COQ9 and cardiomyopathy: Interestingly, changes in FGF21-responsive genes such as OXCT1, the SUCL complex, PDHA1, OGDH, ACO2, IDH3B, and ETC components (MT-CO2, COQ9, UQCRQ, SDHB/D and NDUFB7) are linked to mitochondrial deficiency syndromes manifesting cardiomyopathy and encephalopathy.