinders the possibility to fit in. Not only because of the diet but because when this genetic disorder is in its most damaging stages, having a brain damage make one significally different.