Amyotrophic lateral sclerosis (ALS) is a serious neurological disease that causes muscle weakness, disability and eventually death. ALS is often called Lou Gehrig's disease, after the famous baseball player who died of it in 1941.
Worldwide, ALS occurs in one to three people per 100,000. An inherited form of the disease occurs in 5 to 10 percent of the cases. But in the vast majority of cases, doctors don't yet know why ALS occurs in some people and not in others.
ALS often begins with muscle twitching and weakness in an arm or leg, or with slurring of speech. Eventually, ALS affects your ability to control the muscles needed to move, speak, eat and breathe.