C9orf72 and Alzheimer disease: A large metanalysis suggested the HLA-DR15 locus, encoding for the major MHC-II protein HLA-DR, as a risk factor for AD [36]; moreover, in a large GWAS of FTLD [37], the HLA-DRA/DRB5 locus was associated with disease risk and, most interestingly, genetic variants in the same locus were demonstrated to influence disease onset in C9orf72 expansion carriers [38].