The aim of our study was to examine levels of selected protein CSF biomarkers in neuropathologically confirmed cases of prion diseases, AD, frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), frontotemporal lobar degeneration with tau inclusions (FTLD-tau), and DLB and to determine which of the aforementioned CSF biomarkers, or their ratios, would be helpful in the differential diagnosis of dementia, in cases with overlapping clinical symptoms. This evidence concerns the gene MAPT and Alzheimer disease.