[Clinical analysis of one infantile nephrotic syndrome caused by COQ2 gene mutation and literature review].

To explore the clinical and genetic characteristics of infantile nephrotic syndrome caused by COQ2 variants. The clinical and genetic data of a patient with nephrotic syndrome caused by COQ2 variants diagnosed at pediatric department of Peking University First Hospital from February 2018 to March 2018 were retrospectively analyzed. Related literature retrieved from PubMed, CNKI and Wanfang databases were searched to date (up to July 2018) with "COQ2 gene" or "primary coenzyme Q10 deficiency" and "nephrotic syndrome" or "nephropathy" as key words. A 14-month-old male, presented to local hospital at 11 months of age with edema and severe proteinuria, without hematuria, hypertension or renal dysfunction. He did not have infection or seizure in the course of the disease. He had no response to a more than four-week full-dose prednisone treatment. He had normal birth, mild motor development retardation and moderate language retardation. He was born to non-consanguineous healthy parents. He had two unaffected older sisters and one older sister died of "nephropathy" at one year of age. Genetic testing identified compound heterozygous variants in COQ2 gene: c.518G>A and c.973A>G, both could be predicted by in silico tools to be deleterious in protein function. These variants are not single nucleotide polymorphism and rare in normal populations. Both variants have previously been reported as pathogenic. These missense mutations were inherited from parents in autosomal recessive manner tested by Sanger sequencing. The patient was supplemented with high-dose of coenzyme Q10, at 30 mg/(kg·day) and glucocorticoid was withdrawn. Within three weeks of high dose coenzyme Q10 treatment, the edema disappeared. After seven weeks of high dose coenzyme Q10 treatment, the patient had decreased proteinuria and improved serum albumin levels. The urine protein to creatinine ratio decreased from 22.87 mg/mg to 1.98 mg/mg; Serum albumin increased from 14.2 g/L to 39.9 g/L, with normal kidney function and improved motor development. Primary CoQ10 deficiency is reported to be a rare autosomal recessive mitochondrial disorder with heterogeneous renal, neurologic, and muscular manifestations. To date, COQ2 variants have been reported in 14 children with glomerular involvement. Their age at onset ranged from neonatal period to 10-year-old (8 patients within the first year of life). Steroid resistant nephrotic syndrome (SRNS) is the most common phenotype. Some of these children also had progressing encephalopathy and myopathy, and seizures. Patients with COQ2 variants might show clinical improvement with early high-dose oral CoQ10 supplementation. Literature review revealed two Chinese articles, mainly about adults with neurologic symptoms. SRNS was previously not reported in Chinese pediatric patients. It is necessary to carry out genetic testing for infant with SRNS. The coexistence of some degree of encephalomyopathy, such as development retardation, should raise suspicion of a mitochondrial defect caused by COQ2 variants. Timely diagnostic genetic testing and early high dose of coenzyme Q10 supplement could significantly improve their prognosis.