Heart and Skeletal Muscle Problems in Neuroacanthocytosis

The purpose of this study is to learn about heart and skeletal muscle problems related to neuroacanthocytosis (also called Mcleod's syndrome and Levine-Critchley disease). This inherited condition causes problems of blood, brain, heart and muscle function. About 60 percent of patients have an unusual heart muscle abnormality that increases the risk of sudden death. Although the molecular (genetic) changes responsible for neuroacanthocytosis have recently been identified, the heart and skeletal muscle problems are not well understood. This study will try to correlate the specific genetic abnormalities with the clinical features of the disease and identify possible causes of sudden death. Patients and first degree relatives of patients with neuroacanthocytosis 18 years of age or older may be eligible for this study. Participants will be admitted to the National Institutes of Health Clinical Center for 2 to 5 days for the following tests: * Electrocardiogram - to measure the electrical function of the heart * Echocardiogram - uses ultrasound to measure heart thickness and detect heart vessel obstructions * Cardiac magnetic resonance imaging (MRI) - uses a magnetic field and radio waves to provide pictures of the heart for measurements of muscle thickness and muscle function * Exercise testing on a stationary bicycle - to measure and record symptoms during exercise, exercise duration, heart rate and blood pressure, oxygen consumption and aerobic threshold * Holter monitoring - uses a device attached to the chest for continuous recording of heart rhythms * Blood tests - to look for muscle damage, to exclude other causes of muscle disease, and to perform DNA (genetic) testing * Neurological consultation - to test muscle function, coordination and tests of certain brain functions such as memory and concentration Patients with evidence of muscle disease may also undergo a muscle biopsy. This is done under a local anesthetic and possibly small amounts of sedation. A small