Phenylketonuria (PKU)

Phenylketonuria (PKU) is a genetic condition that causes elevated levels of a substance called phenylalanine to build up in your body. Phenylalanine is found in the body as part of normal biochemical pathways, but problems arise when levels are persistently higher than normal.

Phenylalanine is an amino acid. Amino acids are molecules that form proteins. Many of the foods you eat that contain protein and the artificial sweetener aspartame have phenylalanine. If this condition isn’t treated, buildup of phenylalanine in your body causes symptoms including challenges with cognitive development (intellectual disability).

What are the types of phenylketonuria (PKU)?

There are different types of phenylketonuria (PKU) based on the severity of the diagnosis. Symptoms are worse among severe cases in those who are untreated. Types of PKU include:

• Classic PKU (most severe).
• Moderate or mild PKU.
• Mild hyperphenylalaninemia (least severe).

Who does phenylketonuria (PKU) affect?

Phenylketonuria (PKU) can affect anyone who has mutations in both copies of the PAH gene. Studies suggest that there’s a higher risk among people of Native American or European descent.

If a person with uncontrolled PKU has high levels of phenylalanine during pregnancy, this can cause intellectual disability, birth defects and other problems in their baby, even if the baby doesn’t have PKU.

How common is phenylketonuria (PKU)?

In the United States, phenylketonuria (PKU) affects an estimated 1 in every 10,000 to 15,000 newborns each year.