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Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. The three major features of alkaptonuria are the presence of dark urine, ochronosis, a buildup of dark pigment in connective tissues such as cartilage and skin, and arthritis of the spine and larger joints. Ochronosis starts after age 30 and arthritis in early adulthood. Other features of this condition can include heart problems, kidney stones, and prostate stones. Alkaptonuria is caused by mutations in the HGD gene. It is inherited in an autosomal recessive fashion. There is still no cure for this disease. Treatment includes the management of joint pain, physical and occupational therapy, joint replacements and surgery when needed.
Source: GARD Last updated on 05-01-20
The three main features of alkaptonuria (AKU) are the presence of a substance called homogentisic acid (HGA) in the urine, ochronosis and arthritis. The urine of individuals with AKU turns black when exposed to air. Children do not have symptoms of AKU other than the urine turning black when left to stand for a few minutes. Ochronosis, a buildup of dark pigment in connective tissues such as cartilage and skin, is also characteristic of the disorder. This blue- black pigmentation usually appears after age 30 and commonly affects the cartilage of the ear, ligaments, tendons, blood vessels, kidneys, lungs and prostate. Dark spots on the white of the eye and cornea may also occur. People with alkaptonuria typically develop arthritis, particularly in the spine and large joints, beginning in early adulthood. Other features of this condition can include heart problems, kidney stones, changes of the sound of the voice and prostate stones.
Last updated on 05-01-20
There is no cure for alkaptonuria, but there is treatment for some individual signs and symptoms of the condition. Joint pain may be substantial in individuals with alkaptonuria, and close attention to pain control is usually necessary. Physical and occupational therapy can be important to promote muscle strength and flexibility. Knee, hip, and shoulder replacement surgeries may be options for managing significant arthritis. In general, however, the goal of joint replacement is pain relief rather than increased range of motion. Maintaining joint range of motion through moderate non-weight-bearing exercise such as swimming may have beneficial effects. Treatment of prostate stones and renal stones may include surgery.
No therapy has proven to prevent or correct the pigmentary changes of ochronosis.
Dietary restriction of phenylalanine and tyrosine has been proposed to reduce the production of HGA, but severe restriction of these amino acids is not practical in the long term and may be dangerous.
Last updated on 05-01-20
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