We undertook a meta-analysis of six Crohn's disease genome-wide association studies (GWAS) comprising 6,333 affected individuals (cases) and 15,056 controls and followed up the top association signals in 15,694 cases, 14,026 controls and 414 parent-offspring trios. We identified 30 new susceptibility loci meeting genome-wide significance (P < 5 × 10⁻⁸). A series of in silico analyses highlighted particular genes within these loci and, together with manual curation, implicated functionally interesting candidate genes including SMAD3, ERAP2, IL10, IL2RA, TYK2, FUT2, DNMT3A, DENND1B, BACH2 and TAGAP. Combined with previously confirmed loci, these results identify 71 distinct loci with genome-wide significant evidence for association with Crohn's disease

Genome-wide association studies (GWAS) and candidate gene studies in ulcerative colitis (UC) have identified 18 susceptibility loci. We conducted a meta-analysis of 6 UC GWAS, comprising 6,687 cases and 19,718 controls, and followed-up the top association signals in 9,628 cases and 12,917 controls. We identified 29 additional risk loci (P<5×10-8), increasing the number of UC associated loci to 47. After annotating associated regions using GRAIL, eQTL data and correlations with non-synonymous SNPs, we identified many candidate genes providing potentially important insights into disease pathogenesis, including IL1R2, IL8RA/B, IL7R, IL12B, DAP, PRDM1, JAK2, IRF5, GNA12 and LSP1. The total number of confirmed inflammatory bowel disease (IBD) risk loci is now 99, including a minimum of 28 shared association signals between Crohn’s disease (CD) and UC.

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Inflammatory bowel disease (IBD) is characterized by flares of inflammation with periodic need for increased medication and sometimes even surgery. IBD etiology is partly attributed to a deregulated immune response to gut microbiome dysbiosis. Cross-sectional studies have revealed microbial signatures for different IBD diseases, including ulcerative colitis (UC), colonic Crohn’s Disease (CCD), and ileal CD (ICD). Although IBD is dynamic, microbiome studies have primarily focused on single timepoints or few individuals. Here we dissect the long-term dynamic behavior of the gut microbiome in IBD and differentiate this from normal variation. Microbiomes of IBD subjects fluctuate more than healthy individuals, based on deviation from a newly-defined healthy plane (HP). ICD subjects deviated most from the HP, especially subjects with surgical resection. Intriguingly, the microbiomes of some IBD subjects periodically visited the HP then deviated away from it. Inflammation was not directly correlated with distance to the healthy plane, but there was some correlation between observed dramatic fluctuations in the gut microbiome and intensified medication due to a flare of the disease. These results help guide therapies that will re-direct the gut microbiome towards a healthy state and maintain remission in IBD.

We simultaneously investigated the genetic landscape of ankylosing spondylitis, Crohn's disease, psoriasis, primary sclerosing cholangitis and ulcerative colitis to investigate pleiotropy and the relationship between these clinically related diseases. Using high-density genotype data from more than 86,000 individuals of European-ancestry we identified 244 independent multi-disease signals including 27 novel genome-wide significant susceptibility loci and 3 unreported shared risk loci. Complex pleiotropy was supported when contrasting multi-disease signals with expression data sets from human, rat and mouse, and epigenetic and expressed enhancer profiles. The comorbidities among the five immune diseases were best explained by biological pleiotropy rather than heterogeneity (a subgroup of cases that is genetically identical to another disease, possibly due to diagnostic misclassification, molecular subtypes, or excessive comorbidity). In particular, the strong comorbidity between primary sclerosing cholangitis and inflammatory bowel disease is likely the result of a unique disease, which is genetically distinct from classical inflammatory bowel disease phenotypes.