In contrast to rodents, the expression of resistin in human adipocytes is low, and the main source of resistin in humans is macrophages (Yang et al., 2003), and in obesity, macrophages that have infiltrated into visceral white adipose tissue are the predominant source of resistin (Curat et al., 2006). This evidence concerns the gene RETN and obesity due to melanocortin 4 receptor deficiency.