4. In hereditary forms of prion diseases, a genetic change (a mutation represented by the red dot) in one of the two genes encoding PrP^c, may result in a slightly altered structure of the PrP^c-protein. The mutation makes it easier for PrP^c to change its conformation into PrP^Sc, initating a chain reaction that will result in the accumulation of a large number of PrP^Sc molecules. The filamentous aggregates that are gradually formed may contain both altered normal (unmutated) and mutated PrP^Sc.