EPO and obesity due to melanocortin 4 receptor deficiency: Primary polycythemia is a rare disease,10,11 and most cases of polycythemia in the general population are cases of secondary polycythemia, which is due to an increase in erythropoietin and is caused by various conditions, including smoking, sleep apnea, high altitude, chronic cardiopulmonary diseases, and erythropoietin-producing tumors.12 Moreover, sleep apnea is closely associated with obesity, a central cardiovascular risk factor.13