Genetics of Inflammatory Bowel Diseases McGovern, Dermot P.B; Kugathasan, Subra; Cho, Judy H
Gastroenterology (New York, N.Y. 1943),
10/2015, Letnik:
149, Številka:
5
Journal Article
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In this review, we provide an update on genome-wide association studies (GWAS) in inflammatory bowel disease (IBD). In addition, we summarize progress in defining the functional consequences of ...associated alleles for coding and noncoding genetic variation. In the small minority of loci where major association signals correspond to nonsynonymous variation, we summarize studies defining their functional effects and implications for therapeutic targeting. Importantly, the large majority of GWAS-associated loci involve noncoding variation, many of which modulate levels of gene expression. Recent expression quantitative trait loci (eQTL) studies have established that the expression of most human genes is regulated by noncoding genetic variations. Significant advances in defining the epigenetic landscape have demonstrated that IBD GWAS signals are highly enriched within cell-specific active enhancer marks. Studies in European ancestry populations have dominated the landscape of IBD genetics studies, but increasingly, studies in Asian and African-American populations are being reported. Common variation accounts for only a modest fraction of the predicted heritability and the role of rare genetic variation of higher effects (ie, odds ratios markedly deviating from 1) is increasingly being identified through sequencing efforts. These sequencing studies have been particularly productive in more severe very early onset cases. A major challenge in IBD genetics will be harnessing the vast array of genetic discovery for clinical utility through emerging precision medical initiatives. In this article, we discuss the rapidly evolving area of direct-to-consumer genetic testing and the current utility of clinical exome sequencing, especially in very early onset, severe IBD cases. We summarize recent progress in the pharmacogenetics of IBD with respect to partitioning patient responses to anti-TNF and thiopurine therapies. Highly collaborative studies across research centers and across subspecialties and disciplines will be required to fully realize the promise of genetic discovery in IBD.
Inflammatory bowel disease (IBD) is associated with risk variants in the human genome and dysbiosis of the gut microbiome, though unifying principles for these findings remain largely undescribed. ...The human commensal Bacteroides fragilis delivers immunomodulatory molecules to immune cells via secretion of outer membrane vesicles (OMVs). We reveal that OMVs require IBD-associated genes, ATG16L1 and NOD2, to activate a noncanonical autophagy pathway during protection from colitis. ATG16L1-deficient dendritic cells do not induce regulatory T cells (Tregs) to suppress mucosal inflammation. Immune cells from human subjects with a major risk variant in ATG16L1 are defective in Treg responses to OMVs. We propose that polymorphisms in susceptibility genes promote disease through defects in "sensing" protective signals from the microbiome, defining a potentially critical gene-environment etiology for IBD.
Intestinal fungi are an important component of the microbiota, and recent studies have unveiled their potential in modulating host immune homeostasis and inflammatory disease. Nonetheless, the ...mechanisms governing immunity to gut fungal communities (mycobiota) remain unknown. We identified CX3CR1
mononuclear phagocytes (MNPs) as being essential for the initiation of innate and adaptive immune responses to intestinal fungi. CX3CR1
MNPs express antifungal receptors and activate antifungal responses in a Syk-dependent manner. Genetic ablation of CX3CR1
MNPs in mice led to changes in gut fungal communities and to severe colitis that was rescued by antifungal treatment. In Crohn's disease patients, a missense mutation in the gene encoding CX3CR1 was identified and found to be associated with impaired antifungal responses. These results unravel a role of CX3CR1
MNPs in mediating interactions between intestinal mycobiota and host immunity at steady state and during inflammatory disease.
The intestinal microflora, typically equated with bacteria, influences diseases such as obesity and inflammatory bowel disease. Here, we show that the mammalian gut contains a rich fungal community ...that interacts with the immune system through the innate immune receptor Dectin-1. Mice lacking Dectin-1 exhibited increased susceptibility to chemically induced colitis, which was the result of altered responses to indigenous fungi. In humans, we identified a polymorphism in the gene for Dectin-1 (CLEC7A) that is strongly linked to a severe form of ulcerative colitis. Together, our findings reveal a eukaryotic fungal community in the gut (the "mycobiome") that coexists with bacteria and substantially expands the repertoire of organisms interacting with the intestinal immune system to influence health and disease.
Thiopurine therapy, commonly used in autoimmune conditions, can be complicated by life-threatening leukopenia. This leukopenia is associated with genetic variation in TPMT (encoding thiopurine ...S-methyltransferase). Despite a lower frequency of TPMT mutations in Asians, the incidence of thiopurine-induced leukopenia is higher in Asians than in individuals of European descent. Here we performed an Immunochip-based 2-stage association study in 978 Korean subjects with Crohn's disease treated with thiopurines. We identified a nonsynonymous SNP in NUDT15 (encoding p.Arg139Cys) that was strongly associated with thiopurine-induced early leukopenia (odds ratio (OR) = 35.6; P(combined) = 4.88 × 10(-94)). In Koreans, this variant demonstrated sensitivity and specificity of 89.4% and 93.2%, respectively, for thiopurine-induced early leukopenia (in comparison to 12.1% and 97.6% for TPMT variants). Although rare, this SNP was also strongly associated with thiopurine-induced leukopenia in subjects with inflammatory bowel disease of European descent (OR = 9.50; P = 4.64 × 10(-4)). Thus, NUDT15 is a pharmacogenetic determinant for thiopurine-induced leukopenia in diverse populations.
Microbiota are thought to influence the development and progression of inflammatory bowel disease (IBD), but determining generalizable effects of microbiota on IBD etiology requires larger-scale ...functional analyses. We colonized germ-free mice with intestinal microbiotas from 30 healthy and IBD donors and determined the homeostatic intestinal T cell response to each microbiota. Compared to microbiotas from healthy donors, transfer of IBD microbiotas into germ-free mice increased numbers of intestinal Th17 cells and Th2 cells and decreased numbers of RORγt+ Treg cells. Colonization with IBD microbiotas exacerbated disease in a model where colitis is induced upon transfer of naive T cells into Rag1−/− mice. The proportions of Th17 and RORγt+ Treg cells induced by each microbiota were predictive of human disease status and accounted for disease severity in the Rag1−/− colitis model. Thus, an impact on intestinal Th17 and RORγt+ Treg cell compartments emerges as a unifying feature of IBD microbiotas, suggesting a general mechanism for microbial contribution to IBD pathogenesis.
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•Fecal microbiotas from humans with IBD alter gut CD4+ T cell homeostasis in mice•Microbiotas from individuals with IBD induce more Th2 and Th17 cells•Microbiotas from healthy individuals induce more RORgt+ Treg cells•In a model of colitis, mice colonized with IBD microbiotas get more severe disease
Britton et al. examine 30 human microbiotas from healthy individuals and individuals afflicted with inflammatory bowel disease (IBD). Their findings define an impact on intestinal Th17 and RORγt+ regulatory T cell compartments as a unifying feature of IBD microbiotas, suggesting a general mechanism for microbial contribution to IBD pathogenesis.
Patients with immune-mediated inflammatory diseases such as inflammatory bowel disease (IBD) on immunosuppressive and biologic therapies were largely excluded from severe acute respiratory syndrome ...coronavirus-2 messenger RNA vaccine trials.
We evaluated adverse events (AE) after messenger RNA vaccination in 246 adults with IBD participating in a longitudinal vaccine registry.
In general, AE frequency was similar to that reported in the general population. AEs were more common among younger patients and those with previous COVID-19. AEs were less common in individuals receiving advanced therapies with biologics or small-molecule inhibitors.
Those with IBD and other immune-mediated inflammatory diseases can be reassured that the AE risk is likely not increased, and may be reduced, while on advanced therapies.
Advances in genomic technologies have led to increasing reports of monogenic inflammatory bowel disease (IBD). Here, we systematically review the literature to determine the clinical features, ...genetic profile, and previously used treatment strategies in monogenic IBD.
A systematic review of MEDLINE articles published between January 2000 and December 2020 was conducted. A total of 750 individual monogenic IBD cases were identified from 303 eligible articles.
The most frequently reported monogenic IBD genes were IL10RA/B, XIAP, CYBB, LRBA, and TTC7A. In total, 63.4% of patients developed IBD before 6 years of age, 17.4% developed IBD between ages 10 and 17.9 years, and 10.9% developed IBD after age 18. There was a substantial difference between these age groups and the underlying monogenic disorders. Only 31.7% had any history of extraintestinal comorbidity (EIC) before IBD onset, but 76.0% developed at least 1 EIC during their clinical course. The most common EICs were atypical infection (44.7%), dermatologic abnormality (38.4%), and autoimmunity (21.9%). Bowel surgery, biologic therapy, and hematopoietic stem cell transplantation were performed in 27.1%, 32.9%, and 23.1% of patients, respectively.
Monogenic IBD cases, although rare, have varied extraintestinal comorbidities and limited treatment options including surgery and transplant. Early identification and improved understanding of the characteristics of the genes and underlying disease processes in monogenic IBD is important for effective management.
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Intact ATG16L1 plays an essential role in Paneth cell function and intestinal homeostasis. However, the functional consequences of ATG16L1 deficiency in myeloid cells, particularly macrophages, are ...not fully characterized. We generated mice with Atg16l1 deficiency in myeloid and dendritic cells and showed that mice with myeloid Atg16l1 deficiency had exacerbated colitis in two acute and one chronic model of colitis with increased proinflammatory to anti-inflammatory macrophage ratios, production of proinflammatory cytokines, and numbers of IgA-coated intestinal microbes. Mechanistic analyses using primary murine macrophages showed that Atg16l1 deficiency led to increased reactive oxygen species production, impaired mitophagy, reduced microbial killing, impaired processing of MHC class II Ags, and altered intracellular trafficking to the lysosomal compartments. Increased production of reactive oxygen species and reduced microbial killing may be general features of the myeloid compartment, as they were also observed in Atg16l1-deficient primary murine neutrophils. A missense polymorphism (Thr
Ala) in the essential autophagy gene
is associated with Crohn disease (CD). Previous studies showed that this polymorphism leads to enhanced cleavage of ATG16L1 T300A protein and thus reduced autophagy. Similar findings were shown in primary human macrophages from controls and a population of CD patients carrying the
risk variant and who were controlled for
CD-associated variants. This study revealed that ATG16L1 deficiency led to alterations in macrophage function that contribute to the severity of CD.
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