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.

Synonyms: Alcaptonurias, Alcaptonuria, Alkaptonuria, Homogentisic Acid Oxidase Deficiency, Homogentisic Acidura