For example, some studies reported a positive correlation between serum irisin levels, BMI and adiposity (76, 96, 101, 104, 105), whereas others found a negative correlation between circulating irisin levels, BMI and the amount of fat tissue (101) or could not detect a change in circulating irisin in obesity (71, 73, 75). The gene discussed is FNDC5; the disease is obesity due to melanocortin 4 receptor deficiency.