Alkaptonuria (AKU) is an autosomal recessive disorder, caused by deficiency of the homogentisate 1,2 dioxygenase (HGO), an enzyme which normally catalyses the conversion of homogentisic acid (HGA) into maleylacetoacetic acid, in the tyrosine degradation pathway. AKU is characterized by a plasmatic accumulation and subsequently an increased urinary excretion of HGA. In absence of HGO, HGA is rapidly oxidized to benzoquinone acetic acid (BQA). BQA polymerizes to amelanin-like pigment, which accumulates in connective tissues (ochronosis). This condition leads to a severe and crippling arthropathy. The fragility of the cartilage of AKU patients leads to fragmentation of its upper layer, causing the detachment of small fragments (shards) with consequent exposure of the subchondral bone. For this reason patients suffer joints pain and quickly involved in a multiple joints replacemenT.
Last date updated on July, 2014