Phenylketonuria (PKU)

Phenylketonuria (fee-nyl-key-ton-uria), or PKU, is an inherited metabolic disease that results in severe developmental delay and neurological problems when treatment is not started very early and maintained throughout life. The disease is caused by the absence of the enzyme phenylalanine hydroxylase, which normally converts the amino acid phenylalanine to another amino acid, tyrosine. This results in a build-up of phenylalanine and a low level of tyrosine, which causes a variety of problems, including cognitive decline, learning disabilities, behavior or neurological problems, and skin disorders.

PKU occurs in about 1 in 10,000 births. It is an autosomal recessive disorder, meaning the affected person inherits two copies of the defective gene, one from each parent. Newborn screening for PKU began in the mid-1960s and is now carried out in every state in the United States, as well as in many other countries.

The treatment for PKU consists of a special phenylalanine-restricted diet designed to maintain levels of phenylalanine in the blood between 2 and 6 mg/dl (milligrams per deciliter). All proteins are made up of amino acids; therefore, the diet for PKU consists of foods that contain only enough protein to provide the amount of phenylalanine necessary for growth and development . Foods allowed are primarily vegetables, fruits, and some cereals and grains. A synthetic formula containing all the amino acids except phenylalanine provides the remaining protein and calories for individuals with PKU.

SEE ALSO Amino Acids ; Artificial Sweeteners ; Inborn Errors of Metabolism .

Patricia D. Thomas

Internet Resources

National PKU News. Available from <>

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