RBP4 and obesity due to melanocortin 4 receptor deficiency: Therefore, based on the provided data [23,26], we further focused on specific groups of patients with obesity and periodontitis to analyze the correlation between serum RBP4 and several metabolic or periodontal parameters through Fisher’s Z. Intriguingly, we found a positive association between serum RBP4 and BMI/CAL, which indicated that an increased level of serum RBP4 is associated with a higher degree of BMI value or CAL figure, as it was widely known that BMI or CAL was the most basic index reflecting the degree of obesity or the severity of periodontitis [29,41].