Apart from leptin resistance, congenital lack of leptin, resulting from mutations in the LEP gene, has additionally been associated with extreme obesity, excessive appetite, continual search for food, reduced feeling of fullness, repeated bacterial infections, hepatic steatosis, dyslipidemia, hyperinsulinemia, and hypogonadotropic hypogonadism [44]. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.