Thelansis

 Alkaptonuria, or Black urine disease, is a rare genetic disorder affecting phenylalanine and tyrosine metabolism. This condition is characterized by homogentisic acid (HGA) accumulation and its oxidized product, benzoquinone acetic acid (BQA), in various tissues and body fluids. These compounds cause darkening of urine when exposed to air and blue-grey coloration of the sclera and ear helix, a joint disease involving both the axial and peripheral joints (ochronotic arthropathy), and other complications such as renal and cardiac problems. The underlying cause of alkaptonuria is the loss-of-function mutations in the HGD gene, which encodes homogentisate 1,2-dioxygenase, an enzyme involved in the breakdown of HGA. The inability to break down HGA leads to its accumulation, causing tissue damage by depositing a melanin-like pigment with a high affinity for connective tissue. This pigment triggers redox reactions and induces free radical production, further damaging the connective tissu...