MAPT and Alzheimer disease: AD and FTLD are histopathologically distinct, with AD being characterized by extracellular amyloid plaques and intraneuronal neurofibrillary tangles (Braak and Braak, 1991), and FTLD by the presence of non-AD histological pathology, most commonly either tau-positive inclusions or ubiquitin-positive, TAR DNA-binding protein (TDP)-43-positive inclusions (Cairns et al., 2007).