Causes of Amyotrophic Lateral Sclerosis
The causes of the vast majority of ALS cases are still unknown. Investigators theorize that some individuals may be genetically predisposed to developing the disease, but only do so after coming into contact with an environmental trigger. The interaction of genetics and environment may hold clues as to why some individuals develop ALS. One thing doctors and scientists do know is that ALS cannot be "caught," or transmitted from one person to another.

Although the majority of ALS cases are sporadic, meaning there is no family history of the disease, about 5 to 10 percent of cases are familial, meaning the disease runs in the family. A common misconception is that only familial ALS is "genetic." Actually, both familial and sporadic ALS can stem from genetic causes.  And some people who have a diagnosis of sporadic ALS may carry ALS-causing genetic mutations that can be passed on to offspring. A genetic counselor can help people with ALS understand inheritance and any associated risks for family members.