Incidence of childhood type 1 diabetes mellitus in Yamanashi Prefecture, Japan, 1986-2018.

Introduction: Several studies have examined the incidence of childhood T1DM in Japan from the 1970s onwards, but none have been long-term studies using registration data. We estimate the incidence of childhood type 1 diabetes mellitus (T1DM) from 1986 to 2018 in Yamanashi Prefecture, Japan.

Methods: We began a population-based, long-term study of childhood T1DM in 1986 involving every hospital paediatrics department in Yamanashi Prefecture. In the Prefecture, every child newly diagnosed with T1DM is referred to a hospital, and therefore, almost 100% of new patients aged <15 years are registered. We calculated the incidence of T1DM among children aged <15 years from 1986 to 2018. All cases met the Japan Diabetes Society diagnostic criteria and were tested for T1DM-related autoantibodies whenever possible.

Results: Ninety-nine patients (44 boys and 55 girls) were newly diagnosed with T1DM. The annual incidence among 5- to 9-year-olds increased by 5.35% over the study period (95% confidence interval 2.34%-8.35%, = .0005), and there was a trend towards increasing 3-year incidence (15.52% increase, = .0516). There were also trends towards increasing annual and 3-year incidence among 0- to 14-year-olds. However, there were no changes over time in annual or 3-year incidence in the 0-4 year or 10-14 year age groups.

Conclusions: The incidence of T1DM in Yamanashi Prefecture increased among children aged 0-14 years over the study period, with the most significant increase occurring among 5- to 9-year-olds. These data suggest that the number of children aged <15 years with T1DM is gradually increasing in one of the local prefectures in Japan, Yamanashi Prefecture and that the age of onset is decreasing.