Incidence of new onset type 1 diabetes in siblings of index cases with type 1 diabetes within the first 11 years in Turkish children

Aim Although newly diagnosed type 1 diabetes mellitus (T1DM) occurs sporadically in childhood, there is an increased risk of T1DM for first‐degree relatives of patients that endure into the advanced years. Determination of T1DM incidence in siblings of children with T1DM helps predict the development of new cases. This study focuses on the incidence of the disease in siblings of children with T1DM. Method A total of 1497 siblings of 850 children (403 female; 447 male) diagnosed with T1DM between 2007 and 2018 years were retrospectively screened for T1DM. The patients were divided into four onset age groups: 0–4, 5–9, 10–14 and ≥15. The annual incidence was calculated for the region. Results A total of 34 siblings diagnosed with T1DM were detected. The incidence relating to the years investigated was between 7.42 and 11.73/100 000 for the newly diagnosed indexes while it ranged between 0 and 5.8% for siblings. The 5–9 year group was the most commonly diagnosed onset age group in index (n = 312) and siblings (n = 20). For siblings, the male sex and 5–9 aged at diagnosis of index were significant risk factors for development of T1DM (OR:2.35 and 2.85). Conclusion This study shows that in the first years following the diagnosis of an index, incidence of T1DM among the siblings can rise up to 5.8%, and the age group of 5–9 in the index and the male sex in the sibling are the most important risk factors. These findings show that the risk for siblings of children with T1DM remarkably increases in the first years after diagnosis in index cases.