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Phenylketonuria (PKU) is a rare genetic disease that babies are born with. It occurs due to the lack of an enzyme that helps their bodies break down a specific amino acid. Without this enzyme, the amino acid builds up in your baby’s blood and brain. It can cause toxic effects without treatment. Treatment includes a special diet and medication.
Babies with phenylketonuria appear healthy at birth VSports最新版本. Without treatment, symptoms of PKU will develop slowly over a period of three to six months. During this time, you may notice the first signs of the condition, like developmental delays.
By 1 year old, your baby may have other phenylketonuria (PKU) symptoms, including:
Along with developmental delays and intellectual disability, severe PKU symptoms may eventually develop VSports注册入口. These include:.
If you have untreated phenylketonuria and you’re pregnant, you’re at a high risk for miscarriage V体育官网入口. Babies born to mothers with unmanaged PKU disease may have:.
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If your PKU is well managed, you can have healthy babies.
Changes (pathogenic variants) in the PAH gene cause phenylketonuria. The PAH gene gives your body instructions on how to make an enzyme called phenylalanine hydroxylase (PAH) V体育2025版. This enzyme is responsible for processing the amino acid phenylalanine.
When there are changes in the PAH gene, the PAH enzyme may be missing or defective VSports. Without the PAH enzyme, your baby can’t break down phenylalanine. It builds up in their body, leading to the symptoms of the disease.
Phenylalanine is an essential amino acid. An essential amino acid is one that your body needs but doesn’t produce naturally. You must get it from the foods you eat. Phenylalanine can be found in many high-protein foods, like meat, eggs and dairy.
Normally, your body uses the phenylalanine it needs and then converts the excess into other substances it uses. But when your baby lacks PAH, phenylalanine builds up in their blood and brain.
Phenylketonuria is inherited in an autosomal recessive pattern. That means a baby needs to receive both copies of the changed gene (one from each biological parent) to develop the condition.
Your baby’s healthcare provider will diagnose phenylketonuria shortly after birth. Newborns in every hospital in the U.S. (and many other countries) are tested for PKU disease as part of routine newborn screening. Your baby’s provider will take a sample of blood from your baby’s heel by poking it with a small needle. Only a few drops of blood are necessary for this test.
Newborn screening looks for high levels of phenylalanine in your baby’s blood. If your baby’s phenylalanine levels are high, their provider will order additional blood tests or urine tests. They may also request a genetic test in order to pinpoint the change in the PAH gene responsible for their condition.
Almost all cases of PKU are diagnosed between 24 and 72 hours after birth. But healthcare providers can diagnose the condition at any age. It’s very rare, but providers can miss some cases during the screening process. You can also get tested if you didn’t receive a newborn screening.
If you’re pregnant, a prenatal genetic test can tell you if your baby’s at risk for genetic conditions, including phenylketonuria. A genetic counselor can help you decide if testing is right for you. Then, they can explain the results of the test.
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Prenatal genetic testing may be useful if you already have a child with PKU. This is because you have a higher risk of conceiving another baby with the condition.
There’s no cure for PKU. But treatment for the condition can prevent symptoms and severe complications from developing. Phenylketonuria treatment is lifelong. It consists of a special diet (eating plan) and possibly medication. If you stop following the eating plan or taking the medication, symptoms will quickly return.
People with PKU must carefully follow a special eating plan low in phenylalanine. Foods high in protein — like meat, eggs and dairy — contain phenylalanine. But your body still needs some protein to function. A dietitian can create an eating plan specialized for you that’s well-balanced and full of nutrients. The goal is to consume just enough phenylalanine to keep your body running and no more.
You also need to avoid the artificial sweetener aspartame. This is because aspartame releases phenylalanine into your bloodstream when your body digests it. Aspartame is in many foods, drinks and medications — especially those labeled “diet” or “sugar-free.” Examples of products containing aspartame include:
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If you have phenylketonuria and you’re pregnant, it’s especially important to follow this eating plan throughout your pregnancy. This will ensure your baby is born healthy. Newborns with PKU need to start on a special phenylalanine-free formula right away.
The U.S. Food and Drug Administration (FDA) approves two medications for the possible treatment of phenylketonuria:
Phenylketonuria (PKU) is a lifelong condition with no cure. But with early diagnosis, you can manage PKU and minimize its impact on your health.
You or your child will likely need to be on a low-protein eating plan for life to protect your health. This can be daunting and exhausting to plan your life around. But you’re not alone. Your dietitian will be a go-to source of expertise. You might also want to join a support group of other people living with PKU to learn from their experiences.
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If PKU is causing distress, reach out to a mental health professional for help. Your mental health is just as important as your physical health.
Just as people with diabetes sometimes prefer to be called “diabetics,” the same holds true for people with PKU. They may prefer the term “phenylketonuric.”
Many different foods, drinks and medications are made with the artificial sweetener aspartame. Aspartame contains phenylalanine. Companies that make products with aspartame are required to add a warning label to their packaging. So, on products like diet soda or sugar-free gum, you’ll see the warning: “Phenylketonurics: Contains phenylalanine.” This is to help phenylketonurics avoid them.
When you or your newborn receives a phenylketonuria (PKU) diagnosis, it may be hard to accept. The thought of having to restrict certain foods for the rest of your life may be overwhelming. Work closely with a dietitian to create an eating plan that’s phenylalanine-free but still delicious and nutritious. PKU is a lifelong condition. But by carefully following your eating plan and checking your phenylalanine levels frequently, you can manage how it affects your life.
Do certain health conditions seem to run in your family? Are you ready to find out if you’re at risk? Cleveland Clinic’s genetics team can help.
Last reviewed on 07/16/2025.
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