The first of the spongiform encephalopathies that was described as a genetically inherited trait. –Linkage analysis from GSS families demonstrated that PrP was the responsible gene. –GSS may also arise spontaneously. Fatal Familial Insommnia –FFI: characterized by adults generally over age 50 who present with a progressive sleep disorder who die within about a year of onset. –More than 30 families worldwide have been identified. FSI (fatal sporadic insomnia). The sporadic form of FFI. Kuru –Affects the Fore people of New Guniea. Transmitted through ritual cannabalism.