Missense mutations in the pancreatic islet beta cell inwardly rectifying K+ channel gene (KIR6.2/BIR):: a meta-analysis suggests a role in the polygenic basis of Type II diabetes mellitus in Caucasians

K+ inwardly rectifier channel (KIR) is one of the two sub-units of the pancreatic islet ATP-sensitive potassium channel complex (I-KATP), which has a key role in glucose-stimulated insulin secretion and thus is a potential candidate for a genetic defect in Type II (non-insulin-dependent) diabetes mellitus. We did a molecular screening of the KIR6.2 gene by single strand conformational polymorphism (SSCP) and direct sequencing in 72 French Caucasian Type II diabetic families. We identified three nucleotide substitutions resulting in three amino acid changes (E23K, L270V and I337V), that have also been identified in other Caucasian Type II diabetic subjects. These variants were genotyped in French cohorts of 191 unrelated Type II diabetic probands and 119 normoglycaemic control subjects and association studies were done. The genotype frequencies of the L270V and I337V variants were not very different between Type II diabetic subjects and control groups. In contrast, analysis of the E23K variant showed that the KK homozygocity was more frequent in Type II diabetic than in control subjects (27 vs 14%, p = 0.015) Analyses in a recessive model (KK vs EK/EE) tended to show a stronger association of the K allele with diabetes (p = 0.0097, corrected p-value for multiple testing < 0.02). The data for the E23K variant obtained here and those obtained from three other Caucasian groups studied so far were combined and investigated by meta-analysis. Overall, the E23K variant was found to be significantly associated with Type II diabetes (0.001 less than or equal to p less than or equal to 0.0016, corrected p-values for multiple testing p less than or equal to 0.01). This study shows that KIR6.2 polymorphisms are frequently associated with Type II diabetes in French Caucasians. Further more, a meta-analysis combining different Caucasian groups suggests an significant role of KIR6.2 in the polygenic context of Type II diabetes.