MAPT and semantic dementia: Individuals in the FTLD group were then grouped based on their likely underlying pathology into an FTLD-tau group (containing MAPT mutation carriers, those with a secondary clinical diagnosis of progressive supranuclear palsy, and one patient with bvFTD who had subsequently come to post mortem and was found to have corticobasal degeneration; n=7) and an FTLD-TDP-43 group (containing GRN and C9orf72 mutation carriers, those with a primary clinical diagnosis of semantic variant PPA or a secondary diagnosis of motor neuron disease; n=18) (figure 2).