High frequency of mutations in the HNF-1alpha gene in non-obese patients with diabetes of youth in Japanese and identification of a case of digenic inheritance

Abstract

Aims/hypothesis: There is an emerging epidemic of Type II (non-insulin-dependent) diabetes mellitus of youth in Japan and in many other developed countries. The aim of this study was to determine the prevalence of mutations in the hepatocyte nuclear factor (HNF)-1alpha gene (TCF1) in a large group of Japanese patients with early-onset non-Type I (insulin-dependent) diabetes mellitus. Since approximately 20% of Caucasian patients with HNF-1alpha mutations have been shown to be obese or overweight, we also examined the association of genetic variations in TCF1 with body weight in Japanese subjects.

Methods: We examined 203 patients with non-Type 1 diabetes who had been diagnosed before they reached 15 years of age. Ten exons and flanking introns of TCF1 of these patients were directly sequenced for mutations.

Results: We found 14 different mutations in 18 patients (8.9%), including one that was found to be de novo. The patients with the mutations had lower BMI (20.1+/-3.0 kg/m(2)) at diagnosis than the patients without them (24.5+/-6.0 kg/m(2)) (p=0.0024). All of the patients with the mutations, except for one, Y120, had normal body weight (BMI<25 kg/m(2)); the frequency of HNF-1alpha mutations in the non-obese patients of this study was 17% (17/101). Patient Y120, who had atypical symptoms of mild obesity and insulin resistance at diagnosis, was found to have inherited an additional mutation in an obesity-related gene.

Conclusion/interpretation: A considerable number of non-obese Japanese patients with non-Type 1 diabetes of youth have HNF-1alpha-deficient diabetes. Lack of obesity could well be a characteristic feature of this form of diabetes.