Gene-environment interactions and risk of pediatric-onset multiple sclerosis associated with time spent outdoors.

Background: Our previous study identified a significant association between lower time spent outdoors, as a proxy of sun exposure, and a higher risk of pediatric-onset multiple sclerosis (POMS). UV radiation modulates the expression of several genes, but it is unknown whether these genes modify the effect of sun exposure on POMS risk.

Methods: In an age- and sex-matched case-control study, we evaluated the additive and multiplicative interactions between time spent outdoors and genetic non-HLA risk variants for developing POMS within the metabolic pathways of UV radiation, including CD28(rs6435203), CD86(rs9282641), and NFkB1(rs7665090) and the top two HLA risk factors (presence of DRB1×15 and absence of A*02).

Results: In an adjusted model (332 POMS cases, 534 healthy controls), greater time compared to <30 min/day spent outdoors during the prior summer and higher UV radiation dose were associated with decreased odds of POMS (OR 0.66, 95% CI 0.56-0.78, p < 0.001; OR 0.78, 95 % CI 0.62-0.98, p = 0.04, respectively). No significant additive or multiplicative interactions were found between risk factors.

Conclusions: The exploration of gene-environment interactions in the risk of developing MS can unravel the underlying mechanisms involved. Although we do not have evidence that our candidate genes contribute to interactions, other genes may.