Three classifications of ALS have been described:
The most common form of ALS in the United States is "sporadic" ALS. It may affect anyone, anywhere. "Familial" ALS (FALS) means the disease is inherited. Only about 5 to 10% of all ALS patients appear to have genetic or inherited form of ALS. In those families, there is a 50% chance each offspring will inherit the gene mutation and may develop the disease.