(ALS; also called Lou Gehrig's disease), degenerative nervous-system disorder; destroys nerves controlling muscular movements, causing muscles to weaken and eventually waste away; symptoms include weakness of upper and lower limbs, muscle spasms, and, later, atrophy of respiratory muscles and paralysis; fatal within 2 to 5 years of onset; one type, familial ALS, is hereditary; cause of other types unknown but may be result of nerve damage from toxins or infection; occurs most often in men over 40 years of age; 5,000 cases diagnosed in U.S. annually; no treatment available, though aids (such as wheelchairs) to lessen disabilities may help; named after popular baseball player, Lou Gehrig, who was afflicted; most famous 20th-century case probably that of prolific English physicist Stephen W. Hawking, who has lived long beyond normal 2- to 5-year limit after onset of disease