This illness is more commonly known as "dark urine disease". It is caused by a recessive gene that causes a deficiency of the enzyme homogensitic acid deoxygenase; it was the first recognized genetic disease.

It is characterized by abnormal deposits in the connective tissue and urine which turn dark when exposed to air. Severe arthritis and blockages in arteries and heart valves can occur in later stages of the disease. Its incidence is about one in a million.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.