High frequency of class 3 allele in the human insulin gene in Japanese type 2 (non-insulin-dependent) diabetic patients with a family history of diabetes.

The restriction fragment length polymorphism in the 5' flanking region of the human insulin gene was studied in 155 nonobese Japanese subjects. The subjects consisted of 36 Type 2 (non-insulin-dependent) diabetic patients with a family history of diabetes mellitus, 42 Type 2 diabetic patients without a family history of diabetes, 42 Type 1 (insulin-dependent) diabetic patients, and 35 healthy volunteers who served as control subjects. It was demonstrated that, in Japanese healthy subjects and diabetic patients, the incidence of the insertion into 5' flanking region of the insulin gene was found to be significantly lower (p less than 0.05) than those in Caucasians and other races already investigated. Even though the class 3 gene allelic frequency in Type 2 diabetic patients without a family history of diabetes (0.060) was not higher than that in healthy subjects (0.014), in nonobese Type 2 diabetic patients with a family history of diabetes the allelic frequency of the inserted class 3 gene (0.111) was found to be significantly higher (p less than 0.02) than that in control subjects. These data suggest that the insulin gene polymorphism relates to the aetiology of diabetes mellitus.