The Basic Facts of Alkaptonuria (Alcaptonuria)

Alkaptonuria, also known as black urine disease, is a rare genetic disorder that is inherited as an autosomal recessive trait. The gene that causes this disease is unable to break down certain proteins that are toxic to the body. These proteins are called tyrosine and phenylalanine. They are harmful to the bones and cartilage and are normally excreted in the urine. When a person is unable to break down the proteins a homogentisic acid builds up in the body. Some of this acid leaves the body through the urine and some is deposited in body tissues where it is toxic. When excreted the urine turns a brownish-black as soon as it is exposed to the air.

Alkaptonuriais usually diagnosed when a person begins to suffer from progressive arthritis, particularly in the spine, joint discomfort, and discoloration of the skin. It affects several systems in the body.

Cutaneous (skin): The skins pigmentation starts to take on a bluish black discoloration and is most visible in areas that have been exposed to the sun. Areas with excessive sweat glands are also more susceptible and the sweat may turn a brownish color.

Skeletal: Of the bones and cartilage, the hips, shoulders, knees, and spine are most commonly affected. A premature and progressive deterioration of these joints takes place causing the cartilage to become fragile. The diseased joints are known as arthropathy and are characterized by enlarged bones and swelling of the joints.

Cardiovascular: When pigmentation deposits itself in the arteries an atherosclerotic plaque is formed. This plaque contains fat and cholesterol that is harmful to the heart, especially the mitral heart valves and the aortic heart valves, and can cause the valves to calcify or harden.

Respiratory: The respiratory system involves the organs that are concerned with breathing. Pigmentation may also deposit itself in these structures, the most common being the trachea (windpipe), the bronchi (the air channels that go to the lungs), and the larynx (voice box).

Genitourinary: These are the organs of the urinary system and the genital areas. In men, the prostate gland is most commonly affected. A person may form stones in the prostate if pigmentation deposits itself there.

There is no prevention available and the goal of treatment is to alleviate symptoms. Decreasing protein in the diet may hinder the development of pigmentation. Adding vitamin C has also helped to slow the rate of progression of arthritis. There is no cure for this disease but patients generally have a normal lifespan and don't die from complications of Alkaptonuria.