COX7A1 and type 2 diabetes mellitus: It was shown that, in the elderly or individuals with insulin resistance and T2D, mitochondrial COX7A1 (the subunit of cytochrome c oxidase or complex IV in the respiratory chain) and NDUFB6 (subunit in complex I in the respiratory chain) were dysregulated, concomitant with higher DNA methylation in the promoters of COX7A1 and NDUFB6 [18, 19].