Definition - A disease of the motor neurons, muscle-controlling nerve cells in the brain and spinal cord that control voluntary muscle movement.

Cause - generally unknown, although genetic factors are thought to play a role; about 10 percent of cases are clearly genetic, with a family history

Onset -usually adulthood

Symptoms - generalized weakness and muscle wasting with cramps and muscle twitches common

Progression - ALS first affects legs, arms and/or throat and mouth muscles but ultimately affects all voluntary muscles, resulting in paralysis. Usually progresses rapidly with 3- to 5-year average survival.

Inheritance - primarily sporadic, but can be autosomal dominant and, in very rare cases, autosomal recessive

Facts About Amyotrophic Lateral Sclerosis