Definition: Excretion of homogentisic acid (alkapton) in the urine resulting from congenital lack of the enzyme homogentisate 1,2-dioxygenase, which mediates an essential step in the catabolism of phenylalanine and tyrosine; urine turns dark if it is allowed to stand or is alkalinized (a result of formation of polymerization products of homogentisic acid); frequently occurs throughout relatively long periods or may appear at irregular intervals; arthritis and ochronosis are late complications; autosomal recessive inheritance; caused by mutation in the homogentisate 1,2-dioxygenase gene (HGD) on chromosome 3q.
[alkapton + G. ouron, urine]
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