Case Report: A young man with mitochondrial disease: intellectual impairment and myocardial hypertrophy

Mitochondrial diseases are rare multisystem disorders caused by pathogenic variants in mitochondrial or nuclear DNA. We report a 23-year-old male presenting with exercise intolerance, fatigue, sluggish responsiveness, and a history of ptosis and bilateral hearing loss. Echocardiography revealed left ventricular hypertrophy, while brain MRI showed cerebellar atrophy and ventricular enlargement. Laboratory tests demonstrated elevated serum lactate, HbA1c, and high-sensitivity cardiac troponin T. Targeted sequencing identified a pathogenic m.3243A > G variant in the MT-TL1 gene with 55.6% heteroplasmy, confirming mitochondrial encephalomyopathy with cardiac involvement. This case highlights the phenotypic heterogeneity and diagnostic challenges of m.3243A > G-related disorders.