Alcaptonuria

Definition:

A rare inherited disorder of metabolism characterized by urine which turns black when exposed to air and development of arthritis in adulthood.

Causes, incidence, and risk factors:

Alcaptonuria is an autosomal recessive inherited disorder. It is a disorder of tyrosine (an amino acid) metabolism resulting from a defect in the enzyme homogentisic acid oxidase. Homogentisic acid is excreted in the urine and turns a black color upon exposure to air.