Understanding Causal Relationships between Imaging-Derived Phenotypes and Parkinson’s Disease: A Mendelian Randomization and Observational Study

Background/Objectives: Observational studies have suggested a correlation between brain imaging alterations and Parkinson’s disease (PD). However, data on causal relationships are still lacking. This study aimed to examine the causal relationship between brain imaging-derived phenotypes (IDPs) and PD. Methods: A bidirectional two-sample Mendelian randomization analysis was conducted to explore the causal association between IDPs and PD. Summary-level data for IDPs (n=39,691), PD (n=482,730), and PD symptoms (n=4,093) were obtained from genome-wide association studies of European ancestry. Clinical validation was performed in an Asian cohort, which involved healthy controls (n=81), patients with idiopathic rapid-eye-movement sleep behavior disorder (iRBD) (n=47), and patients with PD (n=85). Results: We found 13 IDPs with significant causal effects on PD and 7 reciprocal effects of PD on IDPs. For instance, increased median T2star in the right caudate (odds ratio=1.23, 95% confidence interval 1.08–1.40, p=0.0057) and bilateral putamen (left: odds ratio=1.25, 95% confidence interval 1.09–1.43, p=0.0056; right: odds ratio=1.25, 95% confidence interval 1.10–1.43, p=0.0056) were associated with PD. Enlargement of the left thalamus (odds ratio=1.50, 95% confidence interval 1.14–1.96, p=0.016) demonstrated causal links with PD. No reverse causal effects were detected. Observational analyses results in the Asian cohort (healthy controls, iRBD, PD) aligned with the Mendelian randomization results. Conclusions: Our results suggest bidirectional causal links between IDPs and PD, offering insights into disease mechanisms and potential imaging biomarkers for PD.