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Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the gut. Genetic association studies have identified the highly variable human leukocyte antigen (HLA) region as the strongest susceptibility locus for IBD and specifically DRB1*01:03 as a determining factor for ulcerative colitis (UC). However, for most of the association signal such as delineation could not be made because of tight structures of linkage disequilibrium within the HLA. The aim of this study was therefore to further characterize the HLA signal using a transethnic approach. We performed a comprehensive fine mapping of single HLA alleles in UC in a cohort of 9272 individuals with African American, East Asian, Puerto Rican, Indian and Iranian descent and 40 691 previously analyzed Caucasians, additionally analyzing whole HLA haplotypes. We computationally characterized the binding of associated HLA alleles to human self-peptides and analyzed the physicochemical properties of the HLA proteins and predicted self-peptidomes. Highlighting alleles of the HLA-DRB1*15 group and their correlated HLA-DQ-DR haplotypes, we not only identified consistent associations (regarding effects directions/magnitudes) across different ethnicities but also identified population-specific signals (regarding differences in allele frequencies). We observed that DRB1*01:03 is mostly present in individuals of Western European descent and hardly present in non-Caucasian individuals. We found peptides predicted to bind to risk HLA alleles to be rich in positively charged amino acids. We conclude that the HLA plays an important role for UC susceptibility across different ethnicities. This research further implicates specific features of peptides that are predicted to bind risk and protective HLA proteins.

Background: Crohn's disease (CD) exhibits variability in colorectal cancer (CRC) incidence and prognostic factors due to diverse clinical and behavioral characteristics, presenting inconsistencies between Western and Eastern patients. Objectives: This study compared clinical characteristics between CD patients with CRC from the US and Korean tertiary referral centers and defined the prognostic factors related to mortality. Design: Retrospective study. Methods: We reviewed the electronic medical records of 236 adult CD patients with colorectal adenocarcinoma evaluated at Mayo Clinic Rochester, Florida, or Arizona (N = 200) and Asan Medical Center in Korea (N = 36) between January 1989 and August 2022. Results: Asan patients had a younger age, shorter CD duration, more colonic involvement (L2 plus L3), penetrating behavior, perianal fistula, and shorter biological treatment duration before CRC diagnosis than Mayo patients. Furthermore, despite significant differences in body mass index, smoking status, primary sclerosing cholangitis, immunomodulators, CRC diagnosis period, clinical presentation, CRC location, surgery, and some histopathological details between the two groups, overall survival was not statistically different (p value, 0.29, log-rank test). Advanced age (adjusted hazard ratio (aHR), 1.03 per year; 95% confidence interval (CI), 1.01–1.04; p value, <0.01), unresectable CRC (aHR, 5.02; 95% CI, 2.49–10.12; p value, <0.01), and advanced CRC stage (aHR, 1.45 per stage; 95% CI, 1.07–1.97; p value, 0.02) were significantly associated with increased risk of death. CD remission at CRC diagnosis (aHR, 0.26; 95% CI, 0.08–0.91; p value, 0.04), CRC diagnosis period of 2011–2022 (aHR relative to 1989–2000, 0.46; 95% CI, 0.25–0.87; p value, 0.02), and CRC diagnosis by surveillance (aHR, 0.56; 95% CI, 0.32–0.98; p value, 0.04) were significantly associated with decreased risk of death. Conclusion: Notably, some clinical features of CD with CRC differed between Asan and Mayo patients; however, overall survival was not different. CD remission, CRC surveillance, and more recent diagnosis of CRC were associated with a reduced risk of death. [ABSTRACT FROM AUTHOR]

Background and aimsRecent meta-analysis of genome-wide association studies have identified over 241 inflammatory bowel disease susceptibility loci. However, the known variants only account for a fraction of inflammatory bowel disease heritability. To identify additional susceptibility loci, we performed a trans-ethnic meta-analysis as well as an Asian-specific meta-analysis, using all published Immunochip association results of inflammatory bowel disease.MethodsAn inverse-variance fixed-effects meta-analysis was carried out across Korean and East Asian Immunochip datasets of 4156 cases and 4904 controls [Asian ancestry]. A trans-ethnic meta-analysis of inflammatory bowel disease was performed together with the European datasets of 38 155 cases and 48 485 controls genotyped on the immunochip using a Bayesian approach, Meta-Analysis of Trans-ethnic Association studies [MANTRA].ResultsWe identified seven novel associations, including three novel susceptibility loci at MYO10-BASP1, PPP2R3C/KIAA0391/PSMA6/NFKB1A and LRRK1 as well as four novel secondary associations within previously known loci at NCF4, TSPAN32, CIITA and VANGL2. The new loci further implicate alterations in B cell biology in Crohn's disease pathogenesis. The effects of five loci were universal across European and Asian ancestries, whereas the NCF4 and CIITA loci showed significant heterogeneity between European and East Asian populations. In addition, 103 previously known IBD loci showed supporting evidence of association with nominal significance [p < 0.05] in Asians.ConclusionsOur findings of new loci not previously associated with IBD support the importance of studying inflammatory bowel disease genetics in diverse populations.

Summary: Background: The impact of continuing or stopping 5‐aminosalicylates (5‐ASA) after commencing anti‐tumour necrosis factor (anti‐TNF) therapy in patients with inflammatory bowel disease (IBD) remains unclear. Aims: To compare the outcomes of patients with IBD who stopped or continued 5‐ASA after starting anti‐TNF therapy. Methods: We analysed data from the Korean National Health Insurance claims database between 2007 and 2020. We compared the clinical outcomes of patients who stopped or continued 5‐ASA within 90 days of anti‐TNF initiation. The primary outcome was any adverse clinical event defined as a composite of new corticosteroid use, IBD‐related hospitalisation, or intestinal surgery. Results: Among 7442 patients included for analysis (4479 [60.2%] with Crohn's disease [CD] and 2963 [39.8%] with ulcerative colitis [UC]), 1037 (13.9%) discontinued 5‐ASA within 90 days of starting anti‐TNF therapy. During a median 4.3‐year follow‐up, discontinuation of 5‐ASA was not associated with an increased risk of adverse clinical events (adjusted hazard ratio 1.01, 95% confidence interval 0.93–1.10). The cumulative incidence of each adverse clinical event and the composite outcome were not significantly different between groups (all, p > 0.05). Additionally, separate analyses in CD and UC cohorts revealed no differences in adverse clinical outcomes between the 5‐ASA continuation and discontinuation groups. Subgroup analyses by presumed risk factors for disease relapse showed no significant differences in the risk of adverse events between groups. Conclusions: In this nationwide population‐based study, discontinuing 5‐ASA after starting anti‐TNF therapy was not associated with an increased risk of adverse events in patients with IBD. [ABSTRACT FROM AUTHOR]

Summary: Background/Aim: We aimed to validate clinical decision support tools (CDSTs) to predict real‐life effectiveness of vedolizumab (VDZ) in patients with inflammatory bowel disease. Methods: We retrospectively enrolled patients with Crohn's disease (CD) or ulcerative colitis (UC) treated with VDZ at 10 tertiary referral centres in Korea between January 2017 and November 2021. We assessed clinical remission (CREM) and response (CRES), corticosteroid‐free clinical remission (CSF‐CREM) and response (CSF‐CRES), biochemical response based on C‐reactive protein (BioRES[CRP]) and faecal calprotectin (BioRES[FC]), endoscopic healing (EH), and the need to optimise or switch drugs based on CDST‐defined response groups. Additionally, the area under the receiver operating characteristics curve (AUC) for the CDSTs was calculated. Results: We included 143 patients with CD and 219 with UC. We observed incremental trends on CSF‐CRES at week 14 (W14) (ptrend = 0.004) and decreasing trends for the need to optimise or switch drugs (ptrend = 0.016) in CD from the low to high probability groups. Except for CSF‐CREM at W54, we noticed incremental trends for all clinical responses at W14, W26 and W54 (ptrend <0.001) in UC. W26 and W54 BioRES[CRP] and W14 EH also showed increasing trends (ptrend <0.05) in UC. With increasing probabilities of response, drug optimisation or switching was less frequently required in UC (ptrend = 0.013). With 26 points cut‐off, CDSTs effectively identified W14 CSF‐CRES, W26 BioRES[CRP], BioRES[FC] and W54 BioRES[CRP] in UC, all with AUCs >0.600, whereas CDSTs showed poor accuracy in CD. Conclusions: CDSTs for VDZ had acceptable accuracy in predicting effectiveness outcomes including clinical and biochemical outcomes in UC. However, their utility in CD was limited. [ABSTRACT FROM AUTHOR]

BackgroundCrohn's disease (CD) is an intractable inflammatory bowel disease of unknown cause. Recent genome-wide association studies of CD in Korean and Japanese populations suggested marginal sharing of susceptibility loci between Caucasian and Asian populations. As the 7 identified loci altogether explain 5.31% of the risk for CD, the objective of this study was to identify additional CD susceptibility loci in the Korean population.MethodsUsing the ImmunoChip custom single-nucleotide polymorphism array designed for dense genotyping of 186 loci identified through GWAS, we analyzed 722 individuals with CD and 461 controls for 96,048 SNP markers in the discovery stage, followed by validation in an additional 948 affected individuals and 977 controls.ResultsWe confirmed 6 previously reported loci in Caucasian: GPR35 at 2q37 (rs3749172; P = 5.30 × 10, odds ratio [OR] = 1.45), ZNF365 at 10q21 (rs224143; P = 2.20 × 10, OR = 1.38), ZMIZ1 at 10q22 (rs1250569; P = 3.05 × 10, OR = 1.30), NKX2-3 at 10q24 (rs4409764; P = 7.93 × 10, OR = 1.32), PTPN2 at 18p11 (rs514000; P = 9.00 × 10, OR = 1.33), and USP25 at 21q11 (rs2823256; P = 2.49 × 10, OR = 1.35), bringing the number of known CD loci (including 3 in the HLA) in Koreans to 15. The 6 additional loci increased the total genetic variance for CD risk from 5.31% to 7.27% in Koreans.ConclusionsAlthough the different genetic backgrounds of CD between Asian and Western countries has been well established for the major susceptibility genes, our findings of overlapping associations offer new insights into the genetic architecture of CD.

Fecal calprotectin (FC) is commonly used to assess Crohn's disease (CD) activity. However, standardized cut-off values accounting for bowel resection history and disease location are lacking. In this study, we analyzed data from patients with CD who underwent magnetic resonance enterography, ileocolonoscopy, and FC measurements from January 2017 to December 2018. In 267 cases from 254 patients, the FC levels in the 'operated' patients were higher when the disease was active compared with those who were in the remission group (178 vs. 54.7 μg/g; p < 0.001), and similar findings were obtained for the 'non-operated' patients (449.5 vs. 40.95 μg/g; p < 0.001). The FC levels differed significantly according to the location of inflammation, with lower levels in the small bowel compared to those in the colon. The FC cut-off levels of 70.8 μg/g and 142.0 μg/g were considered optimal for predicting active disease for operated and non-operated patients, respectively. The corresponding FC cut-off levels of 70.8 μg/g and 65.0 μg/g were observed for patients with disease only in the small bowel. In conclusion, different FC cut-off values would be applicable to patients with CD based on their bowel resection history and disease location. Tight control with a lower FC target may benefit those with a history of bowel resection or small-bowel-only disease. [ABSTRACT FROM AUTHOR]

Background and Aims Creeping fat [CF] is a poorly understood feature of Crohn's disease [CD], characterized by the wrapping of mesenteric adipose tissue [MAT] around the inflamed intestine. The aim of this study was to investigate the transcriptional profile and compositional features of CF. Methods We collected 59 MAT samples: 23 paired samples from patients with CD (CF [CD-CF] and MAT around the uninflamed intestine [CD-MAT]) and 13 MAT samples from non-CD patients [Con-MAT]. Differentially expressed gene [DEG], functional pathway, cell deconvolution, and gene co-expression network analyses were performed. Results By comparing three different MAT samples, we identified a total of 529 DEGs [|log2FoldChange| > 1.5; false discovery rate < 0.05]. Of these, 323 genes showed an incremental pattern from Con-MAT to CD-MAT, and to CD-CF, while 105 genes displayed a decremental pattern. Genes with an incremental pattern were related to immune cell responses, including B- and T-cell activation, while genes with a decremental pattern were involved in cell trafficking and migration. Cell deconvolution analysis revealed significant changes in cellular composition between the CD-CF and Con-MAT groups, with increased proportions of B-cells/plasma cells [ p  = 1.16 × 10−4], T-cells [ p  = 3.66 × 10−3], and mononuclear phagocytes [ p  = 3.53 × 10−2] in the CD-CF group. In contrast, only the B-cell/plasma cell component showed a significant increase [ p  = 1.62 × 10−2] in the CD-MAT group compared to Con-MAT. Conclusion The distinct transcriptional profiles and altered cellular components of each MAT found in our study provide insight into the mechanisms behind CF and highlight its possible role in the pathogenesis of CD. [ABSTRACT FROM AUTHOR]