The G4C2 hexanucleotide repeat expansion in intron 1 of the chromosome 9 open reading frame 72 (c9orf72) gene is the most prevalent factor linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) neurological disorders [110], but doubts still remain as to the importance of the different disease-based molecular mechanisms suggested (Figure 1). Here, C9orf72 is linked to amyotrophic lateral sclerosis.