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The E23K Variant of KCNJ11 Encoding the Pancreatic ß-Cell Adenosine 5'-Triphosphate-Sensitive Potassium Channel Subunit Kir6.2 Is Associated with an Increased Risk of Secondary Failure to Sulfonylurea in Patients with Type 2 Diabetes

Department of Experimental and Clinical Medicine (G.S., E.L., F.A., C.I., A.G., M.L.H., F.P.), University Magna Græcia of Catanzaro, 88100 Catanzaro, Italy; Department of Internal Medicine (M.C., M.L.H., R.L.), University of Rome-Tor Vergata, 00133 Rome, Italy; and Department of Endocrinology and Metabolism (S.D.G., M.G., P.M.), Metabolic Unit, Cisanello Hospital, 56100 Pisa, Italy

Address all correspondence and requests for reprints to: Giorgio Sesti, M.D., Dipartimento di Medicina Sperimentale e Clinica, Università Magna Græcia, Viale Europa, Località Germaneto, 88100 Catanzaro, Italy. E-mail: sesti{at}unicz.it.

Context: Several studies suggest that genetic factors may play a role in the different responses to antidiabetic therapy; however, conclusive evidence is still lacking.

Objective: The objective of the study was to investigate whether diabetic patients carrying the E23K variant in KCNJ11 are at increased risk for secondary sulfonylurea failure.

Design: Secondary sulfonylurea failure was defined as fasting plasma glucose greater than 300 mg/dl despite sulfonylurea-metformin combined therapy and appropriate diet, in the absence of other conditions causing hyperglycemia.

Setting: The study was conducted in an ambulatory care facility.

Patients: A total of 525 Caucasian type 2 diabetic patients were enrolled in the study.

Intervention: Sulfonylurea treatment was followed by sulfonylurea-metformin combined therapy and then insulin treatment.

Main Outcome Measure: Secondary failure was the main outcome measure.

Results: Of the diabetic patients enrolled in the study, 38.5% were E23E homozygous, 51.4% were E23K heterozygous, and 10.1% were K23K homozygous. The frequency of carriers of the K allele was 58 and 66.8% among patients treated with oral therapy or secondary sulfonylurea failure, respectively (odds ratio, 1.45; 95% confidence interval, 1.01–2.09; P = 0.04). Adjustment for age, gender, fasting glycemia, glycosylated hemoglobin, age at diagnosis, and duration of diabetes in a logistic regression analysis did not change this association (odds ratio, 1.69; 95% confidence interval, 1.02–2.78; P = 0.04). Islets isolated from carriers of the K allele showed no differences in glucose-stimulated insulin secretion and a tendency toward reduced response upon glibenclamide stimulation (P = 0.09). After 24-h exposure to high (16.7 mmol/liter) glucose concentration, impairment of glibenclamide-induced insulin release was significantly (P = 0.01) worse with the E23K variant.

Conclusions: These data suggest that the E23K variant in KCNJ11 may influence the variability in the response of patients to sulfonylureas, thus representing an example of pharmacogenetics in type 2 diabetes.

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