Amyotrophic Lateral Sclerosis
ALS is a disease of the parts of the nervous system that control voluntary muscle movement. In ALS, motor neurons (nerve cells that control muscle cells) are gradually lost. As these motor neurons are lost, the muscles they control become weak and then nonfunctional.

The word "amyotrophic" comes from Greek roots that mean "without nourishment to muscles" and refers to the loss of signals nerve cells normally send to muscle cells. "Lateral" means "to the side" and refers to the location of the damage in the spinal cord. "Sclerosis" means "hardened" and refers to the hardened nature of the spinal cord in advanced ALS.

ALS also is called Lou Gehrig’s disease, named after the Yankees baseball player who died of it in 1941. In the United Kingdom and some other parts of the world, ALS is often called motor neurone disease in reference to the cells that are lost in this disorder.

Who gets ALS?
ALS usually strikes in late middle age (the late 50s is average) or later, although it also occurs in young adults and even in children, as well as in very elderly people. Some forms of ALS have their onset in youth. Men are slightly more likely to develop ALS than are women. Studies suggest an overall ratio of about 1.2 men to every woman who develops the disorder.