C9orf72 and amyotrophic lateral sclerosis: More recently, a large hexanucleotide (GGGGCC) repeat expansion in the first intron of the C9orf72 gene (Renton et al., 2014; Herrmann and Parlato, 2018) was identified to account for 35% of familial ALS patients and for ∼5–7% of sporadic cases of European ancestry, whereas it was relatively absent in Asian ALS patients (Majounie et al., 2012; Woollacott and Mead, 2014; Muller et al., 2018).