LEP and obesity due to melanocortin 4 receptor deficiency: Leptin knockout mice (Ob/Ob) are hyperphagic, exhibit severe obesity with a high degree of adiposity, hypertrophied adipocytes, reduced testosterone levels, impairment of steroidogenic pathways, significant cellular changes in the germinal epithelium, and failures in spermatogenesis [23] (Figures 2 and 3).