{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n COQ4 is an essential, non‐enzymatic component of the multisubunit complex that drives coenzyme Q₁₀ (CoQ₁₀) biosynthesis in both yeast and humans. Rather than acting as a catalytic enzyme itself, COQ4 plays a critical structural and organizational role in stabilizing the CoQ biosynthetic machinery, ensuring that other essential enzymes (such as COQ7) are maintained at proper steady‐state levels. Studies in yeast have demonstrated that the Coq4 protein is imported into mitochondria, localizes to the matrix face of the inner mitochondrial membrane, and is required for the assembly and stability of the multiprotein complex responsible for synthesizing the quinone ring of CoQ₁₀."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In human cells, mutations in COQ4 are associated with markedly reduced CoQ₁₀ levels, resulting in a broad spectrum of mitochondrial disorders, including neonatal encephalomyopathy, cardiomyopathy, and epilepsy."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "2", "end_ref": "4"}]}, {"type": "t", "text": " Furthermore, molecular cloning and functional rescue experiments have confirmed that the human COQ4 gene, like its yeast counterpart, is indispensable for proper CoQ₁₀ production, and its dysfunction disrupts the integrity of the CoQ biosynthetic complex."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " The emerging clinical data, including cases identified through diagnostic exome sequencing, underscore that COQ4 mutations lead to CoQ₁₀ deficiency–related diseases with heterogeneous presentations, emphasizing the gene’s key role as an organizational scaffold rather than as a direct catalyst in the synthesis pathway."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "10"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "G I Belogrudov, P T Lee, T Jonassen, et al. 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