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Symptoms
By Mayo Clinic staffNewborns with phenylketonuria initially don't have any symptoms. Without treatment, though, babies usually develop signs of PKU within a few months. Phenylketonuria symptoms can be mild or severe and may include:
- Mental retardation
- Behavioral or social problems
- Seizures, tremors or jerking movements in the arms and legs)
- Hyperactivity
- Stunted growth
- Skin rashes (eczema)
- Small head size (microcephaly)
- A musty odor in the child's breath, skin or urine, caused by too much phenylalanine in the body
- Fair skin and blue eyes, because phenylalanine cannot transform into melanin — the pigment responsible for hair and skin tone
Varying severity
The most severe form of the disorder is known as classic PKU. Children with untreated classic PKU usually develop obvious, permanent mental retardation.
Less severe forms of PKU — sometimes called mild or moderate PKU — have a smaller risk of significant brain damage, but most children with these forms of the disorder still require a special diet to prevent mental retardation and other complications.
Pregnancy and PKU
A woman who has PKU and becomes pregnant is at risk of another form of the condition called maternal PKU. Many people with PKU used to stop following a low-phenylalanine diet during their teen years, as was directed by doctors at the time. But, doctors now know that if a woman doesn't follow the diet during pregnancy, blood phenylalanine levels can become very high and harm the developing fetus. Because of this, and other reasons, doctors recommend that anyone with PKU follow the low-phenylalanine diet for life.
Although babies born to mothers with high phenylalanine levels may have complications at birth, most don't actually inherit PKU and won't need to follow a PKU diet after birth. However, these babies are at risk of being born with:
- Mental retardation
- Abnormally small head (microcephaly)
- Heart defects
- Low birth weights
- Behavioral problems
When to see a doctor
Seek medical advice in these situations:
- Newborns. If routine newborn screening tests show that your baby may have PKU, your child's doctor will want to start dietary treatment right away to prevent long-term problems. Newborns with PKU are given a special formula. Your doctor may refer you to a specialist in genetics and a dietitian or nutritionist who can help you learn about the PKU diet.
- Adults. Older adults with PKU who stopped the PKU diet in their teens also may benefit from a trip to the doctor. Although adolescents with PKU were allowed to go "off-diet" in the past, doctors now recommend that anyone with PKU continue the special diet for life. Returning to the diet may improve mental functioning and behavior and slow damage to the central nervous system in adults with high phenylalanine levels.
- Women. It's especially important for women with a history of PKU to see a doctor and return to the PKU diet before becoming pregnant. Even mild cases of maternal PKU can pose a risk to unborn babies. Pregnant women with PKU who aren't following the special diet also have a higher risk of miscarriage.
- Bodamer OA. Overview of phenylketonuria. http://www.uptodate.com/home/index.html. Accessed Aug. 18, 2009.
- Phenylketonuria. Genetics Home Reference. http://ghr.nlm.nih.gov/condition=phenylketonuria. Accessed Aug. 27, 2009.
- PKU (Phenylketonuria). March of Dimes. http://www.marchofdimes.com/professionals/14332_1219.asp. Accessed Aug. 24, 2009.
- Longo Nicola. Inherited disorders of amino acid metabolism in adults. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aID=2882866. Accessed Aug. 27, 2009.
- Amino acid and organic acid metabolism disorders. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec19/ch296/ch296c.html. Accessed Aug. 27, 2009.
