Neuroacanthocyoses (NA) are rare, closely related clinical syndromes characterized by neurological features and erythrocyte acanthocytosis. Most have a skeletal myopathy as indicated by persistently elevated plasma creatinine kinase, and about 60 percent of the patients have an unusual cardiomyopathy with increased risk of sudden death. The molecular causes of the syndromes have very recently been defined. However, cardiac and skeletal muscle involvement and outcomes have been poorly described and causes of sudden death are unknown. We propose to (1) describe the cardiac and skeletal muscle findings of NA and to identify potential mechanisms of sudden death; (2) correlate the molecular causes of NA with its cardiac and skeletal expressions; and (3) define the specific phenotype, if any, associated with the heterozygous state.