Footnotes

• Contributors JKN, HW, MD, PS, MS, PK and JW took part in study design. JKN, HW, MD and PS acquired and analysed the data. JKN, MS, RDL, PK and JW interpreted the data. JKN and RDL drafted the manuscript. HW, MD, PS, MS, RDL, PK and JW revised the work critically for important intellectual content. All authors approved the final version to be published.

• Funding The research was supported by a grant from Poznan University of Medical Sciences, Poznan, Poland. JKN received a scholarship from the Polish National Science Center (2015/16/T/NZ5/00168).

• Competing interests None declared.

• Ethics approval Bioethical Committee at Poznan University of Medical Sciences, Poznan, Poland (541/15).

• Provenance and peer review Not commissioned; internally peer reviewed.

• Data sharing statement Interested researchers may obtain the study data set from the corresponding author.

• Presented at The abstract was presented during the 2017 Annual Meeting of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) in Prague.