The discovery of prion disease transmission in mammals, as well as a non-Mendelian type of inheritance in yeast, has led to the establishment of a new concept in biology, the prion hypothesis. The prion hypothesis postu-lates that an abnormal protein conformation propagates itself in an auto-catalytic manner using the normal isoform of the same protein as a substrate and thereby acts either as a transmissible agent of disease (in mammals),