LEP and obesity due to melanocortin 4 receptor deficiency: Single gene alterations with Mendelian inheritance account for less than 5% of non-syndromic cases of severe EOO [2], including mutations in the LEP (MIM 164160) or LEPR (MIM 601007) genes [3–5], as well as in MC4R (MIM 155541) [6,7] which are the most common cause of monogenic obesity.