The results of this systematic review partially corroborate the findings of a previous review, which reported reductions in HbA1c in patients with T1DM and that the efficacy of DPP-4 inhibitors depends not only on their primary mechanism of action (increased GLP-1 and GIP), but also on immunomodulatory and anti-inflammatory effects, such as the reduction in pro-inflammatory Th1 and the increase in Tregs [16]. The gene discussed is GCG; the disease is type 1 diabetes mellitus.