What is the Diet for PKU? | How is PKU Monitored?

PKU stands for phenylketonuria. Phenylketonuria is an inherited (genetic) disorder. A person with PKU has inherited the gene for PKU from both his or her mother and father. About one in every 15,000 infants born in the United States has PKU.

People who are born with PKU are normal in every way except that to stay healthy they must follow a strict diet. The diet limits phenylalanine (phe), a common part of most foods. People with PKU do not have sufficient, working amounts of a liver enzyme called phenylalanine hydroxylase. This enzyme works in the body to convert phe to tyrosine.

Normally, phenylalanine is converted to tyrosine by an enzyme called phenylalanine hydroxylase. However, in individuals with PKU, this enzyme is not present in sufficient amounts. This results in a damaging build-up of phenylalanine in the body.

Phenylalanine (phe) is one of many amino acids that join together to form proteins. When a person eats foods containing protein, his or her body uses the amino acids from that protein for growth and repair of body tissues. Often, we eat more amino acids than our bodies need. These excess amino acids are changed by enzymes into other compounds or are used for energy.

Since individuals with PKU are missing the enzyme for phe breakdown, phe builds up in the blood and can damage the brain. If phe levels in the blood stay too high for a long time, the damage to the developing brain is severe and irreversible.

The harmful effects of PKU can be prevented if a diet low in phe is started in early infancy and maintained throughout life. The phe-restricted diet is the only way to bring blood phe levels down to a safe level (less than 6 mg/dL). At these safe levels, the brain can function normally, and the person with PKU can learn easily and have stable emotions.

What is the Diet for PKU? | How is PKU Monitored?