Association of MDR1 C3435T genetic polymorphism with Parkinson's disease: a meta-analysis

Parkinson's disease (PD) is the most common neurodegenerative disease. Several studies have identified the role of multidrug resistance 1 (MDR1) C3435T genetic polymorphism in PD susceptibility. However, the results still remain inconclusive. The objective of this study was to determine the effect of MDR1 C3435T variant on PD. Eligible case-control articles published between January 2000 and 2016 was searched in the electronic databases. The odds ratio (OR) with its 95% confidence interval (CI) was employed to calculate the strength of effect. A total of ten articles were retrieved, including 5408 participants (2349 PD patients and 3059 controls). No significant between-study heterogeneity was observed, and the fixed-effect model was used. Overall, our meta-analysis revealed that MDR1 C3435T was not associated with increased the risk of PD under each genetic models (P<0.05). Subgroup analysis by ethnicity showed no relevant association in either Asians or Caucasians as well. However, we detected that the mutation rate of TT+CT genotypes of MDR1 C3435T variant with pesticide exposure in PD patients was higher than those of non-exposure, and the statistical analysis detected a significant correlation with increased the risk of PD (TT+CT vs. CC: OR=2.85, 95% CI=1.66-4.90, P=0.0002). No publication bias was found in this meta-analysis. Our results suggested that MDR1 C3435T polymorphism might affect the risk of PD developing only in conjunction with exposure to pesticides. Future well-designed studies with more ethnicities are still needed to further evaluate the effect.