C9orf72 and frontotemporal dementia: Several genetic autosomal dominant mutations are linked to FTD; a repeat expansion in the C9orf72 gene and mutations in the progranulin (GRN) gene can lead to FTD with underlying TDP43 pathology, whereas mutations in the Microtubule Associated Protein Tau (MAPT) tau gene result in FTD with underlying tau pathology.