Phenylketonuria occurs in most geographic groups but is rare in Jews of Eastern European ancestry and in blacks. In the United States, the incidence is about 1 in 16,000 live births. The symptoms of phenylketonuria are usually absent in newborns. Rarely, an infant is sleepy or eats poorly. Affected infants tend to have lighter skin, hair, and eyes than family members who don't have the disorder.
Some infants develop a rash that looks like eczema.
If not treated, affected infants soon develop some degree of mental retardation, usually severe. Symptoms in children who have undiagnosed or untreated phenylketonuria include seizures, nausea and vomiting, aggressive or self-injurious behavior, hyperactivity, and sometimes psychiatric symptoms. Phenylketonuria in a pregnant woman has profound effects on the developing fetus, often causing mental and physical retardation in the infant. Strict control of the mother's phenylalanine level during pregnancy usually results in a normal outcome for the fetus. Diagnosis and Treatment Early diagnosis is made when a high phenylalanine level and a low tyrosine level are detected during the screening of a newborn.