Phenylketonuria

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Phenylketonuria test

Phenylketonuria test

Phenylketonuria (PKU) is a rare condition in which the body does not properly break down (metabolize) an amino acid called phenylalanine.

PKU

Phenylketonuria (PKU) is inherited, which means it is passed down through families. Both parents must pass on the defective gene in order for a child to have PKU. This is called an autosomal recessive trait.

PKU occurs when a person is missing an enzyme called phenylalanine hydroxylase, which is needed to break down phenylalanine. Phenylalanine is 1 of the 8 essential amino acids found in foods that contain protein.

Without the enzyme, high levels of phenylalanine and two closely-related substances build up in the body. These substances are harmful to the central nervous system and cause brain damage. If the proteins containing phenylalanine are not avoided, PKU can lead to mental retardation by the end of the first year of life. Older children may develop movement disorders (such as athetosis) and hyperactivity.

Phenylalanine plays a role in the body's production of melanin, the pigment responsible for skin and hair color. Children with phenylketonuria often have lighter complexions than brothers or sisters without the disease. If the condition is untreated or foods containing phenylalanine are not avoided, a "mousy" odor may be detected on the breath and skin and in urine. The unusual odor is due to a build up of phenylalanine substances in the body.

Review Date: 08/18/2006
Reviewed By: Benjamin W. Van Voorhees, MD, MPH, Assistant Professor of Medicine and Pediatrics, The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.