Family histories of diabetes among Japanese patients with type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes.

Family histories of diabetes mellitus in first-degree relatives were compared in Japanese patients with Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes. The frequency of positive family histories for diabetes in first-degree relatives was 24% (13/55) in Type 1,44% (281/631) in Type 2 (p less than 0.01 versus Type 1) and 47% (16/34) when the type of diabetes could not be classified. The prevalence of diabetes in siblings of Type 2 patients was higher than in Type 1 diabetic patients (p less than 0.01). Patients with Type 2 diabetes and definite obesity in the past had a lower frequency of a family history of diabetes (p less than 0.01) and a lower prevalence of diabetes in their parents (p less than 0.01) than did Type 2 patients without obesity. The highest rate of family history for diabetes was observed in non-obese Type 2 diabetic patients of early onset. Our data agree with the previously known higher frequency of familial diabetes in Type 2 compared with Type 1 diabetes, despite the fact that there are significant dissimilarities between Type 1 diabetes in Japanese and Caucasoid population.