For the protein loss‐of‐function mechanism, it has been reported that the RNA transcript and protein levels of C9orf72 are reduced in C9orf72‐linked ALS/FTD, possibly also resulting from the expansion of the hexanucleotide repeat (DeJesus‐Hernandez et al., 2011; Haeusler et al., 2014; Renton et al., 2011). This evidence concerns the gene C9orf72 and frontotemporal dementia.