Different gene defects cause different types of prion disease, which include Creutzfeldt-Jakob disease (CJD) Gerstmann-Sträussler-Scheinker disease (GSS) Diseases with mixed features of CJD and GSS Diseases that are clinically and pathologically different from other prion diseases, such as prion disease associated with diarrhea and autonomic neuropathy Fatal familial insomnia (FFI) To date, researchers have identified only one mutation that causes FFI, the familial form of fatal insomnia.