MAPT and semantic dementia: Among these, the P301L mutation in MAPT exon 10 that results in a Pro→ Leu change at amino acid 301 (Bird et al., 1999; Dumanchin et al., 1998; Hutton et al., 1998; Nasreddine et al., 1999; Rizzu, Van Swieten, Joosse, & Hasegawa, 1999) is most frequently observed in patients with FTDP‐17 (Poorkaj et al., 2001).