In vitro and in vivo studies indicate that VA activates endogenous CoQ synthesis and rescues the phenotype in COQ6 deficiency, while β-RA reduces the DMQ/COQ ratio, and thus might be a suitable approach in patients with defects of CoQ biosynthesis, which cause accumulation of DMQ, as mutations in COQ9, COQ7, or COQ4. This evidence concerns the gene COQ9 and hyperinsulinemic hypoglycemia, familial, 4.