Phenotypic and Genetic Correlates of Diabetes (Non-Type 1) in Young Non-Obese Asian Indians in North India and A Study to Evaluate the Efficacy of Sitagliptin (DPP-4 Inhibitor) in a Sub-group of the Study Population

Inclusion Criteria: * Young (18 to 40 years) patients with diabetes (not on insulin therapy) during the past 6 months and having BMI \<25 kg/m2. * Drug naïve patients * Patients on mono-therapy with metformin (\< 1g/day). Exclusion Criteria: * Type 1 diabetes * Type 2 Diabetes on any other oral hypoglycemic agent other than metformin * Pregnancy or lactation * Insulin or Sulfonylurea treatment within the past 3 months * Has received any investigational drug with the past 60 days * History of prior allergy or hypersensitivity to any drug (unless approved by investigator) * HbA1c \< 7.5% or \> 8.5%. * Unstable glycemic control, requiring addition of 2nd oral agent/insulin or frequent up-titration of dose of metformin. * Any patient on insulin. * Females of child bearing potential who are not using adequate contraception during the study period. * Insulin dependent or history of ketoacidosis requiring hospitalization * Acute infections * Advanced end-organ damage (CLD, CRF etc.) * Diabetes with clinically significant or advanced end-organ damage