Dictionary of Human Evolution and Biology

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Autosomal recessive caused by defects in the enzyme homogentesic acid oxidase (HGO) that normally breaks down homogentesic acid (alkapton); results in the relatively benign excretion of high levels of alkapton, which causes urine to turn black upon exposure to air, especially when allowed to stand; black pigmentation of cartilage and collagenous tissues is also a feature. Most people with alkaptonuria also develop arthritis. This trait was the first ever discovered to be the result of a metabolic block and (among others, such as albinism) resulted in Sir Archibald Garrod’s book Inborn Errors of Metabolism (1909).

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