CD44 is a transmembrane glycoprotein that has a wide variety of biological functions such as axion guidance, lymphocyte activation, cytokine signaling, and cell–cell adhesion; therefore, CD44 is involved in various diseases including arthritis, encephalitis, atherosclerosis, and obesity-related metabolic disorders (27). Here, GPNMB is linked to obesity due to melanocortin 4 receptor deficiency.