[Clinical manifestations and epidemiology of prion diseases in Japan].

In Japan, prion diseases are classified into 76.6％ with sporadic Creutzfeldt-Jakob disease (sCJD), 19.6％ with genetic prion diseases, and 4.9％ with acquired prion disease. In sCJD, MM1 type sCJD, which show typical clinical course of CJD, is the most common. Among atypical sCJD cases, MM2 type sCJD is the most common. In genetic prion diseases, the most common mutation of prion protein gene is V180I. All cases with acquired prion diseases except for one case of variant CJD are dura mater graft-associated CJD (dCJD), and the number of dCJD in Japan is account for more than 60％ of all patients with dCJD all over the world. The remarkable frequency of dura mater graft use in Japan might contribute to the elevated incidence of dCJD, but the possible reasons for the disproportionate use of this procedure in Japan remain unclear. Our recent study revealed that differences in the medical conditions precipitating dura mater graft might contribute to the frequent use of cadaveric dura mater and the higher incidence of dCJD in Japan.