This study tried to replicate in a large sample of white patients with type 2 diabetes (T2D) from Italy a previously reported association of the IRS1 G972R polymorphism with failure to oral antidiabetes drugs (OAD). A total of 2,409 patients from four independent studies were investigated. Case subjects (n = 1,193) were patients in whom, because of uncontrolled diabetes (i.e., HbA1c >8%), insulin therapy had been added either on, or instead of, maximal or near-maximal doses of OAD, mostly metformin and sulfonylureas; control subjects (n = 1,216) were patients with HbA1c <8% in the absence of insulin therapy. The IRS1 G972R polymorphism was typed by TaqMan allele discrimination. In all samples, individuals carrying the IRS1 R972 risk variant tended to be more frequent among case than control subjects, though reaching statistical significance only in one case. As no IRS1 G972R-by-study sample interaction was observed, data from the four samples were analyzed together; a significant association was observed (allelic odds ratio [OR] 1.30, 95% CI 1.03-1.63). When our present data were meta-analyzed with those obtained in a previous study, an overall R972 allelic OR of 1.37 (1.12-1.69) was observed. This study confirms in a large and ethnically homogeneous sample that IRS1 G972R polymorphism is associated with failure to OAD among patients with T2D.
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