C9orf72 and amyotrophic lateral sclerosis: The pathological expansion of a hexanucleotide repeat in the C9orf72 gene is the most common genetic mutation identified in patients with amyotrophic lateral sclerosis (ALS), reported in 40–50% of patients with familial ALS and 5–10% of patients with sporadic ALS (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Majounie et al., 2012).