Phenylketonuria (PKU)
An Amino Acid Disorder

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What is it?
Phenylketonuria (PKU) is a hereditary disease that is caused by the lack of a liver enzyme required to digest phenylalanine. Phenylalanine is an amino acid that is most commonly found in protein-containing foods such as meat, cow's milk, over the counter infant formulas (both regular and soy) and breast milk.

Inheritance and Frequency
The gene defect for phenylketonuria is an autosomal recessive genetic trait and is unknowingly passed down from generation to generation. This faulty gene usually emerges when two carriers have children together and pass it to their offspring. For each pregnancy of two such carriers, there is a 25% chance that the child will be born with the disease and a 50% chance that the child will be a carrier for the gene defect.

Studies show that 1 of every 17,000 live births will have phenylketonuria.

Signs & Symptoms
Newborns affected by PKU usually do not show any signs of the disease at birth. But within the first few weeks of life they begin to show neurologic disturbances such as epilepsy. Children suffering from undiagnosed PKU also may have an unpleasant, musty smell. It has been shown that almost 90% of affected people have blond hair and blue eyes. Signs also include skeletal changes such as a small head, short stature, and flat feet. PKU sufferers may also have a skin disorder called eczema.

Long Term Effects
PKU-affected children who are not diagnosed and do not eliminate phenylalanine from the diet will suffer from irreversible brain damage and mental retardation. Properly treated individuals should live a normal, healthy life.

Treatment
Treatment of PKU is the elimination of phenylalanine from the diet. Phenylalanine is commonly found in protein-containing foods such as meat. Babies who are diagnosed with PKU must immediately be put on a special milk/formula substitute. Later in life, the diet is mainly vegetarian.

Previously, PKU affected individuals were allowed to go off diet after approximately 12 years of age. However, physicians now recommend that this special diet should be followed throughout life.

Females affected by PKU, who become pregnant and have stopped following the appropriate diet, must return to maintaining the diet through the duration of all pregnancies. Babies of females with PKU who are not on diet during pregnancy can be severely malformed and mentally retarded. However, females who are on diet have normal, healthy infants. For more information on maternal PKU, visit Maternal PKU - American Academy of Pediatrics Statement.

History


Screening
Visit the What Does Your State Screen page to learn about newborn screening in your state.

Supplemental Screening
If you live in a state that does not perform screening on its newborns for all detectable disorders, there are laboratories that will provide this screening for you no matter your state of residence. For more information about supplemental screening, visit our supplemental screening page. Also visit our frequently asked questions page for more information on newborn screening.

Other Sites of Reference