Mitochondrial Dysfunctions in Human Primary Coenzyme Q10 Deficiencies

Coenzyme Q10 (CoQ10) is an essential lipid-soluble molecule that plays a central role in mitochondrial energy production as a mobile electron carrier. In addition to its bioenergetic function, CoQ10 participates in antioxidant defense, redox homeostasis, lipid and nucleotide metabolism, and mitochondrial quality control. Primary CoQ10 deficiencies are rare inherited mitochondrial disorders caused by pathogenic variants in nuclear genes involved in CoQ10 biosynthesis. These defects lead to reduced CoQ10 levels and impaired mitochondrial functions. Clinically, primary CoQ10 deficiencies display remarkable phenotypic heterogeneity, ranging from isolated organ involvement, notably renal or cerebellar disease, to severe multisystemic disorders affecting the nervous system, skeletal muscle, heart, and other organs. Disease onset spans from the antenatal period to adulthood, and clinical severity varies widely, even among patients carrying variants in the same gene. This diversity cannot be fully explained by defective ATP production alone. Growing evidence indicates that disruption of non-bioenergetic functions of CoQ10, including oxidative stress regulation and CoQ-dependent metabolic pathways, contributes significantly to disease pathophysiology and tissue vulnerability. In this review, we summarize current knowledge on CoQ10 biology, biosynthesis, and the clinical spectrum of primary CoQ10 deficiencies, and we discuss emerging mechanisms linking CoQ10 depletion to mitochondrial dysfunctions and human diseases.