PRNP and Alzheimer disease: Furthermore, although these 2 patients were homozygous for PRNP p.M129M, a common polymorphism and risk factor for sporadic Creutzfeldt-Jakob disease (sCJD) (Palmer et al., 1991), p.M129M was not significantly associated with AD in this study (p-value = 0.22, OR = 0.75).