Skip to main content
What is Phenylketonuria?

You are listening to Healthy Kids Zone:

What is Phenylketonuria?

May 18, 2015

Babies get tested for many things right after they are born. The heel prick includes a test for phenylketonuria (PKU), a rare birth defect that causes a certain amino acid to build up in the body. Dr. Gellner talks about this disorder and what a PKU diagnosis means for you and your new baby.

Episode Transcript

Dr. Gellner: What is PKU and why is it so important my child be tested for it? I am Dr. Cindy Gellner and we will discuss that today on The Scope.

Announcement: Medical news and research from University of Utah physicians and specialists you can use for a happier and healthier life. You're listening to The Scope.

Dr. Gellner: When your child has the newborn screening test before they leave the hospital and at the two-week well visit, one of the things they're checking for is phenylketonuria or PKU. It's a rare birth defect and it pretty much means the body is not able to break down an amino acid called phenylalanine.

You may have seen the warning labels on soda labels that say, "Attention phenylketonurics, contains phenylalanine." Amino acids are the building blocks for protein, but too much of this amino acid can be dangerous for people with PKU.

The cause of PKU is completely genetic. For a child to be born with PKU both parents must have the PKU gene. If only one parent has the gene, the child will not have PKU. A parent can have the PKU gene, but not have the disease and this is called being a carrier. If a pregnant woman with PKU does not follow a PKU diet during pregnancy, the baby may be born with intellectual disabilities, an abnormally small head, or even heard defects. PKU is much more common in Caucasians than any other ethnic population.

Newborns who have PKU do not show symptoms right away, but without treatment babies usually show signs of PKU within a few months. Symptoms can be mild or severe and may include a musty odor to the child's breath, skin or urine, a small head-size and slow growth, vomiting with feeds, not just normal spit-ups, or rocking back and forth and having seizures. Untreated PKU does lead to brain damage within the first few months of life.

So the newborn screening that your child gets before they leave the newborn nursery and again at two weeks after birth, picks this disease up along with numerous other medical conditions. All 50 states test newborns for PKU. If the PKU test is positive, you and your pediatrician will be notified right away by the Health Department. The main treatment for PKU is a strict diet that limits that amino acid, phenylalanine. Because regular infant formula and breast milk contain phenylalanine, babies with PKU are put on a special infant formula. A small amount of breast milk may be okay for some babies.

Children with PKU are followed closely by genetics doctors. These specialists will work with the family to monitor the levels of phenylalanine in the child's blood. Genetics doctors also work closely with dietitians familiar with PKU that can help the families with getting these special formulas and other drinks that they need as they get older.

So how can I help my child if I find out that they do have PKU? The first thing is to monitor what your child eats every day. Milk, eggs, and other common foods contain phenylalanine. Often you'll find that information on a label like you do on the soda cans. Give your child a low-protein diet, including rice, pasta, tortillas, bagels, breads, and egg substitutes and imitation cheeses. Teach your child to also avoid foods and medicine containing aspartame. Aspartame is a sweetener and it's found in NutraSweet and Equal and many other products that are low-sugar. Aspartame releases phenylalanine when it's digested. Again, a safe amount of phenylalanine differs for every child and your genetics doctor and their dietician can help you determine what this level is.

Can you prevent PKU? No, you can not. If either parent has a family history of PKU, the parent can have a blood test before pregnancy or birth that can tell you if you are a PKU carrier. If you have PKU, you can prevent birth defects by sticking to the PKU diet and even if you only have mild PKU, you should follow the diet if you are pregnant.

Announcement: is University of Utah Health Sciences radio. If you like what you heard, be sure to get our latest content by following us on Facebook. Just click on the Facebook icon at