NDUFA9 and polycystic ovary syndrome: Confirming results from the pathway enrichment analysis, qRT-PCR results showed a significant lower expression of the respiratory complexes genes NDUFA9 (P = 0.001), SDHB (P < 0.001), UQCRC2 (P = 0.024), COX4a1 (P < 0.001) and ATP5PD (P = 0.002) and the mitochondrial ribosome genes MRPL41 (P = 0.031) and MRPS7 (P = 0.008) in skeletal muscle of women with PCOS (Fig. 4A, B and Supplementary Fig. 2).