MELAS Syndrome Presenting with Hypertrophic Cardiomyopathy and Advanced Heart Failure: A Multisystem Diagnostic Challenge

<b>Background:</b> Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a rare multisystem disorder caused by mitochondrial DNA mutations, most commonly the m.3243A>G variant in the MT-TL1 gene. Although neurological manifestations predominate, cardiac involvement, including hypertrophic cardiomyopathy (HCM), heart failure (HF), and arrhythmias, may be the initial or dominant presentation and often remains underrecognized. <b>Case Presentation:</b> We report a 43-year-old man with chronic kidney disease (CKD) and long-standing bilateral sensorineural hearing loss who presented with progressive dyspnea and acute decompensated HF. Transthoracic echocardiography revealed severe left ventricular (LV) systolic dysfunction with diffuse hypertrophy. Cardiac magnetic resonance showed non-ischemic cardiomyopathy with diffuse late gadolinium enhancement and increased LV wall thickness. Coronary angiography excluded obstructive disease. Initial endomyocardial biopsy performed at a referring center showed nonspecific hypertrophy and fibrosis without diagnostic features. Given the multisystem involvement, a metabolic or genetic etiology was suspected. Whole-exome sequencing identified the pathogenic m.3243A>G MT-TL1 mutation, confirming MELAS syndrome. The patient was managed with guideline-directed HF therapy, received an implantable cardioverter-defibrillator for primary prevention, and was subsequently evaluated for heart transplantation. <b>Conclusions:</b> This case highlights the importance of considering mitochondrial disorders in the differential diagnosis of unexplained cardiomyopathy, particularly when cardiac dysfunction coexists with renal impairment and auditory deficits. Comprehensive multimodality evaluation and genetic testing are essential to establishing a unifying diagnosis and optimizing management.