Three monozygotic twin pairs with the Creutzfeldt-Jakob diseases-specific mutation E200K are described. All three have been concordant for genetic CJDE200K and discordant for the age at death and the duration of the disease. Twin pairs have been compared with genetically non - identical sibling pairs also concordant for genetic CJDE200K and discordant for the age at death. The difference of the mean age at death in compared subgroups was not significant. Detailed analysis of twin pairs revealed considerable differences in the duration and quality of chronic stress, induced by the analysed exogenous factors. The stress was evidently of higher intensity in two of the three earlier affected twins. Clear correlation between the age at death and medical history of twins was not observed. The discordance of twins with genetic CJDE200K in the age at death and the striking correlation with the discordant intensity of analysed exogenous influence, draw attention to described potential risk factors (mainly to chronic social, economic and emotional stress) and support their role in accelerating the clinical onset of genetic CJDE200K.