[Formation of the urinary stones in alkaptonuria patients].

Alkaptonuria is an autosomal recessive disease with late complications (arthritis and ochronosis). Excretion of alkapton (homogentisic acid) in the urine is due to congenital lack of the enzyme homogentisate 1,2-dioxygenase, which mediates the essential step in the catabolism of phenylalanine and tyrosine. Urine excretion of homogentisic acid is very high, urine turns dark if allowed to stand or is alkalinized (a result of formation of polymerization products of alkapton).