Alkaptonuria: Black Urine Disease

Alkaptonuria is a defect in the HGD gene. The proteins tyrosine and phenylalanine are unable to properly break down. When this occurs, toxic tyrosine byproduct known as homogentisic acid accumulates in the blood and large amounts are excreted in the urine. Excessive amounts of homogentisic acid causes damage to cartilage which leads to osteoarthritis. Alkaptonuria is an inherited disease that causes the urine to turn black when left standing or becomes exposed to air. This condition is inherited and is passed from parent to child.

When it comes in contact with air, homogentisic is oxidized and then forms pigment like polymeric material. This material is responsible for the black color of urine when exposed to air or left standing. Homogentisic acid blood levels are low, this is due to rapid kidney clearance. Homogentisic acid is deposited in cartilage throughout the body, then converts to the pigment like polymer through an enzyme-mediated reaction. This occurs in the collagenous tissue. Polymer accumulates in cartilage; this process takes many years. The cartilage, which is normally transparent tissue becomes slate blue. The effect of this process is not often seen until adulthood.

People with this disorder can expect to live a normal life. Health problems are associated with this disorder. At about 30 years of age, back pain occurs due to discs being affected around the thoracic and lumbar areas. As people get older with this disorder, joints become effected. Eventually, joint replacement surgery may be required. The Achilles tendon is commonly affected and can result in a tear. The aortic and mitro valve leaflets can become affected. Calcifications can form on the coronary arteries. This occurs in half of patients before reaching 60 years of age.

Alkaptonuria affects both men and women equally. This is because Alkaptonuria is an autonomic recessive or dominate trait. Men can experience severe arthritis symptoms more than women. The reason for this is unsure.

Treatments for this condition to manage the pain is physical therapy and occupational therapy. Therapy is important to promote flexibility and optimal muscle strength. Medicine and rehabilitation can be done if there is a limited range of motion or joint pain. Evaluation for presence of renal calculi can be performed by a renal ultrasound examination or helical abdominal CT. Joint range and motion can have beneficial effects when doing non-weight-bearing exercise, like swimming. Alkaptonuria can not be cured, although it can be managed and a person can live a long life.

Sources

eMedicine: http://emedicine.medscape.com/article/941530-overview