Genetic factors play an important role in the pathogenesis of
type 2 diabetes. The relevance to
type 2 diabetes of the common polymorphism Glu23Lys in the
potassium inward rectifier 6.2 (KIR6.2) gene is still controversial. The aim of this study was to assess whether this polymorphism influences beta-cell function, alpha-cell function, or
insulin action. We therefore studied 298 nondiabetic subjects using an oral
glucose tolerance test (OGTT) and 75 nondiabetic subjects using a hyperglycemic clamp (10 mmol/l) with additional
glucagon-like peptide (GLP)-1 and
arginine stimulation. The prevalence of the Lys allele was approximately 37%, and the Lys allele was associated with higher incremental plasma
glucose during the OGTT (P = 0.03, ANOVA). Neither first- nor second-phase
glucose-stimulated
C-peptide secretion was affected by the presence of the polymorphism; nor were maximal
glucose-, GLP-1-, or
arginine-induced
C-peptide secretion rates; nor was
insulin sensitivity (all P > 0.7). However, the relative decrease in plasma
glucagon concentrations during the 10 min after the
glucose challenge was reduced in carriers of the Lys allele (10 +/- 3% decrease from baseline in
Lys/Lys, 18 +/- 2% in Glu/Lys, and 20 +/- 2% in
Glu/Glu; P = 0.01, ANOVA). In conclusion, our findings suggest that the common Glu23Lys polymorphism in KIR6.2 is not necessarily associated with beta-cell dysfunction or
insulin resistance but with diminished suppression of
glucagon secretion in response to
hyperglycemia. Our findings thus confirm its functional relevance for
glucose metabolism in humans.