We investigated the risk associated with the codon 129 polymorphism in the prion protein gene (PRNP) and apolipoprotein E gene (APOE) isoforms for development of Creutzfeldt-Jakob disease (CJD) (n = 126) and the possible influences on the disease pathology and its most important clinical characteristics. The PRNP M129V (PRNP129) polymorphism was determined using both DNA extracted from formalin fixed and paraffin embedded brain tissue (n = 59) and leukocyte extracted DNA (n = 67). In the latter group also the PRNP open reading frame and the APOE genotype were analysed and compared to a neurologically unaffected, age and sex matched control group (n = 79). We found that methionine homozygosity of the PRNP129 increases the risk for developing CJD. PRNP129 also influenced the prion accumulation patterns in brain. The APOE 4 allele was an independent risk factor for developing CJD. We further observed a significant dose dependent APOE 4 effect on the number and type of amyloid-beta plaques in the brain of CJD patients. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.