Homogentisate 1,2-dioxygenase or HGD is involved in the catabolism of aromatic rings, more specifically in the breakdown of the amino acids tyrosine and phenylalanine.

The other effect of the ochronotic pigment is that it can accumulate in the body’s connective tissue leading to degenerative arthritis, as the person grows older.

[2] Alkaptonuria has another effect in that it can cause the urine to turn black as well if let to sit for long enough to become oxidized, though is this often a method for testing for the genetic defect.

The metabolic disease is autosomal recessive, such that both parents must pass the gene on to their children in order for child to have the defect.

[citation needed] Borowski et al. propose a mechanism for HGD in their article featured in the Journal of the American Chemical Society.