Phenylketonuria (PKU)

Topic Overview

What is phenylketonuria (PKU)?

Phenylketonuria (PKU) is a rare genetic disorder in which the body cannot break down an amino acid called phenylalanine, which is a part of protein. If PKU is not treated soon after birth, phenylalanine (say "fehn-uhl-A-luh-neen") builds up in the blood and brain. This buildup can lead to intellectual disability and central nervous system problems. But treating PKU soon after birth can prevent all or most of these problems.

What causes PKU?

PKU is passed down through families. To have the disease, a baby must get the gene from both parents. If a baby gets the gene from only one parent, he or she is a carrier of the PKU gene but does not have the disease.

What are the symptoms?

Symptoms usually start within a few months after birth, after phenylalanine has built up in the baby's body from the protein in formula or breast milk.

Early symptoms of PKU in a baby include:

• A musty odor to the skin, hair, and urine.
• Skin problems.
• Losing weight from vomiting and diarrhea.
• Acting fussy.
• Being sensitive to light.

If PKU is not treated early enough, the child may have growth problems, developmental delays, seizures, and severe intellectual disability.

How is PKU diagnosed?

Finding and treating PKU early usually can prevent brain damage and other long-term problems. So all babies born in the United States are tested for PKU within a few days after birth. The test may be repeated within the first week or two after birth.

How is it treated?

The main treatment for PKU is a lifelong reduced-protein diet. Your baby’s doctor can help you choose the right formula for your baby. You may be able to feed your baby some breast milk, but talk to your baby’s doctor first. When your child gets older, a registered dietitian can help you choose the right foods and recipes.

People who have PKU need regular blood tests to check phenylalanine levels.

If you or your child has PKU, it’s normal to feel a wide range of emotions. You may want to join a support group. Your doctor also can help.

Can PKU be prevented?

If you have a child with PKU, it may be helpful to get genetic counseling if you are thinking about having another child. If you have a family history of PKU, talk with your doctor about genetic testing.

If you have PKU and you want to have a baby, you must carefully control your phenylalanine levels. Babies born to mothers who have high levels of phenylalanine during pregnancy are at risk for:

• Severe problems with cognitive development.
• Growth problems.
• Heart problems present from birth (congenital heart disease).
• Having a very small head (microcephaly).

Frequently Asked Questions

Learning about phenylketonuria (PKU):	What is PKU? What causes it? What are the symptoms of PKU?
Being diagnosed:	How is PKU diagnosed?
Getting treatment:	How is PKU treated? What can I do to treat PKU at home?

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Author:	Debby Golonka, MPH	Last Updated: February 27, 2008
Medical Review:	Michael J. Sexton, MD - Pediatrics Thomas Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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