The healthy human brain exhibits a 1/1 ratio of tau 3R/4R and deviation from this ratio are pathological features of FTD taupathies (Goedert et al., 1988, 1989a,b; Hutton et al., 1998; Spillantini et al., 1998; Goedert and Spillantini, 2011). The gene discussed is MAPT; the disease is frontotemporal dementia.