Association of a SNP in the IAPP gene and hyperglycemia on β-cell dysfunction in type 2 diabetes: the Toon Genome Study

Objective In type 2 diabetes, the significant pathological change in pancreatic islets is amyloid deposits. Its major component is islet amyloid polypeptide (IAPP). The objective of this study was to evaluate the possibility that the effect of the IAPP genotype on β-cell dysfunction in type 2 diabetes is modified by variations in plasma glucose levels. Methods Participants from the Toon Genome Study underwent a 75 g OGTT for the diagnosis of glucose tolerance and the evaluation of insulin secretion. We examined the effect of a SNP, rs77397980, on β-cell function by analyzing an interaction (statistics) between the IAPP genotype and AUC glucose. Results The ratio of the C-allele carriers was essentially the same among subjects with normal glucose tolerance, impaired glucose tolerance and diabetes. In subjects with diabetes, along with an increase in AUC glucose, fasting insulin remained constant in the T/T homozygotes and appeared to decrease in the C-allele carriers. A homeostasis model assessment (HOMA)-IR appeared to be increased in the former and decreased in the latter. In subjects with diabetes stratified into cases with higher AUC glucose than the median, fasting insulin and HOMA-IR were lower in the C-allele carriers than in the T/T homozygotes. An interaction between the IAPP genotype and AUC glucose was indicated in the effect on HOMA-IR. Conclusions The possibility that the association between IAPP genotype and basal insulin level is modified by variation in plasma glucose, resulting in a decreased basal insulin in type 2 diabetes, cannot be excluded.