Phenylketonuria (PKU) is a rare metabolic disorder. Children with PKU can’t process an amino acid called phenylalanine. Phenylalanine is in many common foods. It helps the body make protein. It is also important for brain growth. It is normally changed to tyrosine, which helps create all of the body's proteins. But with PKU, the amino acid can build up in the bloodstream and cause harm. PKU is found with a simple blood test. All newborn babies in the U.S. are screened for PKU.
PKU is caused by a defect in a gene known as the PAH gene. This defect changes the way that phenylalanine is broken down by the body during digestion. PKU is passed on to children when each parent has 1 mutated gene. This means that neither parent has any symptoms of PKU, but both are carriers of the faulty gene. PKU is an autosomal recessive disease. This means that a child needs to inherit 1 faulty gene from each parent to show signs of the disorder.
A child is more at risk for PKU if his or her parents each have 1 faulty PAH gene. PKU affects 1 out of every 10,000 to 15,000 newborns born in the U.S.
If a baby is not tested and has undiagnosed PKU, he or she may show signs or symptoms at several months old. Some babies with PKU may seem more drowsy and listless than normal. They may have feeding problems. As they continue to take in protein and phenylalanine through their diets, they may have growth, mood, behavior, and thinking problems, as well as other problems. Symptoms can range from mild to severe based on how much phenylalanine is in the blood.
The symptoms of PKU can be like other health conditions. Make sure your child sees his or her healthcare provider for a diagnosis.
All newborn babies in the U.S. are screened for PKU with a blood test. If you adopt a child from another country, he or she may need to be screened for PKU and other genetic diseases.
PKU is treated with a special diet. Newborn babies who test positive for PKU are placed on phenylalanine-free formula right away.
As babies start to eat solid food, their diet will need to be restricted. This is because phenylalanine is found in many foods with protein. A child with PKU should not eat milk, fish, cheese, nuts, beans, or meat. A child with PKU can eat many foods low in protein, such as vegetables, fruits, and some cereals. Your child may also need to take mineral and vitamin supplements to make up for nutrients missing from the diet.
Children with PKU can’t tolerate the sugar substitute called aspartame. Aspartame contains phenylalanine. You will need to read all food labels to make sure your child avoids foods and drinks that contain this sweetener.
A baby born to a woman who has PKU that is not controlled with a special diet is at high risk for serious problems. The developing baby in the uterus can be exposed to very high levels of phenylalanine. This can cause low birth weight, slow growth, small head, behavior problems, and heart disorders. These mothers are also at risk for pregnancy loss.
If PKU in a child is not diagnosed and treated, phenylalanine will build up in the bloodstream until it reaches levels that can cause brain damage. It can also cause permanent damage to organs and tissues around the body. PKU can lead to:
Women with PKU who are of childbearing age should be careful to follow a strict low-protein diet. Your healthcare provider may advise genetic counseling. You can discuss with a counselor the risk for PKU in a future pregnancy.
Children born with PKU will need to follow a lifelong low-protein diet and stay away from aspartame. If they don't, they may have mood disorders, poor memory and problem-solving skills, depression, and uncontrollable shaking (tremors).
If your baby is born with PKU, you can do certain things to take care of him or her:
Call the healthcare provider if your child has:
Tips to help you get the most from a visit to your child’s healthcare provider:
Article Last Updated: February 12, 2019
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