MAPT and semantic dementia: The variants of FTD all involve a frontotemporal network-based, prion-like spread of a misfolded protein.15 In semantic dementia, most cases are caused by a mutant version of a transcriptional repressor called Tar DNA Bind Protein-43 (TDP-43) Type C. This differs from behavioural variant FTD (bvFTD), which has less predictable pathology as it can be caused by mutant TDP-43, but also by tau and fused in sarcoma (FUS) protein (in order of decreasing pathological frequency).16