PCOS women with MetS had significantly higher serum irisin (12.15 (9.5-19.02) vs 8.28 (2.9-12.6) ng/mL, P = 0.015), serum testosterone (41.5 (37.5-49.8) vs 36.5 (36-40.5) ng/dL, P = 0.046), body fat percentage (44.20 ± 6.39 vs. 36.7 ± 6.71, P = 0.008), visceral fat percentage (12.38 ± 2.78 vs. 9.50 ± 2.11, P = 0.004), FMI (20.76 ± 4.96 vs. 13.15 ± 3.46, P <0.001), and FFMI (17.36 ± 1.95 vs. 14.89 ± 1.75, P = 0.002) as compared to women with PCOS without MetS. This evidence concerns the gene FNDC5 and metabolic syndrome.