Conditions associated with CoQ10 deficiency can be divided into three main groups: (1) CoQ10 nutritional deficiency, including intake of CoQ10 itself and nutrients and vitamins necessary for its synthesis (vitamin B6 is a cofactor in the pathway of CoQ10 biosynthesis); (2) CoQ10 synthesis genes (COQ family genes: COQ1 and the Complex Q genes including the mammalian homolog of the yeast Coq11 gene; the Complex I subunit NDUFA9), and acquired disorders impairing CoQ10 synthesis (statin use) [59,60,61]; and (3) medical conditions associated with decreased levels of CoQ10 [45,46]. The gene discussed is NDUFA9; the disease is coenzyme Q10 deficiency.