C9orf72 and amyotrophic lateral sclerosis: After excluding pathogenic mutations in the main amyotrophic lateral sclerosis–related genes (i.e. C9orf72, SOD1, FUS and TARDBP), MFN2 variants were classified based on the American College of Medical Genetics and Genomics guidelines, and demographic and clinical data of MFN2-mutated patients were retrieved.