HealthDay News — Smoking may modify a previously reported genetic association with Parkinson’s disease (PD), according to an analysis published online in the Annals of Neurology.

Yu-Hsuan Chuang, MPH, from the University of California, Los Angeles, and colleagues conducted a pooled analysis of the interaction between HLA-DRB1 and smoking in PD in 3 population-based case-control studies from Denmark and France involving 2056 cases and 2723 controls. Genotyping of the rs660895 polymorphism in the HLA-DRB1 region was based on blood or saliva DNA samples.

The researchers found that carrying rs660895-G (AG vs AA: odds ratio [OR], 0.81; GG vs AA: OR, 0.56; P-trend =.003) and ever smoking (OR, 0.56; P <.001) were inversely associated with PD. There was a multiplicative interaction between rs660895 and smoking using codominant, additive (P =.005), and dominant (P =.001) genetic models without any heterogeneity. An inverse association of rs660895-(AG+GG) and PD in never smokers (OR, 0.64; P <.001) disappeared among ever smokers (OR, 1; P =.99). Similar interactions were noted when light and heavy smokers were investigated separately.

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“Our study provides the first evidence that smoking modifies the previously reported inverse association of rs660895-G with PD, and suggests that smoking and HLA-DRB1 are involved in common pathways, possibly related to neuroinflammation,” conclude the authors.

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Chuang Y-H, Lee P-C, Vlaar T, et al. Pooled analysis of the HLA-DRB1 by smoking interaction in Parkinson disease [published online October 5, 2017]. Ann Neurol. doi:10.1002/ana.25065