Upon clinical suspicion of a mitochondrial disease, WES was performed, followed by Sanger sequencing for confirmation of the findings.<h4>Outcomes</h4>The patient clinically improved, with cessation of seizures, recovery from pneumonia, and confirmed diagnosis of COXPD35.<h4>Lessons</h4>The identification of new TRIT1 variants and the expanding phenotypic spectrum of COXPD35 provides insights into its clinical and genotypic characteristics. Here, TRIT1 is linked to inborn mitochondrial metabolism disorder.