Living With Phenylketonuria (PKU)

What is PKU?

PKU is a rare genetic disorder affecting about 16,500 people in the U.S. It is caused by a defect in the gene that helps create the enzyme responsible for breaking down an amino acid called phenylalanine.

Without this enzyme, phenylalanine builds up in the body. If phenylalanine, or Phe, levels get too high and are not treated, they can lead to health problems like:

Trouble focusing or concentrating

Neurological problems, including seizures

Behavioral, emotional or social problems

Irreversible brain damage

In PKU, different people may have more or less severe forms of the disorder. In severe PKU, the enzyme needed is missing or severely reduced, resulting in high levels of phenylalanine in your blood.

How is PKU caused?

Both mother and father must have and pass on the defective gene to their child (this pattern is called autosomal recessive).

It’s possible for a parent to be a carrier—to have one copy of the defective gene that causes PKU—but not have the disease.

Most of the time, PKU is passed to children by two parents who are carriers but don’t know it.

If only one parent has the defective gene, there’s no risk of passing PKU to their child, but the child may be a carrier.


If you have PKU, you were most likely diagnosed when you were a baby. Recognizing PKU right away can help prevent major health problems.

How is PKU treated?

There is no cure for PKU. However, people with PKU manage their Phe levels and their symptoms in a few ways:

PKU medical food:

Many people with PKU take a special nutritional supplement to make sure they get enough essential protein (without phenylalanine) and nutrients that are crucial for health. This also includes foods that are specially formulated and processed to be low in protein.

Strict low-protein diet:

Phenylalanine enters the body mainly through the protein we eat, as well as through aspartame, an artificial sweetener. People with PKU adhere to a strict low-protein and aspartame-restricted diet to limit their intake of phenylalanine and help keep their Phe levels low.


There are drugs approved by the Food and Drug Administration (FDA) for the treatment of PKU. Some are used in combination with a PKU diet. These drugs may or may not work for everyone and can include serious side effects.