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Lack of replication of interaction between EBNA1 IgG and smoking in risk for multiple sclerosis
Emilie Sundqvist1, Peter Sundström, Magdalena Lindén
1From the Neuroimmunology Unit, Karolinska Institutet, Stockholm, Sweden. Emilie.Sundqvist@ki.se
Background:
Epstein-Barr virus infection, smoking, HLA-A*02, and DRB1*15 have all been proposed as risk factors for multiple sclerosis (MS). In 2010, Simon et al. described an interaction on the multiplicative scale between EBNA1 immunoglobulin G (IgG) and smoking regarding risk of MS, a finding that we attempted to replicate.
Methods:
This Swedish case-control study consisted of patients with newly diagnosed MS and matched controls. Using logistic regression, we analyzed association to MS risk and interactions between EBNA1 IgG and smoking, HLA-DRB1*15, and A*02, respectively, on the multiplicative scale. In addition, we analyzed interactions on the additive scale using attributable proportion due to interaction (AP).
Results:
We did not observe any interaction on the multiplicative scale between EBNA1 IgG and any of the 3 risk factors, smoking, DRB1*15, or absence of A*02, although in a conditional analysis the interaction with absence of A*02 becomes significant. However, we observed interactions on the additive scale between EBNA1 IgG and DRB1*15 (AP = 0.34, 95% confidence interval 0.11-0.57, p = 5 × 10⁻³) and between EBNA1 IgG and absence of A*02 (AP = 0.36, 0.13-0.59, p = 2 × 10⁻³) but not between smoking and DRB1*15 and EBNA1 IgG. The interaction between EBNA1 IgG and DRB1*15 was not significant in the conditional analysis.
Conclusion:
We did not observe any interaction between EBNA1 IgG and smoking, regardless of scale used, and thus did not replicate the observations from Simon et al.
