Most cases of PPA have a non-Alzheimer pathological substrate within the frontotemporal lobar degeneration spectrum, and are usually associated predominantly with either tau- or TAR (trans-activation-response) DNA binding protein 43 (TDP-43)-positive cellular inclusions (known as FTLD-tau or FTLD-TDP pathology), respectively (Knibb et al., 2006; Snowden et al., 2007). This evidence concerns the gene MAPT and frontotemporal dementia.