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). The presence of alkapton in urine has high lithogenic effect. We report 71 years old man suffering from alkaptonuria with present severe late complications. In this man black coloured urinary calculus was extracted from the urethra. This calculus was formed of organic amorphous part and crystallized part analyzed by X-ray diffraction and infrared spectroscopy identifying weddelite and whitlockite (1:1), and trace amounts of carbonate apatite.