ALS (Amyotrophic lateral sclerosis) is a disease of the nervous system that damages a specific type of nerve cell in the brain and spinal cord. In the United States, ALS is often called Lou Gehrig’s Disease, after baseball legend Lou Gehrig, who was diagnosed with ALS in the 1930s. In some other parts of the world, ALS is known as maladie de Charcot, after the French doctor who discovered the disease in 1869, or simply as motor neuron disease, after the type of nerve cells it destroys.

Motor neurons are the nerve cells that send signals from your brain to your muscles so you can move. Whenever you want to move a muscle, your brain uses upper motor neurons to send a message to your spinal cord. Lower motor neurons transmit the same message from your spinal cord to the muscle, and the muscle moves. Every conscious movement you make is controlled by motor neurons.

If you have ALS, the motor neurons weaken and eventually die, so that your brain cannot tell your muscles to move. The muscles may twitch or weaken at first. Over time, the muscles shrink and eventually stop working and become paralyzed.

The heart and the muscles in your digestive system usually aren’t affected^. Most people with ALS also keep their bowel and bladder control. ALS also doesn’t affect nerve cells other than motor neurons, so your senses are not affected. ALS can affect some people’s ability to think, but it usually doesn’t. ALS can eventually affect the muscles you use to swallow food, and to breathe.

Each year, ALS strikes one out of every 50,000 Americans, and kills almost the same number. This amounts to roughly 5,600 Americans diagnosed with ALS each year, and about 30,000 with the disease at any given time.

ALS is not contagious, and it can strike anyone, regardless of race, class, or ethnic background.