MAPT and frontotemporal dementia: Tau isoforms with three microtubule-binding domains, designated as 3-repeat tau (3R-tau), are generated by the splicing of exon 10 and are observed in Pick's disease (18), whereas tau isoforms with four microtubule-binding domains, designated as 4-repeat tau (4R-tau), accumulate in PSP and corticobasal degeneration (19).