E70.29

An inborn error of amino acid metabolism resulting from a defect in the enzyme HOMOGENTISATE 1,2-DIOXYGENASE, an enzyme involved in the breakdown of PHENYLALANINE and TYROSINE. It is characterized by accumulation of HOMOGENTISIC ACID in the urine, OCHRONOSIS in various tissues, and ARTHRITIS.

The yellowish discoloration of connective tissue due to deposition of HOMOGENTISIC ACID (a brown-black pigment). This is due to defects in the metabolism of PHENYLALANINE and TYROSINE. Ochronosis occurs in ALKAPTONURIA, but has also been associated with exposure to certain chemicals (e.g., PHENOL, trinitrophenol, BENZENE DERIVATIVES).