MAPT and Alzheimer disease: While neurodegenerative disorders are often distinguished by their dominant types of protein aggregates—such as amyloid-beta and tau in AD, alpha-synuclein in PD and other synucleinopathies, and TAR DNA-binding protein 43 (TDP-43) in ALS [1]—patients with one neurodegenerative disorder often present with protein aggregates characteristic of another disorder [2, 3].