LEP and obesity due to melanocortin 4 receptor deficiency: Such forms of obesity are often due to mutations in genes of the leptin/melanocortin axis involved in food intake regulation [genes of leptin (LEP) and leptin receptor, proopiomelanocortin (POMC), proconvertase 1] or other genes linked to these pathways.14 As this Review focuses on epigenetic factors leading to an increased propensity for obesity development, monogenic obesity will not be discussed; an overview can be found here.15, 16