There are two major categories of ALS cases.
Sporadic ALS – which refers to cases with no known family history or genetic cause -- is the most common form of the disease in the U.S. It accounts for 90-95% percent of all cases. It may affect anyone, anywhere.
Familial ALS (FALS) – which refers to cases where there is a known family history of the disease – accounts for 5-10% of all cases in the U.S. In families with FALS, there’s a 50% chance each offspring will inherit the gene mutation and may develop the disease.