Adiponectin, a 30 kilodalton peptide, which forms large homodimers and structurally resembles complement factor C1q, is selectively produced by adipocytes in white adipose tissue (Scherer et al., 1995) and capable of reversing the insulin resistance associated with both obesity and lipodystrophy (Berg et al., 2001; Yamauchi et al., 2001). This evidence concerns the gene ADIPOQ and obesity due to melanocortin 4 receptor deficiency.