Stable heritability of type 1 diabetes in a Swedish Nationwide Cohort Study

Incidence of type 1 diabetes is increasing globally, which is hypothesized to be due to environmental influences. We leverage Swedish nationwide registers linked to all children (n = 2,928,704) born in 1982-2010 to investigate if the heritability of childhood-onset type 1 diabetes has changed over time and how alterations in environmental factors have contributed to the rising type 1 diabetes incidence. The heritability is estimated at 0.83 (95% confidence interval: 0.79, 0.86) and stable over the observation period (0.80 [0.71, 0.86] in 1982, 0.83 [0.79, 0.86] in 2000, and 0·83 [0.79, 0.86] in 2010, respectively). Environmental factors including maternal smoking during pregnancy and childhood adiposity explain <10% of the increasing type 1 diabetes incidence. In this work, the heritability of childhood-onset type 1 diabetes has remained high and stable over the last 30 years. Our findings indicate that the available environmental factors are not the major contributors to the rise in type 1 diabetes in Sweden.