These findings support the use of FCPGR as an indicator of β-cell function since good glycemic control in the absence of significant difference among the subgroups regarding other variables (age, BMI, duration of T2DM, MetS index score, duration on insulin therapy, insulin dosing, or being combined with oral antidiabetic agents) would reflect endogenous β-cell reserve. This evidence concerns the gene INS and type 2 diabetes mellitus.