Amyotrophic lateral sclerosis (ALS) is a progressive nervous system disorder. It gradually destroys the nerves responsible for muscle movement. Over time, ALS leads to almost total paralysis of muscle movement, including breathing.

Prognosis is poor in most cases because of the progressive nature of the condition. Eventually, the disorder leads to respiratory failure. After diagnosis, life span ranges from 2 to 5 years. The five-year survival rate ranges from 14% to 25%. Up to 10% of patients will survive more than 10 years. In general, the younger the age of onset, the slower the disease progresses.

The Nervous System
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The cause of ALS is unknown. In a small number of cases, it appears that genes may play a role. Also, research has shown that there may be a reduced response to cell stress and cell toxicity. The reduced response may be due to a build-up of certain protein in the brain.