Leptin resistance is found in obesity and is caused by several mechanisms such as: defect access of leptin to its receptor (decrease receptor expression or impairment of post-receptor signaling including epigenetic process) [39], defect in the leptin blood–brain barrier, or weakening of leptin signaling due to inactivation of JAK-STAT pathway (via inhibition of suppressor of cytokine-signaling-3), endoplasmic reticulum stress, and inflammation [40]. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.