TOP3A pathogenic variants presenting as dilated cardiomyopathy and heart failure in three pediatric cases.

Dilated cardiomyopathy (DCM) is the most prevalent form of cardiomyopathy in children, characterized by left ventricle dilation and impaired systolic function. The etiology critically influences clinical trajectory and prognosis. Mitochondrial disorders represent a rare but increasingly recognized cause of DCM. Herein, we report three pediatric patients, diagnosed with early-onset DCM at ages of 8, 9, and 8, who progressed rapidly to end stage heart failure, resulting in two fatalities and one cardiac transplantation. Whole exome sequencing (WES) analysis identified compound heterozygous TOP3A pathogenic variants in all three cases, accompanied by reduced mitochondrial DNA copy number. Therefore, this report expands the recognized etiologies of childhood DCM and delineates a severe cardiac phenotype within the TOP3A pathogenic variant spectrum. Trial Registration: Registered at Chinese Clinical Trial Registry (ChiCTR2600117173). Registered 20/01/2026. Retrospectively registered.