1. Department of Pediatric Gastroenterology and Metabolic Diseases, Poznań University of Medical Sciences, Poznań, Poland
2. Department of Pediatric Gastroenterology and Nutrition, Medical University of Warsaw, Warsaw, Poland
3. Department of Pediatrics, Faculty of Medical Sciences in Zabrze, Medical University of Silesia, Zabrze, Poland
4. Department of Pediatric Endoscopy and Gastrointestinal Function Testing, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Toruń, Bydgoszcz, Poland
5. Department of Pediatrics, Faculty of Medical Sciences, Medical University of Silesia, Katowice, Poland
6. Department of Gastroenterology, Hepatology, Feeding Disorders and Paediatrics, The Children’s Memorial Health Institute, Warsaw, Poland