Objective:To explore the genetic etiology and clinical outcome of a child with co-morbid progressive IgA nephropathy and COQ8B-associated glomerulopathy. Methods:A child who was admitted to Peking University First Hospital on March 2, 2021 was selected as the study subject. Genomic DNA was extracted from peripheral blood samples from the child and his parents and sister. Whole exome sequencing was carried out, and candidate variant was verified by Sanger sequencing. This study was approved by Medical Ethics Committee of the Peking University First Hospital (Ethics No. 2016[1029]).Results:The child, a 7-year-old boy who had developed proteinuria 8 months before, was diagnosed with IgA nephropathy (M1E1S1T1C1). With steroid, cyclophosphamide, cyclosporine and angiotensin-converting enzyme inhibitor therapy, partial remission of proteinuria was achieved. However, his serum creatinine level had increased from 53.8 mol/L at the onset of disease to 86.7 mol/L after 3.9 years, along with massive proteinuria. Kidney biopsy still indicated IgA nephropathy (M0E0S1T0C0). The child was found to harbor a homozygous c. 737G>A (p.Ser246Asn) missense variant of the COQ8B gene, for which his parents and sister were heterozygous carriers. The variant was predicted to be pathogenic (PS1+ PM2_Supporting+ PM3+ PP3+ PP4) based on the guidelines from the American College of Medical Genetics and Genomics. The child was treated with high-dose coenzyme Q10 in combination with steroid and/or mycophenolate mofetil, though his serum creatinine level still increased to 286 mol/L after 7.3 years, which conformed to a chronic kidney disorder with glomerular filtration rate category of G3b. Conclusion:The homozygous c.737G>A missense variants of the COQ8B gene probably underlay the progressive kidney dysfunction in this child. For children with IgA nephropathy presenting with atypical clinical manifestations, unsatisfactory therapeutic effect, and/or early onset of kidney function decline, coexistence of other diseases should be suspected.