Science / Medicine : Cause of Disease That Weakens Muscles Found

An international team of researchers reported last week that they had identified the genetic defect that causes spinal and bulbar muscular atrophy, a rare disease in which nerve cells that control voluntary muscles--so-called motor neurons--degenerate. The finding represents the first time that researchers have identified the exact cause of a motor neuron disease, and could open the door to pinpointing the causes of other motor neuron diseases, such as amyotrophic lateral sclerosis. Alzheimer’s, Parkinson’s and Huntington’s diseases.

Spinal and bulbar muscular atrophy, also known as Kennedy’s disease, affects only males and usually begins at about age 30. It starts with weakness and muscle wasting in the legs, followed by difficulty in speaking and swallowing.

The team, headed by neurologist Kenneth H. Fischbeck of the University of Pennsylvania School of Medicine, reported in the British journal Nature that the disorder is caused by an abnormality in the gene that is the blueprint for androgen receptors--molecules on the surface of cells that bind to the male sex hormone androgen.

The finding should lead to new ways to diagnose the disorder and perhaps to therapies for it.