MAPT and primary progressive aphasia: However, clinicopathological correlation is poor and diagnosing the correct proteinopathy during life is difficult except when a genetic cause is present (mutations in MAPT cause tau pathology, while mutations in GRN and C9orf72 cause TDP-43 pathology) or for certain phenotypes (eg, the semantic variant of PPA and FTD with motor neuron disease (MND) are both commonly associated with TDP-43 pathology).1