Infantile and pediatric quinone deficiency diseases

Coenzyme Q₁₀ (CoQ₁₀) plays a pivotal role in oxidative phosphorylation (OXPHOS) as it distributes electrons between the various dehydrogenases and the cytochrome segments of the respiratory chain. Primary coenzyme Q₁₀ deficiency is a rare, but possibly treatable, autosomal recessive condition with four major clinical presentations, an encephalomyopathic form, a generalized infantile variant with severe encephalopathy and renal disease, a myopathic form and an ataxic form. The diagnosis of ubiquinone deficiency is supported by respiratory chain analysis and eventually by the quantification of CoQ₁₀ in patient tissues. We review here the infantile and pediatric quinone deficiency diseases as well as the clinical improvement after oral CoQ₁₀ therapy. The clinical heterogeneity of ubiquinone deficiency is suggestive of a genetic heterogeneity that should be related to the large number of enzymes, and corresponding genes, involved in ubiquinone biosynthesis.