The majority of ALS-associated mutations displays an extreme variability in clinical manifestations, which may present asALS-plus phenotypes in the same individuals (e.g., ALS and parkinsonism) and/or different clinical pictures in the carriers belonging to the same family (e.g., ALS, FTD, or both in C9orf72 families). This evidence concerns the gene C9orf72 and Parkinson disease.