METHODS: This Swedish case-control study consisted of MSers with newly diagnosed MS and matched controls. Using logistic regression, they 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, they analyzed interactions on the additive scale using attributable proportion due to interaction (AP).
RESULTS: They 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 became significant. However, they observed interactions on the additive scale between EBNA1 IgG and DRB1*15 (AP = 0.34, 95% confidence interval 0.11-0.57, p = 0.005 and between EBNA1 IgG and absence of A*02 (AP = 0.36, 0.13-0.59, p = 0.02) 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: They 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.