Alkaptonuria is a rare genetic disorder caused by a deficiency of the enzyme homogentisate oxidase. This enzyme is essential for breaking down the amino acids tyrosine and phenylalanine. When it is lacking, a substance called homogentisic acid accumulates in the body, leading to various health issues. One of the most noticeable symptoms of alkaptonuria is the darkening of urine when exposed to air. Over time, the buildup of homogentisic acid can also cause joint pain and damage, a condition known as ochronosis. Although there is no cure, management focuses on alleviating symptoms and preventing complications.