As a result of these different mechanisms, mRNA and protein levels of C9ORF72 were found to decrease to near 50% in C9ALS/FTD-affected patients (Figure 1), proposing a pathogenic loss of function of the protein in the disease (Ginsberg et al., 2010; DeJesus-Hernandez et al., 2011; Cooper-Knock et al., 2014; Waite et al., 2014; Xiao et al., 2015; Gijselinck et al., 2016). This evidence concerns the gene C9orf72 and frontotemporal dementia.