To date, 10 genes encoding CoQ10 biosynthetic proteins have been shown to cause primary CoQ10 deficiency: PDSS1, PDSS2, COQ2, COQ4, COQ5, COQ6, COQ7, COQ8A, COQ8B, and COQ9 [Figure 1]. The gene discussed is COQ2; the disease is coenzyme Q10 deficiency.