Giant Ring Mitochondria in a Patient With Heart Failure and Cerebral White Matter Disease Resulting From an MT-TL1 Mitochondrial Gene Mutation

Background: The presence of giant ring mitochondria on endomyocardial biopsy is rarely reported and does not have a well-defined differential diagnosis. Methods: We report the case of a 54-year-old man with heart failure and preserved ejection fraction and left ventricular hypertrophy, initially thought to have an infiltrative cardiomyopathy. Results: The patient was found to have extensive vacuolization caused by giant ring mitochondria on endomyocardial biopsy. Mitochondrial genetic testing revealed an A3243G mutation in the MT-TL1 gene, which is a mitochondrial encoded transfer RNA-leucine molecule. Conclusions: Mitochondrial disease should be considered in patients presenting with unexplained cardiomyopathy and skeletal muscle, cerebral, or metabolic abnormalities. In this case, the presence of unexpected extensive cardiomyocyte vacuolization and giant, ring-shaped mitochondria on endomyocardial biopsy prompted mitochondrial genetic testing, which ultimately resulted in the correct diagnosis and treatment.