C9orf72 and amyotrophic lateral sclerosis: With respect to familial ALS and FTLD, a non-coding hexanucleotide repeat expansion (GGGGCC) mutation in the 50 non-coding region of the C9orf72 gene identified in familial ALS and FTLD in 2011 has provided important insights into the pathophysiological backgrounds of ALS and FTLD (DeJesus-Hernandez et al., 2011).