Phenylketonuria (fen-ul-kee-tuh-NUR-ee-uh), or PKU, is a metabolic disorder that
some babies are born with. It's caused by a defect in the enzyme that breaks down
the amino acid phenylalanine.
Newborn babies in the United States have their blood tested for PKU as part of
screening. This lets doctors start treatment, usually a special diet, right away
to help prevent problems.
What Are the Signs & Symptoms of PKU?
The body uses amino acids to build proteins. Phenylalanine (fen-ul-AL-uh-neen)
is needed for normal growth in infants and children and for normal protein production.
But if too much builds up in the body, the brain is affected. Phenylketonuria that's
not treated can lead to developmental delays and permanent intellectual disability.
Phenylalanine also affects melanin, the pigment responsible for hair color and
So kids with PKU often have fair skin, light hair, and blue eyes.
Treatment for PKU involves following a strict diet that is low in phenylalanine.
Babies with PKU need to be on a special formula as soon as possible.
Children and adults with PKU should eat a low-protein diet. They should avoid high-protein
foods, like milk, dairy, meats, eggs, nuts, soy, and beans. A person with PKU also
should avoid the artificial sweetener aspartame, which contains phenylalanine. Special
formulas may be needed at any age for the person to get the right amount of calories
and essential nutrients.
The special diet should start as soon as PKU is diagnosed and continue for the
rest of the person's life. New medicines are being developed to lower PKU in the blood,
but medical nutrition therapy is the main treatment for PKU.
What Else Should I Know?
PKU is treatable when found early. Doctors will closely watch kids who have it.
People with PKU must strictly follow the right diet for the rest of their lives. This
can prevent the problems caused by too much phenylalanine.
If your child has phenylketonuria, work with the health care team to help keep
phenylalanine levels in an acceptable range. Your doctor will check the level of phenylalanine
in your child's blood regularly.
Because PKU is a genetic condition, you may want to speak to a genetic
counselor about testing other family members and how PKU runs in families. You
also can find more information and support online at: