To investigate whether reduction of HbA1c by sitagliptin could be predicted by baseline clinical parameters, we used the linear mixed effect model with candidate predictive factors such as age, gender, duration of type 2 diabetes, BMI, HbA1c level, eGFR and type of anti-diabetes drugs (sitagliptin monotherapy vs. sitagliptin plus SUs vs. sitagliptin plus OHAs except SUs and/or insulin) at baseline as independent variables. The gene discussed is INS; the disease is diabetes mellitus.