As indicated in previous sections, the expansion of a repeat region of six‐nucleotide motifs (GGGGCC)n (G4C2) in the 5’ region of the C9ORF72 gene is the most common genetic cause of ALS and frontotemporal dementia (FTD; DeJesus‐Hernandez et al., 2011; Renton et al., 2011; Zu et al., 2013). Here, C9orf72 is linked to frontotemporal dementia.