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Phenylketonuria and Related Disorders

What is Phenylketonuria?

Phenylketonuria (PKU) is part of a spectrum of related genetic disorders. These disorders are characterized by intellectual disability, seizures, and skin problems. A person must have two variants in the PAH gene in order to have one of these disorders. People with just one variant in the PAH gene are called carriers. They're not expected to have the condition themselves, but they could pass their variant on to their future children.

Causes of phenylketonuria

PKU and related disorders are caused by variants (differences) in the PAH gene. The PAH gene contains instructions for making an enzyme called phenylalanine hydroxylase. This enzyme helps break down an amino acid called phenylalanine, which is found in some foods. Certain variants in PAH disrupt its function, resulting in a harmful buildup of phenylalanine.

When symptoms develop

Symptoms of PKU typically develop soon after birth.

Typical signs and symptoms

  • Intellectual disability
  • Seizures
  • Behavioral problems
  • Eczema

Ethnicities most affected

Phenylketonuria and related disorders occur worldwide, but are more common in people of Irish, European, Turkish, and East Asian descent.

Explore more

Curious to learn more? 23andMe can tell you whether you might be a carrier for phenylketonuria or a related disorder. Being a carrier means you have a genetic variant that you could pass down to your future children. 23andMe does not test for all possible genetic variants linked to phenylketonuria, and individuals who have zero variants detected still have a chance of being a carrier for phenylketonuria or a related disorder.

23andMe tests for 23 variants linked to phenylketonuria or a related disorder and is most relevant for people of Irish and Northern European descent. The Phenylketonuria and Related Disorders Carrier Status report* is available through the 23andMe Health + Ancestry Service.

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