Abstract

Objective: We aimed at characterizing familial risks for type 2 diabetes by the type and number of affected family members, including half siblings, adoptees and spouses in order to quantify risks and estimate the contribution of environmental effect.

Research design & methods: Families were identified from the Multigeneration Register and type 2 diabetes patients were obtained from the Hospital Discharge Register. Standardize incidence ratios (SIR) were calculated for offspring type 2 diabetes whose family members were hospitalized for type 2 diabetes at ages over 39 years compared to those lacking affected family members.

Results: The number of hospitalized type 2 diabetes patients was 157,549. Among 27,895 offspring, 27.9% had a parent or sibling also hospitalized for type 2 diabetes. The familial relative risk ranged from 2.0 to over 30, depending on the number and type of probands. The highest relative risks of type 2 diabetes were found in individuals who had at least two siblings affected by type 2 diabetes, irrespective of the parental disease. Adoptees showed no risk from adopted parents.

Conclusions: The study, the largest yet published, showed that familial relative risks varied by the number and type of affected family member. Assumably, much of the familial clustering remains yet to be genetically explained. The high risk should be recognized in clinical genetic counseling. The data from adoptees confirmed the genetics basis of the familial associations but those from half siblings and spouses suggested that a smaller part of familial clustering may be accounted for by environmental factors.