C9orf72 and amyotrophic lateral sclerosis: In 2011 a worldwide effort identified a hexanucleotidic expansion in the c9orf72 gene as the major genetic determinant of both ALS and FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011), thus revolutionizing our knowledge of genetic pleiotropy of ALS.