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Alkaptonuria is an inherited condition in which a particular enzyme does not function properly, creating a buildup of homogentisic acid (HGA) in the body. This accumulation causes alkaptonuria’s more visible symptoms, which include a brownish-black coloration to the urine when it mixes with air and a darkening of the body’s connective tissues after the age of 30. Excess HGA can also lead to arthritis, often beginning in early adulthood, as well as heart problems, kidney stones, and prostate stones.
A minority of patients do not have discolored urine, and for them arthritis may be the first noticeable sign of the disease. Arthritis often begins in the spine or major joints and appears in one’s 30s. In one large study of people with alkaptonuria, roughly half reported lower back pain in their 30s, and 94% reported the symptom by age 40. Hips, knees, and shoulders are frequently affected by alkaptonuria, though smaller joints are not. Studies indicate half of people with alkaptonuria require at least one joint replacement by the age of 55.
By the mid-60s, half of patients with alkaptonuria will have experienced kidney stones. Some men with alkaptonuria also experience painful prostate stones. In their 60s, people with the disease frequently experience a hardening, thickening, and/or narrowing of the heart’s aortic or mitral valve. The coronary arteries of the heart may also harden.
Connective tissue pigmentation is most noticeable on the outside of the ear and may also be seen as a purple discoloration on the hands. The disease can also cause the body’s sweat to darken in color, which can stain clothing.
Alkaptonuria affects between 1 in 250,000 and 1 in 1,000,000 people globally. It is more common in the Dominican Republic and in certain areas of Slovakia. In Slovakia, 1 in 19,000 people are affected.
There is no treatment for the root cause of alkaptonuria. High doses of vitamin C have been shown to decrease the accumulation of pigment in the cartilage and may slow the development of arthritis.
Physical therapy can help patients maintain muscle strength and flexibility. Nearly all will require long-term pain management for their joint pain. Non-weight-bearing exercises, such as swimming, may be beneficial. Patients should avoid putting physical stress on their spine and major joints. For this reason, heavy manual labor and high-impact sports are not recommended at any age.
Some patients will require surgery for joint replacement or kidney or prostate stone elimination.
All people with alkaptonuria will experience chronic joint pain, usually beginning in their 30s. The disease does not reduce one’s lifespan.
Explanations of an extensive number of genetic diseases written for everyday people by the U.S. government's National Institutes of Health.