aciduria homogentisic aciduria 2018-08-24T11:55:51Z excretion of excessive amounts of homogentisic acid (an intermediate in the tyrosine degradation pathway) and its oxidized form (benzoquinoneacetate) in the urine, giving it an unusually dark color on prolonged exposure to air MP:0030619 increased urine homogentisic acid level Homogentisic aciduria is one of the three distinct clinical features of alkaptonuria (AKU), along with ochronosis and ochronotic osteoarthropathy; the darkening of urine occurs because the HGA pigment oxidizes to benzoquinoneacetate (BQA), which forms a melanin-like polymer that slowly turns urine black MPheno.ontology