IFIH1 and type 1 diabetes mellitus: In that study, Caesarean section appeared to interact with type 1 diabetes susceptibility genes, in particular the IFIH1 gene (interferon induced with helicase C domain 1), suggesting modulation of the response to a diabetes-relevant environment by both Caesarean section and IFIH1. Here, the aim was to validate and extend these findings in the international TEDDY study including over 8000 prospectively followed children with type 1 diabetes-susceptible HLA genotypes, a group representing approximately 50% of children with type 1 diabetes.