PRNP and prion disease: A decrease in PrPC sialylation could lead to a dramatic plunge of PrPC-to-PrPSc barriers in vivo and provide favorable conditions for (i) lowering the energy barrier of the spontaneous PrPC-to-PrPSc conversion in sporadic prion diseases; (ii) successful infection of a host or tissues with abnormally low sialylation status by low prion doses; and (iii) crossing the species barrier.