C9orf72 and amyotrophic lateral sclerosis: The greatest proportion of ALS and FTD cases are caused by hexanucleotide (GGGGCC) repeat expansions in the first intron of the C9ORF72 gene, which are responsible for 40% of familial and 8% of sporadic ALS cases in Europe/North America (Lee et al., 2013; Ling et al., 2013; Balendra and Isaacs, 2018).