C9orf72 and amyotrophic lateral sclerosis: In 2011, the hexanucleotide GGGGCC (G4C2) repeat expansions of the chromosome 9 open reading frame 72 gene (C9orf72) C9orf72 gene were found as a common cause of both FTD and amyotrophic lateral sclerosis (ALS) (15, 16).