LEPR and obesity due to melanocortin 4 receptor deficiency: Zucker rats have a missense mutation (fa) in the leptin receptor (Lepr) gene [12,13,14] and because of this point mutation, the homozygous (fa/fa) mutants exhibit hyperphagia, defective non-shivering thermogenesis, and energy deposition in the adipose tissue, which consequently lead to obesity [15].