In another meta-analysis of 23 studies involving 1745 diabetic patients (T2DM, T2DM, and gestational diabetes mellitus [GDM]) and 1337 non-diabetic controls, circulating irisin levels were decreased in patients with T2DM and GDM, but not in patients with T1DM [37]. This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.