Primary CoQ10 deficiency was first described in 1989 but only in the last decade the molecular bases of this disorder have been elucidated.[16] To date, mutations in 8 genes (PDSS1, PDSS2, COQ2, COQ4, COQ6, ADCK3, ADCK4, and COQ9) have been associated with CoQ10 deficiency presenting with a wide variety of clinical manifestations.[17,18] It is of great importance that physicians should promptly recognize these disorders because most patients respond to oral administration of CoQ10. Here, COQ9 is linked to coenzyme Q10 deficiency.