GPR39 and obesity due to melanocortin 4 receptor deficiency: Nevertheless, these remarkable phenotypic differences between Gpr39−/− and wild-type mice mentioned above were only observed at old age (about 50 weeks for obesity and 25 weeks for cholesterol) [27], suggesting that deleterious mutations in Gpr39 may increase the risk for late-onset obesity and atherosclerotic coronary heart disease.