My Baby Has Been Diagnosed with Phenylketonuria, Now What?

My Baby Has Been Diagnosed with Phenylketonuria, Now What?

When they are born, all babies undergo a newborn screening, which tests them for certain conditions. To do this, doctors perform a heel stick, usually on the first day the baby is born, to collect a small drop of blood for testing.

One of the conditions doctors are testing for is phenylketonuria (PKU), a rare metabolic disorder characterized by abnormally high levels of phenylalanine (a protein building block, also called an amino acid) in the body.

It is very important that this test be performed for every newborn because if PKU is detected at birth, children can be treated and, with minor lifestyle changes, lead a completely normal life. Without intervention, the disease can cause severe learning disabilities and irreversible brain damage.

As a new parent, learning your child has a genetic disease can be frightening. Here are a few FAQs and answers to help you.

What causes PKU?

PKU is a genetic disease caused by mutations in a gene called PAH. This gene provides instructions for making an enzyme that breaks down the amino acid phenylalanine. Without this enzyme, phenylalanine builds up in the body to what can become toxic levels.

In most cases, both parents of an affected baby are carriers of mutations in the PAH gene. Because each parent has one healthy copy of the gene, they do not have the disease. A child must inherit two copies of a disease-causing mutation (one from each parent) to develop PKU.

Is PKU contagious?

No, PKU is a genetic disease and is not contagious.

How common is PKU?

In the U.S., it’s estimated that 1 in 10,000 to 1 in 15,000 babies are born with PKU. Around the world, the incidence of PKU varies widely based on the country. In Ireland, the rate is slightly higher than the U.S. at 1 in 4,500 births, while in Finland, the rate is much lower at 1 in 100,000 births.

How do doctors treat PKU?

PKU is completely treatable with a low-protein diet to keep phenylalanine levels low. Breast milk is naturally low in phenylalanine. You can supplement this with a special baby milk formula that is also low in phenylalanine. As your baby grows, you will have to make sure he or she maintains a low-protein diet — avoiding cheese, meat, poultry, eggs, and milk, and substituting their diet with a protein supplement that provides other amino acids, but is low in phenylalanine.

Will my child have a normal life?

Children with PKU will grow and develop normally, be able to go to school, and have a normal lifespan as long as they maintain the low phenylalanine diet. They will also be able to have children of their own, though some precautions are necessary during pregnancy for women with PKU.

What happens if my child has high phenylalanine levels?

The wrong foods, illness, and lack of food can all cause phenylalanine levels to increase. Your dietitian will show you what to watch for and how to quickly counteract high levels of phenylalanine.

How can I find more information about PKU?

This website, Phenylketonuria News, is a good source of information for news and updates on ongoing research about PKU. It regularly publishes new information about the disease and new treatments under development. The following websites are also good places to get more information and connect with other families affected by PKU.


Last updated: March 26, 2020


Phenylketonuria News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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