The COQ2 genotype predicts the severity of coenzyme Q10 deficiency

COQ2 (p-hydroxybenzoate polyprenyl transferase) encodes the enzyme required for the second step of the final reaction sequence of Coenzyme Q(10) (CoQ) biosynthesis. Its mutations represent a frequent cause of primary CoQ deficiency and have been associated with the widest clinical spectrum, ranging from fatal neonatal multisystemic disease to late-onset encephalopathy. However, the reasons of this variability are still unknown. We have characterized the structure of human COQ2, defined its subcellular localization and developed a yeast model to validate all the mutant alleles reported so far. Our findings show that the main functional transcript of COQ2 is shorter than what was previously reported and that its protein product localizes to mitochondria with the C-terminus facing the intermembrane space. Complementation experiments in yeast showed that the residual activity of the mutant proteins correlates with the clinical phenotypes observed in patients. We defined the structure of COQ2 with relevant implications for mutation screening in patients and demonstrated that, contrary to other COQ gene defects such as ADCK3, there is a correlation between COQ2 genotype and patient's phenotype.