In this review we highlight progress since 2010 in determining genetic susceptibility to prion diseases. The use of human genome-wide association studies (GWAS) and complementary mouse studies reinforce

the key role of PRNP and identify new genetic modifiers. We outline the challenge of verifying the role of putative modifiers and propose a way find protocol forward for gene identification and validation ( Figure 1). Recent work has focussed on the collection of large patient cohorts for GWAS, which has necessarily been an international collaborative endeavour given that human prion diseases are rare. As a generality from common diseases, genetic risk factors discovered by GWAS have been modest in their effects (odds ratios 1–1.2) requiring sample sizes of several thousand to have the statistical power required for unequivocal detection of significant variants. Two collaborative groups are working in prion disease GWAS. The UK MRC Prion Unit in collaboration with the Universities of Munich, Gottingen and Perth has conducted a GWAS of sporadic CJD, variant CJD, iatrogenic CJD, inherited prion disease, and kuru involving over 2000 samples [7 and 8••]. A Europe-wide collaboration

led by Dutch and Spanish investigators published a GWAS of vCJD involving 93 samples [9••]. In these studies, the PRNP locus was unequivocally and strongly associated with risk of prion disease, driven by the known Pembrolizumab in vitro coding variation at PRNP codon 129. In the European vCJD GWAS two single nucleotide polymorphisms (SNPs) (rs4921542 and rs7565981) reached genome-wide significance after pooling discovery and replication populations. Rs4921542 (p = 1.6 × 10−8) is an intronic variant in the myotubularin related protein 7 gene (MTMR7), which is specifically expressed in the central nervous system and dephosphorylates phosphatidylinositol 3-phosphate and inositol 1,3-bisphosphate. Rs7565981 (p = 4.2 × 10−8) is in an intergenic region upstream of the neuronal PAS (per-ARNT-sim) domain-containing protein 2 gene (NPAS2), a regulatory gene belonging to a family of transcription factors. In the UK-German sporadic CJD study, no non-PRNP loci achieved genome-wide signficance. SNPs at the ZBTB38-RASA2

locus were associated with CJD in the UK (rs295301, p = 3.13 × 10−8) but these SNPs showed no replication evidence of association in German sporadic CJD or in kuru based tests. Overall, it is likely that the PRNP locus Branched chain aminotransferase contains the only strong risk factors which act universally across human prion diseases. Whilst some genome wide significant loci have been proposed in vCJD, the low incidence of this condition means that there is no way at present to generate unequivocal genetic evidence at these loci. The collective data are most consistent with the findings in other diseases, of strong effects being the exception but many risk loci of modest effects. In prion disease this will require large collaborative GWAS in sCJD to provide definitive statistical evidence of these weak effects.