In addition to Atp5a1, which encodes a subunit of mitochondrial ATP synthase (complex V), other mitochondrial complex I and II subunit-encoding genes (e.g., Ndufb5, Ndufb9 and Sdhd) were downregulated in obese subjects and type 2 diabetic patients, and impaired mitochondrial OXPHOS was proposed as an etiological mechanism underlying insulin resistance [41]. Here, NDUFB9 is linked to type 2 diabetes mellitus.