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Alternative names
Alcaptonuria; Homogentisic acid oxidase deficiency; OchronosisDefinition Return to top
Alkaptonuria is a rare inherited disorder of metabolism characterized by urine which turns black when exposed to air. Another characteristic is the development of arthritis in adulthood.Causes, incidence, and risk factors Return to top
Alkaptonuria is an autosomal recessive inherited disorder. In affected individuals, an amino acid known as tyrosine is not properly metabolized, due to a defect in an enzyme called homogentisic acid oxidase.
Because of the defect, homogentisic acid is excreted in the urine and turns a brown color upon exposure to air. This is the result of a dark pigment with an ochre color (earthy red or yellow), which led to the name ochronosis. The bones and cartilage of the body can be brown colored.
Symptoms Return to top
Infant/child:Signs and tests Return to top
Urinalysis is positive for reducing substance. Further urine testing shows a positive ferric chloride test.Treatment Return to top
Some patients benefit from high-dose vitamin C. This has been shown to decrease the build up of brown pigment in the cartilage, which may slow the rate of development of arthritis.
Expectations (prognosis) Return to top
The outcome is expected to be good.Complications Return to top
Calling your health care provider Return to top
Call your health care provider if you notice that your own urine or your child's urine becomes dark brown or black upon exposure to air.Prevention Return to top
Like most genetic diseases, alkaptonuria itself cannot be prevented, but some of the manifestations, such as arthritis, can be minimized by treatment. Update Date: 8/6/2003 Updated by: Douglas R. Stewart, M.D., Division of Medical Genetics, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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Page last updated: 28 October 2004 |