Alkaptonuria is a rare genetic disorder that affects the body's ability to break down homogentisic acid due to a deficiency of the enzyme homogentisic dioxygenase (HGD). This leads to the accumulation of homogentisic acid, causing urine to turn dark brown or black when exposed to air—often one of the first noticeable symptoms.

Over time, this buildup results in a condition called ochronosis, where cartilage and connective tissues darken and become brittle, leading to joint pain, stiffness, and early-onset osteoarthritis, particularly in the spine, hips, and knees. Other signs include black earwax, darkened sweat stains, and even heart valve damage due to calcification.

Although there is no definitive cure, treatment focuses on managing symptoms. Pain relief, physical therapy, and lifestyle adjustments can help maintain mobility and reduce discomfort. In severe cases, joint or heart valve replacement may be necessary.

Despite its challenges, people with alkaptonuria can lead fulfilling lives with proper medical care and regular monitoring. Early diagnosis and proactive management are key to reducing complications and improving quality of life.