What is Phenylketonuria?

Phenylketonuria, which is also referred to as PKU, is a rare condition that affects infants. These babies are born unable to break down phenylalanine, which is an essential amino acid.

This disorder is inherited, and it causes a baby to be born without an enzyme referred to as phenylalanine hydroxylase. This enzyme is required to break down phenylalanine, which is found in food that has protein.

Because this enzyme is missing, the level of phenylalanine will increase within the body, and that could result in damage to the central nervous system, as well as brain damage.

What are the Symptoms of Phenylketonuria?

Symptoms of PKU could be mild, moderate, or severe.

Because phenylalanine affects the production of melanin, infants who have PKU will typically exhibit lighter hair, eyes, and skin.

The most severe form of phenylketonuria is referred to as classic PKU. In this case, the infant would appear normal over the course of the first few months of life, but symptoms will begin to develop. These include shaking, trembling, tremors, seizures, stunted growth, skin conditions, hyperactivity, and a musty odor of the urine, skin, earwax, or breath.

How is Phenylketonuria Treated?

Phenylketonuria needs to be caught and treated early to prevent severe damage and complications. This condition is treatable, however, by following a strict diet that’s extremely low in phenylalanine.

Foods that are high in protein should be avoided. These include fish, pork, beef, chicken, beans, nuts, milk, cheese, and eggs.

Patients can also take sapropterin, which is a medication approved by the FDA to treat PKU. This medicine will be effective in children that have mild cases of the disorder, and it will help to lower phenylalanine levels in the body, but it has to be used with a custom meal plan.

Last Reviewed:
October 08, 2016
Last Updated:
August 24, 2017