TREM2 and Parkinson disease: Interestingly, one study reported that deletion of TREM2 aggravated neurodegeneration in mice injected with AAV‐α‐syn at 3–8 mpi.[39] Another study revealed that TREM2 overexpression attenuates neuroinflammation and protects dopaminergic neurons in an MPTP‐induced mouse model of PD.[40] These results suggest that TREM2 may exert different effects under different conditions.