MAPT and proteostasis deficiencies: Thirdly, there appears to be a higher than expected coincidence of repeat expansions in individuals carrying other genetic variants involving mutations in GRN with C9ORF72[54, 55] or MAPT with C9ORF72[54–57] (so called oligogenic inheritance), suggesting that another ‘hit’ may be necessary for clinical disease, yet in these dual mutation cases, apart from the DPR changes, either a TDP-43 proteinopathy, or tauopathy, typical of the accompanying (GRN or MAPT) mutation prevails.