In accordance with previous studies [15,22], Y123F HOM mice displayed early-onset obesity (from 4 weeks of age) and they had higher BWs and more abdominal fat deposits than their WT littermates, though these differences were less pronounced than in db/db mice [15], fully illustrating the importance of leptin and LepR in adiposity metabolism and energy balance. This evidence concerns the gene LEPR and obesity due to melanocortin 4 receptor deficiency.