Abnormal expansion of a GGGGCC hexanucleotide (G4C2) repeat in a noncoding region of C9ORF72 is the most commonly identified genetic variant associated with both familial amyotrophic lateral sclerosis (ALS) and familial frontotemporal dementia (FTD) (DeJesus-Hernandez et al., 2011; Renton et al., 2011). This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.