Epidemiology of Creutzfeldt‐Jakob disease—past and present uncertainties

Annual incidence rate of Creutzfeldt‐Jakob disease (CJD) is approximately equal to one per million. Because of misdiagnosis, especially in older individuals, and censoring by competitive cause of death, the true incidence of the disease might be underestimated. Incidence rates of CJD increased in all countries during the last 20 years; this increase is likely due to greater interest in this disease. Foci have been described in Lybian Jews in Israel and Slovakia; in these foci the codon 200 mutation of the PRNP gene was found in all CJD cases. Up to now, no CJD focus which might be explained by environmental exposure has ever been documented. Overall, about 85% of CJD cases are sporadic and 15% are associated with different mutations of the PRNP gene. More than half of CJD cases with PRNP mutation have no known family history of CJD. About 100 iatrogenic CJD cases have been published; most have been related to human growth hormone treatment. The causes of sporadic CJD are unknown. Except the codon 129 polymorphism of the PRNP gene, there are no well established risk factors for sporadic CJD. The recent occurence of a new variant of CJD which might be linked with bovine spongiform encephalopathy raises new issues about the role of environmental exposures in sporadic CJD.