1. Department of Epidemiology, Tulane University, New Orleans, LA 70112, USA
2. Institute of Clinical Medical Science, China-Japan Friendship Hospital, National Clinical Research Center of Respiratory Diseases, Beijing, China
3. Department of Epidemiology and Biostatistics, University of Georgia, Athens, GA 30602, USA
4. Children's Minnesota Research Institute, Children's Hospitals and Clinics of Minnesota, Minneapolis, MN 55404, USA
5. School of Medicine, University of California San Francisco, San Francisco, CA 94143, USA
6. Metabolon, Inc., Durham, NC 27560, USA