Department of Child Neurology, Medical University of Warsaw, Warsaw, Poland; Department of Gastroenterology, Hepatology, Nutritional Disorders and Paediatrics, Children's Memorial Health Institute, Warsaw, Poland. Electronic address: wegner.agnieszka@gmail.com. Department of Paediatrics, Gastroenterology and Nutrition, Medical University of Warsaw, Warsaw, Poland. Department of Gastroenterology, Hepatology, Nutritional Disorders and Paediatrics, Children's Memorial Health Institute, Warsaw, Poland. Department of Paediatrics, Gastroenterology and Eating Disorders, Medical University of Gdansk, Gdansk, Poland. Department of Paediatrics, Gastroenterology and Rheumatology, Children's Hospital, Szczecin, Poland. Department of Paediatrics, Gastroenterology Unit, Medical University of Silesia, Katowice, Poland. Department of Gastroenterology, Hepatology of Children, Medical University of Silesia, Zabrze, Poland. Department of Paediatrics, Gastroenterology and Rheumatology, Children's Hospital, Szczecin, Poland; Paediatrics and Paediatric Nursery Unit, Pomeranian Medical University, Szczecin, Poland.