A progressive chronic disease of nerves from the spinal cord that are responsible for supplying electrical stimulation to the muscles. Abbreviated ALS. ALS is progressive and usually fatal in less than eight years, from ill- nesses that strike as the body becomes weaker. ALS occurs most often in adults over 50. The cause of ALS is unknown. It is sometimes called Lou Gehrig’s disease, after a great baseball player who was its best-known victim.