Polymorphisms in the prion protein gene and in the doppel gene increase susceptibility for Creutzfeldt-Jakob disease

The prion protein gene (PRNP) plays a central role in the origin of Creutzfeldt-Jakob disease (CJD), but there is growing interest in other polymorphisms that may be involved in CJD. Polymorphisms upstream of PRNP that may modulate the prion protein production as well as polymorphisms in the prion-like doppel gene (PRND) have been studied, with inconsistent findings. We investigated the role of a single-nucleotide polymorphism (SNP 1368) located upstream of PRNP and three polymorphisms in PRND (T26M, P56L and T174M) in CJD. The study included a population-based sample of 52 patients with sporadic CJD and 250 controls. We analysed our data as single markers and haplotypes. Further, we conducted a meta-analysis on PRND T174M comparing the data of the four studies conducted to date. For SNP 1368 and PRNP M129V, we found significant evidence for linkage disequilibrium. No evidence was found for a relation of SNP 1368 to CJD independent of PRNP M129V. We further found a significant increased prevalence of M homozygotes at PRND T174M among sporadic CJD patients, when adjusting the analyses for the other genotypes. In the haplotype analyses, the association was strongest for persons homozygous for PRNP 129M and PRND 174M (odds ratio 4.35, 95% confidence interval 1.05-8.09; P=0.04). The meta-analysis on the PRND T174M polymorphism did not show a consistent effect across studies, raising the question as to whether PRND 174M is causally related to CJD, or whether the PRND allele is in linkage disequilibrium with another polymorphism related to CJD.