PRNP and early-onset autosomal dominant Alzheimer disease: Neuropathological examination of the 3 patients all found degeneration of the thalamus and olive nucleus, and gene sequencing revealed the PRNP gene 178 mutation.[18] For example, some scholars have studied cases of dementia that were misdiagnosed as Alzheimer's disease, and then they were further diagnosed as having FFI through genetic testing.