Causes

ALS affects the nerve cells that control voluntary muscle movements such as walking and talking (motor neurons). ALS causes the motor neurons to gradually deteriorate, and then die. Motor neurons extend from the brain to the spinal cord to muscles throughout the body. When motor neurons are damaged, they stop sending messages to the muscles, so the muscles can't function.

ALS is inherited in 5% to 10% of people. For the rest, the cause isn't known.

Researchers continue to study possible causes of ALS. Most theories center on a complex interaction between genetic and environmental factors.