Conclusions: This cellular model has provided insight into the effect of CoQ10 deficiency on neuronal ETC function and oxidative stress and will enable the efficacy of potential treatments to restore mitochondrial function. This project is funded by Ataxia UK (www.ataxia.org.uk). Objective: coenzyme Q10 (CoQ10) deficiency due to mutation in the COQ2 with a new clinical presentation. Case report: At the age of 3 weeks, patient developed myoclonic seizures. Both plasma and CSF lactate were increased. Brain MRI was normal and muscle biopsy performed at 2 months of age did not disclose morphological or OXPHOS abnormality. Despite supplementation with riboflavin, biotin, pyridoxine and CoQ10 and several anti-epileptic drugs he continued to have partial and myoclonic seizures, evolving into epilepsia partialis continua. At 5 months he developed a nephrotic syndrome and CoQ10 was increased to 30 mg/kg /day but he expired. Results: Renal biopsy showed focal segmental glomerulosclerosis and on ultrastructural examination enlarged podocytes with hyaline cytoplasmic vacuoles. Respiratory chain activities of renal cortex demonstrated decreased activities of complexes II+III. A homozygous mutation c.326 G>A (p. Ser109Asn) in exon 2 of CoQ2 gene was found. Both parents were heterozygous carriers. CoQ10 concentration in fibroblasts was 16nmolCoQ/gr prot (mean 67). Conclusion: In contrast to previous reports of COQ2 nephropathy, in this case, kidney was not the only target. Therefore, this report extends in COQ2 mutation causing primary CoQ10 deficiency, the spectrum of the phenotype of severe early myoclonic epilepsy, subsequently nephrotic syndrome. 