Alkaptonuria

Alkaptonuria, a rare disorder of intermediate protein metabolism, characterized by the appearance of homogentisic acid in urine. The latter is formed in a healthy person during the breakdown of protein molecules containing aromatic amino acids, tyrosine and phenylalanine. The alkaptonuric organism loses the ability to break down homogentisic acid, which is then excreted in urine. It is optically inactive and incapable of fermentation. Its aqueous solutions, as well as the urine of alkaptonurics, darken on the surface after the addition of a small amount of caustic soda or ammonia, but after shaking they quickly take on a dark brown color. This acid has the ability to reduce an alkaline copper solution even with slight heating, whereas an alkaline bismuth solution is not reduced by it. Among the accompanying manifestations of A., the dark brown coloration of cartilages should be noted, which is most noticeable in the cartilages of the auricles and nose; sometimes pain during urination occurs. A. is more often observed in men than in women. It has been noted that children of blood relatives are predisposed to alkaptonuria.