In gender-based analysis, irisin levels did not differ between males and females in PWS (17.9 ± 1.8 and 18.3 ± 1.4 ng/ml) as well as controls with common obesity (26.1 ± 2.4 and 24.8 ± 2.1 ng/ml), while males from the lean group exhibited non-significantly higher irisin levels than females (20.7 ± 3.1 and 12.7 ± 1.8 ng/ml, p = 0.06). This evidence concerns the gene FNDC5 and obesity disorder.