C9orf72 and amyotrophic lateral sclerosis: Expanded GGGGCC repeats in intron 1 of the C9orf72 gene represent the most common cause of familial amyotrophic lateral sclerosis (ALS) and familial frontotemporal degeneration (DeJesus-Hernandez et al., 2011; Renton et al., 2011), though how this genetic change results in neuronal injury is not yet understood.