Glucose uptake depends on the level of GLUT4 expression [99], and treatment with metformin increases GLUT4 mRNA and protein expression in endometrial cells from women with PCOS in vivo [81,103] and in vitro [104], possibly through the activation of AMPK and its downstream targets such as myocyte enhancer factor 2A [81]. This evidence concerns the gene SLC2A4 and polycystic ovary syndrome.