1. Michigan State University, Department of Internal Medicine, East Lansing, MI, USA, Tel.: +1 517 775 7354; Fax: +1 517 432 2759;
2. Center for Functional GI & Motility Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA and, Department of Internal Medicine, Michigan State University, East Lansing, MI, USA, Tel.: +1 517 974 1601; Fax: +1 517 432 2759;
3. Center for Functional GI & Motility Disorders, University of North Carolina, Campus Box 7080, Chapel Hill, NC 27599-7080, USA, Tel.: +1 919 966 6708; Fax: +1 919 966 7592;