GRN and frontotemporal dementia: In FTD, pathogenic repeat expansion in C9ORF72 accounts for 20–30% of familial form and about 6% of sporadic form of FTD (DeJesus-Hernandez et al., 2011), and is the most common cause of disease besides pathogenic mutations in GRN and MAPT (Sirkis et al., 2019).