For example, the respiratory chain genes NADH dehydrogenase (NDUFA1/A12/B1/B2/B4/B9), Cytochrome C Oxidase (COX7A1), and Ubiquinol-Cytochrome C Reductase (UQCRQ) are all downregulated in T2D patients, but largely homogeneous within the cells from individual donors. Here, COX7A1 is linked to type 2 diabetes mellitus.