Alkaptonuria
Alkaptonuria
Cause: Autosomal recessive defect in homogentisate oxidase (enzyme in tyrosine catabolism).
Effect: Accumulation of homogentisic acid in tissues and urine.
Key Facts / Data: Urine turns black on standing due to oxidation of homogentisic acid; incidence ≈ 1 in 250,000–500,000 births.
Clinical features: Dark urine, ochronosis (bluish-black connective tissue pigmentation), arthritis in adulthood.