There are two different types of ALS, sporadic and familial.
Sporadic (or singleton ALS) is when a person with ALS does not have a family history of ALS. It is the most common form of the disease in the U.S. and accounts for 90 to 95 percent of all cases. It may affect anyone, anywhere.
Familial ALS is when a person with ALS has a family history of the disease. Approximately 10% of ALS cases are familial.
About two thirds of individuals with familial ALS and 10 percent of people with sporadic or singleton ALS (with no known family history) have a known ALS-associated genetic mutation. If you have familial ALS, a genetic test may help you determine what is causing your ALS, as well as the risk of disease in your family members.