CD226 and obesity due to melanocortin 4 receptor deficiency: We examined the serum concentration of soluble CD226 in 79 human clinical samples (Normal 35, Overweight 31, Obesity 13), and found that the concentration of serum CD226 was significantly higher in the obesity cohort (median: 7.47 ng/ml, interquartile range [IQR]: 5.33–9.60 ng/ml) compared with the both normal (median: 3.96 ng/ml, IQR: 1.76–6.69 ng/ml) and overweight (median: 4.90 ng/ml, IQR: 3.10–6.75 ng/ml) groups (Fig. 1A), suggesting that CD226 might be related to the occurrence of obesity.