We previously reported a relationship between air pollutants and increased risk of pediatric MS (ped-MS). Environmental risk factor research in ped-MS offers the advantage of shorter duration between exposure and disease onset. Ozone, an air pollutant, is a major global health hazard thought to have a role in MS pathoetiology. Identifying gene-environment interactions advances the understanding of biological processes at play in MS susceptibility.
We sought to examine the interaction between ozone pollution and DRB1*15 status as the main genetic variant associated with MS susceptibility.
Cases and controls enrolled in the Environmental and Genetic Risk Factors for Pediatric MS study of the US Network of Pediatric MS Centers were analysed. County-level modeled ozone data were acquired from the CDC’s Environmental Tracking Network air pollution database. Participants were assigned ozone values based on county of residence. Values were categorized into tertiles based on healthy controls. The association between ozone tertiles and having MS were assessed by logistic regression. Interaction between tertiles of ozone level and presence of DRB1*15 alleles on odds of ped-MS was evaluated. Models were adjusted for sex, race, ethnicity, age, second-hand smoke exposure, and mother’s education. Additive interaction was estimated using relative risk due to interaction (RERI) and attributable proportion of disease were calculated.
355 ped-MS cases and 565 controls contributed to the analyses. Ozone levels were associated with MS with an odds ratio (OR) of 2.35 (95%CI 1.57–3.51) and 2.21 (95%CI 1.48–3.32) in the upper two tertiles, respectively, compared with the lowest tertile. DRB1 status was also independently associated with MS (OR 1.99; 95%CI 1.43–2.78). There was a significant additive interaction between ozone and DRB1, with a RERI of 2.74 (95%CI 0.50–4.98) and 2.43 (95%CI 0.36–4.5) in the upper two tertiles, respectively. Approximately 60% of the ped-MS risk in those with HLA-DRB1*15 haplotype and high ozone exposure was attributable to the interaction between these risk factors.
Our data revealed additive interaction between higher exposure to ozone and DRB1 alleles on ped-MS susceptibility. Further evaluation of additional genetic variants that might play a role in ozone-induced ped-MS is underway to provide mechanistic insight.