Based on the hypothesis that mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) are caused by impaired vasodilation in an intracerebral artery, the authors evaluated the effects of administering l-arginine, a nitric oxide precursor. Patients were administered L-arginine intravenously at the acute phase or orally at the interictal phase. L-arginine infusions significantly improved all strokelike symptoms, suggesting that oral administration within 30 minutes of a stroke significantly decreased frequency and severity of strokelike episodes.

The authors evaluated endothelial function in patients with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke) by flow-mediated vasodilation (FMD) and found a significant decrease vs controls. Two years of supplementation with oral l-arginine, a nitric oxide precursor, significantly improved endothelial function to control levels and was harmonized with the normalized plasma levels of l-arginine in patients. l-Arginine therapy improved endothelial dysfunction and showed promise in treating strokelike episodes in MELAS.

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Conclusion-The most severe clinical phenotype, LS 3243, was associated with the highest proportion of the A3243G mutation as well as the most prominent histological and biochemical abnormalities. (Arch Dis Child 2000;82:407-411)