CD33 and Parkinson disease: Neuroinflammation, particularly from chronically dysregulated microglia, plays a central role in PD progression and genome-wide association studies further implicate microglia by identifying PD risk variants enriched in microglial genes, such as LRRK2, HLA-DRB5, and CD33 (Gelders et al., 2018; Guillot-Sestier and Town, 2018; Masuda et al., 2020; Tansey and Romero-Ramos, 2019).