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What is Alkaptonuria?

Alkaptonuria is an inherited condition in which a particular enzyme does not function properly, causing homogentisic acid (HGA) to build up in the body. The accumulation of HGA causes alkaptonuria’s more visible symptoms, which include a brownish-black coloration of 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.

Some people with alkaptonuria will not have discolored urine. For them, arthritis may be the first noticeable sign of the disease. Arthritis often begins in the spine or major joints between age 30 and 40. 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 will 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 can also experience painful prostate stones. After age 60, people with the disease frequently experience 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. Alkaptonuria can also cause a person's sweat to be darker, which can stain clothing.

How common is Alkaptonuria?

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 parts of Slovakia. In Slovakia, approximately 1 in 19,000 people has alkaptonuria.

How is Alkaptonuria treated?

There is no treatment for the root cause of alkaptonuria, though clinical trials for new treatments are under way. 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 and occupational 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.

Studies indicate half of people with alkaptonuria will require at least one joint replacement by the age of 55. Surgery may also be needed for elimination of kidney or prostate stones. A small number of patients may need surgery to replace valves in the heart.

What is the prognosis for a person with Alkaptonuria?

All people with alkaptonuria will experience chronic joint pain, usually beginning in their 30s. This disease does not usually reduce a person's lifespan.


AKU Society of North America

An organization that focuses on improving the quality of life of AKU patients and their families by providing education, resources, and opportunities for interaction for patients, families, and physicians associated with alkaptonuria.

10451 Roselle Street #300
San Diego, CA 92121
United States
Phone: 800-549-8110

Alkaptonuria Society

A UK-based community dedicated to improving the lives of people with alkaptonuria by providing peer-to-peer support to patients, building community, and supporting medical research including supporting clinical trials in alkaptonuria treatment.

66 Devonshire Road
Cambridge CB1 2BL
United Kingdom
Phone: +44(0)1223-322897

Genetics Home Reference

Explanations of an extensive number of genetic diseases written for everyday people by the U.S. government's National Institutes of Health.

Other names for Alkaptonuria

  • Homogentisic Acidura
  • Alcaptonuria
  • AKU
  • Alkaptonuria
  • Homogentisic Acid Oxidase Deficiency

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