MAPT and Alzheimer disease: Overall, C9orf72 seems to be the most common worldwide cause of genetic FTD, followed by GRN and then MAPT. A list of pathogenic and other variants in these genes has been collated online in the AD&FTD Mutation Database (http://www.molgen.ua.ac.be/FTDmutations): 79 GRN and 45 MAPT pathogenic variants are currently described.