MAPT and frontotemporal dementia: The frequency of MAPT gene mutations is highly variable, ranging from 0–3% in sporadic FTD to 5–20% in familial cases (Houlden et al., 1999; Rizzu et al., 1999; Poorkaj et al., 2001; Binetti et al., 2003; Rademakers et al., 2004; Kaivorinne et al., 2008; Pickering-Brown et al., 2008).