1. Division of Cardiovascular Medicine, Department of Medicine, Stanford University, Stanford, California;
2. Åstrand Laboratory of Work Physiology, The Swedish School of Sport and Health Sciences, Stockholm, Sweden;
3. Center for Inherited Cardiovascular Disease, Division of Cardiovascular Medicine, Stanford University, Stanford, California;
4. Division of Medical Genetics, Department of Pediatrics, Stanford University, Stanford, California; and
5. Department of Genetics, Stanford University, Stanford, California