1. Cleveland Clinic, Digestive Disease and Surgery Institute, Cleveland, Ohio, USA
2. Boston University School of Medicine, Boston, Massachusetts, USA
3. Department of Neurology, Boston University School of Medicine and Sleep Disorders Center, Boston Medical Center, Boston, Massachusetts, USA
4. Section of Gastroenterology, Boston Medical Center, Boston, Massachusetts, USA
5. Boston University School of Public Health, Department of Biostatistics, Boston, Massachusetts, USA
6. Department of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, Florida, USA