Association between interferon-induced helicase (IFIH1) rs1990760 polymorphism and seasonal variation in the onset of type 1 diabetes mellitus.

Background: Infections, mostly of viral origin, may contribute to the seasonal variation in the onset of type 1 diabetes mellitus (T1DM). The rs1990760 (A>G, Ala946Thr) polymorphism (GG genotype) of the interferon induced helicase (IFIH1), a virus recognition receptor, confers a modest protection for T1DM. The aim of our study was to evaluate a possible association between this IFIH1 polymorphism and the seasonal variation in the onset of T1DM. Materials and Methods: The IFIH1 rs1990760 polymorphism was genotyped in 1055 patients of Central-Eastern European ancestry with T1DM (median age at diagnosis: 8.2 [interquartile range, IQR 4.8-11.8] years). T1DM onset was recorded in monthly intervals. Results: The IFIH1 genotype distribution was the following: 436 patients (41.3%) had AA genotype, 483 patients (45.8%) had AG genotype, and 136 patients (12.9%) had GG genotype. Significant seasonal variation in manifestation of T1DM (highest rate in winter and lowest rate in summer period) was observed in the total cohort (n = 1055), irrespective of gender. The disease predisposing AA genotype was more frequently found among new cases with onset in summer vs in those with onset in winter (44.3% vs 37.9%); conversely, the protective GG genotype was less frequent (9.3% vs 12.9%, respectively; P = .0268 for trend). Significant effect of genotype (P = .0418) was found on the seasonal variability of T1DM onset in the total cohort. Conclusions: The IFIH1 rs1990760 polymorphism seems to be associated with the seasonal manifestation of T1DM. Our findings suggest that this virus receptor gene may contribute to T1DM manifestation primarily in the summer period.