ATXN2 and Alzheimer disease: In AD, Aβ plaques coexist with tau tangles, α-synuclein or TDP-43 aggregates; in PD and other synucleinopathies, α-synuclein aggregates coexist with aggregates composed of Aβ, tau or TDP-43; and in ALS, TDP-43 aggregates can coexist with other aggregates formed by various proteins, including VCP, FUS, ATXN2, RBM45, P62, OPTN, TIA1, and others [66–68].