Lack of an evident association between the serum concentrations of fT3 and TG in overweight subjects remains unexplained although several mechanisms have been proposed to account for changes in thyroid hormone concentrations in obesity, including adaptive thermogenesis to increase energy expenditure, hyperleptinemia, altered peripheral deiodinase activity, thyroid hormone resistance, chronic low-grade inflammation and insulin resistance7,11,17. The gene discussed is TG; the disease is obesity due to melanocortin 4 receptor deficiency.