Alkaptonuria

Alkaptonuria is a rare inherited disorder of metabolism, characterized by urinethat turns black when exposed to air. Another characteristic is the development of arthritis in adulthood.

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 bodymay be brown-colored.

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