Amyotrophic lateral sclerosis (a-my-o-TROE-fik LAT-ur-ul skluh-ROE-sis), or ALS, is a progressive nervous system (neurological) disease that destroys nerve cells and causes disability.

ALS is often called Lou Gehrig's disease, after the famous baseball player who was diagnosed with it. ALS is a type of motor neuron disease in which nerve cells gradually break down and die.

Doctors usually don't know why ALS occurs. Some cases are inherited.

ALS often begins with muscle twitching and weakness in a limb, or slurred speech. Eventually, ALS affects control of the muscles needed to move, speak, eat and breathe. There is no cure for ALS, and eventually the disease is fatal.

ALS care at Mayo Clinic