RCAN2 and obesity due to melanocortin 4 receptor deficiency: In this study, we planned to 1) investigate the serum RCAN2 concentrations of 348 participants with normal weight, 397 participants with overweight, and 127 participants with obesity; 2) analyze the correlation between serum RCAN2 concentrations and clinical indicators and metabolic indicators; 3) explore the diagnostic value of serum RCAN2 for discriminating individuals with obesity from controls.