Insulin resistance and progression to type 1 diabetes in the European Nicotinamide Diabetes Intervention Trial (ENDIT): response to Bingley et al.

OBJECTIVE Insulin resistance can modulate progression to type 1 diabetes in individuals with ongoing islet autoimmunity. We wanted to see whether measures of insulin resistance improved risk assessment in islet cell antibody (ICA)-positive relatives when added to other immune and metabolic markers. RESEARCH DESIGN AND METHODS The retrospective cohort analysis included 213 family members participating in the European Nicotinamide Diabetes Intervention Trial. All were aged <25 years, with at least one islet antibody in addition to ICA >or=20 Juvenile Diabetes Foundation units. Median length of follow-up was 4.21 years, and 105 individuals developed diabetes. Oral and intravenous glucose tolerance tests were performed at baseline; antibodies to GAD, IA-2, and insulin were determined by radioimmunoassay; and insulin resistance was estimated by homeostasis model assessment. Risk was assessed by Cox regression analysis RESULTS The overall cumulative risk of diabetes within 5 years was 54.1% (95% CI 46.0-62.3). Multivariate analysis confirmed that baseline first-phase insulin response (FPIR) quartile (P < 0.0001), number of additional antibody markers (P < 0.0001), and 120-min glucose in the oral glucose tolerance test (P < 0.0001) were independent determinants of risk of progression, whereas addition of homeostasis model assessment of insulin resistance (HOMA2-IR) achieved only borderline significance (P = 0.06). HOMA2-IR was an independent determinant in participants with loss of FPIR (P = 0.025) but not in those with preserved FPIR (P = 0.3). CONCLUSIONS These data suggest that insulin resistance accelerates progression to type 1 diabetes in antibody-positive relatives in whom insulin secretion is markedly reduced but does not affect progression when insulin secretion is relatively well preserved.