LEP and obesity due to melanocortin 4 receptor deficiency: Leptin acts through its receptor, the product of the db gene, which has at least six isoforms.20 Mutation in OBR causes early onset obesity, hyperphagia and hypothalamia.21 In comparison with other five short isoforms of leptin receptors, the role of long signaling form (OBRb) in leptin signaling is well studied and recognized as the main signal mediator of leptin.