In the ETC, most dysregulated genes (COX5B, COX6C, CYC1, SDHA, SDHB, UQCRC1, and UQCRFS1) showed a discordant expression pattern, as they were upregulated in major depressive disorder and downregulated in ketosis, whereas CYCS, COX4I1, and SDHAF3 showed a concordant expression pattern, being upregulated in both states. Here, CYCS is linked to major depressive disorder.