PHF1 and glycogen storage disease VI: Interestingly, pSer396 and PHF1 (pSer396/pSer404) expression, both with the phosphorylation sites in the c-terminal domain of the tau protein, was modest but supports further evidence of mechanistic differences between FTLD-MAPT and other FTLD-tau diseases, with FTLD-MAPT showing no significant difference in abundance of either epitope.