What causes ALS?
In about 10 percent of cases, ALS is caused by an inherited genetic defect. In all other cases, the cause is unknown. ALS currently affects about five out of every 100,000 people worldwide.
There is no known risk factor for ALS, except for having a family member who has had the hereditary form of the disease. The biological mechanisms that cause ALS are only partially understood and may be due to a particular gene called SOD1. A mutation in this gene is thought to make a protein that is toxic to the motor nerve cells. Due to the accumulation of this toxin, people with ALS progressively lose the ability to function and care for themselves. They no longer have voluntary control over their muscles and eventually lose involuntary control that is required for vital organ systems.