The most common genetic cause of ALS and FTD is a hexanucleotide repeat expansion of GGGGCC in the first intron of the C9ORF72 gene (collectively termed C9ALS/FTD) (DeJesus-Hernandez et al., 2011; Renton et al., 2011). Here, C9orf72 is linked to frontotemporal dementia.