Seasonality of month of birth of children and adolescents with type 1 diabetes mellitus in homogenous and heterogeneous populations

Background: Type 1 childhood-onset diabetes mellitus has a multifactorial origin involving an interplay between genetic and environmental factors. We have previously shown that many children who subsequently develop T1DM have a different seasonality of birth than the total live births of the same population, supporting the hypothesis that perinatal viral infection is a trigger for the autoimmune process of T1DM. Objectives: To compare the seasonality of children with T1DM in different populations around the world for which data were available. Methods: We analyzed large cohorts of T1DM patients with a clinical disease onset before age 14 or 18 years. Results: We found a seasonality pattern only in ethnically homogenous populations (such as Ashkenazi Jews, Israeli Arabs, individuals in Sardinia and Canterbury, New Zealand, and Afro-Americans) but not in heterogeneous populations (such as in Sydney, Pittsburgh and Denver). Conclusions: Our findings attempt to explain the controversial data in the literature by showing that ethnically heterogeneous populations comprising a mixture of patients with various genetic backgrounds and environmental exposures mask the different seasonality pattern of month of birth that many children with diabetes present when compared to the general population.