WHAT IS AKU?

A lay person's description of the condition.

The information here merely provides a general description of the condition without being too detailed or technical. More detailed explanations are available here...

Alkaptonuria is a rare disease in which the body does not have enough of an enzyme called homogentisic acid oxidase (HGAO). It is a genetic disease, meaning that it is inherited from a family member.

Because normal amounts of the HGAO enzyme are missing, homogentisic acid (HGA) is not used and builds up in the body. Some is eliminated in the urine, and the rest is deposited in body tissues where it is toxic. The result is ochronosis, a blue-black discoloration of connective tissue including bone, cartilage, and skin caused by deposits of ochre-colored pigment.

Patients with alkaptonuria are usually not aware of the disease until about age 40 when symptoms are present. Dark staining of the diapers sometimes can indicate the disease in infants, but usually no symptoms are present until much later in life.

Alkaptonuria and ochronosis affect many body systems, as described below:

Skeletal (bones and cartilage)--The knees, shoulders, and hips are most affected; arthropathy (diseased joints) is common. Deposits of pigment cause cartilage to become brittle and eventually to fragment (break apart).

Cardiovascular (heart and blood vessels)--The aortic and mitral heart valves are most affected. Ochronotic granules can cause valves to calcify or harden. Pigment deposits also can lead to the formation of atherosclerotic plaques (hard spots in arteries) containing cholesterol and fat.

Genitourinary (genital and urinary systems and organs)--In men, the prostate is most commonly affected. Pigment deposits can form stones in the prostate.

Respiratory (organs and structures involved in breathing)--Heavy pigment deposits in the cartilage of the larynx (voice box), the trachea (windpipe), and the bronchi (air passages to the lungs) are common.

Ocular (eyes)--Vision is not usually affected, but pigmentation in the white part of the eye is evident in most patients by their early forties.

Cutaneous (skin)--Effects are most noticeable in areas where the body is exposed to the sun and where sweat glands are located. Skin takes on a blue-black speckled discoloration. Sweat can actually stain clothes brown.

Other--The teeth, central nervous system (brain and spinal cord), and endocrine organs (which make hormones) also may be affected.

Arthropathy (joint disease characterized by swelling and enlarged bones) and discoloration of the skin cause the greatest disability.

Usually a physician can diagnose alkaptonuria based on symptoms of joint discomfort and skin discoloration. The diagnosis is confirmed by verifying family history of the disease, examining skin cells, and testing the urine. Urine left standing for several hours will turn brownish black if a patient has alkaptonuria.

Diets low in protein, especially in amino acids, phenylalanine (found in aspartame), and tyrosine-help reduce the levels of HGA, thereby lessening the amount of pigment deposited in body tissues. Symptoms of alkaptonuria (e.g. arthropathy, cardiovascular disease) are treated when possible. Unfortunately, the course of the disease remains unchanged, and no cure is available. However, patients tend to have a normal life span and die of causes comparable to those of the general population.

 
Information provided by the
National Heart, Lung, and Blood Institute
National Institutes of Health