Alkaptonuria is a genetic disorder that results in a defect in the gene that makes the body unable to properly break down certain amino acids tyrosine and phenylalanine.
It is an autosomal recessive disease. It means both the parents should pass a copy of defective genes to the child if the child gets the disorder.
Due to this inefficient breakdown, a substance called homogentisic acid builds up in the skin and other body tissues.
The acid leaves the body through the urine. The urine turns brownish-black when it mixes with air.