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Black Bone Disease

Black Bone Disease is a rare genetic disease, caused by a defective HGD gene, for which there is no cure. It affects one out of 250,000 to 1 million people (especially in Slovakia and Dominican Republic) and can cause severe osteoarthritis in those affected. The buildup of acid in the body creates black pigment that attaches to cartilage surrounding the joints, hence the name "black bone" disease.

  1. Definition

    • The scientific name for Black Bone Disease is "Alkaptonuria," a rare condition that may first be identified when a baby's urine turns dark brown or black when exposed to oxygen. The disease is also known as "AKU," "Alcaptonuria," "homogentisic acid oxidase deficiency," and "homogentisic acidura."

    Symptoms

    • Besides the earliest symptom of darkening urine, those who have Alkaptonuria may exhibit dark spots on the white of the eye, darkened skin on the ear, and most seriously, arthritis of the spine that can become more severe with time.

    Cause

    • A defective HGD gene (one from each parent) prevents the body from breaking down two amino acids: tyrosine and phenylalanine. Homogentisic acid accumulates in the skin and body tissues and is eliminated from the body through the urine, which turns black after exposure to the air. Some of the acid remains in the body, gets into the bloodstream, and creates a black pigment that adheres to joint cartilage as well as to skin and bone.

    Complications

    • The acid in the cartilage causes osteoarthritis in 50 percent of affected adults. Accretions of acid on the heart valves can require mitral valve replacement. Kidney stones and coronary artery disease are also possible complications of Black Bone Disease.

    Diagnosis

    • Black Bone Disease can be detected through urinalysis. A positive test results when ferric chloride is added to urine and turns it black.

    Research

    • Professor Jim Gallagher of Liverpool University, England, found that the black pigment that attaches itself to cartilage does so at only specific points of the cartilage. When researchers discover why this is, they can one day prevent the pigment from binding at all.

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