Mitochondrial encephalopathies and myopathies: Our tertiary center's experience.

Mitochondrial diseases have a heterogeneous phenotype and can result from mutations in the mitochondrial or nuclear genomes, constituting a diagnostically and therapeutically challenging group of disorders. We report our center's experience with mitochondrial encephalopathies and myopathies with a cohort of 50 genetically and phenotypically diverse patients followed in the Neurology clinic over the last ten years. Seventeen patients had mitochondrial DNA mutations, presented over a wide range of ages with seizures, feeding difficulties, extraocular movements abnormalities, and had high rates of stroke-like episodes and regression. Twenty-seven patients had nuclear DNA mutations, presented early in life with feeding difficulty, failure-to-thrive, and seizures, and had high proportions of developmental delay, wheelchair dependence, spine abnormalities and dystonia. In six patients, a mutation could not be identified, but they were included for having mitochondrial disease confirmed by histopathology, enzyme analysis and clinical features. These patients had similar characteristics to patients with nuclear DNA mutations, suggesting missed underlying mutations in the nuclear genome. Management was variable among patients, but outcomes were universally poor with severe disability in all cases. Therapeutic entryways through elucidation of disease pathways and remaining unknown genes are acutely needed.