Genetic Testing for ALS. Genetic Testing for ALS - ALS is directly hereditary in only 10 percent of families. The vast majority of ALS cases are sporadic, meaning that although there is likely a genetic predisposition involved, ALS is not directly inherited in a family. Although there is a genetic test for ALS, it is still quite limited. In 20 percent of families with inherited ALS, a change in the gene called SOD1 on chromosome 21 has been found, however, 80 percent of families with inherited ALS do not show a change in their SOD1 gene.