This study had a number of limitations. First, a self-report of diabetes and use of medication for diabetes was used to define cases and controls. We observed that approximately 1% of a random sample of the controls in this study had HbA1C levels above 7.0%, which suggests that only a small portion of controls had undiagnosed diabetes (see Materials and Methods). Also, our case definition did not differentiate between T1D and T2D, however we expect this misclassification to be minor as <3% of T2D cases had a previous diagnosis of T1D based on other sources (see Materials and Methods). The highly consistent findings of this study, as compared to the discovery GWAS reports, argue that our phenotypic characterization is adequate to observe the association to T2D.
