Behavioral variants of FTD, which are associated with tau pathology and in particular, microtubule-associated tau mutations (MAPT), may demonstrate semantic memory impairment during the course of the disease.[74] Predictive value of clinical diagnosis can be improved by subtyping PNFA into agrammatic and logopenic suggested one recent study as most of the agrammatics had FTLD-T and the logopenics had AD.[70] Similar robust clinicopathological correlations are reported by a longitudinal study which investigated 18 patients of PPA over a 15 year period and classified PPA into 5 different types. This evidence concerns the gene MAPT and Alzheimer disease.