FNDC5 and Prader-Willi syndrome: Mean serum irisin levels did not change significantly between PWS children and controls (4.37 ± 2.30 μg/ml vs 5.31 ± 2.13 μg/ml, respectively) as well as between adult PWS and controls (6.65 ± 4.49 μg/ml vs 7.24 ± 5.20 μg/ml, respectively) (Fig. 1).