amyotrophic lateral sclerosis
amyotrophic lateral sclerosis (ALS) (ā´mīətrōf´ik, sklĬrō´sĬs) or motor neuron disease, sometimes called Lou Gehrig's disease, degenerative disease that affects motor neurons in the brain and spinal cord, preventing them from sending impulses to the muscles. The muscles atrophy quickly, causing weakness, paralysis, and eventual death, usually when the muscles that control respiration fail. The intellect, eye motion, and bladder control are not affected. ALS sometimes originates in the brain, causing initial symptoms such as difficulty in swallowing or talking; in other cases it originates in the spinal cord, causing initial symptoms such as weakness in the extremities. About a tenth of ALS cases are hereditary. ALS usually develops after age 40; more men are affected than women.
There appear to be several causes of ALS, and a number of genetic mutations have been linked to about a third of all ALS cases. In 1991 a research team led by Teepu Siddique and Robert H. Brown, Jr. located a gene for familial ALS on chromosome 21. A later discovery pinpointed a mutation in the gene that codes for an enzyme, superoxide dismutase (SOD), as responsible for a percentage of familial cases. These defects do not appear to be present in the more common nonfamilial, or "sporadic," form of the disease. Since then, however, two defective proteins have been found to be associated with both inherited and sporadic ALS, one involved in regulating RNA and the other involved in clearing defective or unneeded proteins. Scientists also have studied the buildup of the chemical glutamate that occurs in ALS patients. Glutamate normally acts as a neurotransmitter in the brain, with excess amounts being absorbed by the cells. In ALS patients the reabsorption process fails, and the buildup of glutamate selectively destroys motor neurons. Other possible causes of ALS include defects in the gene that makes the neurofilament proteins that support nerve cell axons, and antibodies that interfere with calcium channels in the cells and cause a toxic buildup of calcium in the neurons.
There is no cure for ALS. Devices such as wheelchairs and speech synthesizers can help patients maintain independence. Research into treatment has concentrated on neurotrophic factors (proteins that assist nerve growth and health) and glutamate blockers. Rilutek (formerly Riluzole), the first drug approved by the Food and Drug Administration for treatment of ALS (1995), adds a few months to the life expectancy of most patients but does not relieve symptoms. Another drug, myotrophin, seemed somewhat promising in early studies (1996), but its effectiveness was not confirmed and it has not been approved. Baseball star Lou Gehrig died of ALS in 1941, bringing it national attention.