The recent discovery of hexanucleotide G4C2 repeat expansions in the intronic region of C9orf72 as a common genetic cause of fALS [5] and frontotemporal dementia (FTD) has profoundly changed our understanding of ALS, explaining almost 40% of the familial cases, in addition to near 10% of sporadic ALS (sALS) [5, 6]. This evidence concerns the gene C9orf72 and frontotemporal dementia.