Baylor College of Medicine and Texas Children's Hospital are recruiting individuals with MELAS syndrome for a clinical study. MELAS syndrome is a mitochondrial disease; patients with this disease have muscle weakness and often develop brain strokes, where blood does not flow normally to different parts of the brain. It is believed that these strokes could be due to decreased production of nitric oxide, a naturally occurring compound important for normal blood vessel function. Nitric oxide is made from arginine and citrulline that are normally found in our bodies.