Supplementary Material for: Coenzyme Q10 Supplementation in a Child with Biallelic COQ8A Variants: A Case Report

Pathogenic variants in COQ8A cause a rare form of primary coenzyme Q10 (CoQ10) deficiency that can lead to childhood-onset cerebellar ataxia and developmental delay. Reports of pediatric cases remain limited. We describe a 7-year-old boy with compound heterozygous COQ8A variants who presented with progressive cerebellar ataxia and intellectual disability. CoQ10 supplementation (10 mg/kg/day) was initiated after institutional ethics approval. During 1 year of therapy, the Scale for the Assessment and Rating of Ataxia (SARA) score improved from 17 to 9, serum CoQ10 concentration increased from 622 to 9,100 ng/mL, and mild cognitive improvement was noted (IQ 53 to 64). Brain MRI demonstrated cerebellar atrophy remained radiologically stable. No adverse effects were observed. This case highlights the clinical benefit and safety of CoQ10 supplementation in pediatric-onset COQ8A-related ataxia and emphasizes the importance of early genetic diagnosis and treatment initiation.