C9orf72 and amyotrophic lateral sclerosis: The majority of ALS cases are sporadic (sALS), but ∼10% are familial (fALS) and are generated by mutations in at least 24 identified ALS-associated gene loci, including those for superoxide dismutase (SOD1) and transactive response DNA-binding protein 43 (TDP-43), as well as by hexanucleotide expansion in C9orf72 (Bento-Abreu et al., 2010; DeJesus-Hernandez et al., 2011; Ferraiuolo et al., 2011; Renton et al., 2011, 2014; Wegorzewska and Baloh, 2011; Sreedharan and Brown, 2013).