Ulcerative colitis and Crohn’s disease are the two main forms of inflammatory bowel disease (IBD). Here, we report the first trans-ethnic association study of IBD, with genome-wide or Immunochip genotype data from an extended cohort of 86,640 European individuals and Immunochip data from 9,846 individuals of East-Asian, Indian or Iranian descent. We implicate 38 loci in IBD risk for the first time. For the majority of IBD risk loci, the direction and magnitude of effect is consistent in European and non-European cohorts. Nevertheless, we observe genetic heterogeneity between divergent populations at several established risk loci driven by a combination of differences in allele frequencies (NOD2), effect sizes (TNFSF15, ATG16L1) or a combination of both (IL23R, IRGM). Our results provide biological insights into the pathogenesis of IBD, and demonstrate the utility of trans-ethnic association studies for mapping complex disease loci and understanding genetic architecture across diverse populations.

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Previously, we proposed a rare autosomal recessive inherited enteropathy characterized by persistent blood and protein loss from the small intestine as chronic nonspecific multiple ulcers of the small intestine (CNSU). By whole-exome sequencing in five Japanese patients with CNSU and one unaffected individual, we found four candidate mutations in the SLCO2A1 gene, encoding a prostaglandin transporter. The pathogenicity of the mutations was supported by segregation analysis and genotyping data in controls. By Sanger sequencing of the coding regions, 11 of 12 other CNSU patients and 2 of 603 patients with a diagnosis of Crohn’s disease were found to have homozygous or compound heterozygous SLCO2A1 mutations. In total, we identified recessive SLCO2A1 mutations located at seven sites. Using RT-PCR, we demonstrated that the identified splice-site mutations altered the RNA splicing, and introduced a premature stop codon. Tracer prostaglandin E2 uptake analysis showed that the mutant SLCO2A1 protein for each mutation exhibited impaired prostaglandin transport. Immunohistochemistry and immunofluorescence analyses revealed that SLCO2A1 protein was expressed on the cellular membrane of vascular endothelial cells in the small intestinal mucosa in control subjects, but was not detected in affected individuals. These findings indicate that loss-of-function mutations in the SLCO2A1 gene encoding a prostaglandin transporter cause the hereditary enteropathy CNSU. We suggest a more appropriate nomenclature of “chronic enteropathy associated with SLCO2A1 gene” (CEAS).

BackgroundChronic enteropathy associated with SLCO2A1 gene (CEAS) is a hereditary disease caused by mutations in the SLCO2A1 gene and characterized by multiple small intestinal ulcers of nonspecific histology. SLCO2A1 is also a causal gene of primary hypertrophic osteoarthropathy (PHO). However, little is known about the clinical features of CEAS or PHO.MethodsSixty-five Japanese patients recruited by a nationwide survey of CEAS during 2012–2016 were enrolled in this present study. We reviewed the clinical information of the genetically confirmed CEAS patients.ResultsWe identified recessive SLCO2A1 mutations at 11 sites in 46 patients. Among the 46 patients genetically confirmed as CEAS, 13 were men and 33 were women. The median age at disease onset was 16.5 years, and parental consanguinity was present in 13 patients (28%). Anemia was present in 45 patients (98%), while a single patient experienced gross hematochezia. All patients showed relatively low inflammatory markers in blood tests (median CRP 0.20 mg/dl). The most frequently involved gastrointestinal site was the ileum (98%), although no patient had mucosal injuries in the terminal ileum. Mild digital clubbing or periostosis was found in 13 patients (28%), with five male patients fulfilling the major diagnostic criteria of PHO.ConclusionsThe clinical features of CEAS are distinct from those of Crohn’s disease. Genetic analysis of the SLCO2A1 gene is therefore recommended in patients clinically suspected of having CEAS.Electronic supplementary materialThe online version of this article (10.1007/s00535-017-1426-y) contains supplementary material, which is available to authorized users.