MAP2K5 and obesity due to melanocortin 4 receptor deficiency: Several genome-wide association studies (GWASs) have revealed certain susceptible genetic polymorphisms, such as fat-mass and obesity-associated gene (FTO) rs1421085, SH2B adapter protein 1 (SH2B1) rs4788099 and mitogen-activated protein kinase kinase 5 (MAP2K5, the encoded protein named MEK5) rs2241423 (Thorleifsson et al., 2009; Speliotes et al., 2010).