[Endogenous ochronosis: a case description].

Endogenous ochronosis or alkaptonuria is an autosomal recessive disease caused by a deficiency of the enzyme homogentisic acid oxidase. Affected individuals excrete high levels of homogentisic acid in the urine, which darkens when it is alkalinized or oxidized. Deposits of blackish-brown pigment also occur in connective tissue; this causes, usually starting around the age of 40, the typical external manifestations of this disease, along with disorders in other organs.