COQ2‐Associated Primary Coenzyme Q10 Deficiency Presenting With Proteinuria: A Case Report and Literature Review

ABSTRACT Background Primary coenzyme Q10 (CoQ10) deficiency (PCOQ10D) is an autosomal recessive mitochondrial disorder caused by pathogenic variants in genes involved in the CoQ10 biosynthetic pathway, including PDSS2, COQ2, COQ6, and COQ8B/ADCK4. Among these, pathogenic variants in the COQ2 gene impair oxidative phosphorylation and mitochondrial biogenesis in podocytes, often leading to encephalopathy and nephropathy. Methods Clinical data were collected from a pediatric patient with proteinuria caused by COQ2 gene variants, who was admitted to the Children's Hospital Affiliated to Nanjing Medical University in June 2025. Relevant examinations were completed, and whole‐exome sequencing (WES) was performed to screen for potential genetic variants in the patient's genomic DNA. Pathogenicity assessment of the identified variants was conducted in accordance with the American College of Medical Genetics and Genomics (ACMG) guidelines and online bioinformatics tools. Additionally, a systematic literature review on COQ2‐associated nephropathy was carried out in this study. Results The patient initially presented with global developmental delay accompanied by neurological lesions and developed proteinuria at 6 months of age. Genetic testing revealed two pathogenic variants: c.368G>A, p.(Arg123His) and c.908A>G, p.(Tyr303Cys). After oral administration of high‐dose CoQ10 (85 mg/kg/d) combined with enalapril maleate (0.80 mL/kg/d), the patient achieved complete remission of proteinuria and maintained stable renal function. Conclusions PCOQ10D exhibits marked phenotypic heterogeneity, characterized by variations in age of onset, organ involvement, and clinical severity, as well as significant interindividual differences in treatment responses to CoQ10 supplementation. This case expands the phenotypic spectrum of the disease. Moreover, the therapeutic outcomes suggest that all diagnosed patients require long‐term supplementation with adequate doses of CoQ10, which is of great significance for delaying disease progression.