C9orf72 and amyotrophic lateral sclerosis: C9orf72 genetic mutations are the most frequent known cause of ALS (Majounie et al., 2012); with around 40% of FALS cases exhibiting various numbers of repeat expansions (Renton et al., 2011) and C9orf72 is also the only locus to show a genome-wide significance in meta-analysis studies (Malek et al., 2012; Al-Chalabi and Visscher, 2014).