Alternative spicing of Mapt (12, 13, 14, 15), which forms NFTs and is mutated in frontotemporal dementia (16, 17, 18, 19, 20, 21, 22, 23), leads to expression of tau isoforms with three or four microtubule-binding domains (3R and 4R, respectively). Here, MAPT is linked to frontotemporal dementia.