A rare condition in which the ligaments and cartilages of the body, and sometimes the conjunctiva (see EYE), become stained by dark brown or black pigment. This may occur in chronic carbolic poisoning, or in a congenital disorder of metabolism in which the individual is unable to break down completely the tyrosine of the protein molecule – the intermediate product, homogentisic acid, appearing in the urine, this being known as alkaptonuria.... ochronosis
(alkaptonuria) n. the congenital absence of an enzyme, homogentisic acid oxidase, that is essential for the normal breakdown of the amino acids tyrosine and phenylalanine. Accumulation of *homogentisic acid causes dark brown discoloration of the skin and eyes (ochronosis) and progressive damage to the joints, especially of the spine. The gene responsible for the condition is recessive, so that a child is affected only if both parents are carriers of the defective gene.... alcaptonuria
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