Phenylketonuria (PKU)

Phenylketonuria (fen-ul-ke-ton-U-ree-a), or PKU, is an inherited metabolic disease in which the body cannot change one essential amino acid, phenylalanine (fen-ul-AL-a-neen), into another needed amino acid, tyrosine (TΎ-ro-seen). Untreated, PKU often results in severe intellectual disabilities, but if it is detected at birth and these children are put on a special diet, they can lead normal lives.

Children with a Strange Smell

In 1934 a mother with two children with intellectual disabilities went to a Norwegian medical doctor, Asbjθrn Felling (1888–1973). Felling became interested in the children's condition when the mother described the children's odd musty odor. The children, four and six years of age, had severe intellectual disabilities. The younger child could not speak or walk and still wore diapers. The older child could speak only a few words and had problems walking.

FØlling examined the children's urine and found no protein or glucose in it, but he was puzzled when their urine turned a deep green, instead of staying brownish, after he added the chemical compound ferric chloride to it. Felling expanded his study to other children whose urine produced the same kind of reaction and concluded that the unusual quality of the urine seemed to be connected with intellectual disabilities. Thus, he discovered PKU, which he concluded was a genetic error in the children's metabolism * .

What Causes Phenylketonuria?

PKU is a disruption in normal metabolism. Normally, an enzyme * in the body called phenylalanine hydroxylase (fen-ul-AL-a-neen hyDROK-silase) changes the essential amino acid * phenylalanine to another needed amino acid called tyrosine. If phenylalanine hydroxylase is missing, as it is in PKU, phenylalanine builds up in the blood and passes out of the body in urine.

PKU affects on average 1 out of every 10,000 to 15,000 babies in the United States. Because PKU is an inherited disorder, there is considerable variation among different ethnic and racial groups. The condition is found less often in people of African descent (1 in every 50,000 babies) and in Ashkenazi Jews.

What Are the Signs and Symptoms of Phenylketonuria?

Infants with PKU usually have lighter skin, hair, and eyes than the rest of their families, but symptoms do not appear until they are about three to six months old. These may include the following: