Alkaptonuria is an uncommonly occurring disease in many parts of the world. Usually, it may affect about four in one million people, but some small areas of the world have a much higher incidence of this condition. It occurs in places like Slovakia with much greater regularity, affecting about one in twenty thousand folks, and it is also has a higher incidence in the Dominican Republic. The disease is still rare, and its inheritance through an autosomal recessive mechanism means that two people with recessive genes for it, and no presence of the disease, would only have a one in four chance of passing it onto each child.
Few symptoms of alkaptonuria may be present when people are born with this condition. Sometimes it is caught in infants because diapers that are left out for several hours may stain black or brown. The discoloration of urine is why the disease may be called black urine disease. Usually, this won’t be noticed, and most people using a toilet flush right away and thus have no time to see discoloration of urine.
The symptoms that may be noticed later, usually when people are in their 30s or 40s, is darkening of the skin around the ears and any area that receives sun exposure. Sweat may also be colored brown, though this may unnoticed too. As the condition develops, people may have arthritis, and they’re at higher risk for developing kidney stones. Some people may have damage to the mitral valve in the heart and require repair or replacement of it.
What’s occurring with alkaptonuria is dysfunction of the HGD gene, which produces an enzyme called homogentisate oxidase. This enzyme breaks down tyrosine and phenylalanine. When breakdown doesn’t occur, these can build up in the body and start to cause cartilage and tissue damage. Excess amounts still get excreted from the body in sweat and urine.
There are few treatments for alkaptonuria. Taking large doses of Vitamin C may help retard tyrosine and phenylalanine accumulation. Some doctors also advocate dietary restriction of these substances. This appears to be most effective in slowing the course of the disease when children are placed on restrictive diets, but it may not be helpful in adults. Unfortunately, most of the time, the condition isn’t noted until people are well into adulthood.
Unless complications of the heart occur, people may live fairly healthy and normal lives with alkaptonuria. They may experience more pain due to arthritis or to presence of frequent kidney stones. However, in most cases, the disease is survivable, and treatment with Vitamin C may help to control or lessen development of symptoms.