ADRB2 and Parkinson disease: We found a decreased PD risk with the higher expression of the β2 adrenergic receptor (ADRB2) gene in blood with the results of IVW as the primary causal effect estimates (OR, 0.85; 95% CI, 0.73–0.99), while no association between β1 adrenergic receptor (ADRB1) gene expression and PD risk was found (OR, 0.94; 95% CI, 0.87–1.03)(Fig. 4).