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Alkaptonuria
Definition:
Alkaptonuria is a rare inherited disorder of metabolism, characterized by urine that turns black when exposed to air. Another characteristic is the development of arthritis in adulthood. Alternative Names:
Alcaptonuria; Homogentisic acid oxidase deficiency; Ochronosis Text Continues Below
Causes, incidence, and risk factors:
Alkaptonuria is an autosomal recessive inherited disorder. In affected individuals, an amino acid known as tyrosine is not properly metabolized, due to a defect in an enzyme called homogentisic acid oxidase. Because of the defect, homogentisic acid is excreted in the urine and turns a brown color upon exposure to air. This is the result of a dark pigment with an ochre color (earthy red or yellow), which led to the name ochronosis. The bones and cartilage of the body may be brown-colored.
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