CST3 and obesity due to melanocortin 4 receptor deficiency: In model 2, taking the cystatin C first quartile level as the reference group, the risk of obesity was reduced by 10% at the second quartile level (OR = 0.90, 95% CI: 0.34–2.39, P = 0.826), while it was increased by 25% at the third quartile level (OR = 1.25, 95% CI: 0.49–3.19, P = 0.646) and 38% at the fourth quartile level (OR = 1.38, 95% CI: 0.50–3.82, P = 0.539) cystatin C levels.