Abstract
We compared the incidence of familial diabetes in patients with type I (insulin-dependent) and type II (insulin-independent) diabetes. In type II patients, we also analyzed the familial incidence with reference to the maximal past body weight index and the number of children.
Full pedigrees of first-degree relatives were recorded in 671 patients with definite diabetes. The family history of diabetes was judged as positive when either of their parents, siblings or children had diabetes. The occurrence of diabetes in other relatives was disregarded. Among 229 insulintreated patients, 48 cases who appeared to be absolutely insulin-dependent were classified as type I diabetics. Among diet-, SU-, and insulin-treated patients, 580 were classified as type II and the remaining 43 cases as being of unknown type.
The overall incidence of familial diabetes was 42%(282/671), which represented the highest figure in the Japanese literature. The incidence of familial diabetes in type I diabetes (12/48=25%) was significantly lower than that in type II diabetes (251/580=43%)(p<0.02). The incidence was 44%(19/43) in patients with diabetes of unknown type. It was 27% in type I and 48% in type II (p<0.01) in patients with diabetes onset before the age of 50 years.
Type II diabetic patients with more marked obesity in the past had a lower incidence of familial diabetes. The highest incidence was observed in non-obese, type II diabetics of young onset. In females who developed type II diabetes after 40 years old, the frequency of diabetes in the parents and siblings did not differ significantly with the number of children.These data not only confirm the previously known higher incidence of familial diabetes in type II than in type I, but also demonstrate that this difference is not confined to young-onset diabetes.
Genetic factors seem to play a more important role in the pathogenesis of type II diabetes than that of type I diabetes. Excessive obesity is apparently so strongly diabetogenic as to induce diabetes in subjects with lesser genetic disposition for diabetes. Pregnancy is probably less important than obesity as a factor inducing diabetes.
