Creutzfeldt-Jakob disease (CJD) linked to the E200K mutation of the prion protein (PrP) gene presents within a wide range of phenotypic heterogeneity, including the age at disease onset. We report an earlier disease onset for mutation carriers of the offspring generation when compared with that of their parents, suggesting the possibility of anticipation. A still unidentified environmental or genetic element may affect the age at onset in mutation carriers of different generations.