Strong family history predicts a younger age of onset for subjects diagnosed with type 2 diabetes

Aims: Age of onset of type 2 diabetes is becoming earlier and with it there is an increase in the development of chronic complications. This study examined the relationship between the strength of family history of diabetes on (i) age of diabetes onset and (ii) prevalence of diabetic complications. Research design and methods: Data on family history of diabetes and age of diabetes onset were prospectively collected on 5193 subjects. Family members were deemed to include grandparents, parents, siblings, aunts/uncles and children. To adjust for family size and to assess effects of pathway to diagnosis, we also contacted a subset of 180 patients selected on the basis of the strength of family histories of diabetes. A full assessment for diabetic complications including retinopathy, neuropathy and renal and macrovascular status was performed for the total cohort. Results: The more cases of diabetes found in a family, the younger the age of onset of type 2 diabetes. This phenomenon does not appear to be due to patients with strong family history of diabetes being more concerned about the possibility of having diabetes. The effect of strong family history is also evident in many ethnic groups when examined individually, although they differ from each other in their characteristic age of onset of diabetes. Once adjusted for duration of diabetes, strength of family history does not appear to affect metabolic profiles or prevalence of chronic complications. Conclusions: There is a strong relationship between the number of affected family members with diabetes and age of developing diabetes. The genetic and environmental factors underlying this phenomenon remain to be elucidated. However, it may be one of the reasons explaining why type 2 diabetes is affecting younger people worldwide.