Genetic and transcriptional analysis of inflammatory bowel disease-associated pathways in patients with GUCY2C-linked familial diarrhea

Abstract

Objective: Activating mutations in the GUCY2C gene, which encodes the epithelial receptor guanylate cyclase C, cause diarrhea due to increased loss of sodium chloride to the intestinal lumen. Patients with familial GUCY2C diarrhea syndrome (FGDS) are predisposed to inflammatory bowel disease (IBD). We investigated whether genes in the guanylate cyclase C pathway are enriched for association with IBD and reversely whether genetic or transcriptional changes associated with IBD are found in FGDS patients.

Methods: (1) A set of 27 genes from the guanylate cyclase C pathway was tested for enrichment of association with IBD by Gene Set Enrichment Analysis, using genome-wide association summary statistics from 12,882 IBD patients and 21,770 controls. (2) We genotyped 163 known IBD risk loci and sequenced NOD2 in 22 patients with FGDS. Eight of them had concomitant Crohn's disease. (3) Global gene expression analysis was performed in ileal tissue from patients with FGDS, Crohn's disease and healthy individuals.

Results: The guanylate cyclase C gene set showed a significant enrichment of association in IBD genome-wide association data. Risk variants in NOD2 were found in 7/8 FGDS patients with concomitant Crohn's disease and in 2/14 FDGS patients without Crohn's disease. In ileal tissue, downregulation of metallothioneins characterized FGDS patients compared to healthy controls.

Conclusions: Our results support a role of guanylate cyclase C signaling and disturbed electrolyte homeostasis in development of IBD. Furthermore, downregulation of metallothioneins in the ileal mucosa of FGDS patients may contribute to IBD development, possibly alongside effects from NOD2 risk variants.

Keywords:

• Diarrhea
• guanylate cyclase C
• Crohn´s disease
• inflammatory bowel disease
• metallothionein
• NOD2

Acknowledgements

The authors would like to thank all study participants for co-operation, Hilde Rusaas and Paal Borge (Department of Medical Genetics, Bergen) for technical assistance, Kjersti Alfheim Boge (Department of Medical Genetics, Bergen) and Hege Dahlen Sollid (Norwegian PSC Research Centre, Oslo) for help with patient contacts and coordination of the study, Tina Rosvold Eik (Department of Clinical Biochemistry, Haukeland University Hospital, Bergen) for trace element measurements.

Tarek Mazzawi (Department of Clinical Medicine, University of Bergen) and Bjarte Håvik (Department of Clinical Science, University of Bergen) provided help with immunohistochemistry and medical illustrations respectively. We further acknowledge the research infrastructure provided by the Genomics Core Facility (GCF) at the University of Bergen, Norway.The Department of Clinical Science and the Department of Clinical Medicine, University of Bergen, the Department of Paediatrics and the Department of Medicine, Haukeland University Hospital are thanked for facilitating clinical follow up of FGDS patients.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Western Norway Regional Health Authority under Grant number 911763 (RRT) and number 911796 (TF); and the European Union Seventh Framework Programme (FP7-PEOPLE-2013-COFUND) under Grant number 609020 – Scientia Fellows (EE).