Alternatively, leptin holds positive effects when in physiological concentrations (enhancing the activity of GLUT2 and LDH [136], upregulating steroidogenic enzymes [137], increasing the number of seminiferous tubules engaged in the first stages of spermatogenesis [137]) and negative effects when in supraphysiological concentrations—as is the case in obesity (reducing sperm progressive motility [138] and count [139], increasing DNA fragmentation [140], changing the structure of the seminiferous tubules [139]). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.