The difference between familial and genetic ALS lies in the family history of the disease. Familial ALS (FALS) is present when several members of a family are affected by ALS (or have had the disease in the past). In contrast, the term “genetic ALS” is used when a genetic mutation is detected in one of the known ALS genes—regardless of whether other family members have the disease or not. This means that even without a family history of ALS, genetic ALS can be diagnosed if a corresponding mutation is present. The terms “familial ALS” and “genetic ALS” overlap—but they are not synonymous.