TREM2 and Parkinson disease: Several neurodegenerative-derived molecules (aggregated amyloid-β, Aβ, α-synuclein of Lewy bodies in Parkinson's disease, mutant huntingtin, superoxide dismutase-1, and chromogranin A) can activate pattern recognition receptors (PRRs) expressed on the microglial surface, such as toll-like receptors (TLR2, TLR4, and TLR6), CD36, and triggering receptor expressed by myeloid cells 2 (TREM2).