A common genetic background could explain early-onset Crohn's disease

Mechanisms of Disease: Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs), represented by Crohn disease and ulcerative colitis, are associated with major morbidity in Western countries and with increasing incidence in the developing world. Although analysis of the genome of patients with IBD, especially through genome-wide association studies, has unraveled multiple pathways involved in IBD pathogenesis, only part of IBD heritability has been explained by genetic studies. This finding has revealed that environmental factors also play a major role in promoting intestinal inflammation, mostly through their effects in the composition of the microbiome. However, in order for microbial dysbiosis to result in uncontrolled intestinal inflammation, the intestinal barrier formed by intestinal epithelial cells and the innate immune system should also be compromised. Finally, activation of the immune system depends on the working balance between effector and regulatory cells present in the intestinal mucosa, which have also been found to be dysregulated in this patient population. Therefore, IBD pathogenesis is a result of the interplay of genetic susceptibility and environmental impact on the microbiome that through a weakened intestinal barrier will lead to inappropriate intestinal immune activation. In this article, we will review the mechanisms proposed to cause IBD from the genetic, environmental, intestinal barrier, and immunologic perspectives.

Prevalence of Apical Periodontitis in Patients with Inflammatory Bowel Diseases: A Retrospective Clinical Study

AIM

We evaluated the prevalence of apical periodontitis (AP) and the oral health status in patients with inflammatory bowel diseases (IBDs) treated with immunomodulators, with particular attention to biologic medications (BMs).

METHODS

One hundred ten patients, 49 men and 61 women (average age, 46 ± 13.8 years), from the Gastroenterology Unit of the University Hospital with IBDs who were treated with BMs or corticosteroids were included in the study. One hundred ten patients who registered for a dental check-up at the Dental Clinic were matched for age, sex, and physical characteristics with the study group without systemic diseases and not taking medications who were the control. Patients underwent a complete oral, dental, and radiographic examination. Decayed, missing, and filled teeth and periapical index score indexes were recorded. Student t test, χ², and Mann-Whitney U test were used as appropriate.

RESULTS

The prevalence of AP was 64% in IBD patients and 59% in the control; according to the gender-stratified analysis, the difference was not significant among the male groups, whereas the number of teeth with AP was significantly higher in female patients with IBDs than in the controls (P ≤ .05). The prevalence of AP in patients treated with BMs was 65%; women showed 69% higher risk for AP and presented a significantly higher number of teeth with AP (P ≤ .05). Decayed, missing, and filled teeth index was similar in both groups, whereas patients with IBDs had a higher periapical index score than the controls.

CONCLUSIONS

Women with IBDs and taking immunomodulators had a higher prevalence of AP. All patients with IBDs had larger lesions than healthy subjects. These data emphasize the influence of the status of the immune system in the onset of AP and the need for further studies to confirm these findings.

Genetics of inflammatory bowel disease from multifactorial to monogenic forms

Inflammatory bowel disease (IBD) is a group of chronic multifactorial disorders. According to a recent study, the number of IBD association loci is increased to 201, of which 37 and 27 loci contribute specifically to the development of Crohn’s disease and ulcerative colitis respectively. Some IBD associated genes are involved in innate immunity, in the autophagy and in the inflammatory response such as NOD2, ATG16L1 and IL23R, while other are implicated in immune mediated disease (STAT3) and in susceptibility to mycobacterium infection (IL12B). In case of early onset of IBD (VEO-IBD) within the 6^th year of age, the disease may be caused by mutations in genes responsible for severe monogenic disorders such as the primary immunodeficiency diseases. In this review we discuss how these monogenic disorders through different immune mechanisms can similarly be responsible of VEO-IBD phenotype. Moreover we would highlight how the identification of pathogenic genes by Next Generation Sequencing technologies can allow to obtain a rapid diagnosis and to apply specific therapies.

Genetics of Inflammatory Bowel Diseases

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.

Dissecting Allele Architecture of Early Onset IBD Using High-Density Genotyping

Background

The inflammatory bowel diseases (IBD) are common, complex disorders in which genetic and environmental factors are believed to interact leading to chronic inflammatory responses against the gut microbiota. Earlier genetic studies performed in mostly adult population of European descent identified 163 loci affecting IBD risk, but most have relatively modest effect sizes, and altogether explain only ~20% of the genetic susceptibility. Pediatric onset represents about 25% of overall incident cases in IBD, characterized by distinct disease physiology, course and risks. The goal of this study is to compare the allelic architecture of early onset IBD with adult onset in population of European descent.

Methods

We performed a fine mapping association study of early onset IBD using high-density Immunochip genotyping on 1008 pediatric-onset IBD cases (801 Crohn’s disease; 121 ulcerative colitis and 86 IBD undetermined) and 1633 healthy controls. Of the 158 SNP genotypes obtained (out of the 163 identified in adult onset), this study replicated 4% (5 SNPs out of 136) of the SNPs identified in the Crohn’s disease (CD) cases and 0.8% (1 SNP out of 128) in the ulcerative colitis (UC) cases. Replicated SNPs implicated the well known NOD2 and IL23R. The point estimate for the odds ratio (ORs) for NOD2 was above and outside the confidence intervals reported in adult onset. A polygenic liability score weakly predicted the age of onset for a larger collection of CD cases (p< 0.03, R²= 0.007), but not for the smaller number of UC cases.

Conclusions

The allelic architecture of common susceptibility variants for early onset IBD is similar to that of adult onset. This immunochip genotyping study failed to identify additional common variants that may explain the distinct phenotype that characterize early onset IBD. A comprehensive dissection of genetic loci is necessary to further characterize the genetic architecture of early onset IBD.

Curcumin and inflammatory bowel disease: potential and limits of innovative treatments

Curcumin belongs to the family of natural compounds collectively called curcuminoids and it possesses remarkable beneficial anti-oxidant, anti-inflammatory, anti-cancer, and neuroprotective properties. Moreover it is commonly assumed that curcumin has also been suggested as a remedy for digestive diseases such as inflammatory bowel diseases (IBD), a chronic immune disorder affecting the gastrointestinal tract and that can be divided in two major subgroups: Crohn’s disease (CD) and Ulcerative Colitis (UC), depending mainly on the intestine tract affected by the inflammatory events. The chronic and intermittent nature of IBD imposes, where applicable, long-term treatments conducted in most of the cases combining different types of drugs. In more severe cases and where there has been no good response to the drugs, a surgery therapy is carried out. Currently, IBD-pharmacological treatments are generally not curative and often present serious side effects; for this reason, being known the relationship between nutrition and IBD, it is worthy of interesting the study and the development of new dietary strategy. The curcumin principal mechanism is the suppression of IBD inflammatory compounds (NF-κB) modulating immune response. This review summarizes literature data of curcumin as anti-inflammatory and anti-oxidant in IBD, trying to understand the different effects in CD e UC.

Role of genetics in pediatric inflammatory bowel disease

Inflammatory bowel disease (IBD), encompassing Crohn's disease (CD), ulcerative colitis (UC), and unclassified IBD, is characterized by chronic intestinal inflammation and has a multifactorial etiology with complex interactions between genetic and environmental factors. The genetics of IBD are believed to be common and complex with over 163 associated genetic loci. However, the genetic contribution of the majority of these common loci is small, and the effect sizes are low. Although childhood onset IBD represents only 10% to 25% of all IBD cases, in depth research into the genetic networks of pediatric IBD has revealed exciting new developments and unsuspected pathways. Recent pediatric studies have revealed an increasing spectrum of human monogenic diseases with high effect sizes or penetrance that can present with IBD or IBD-like intestinal inflammation. A substantial proportion of patients with these genetic defects present with very early onset of intestinal inflammation, with onset of IBD at less than 10 years of age. There is also considerable overlap with primary immunodeficiencies and very early onset IBD. This review summarizes the current understanding of the genetics of pediatric IBD with a focus on the very early onset population and discusses the promising results from the effort of finding missing heritability of IBD from studying pediatric population.

Genetic and functional profiling of Crohn's disease: autophagy mechanism and susceptibility to infectious diseases

Crohn's disease is a complex disease in which genome, microbiome, and environment interact to produce the immunological background of the disease. Disease in childhood is more extensive and characterized by a rapid progression, leading to severe repercussions in the course of the disorder. Several genetic variations have been associated with an increased risk of developing the disease and most of these are also implicated in other autoimmune disorders. The gut has many tiers of defense against incursion by luminal microbes, including the epithelial barrier and the innate and adaptive immune responses. Moreover, recent evidence shows that bacterial and viral infections, as well as inflammasome genes and genes involved in the autophagy process, are implicated in Crohn's disease pathogenesis. The aim of this review is to establish how much the diagnostic system can improve, thus increasing the success of Crohn's disease diagnosis. The major expectation for the near future is to be able to anticipate the possible consequences of the disease already in childhood, thus preventing associated complications, and to choose the best treatment for each patient.

Crohn's and colitis in children and adolescents

Crohn's disease and ulcerative colitis can be grouped as the inflammatory bowel diseases (IBD). These conditions have become increasingly common in recent years, including in children and young people. Although much is known about aspects of the pathogenesis of these diseases, the precise aetiology is not yet understood, and there remains no cure. Recent data has illustrated the importance of a number of genes-several of these are important in the onset of IBD in early life, including in infancy. Pain, diarrhoea and weight loss are typical symptoms of paediatric Crohn's disease whereas bloody diarrhoea is more typical of colitis in children. However, atypical symptoms may occur in both conditions: these include isolated impairment of linear growth or presentation with extra-intestinal manifestations such as erythema nodosum. Growth and nutrition are commonly compromised at diagnosis in both Crohn's disease and colitis. Consideration of possible IBD and completion of appropriate investigations are essential to ensure prompt diagnosis, thereby avoiding the consequences of diagnostic delay. Patterns of disease including location and progression of IBD in childhood differ substantially from adult-onset disease. Various treatment options are available for children and adolescents with IBD. Exclusive enteral nutrition plays a central role in the induction of remission of active Crohn's disease. Medical and surgical therapies need to considered within the context of a growing and developing child. The overall management of these chronic conditions in children should include multi-disciplinary expertise, with focus upon maintaining control of gut inflammation, optimising nutrition, growth and quality of life, whilst preventing disease or treatment-related complications.

Association between genetic variants in the HNF4A gene and childhood-onset Crohn's disease

Hepatocyte nuclear 4 alpha (HNF4α), involved in glucose and lipid metabolism, has been linked to intestinal inflammation and abnormal mucosal permeability. Moreover, in a genome-wide association study, the HNF4A locus has been associated with ulcerative colitis. The objective of our study was to evaluate the association between HNF4α genetic variants and Crohn's disease (CD) in two distinct Canadian pediatric cohorts. The sequencing of the HNF4A gene in 40 French Canadian patients led to the identification of 27 single nucleotide polymorphism (SNP)s with a minor allele frequency >5%. To assess the impact of these SNPs on disease susceptibility, we first conducted a case-control discovery study on 358 subjects with CD and 542 controls. We then carried out a replication study in a separate cohort of 416 cases and 1208 controls. In the discovery cohort, the genotyping of the identified SNPs revealed that six were significantly associated with CD. Among them, rs1884613 was replicated in the second CD cohort (odds ratio (OR): 1.33; P<0.012) and this association remained significant when both cohorts were combined and after correction for multiple testing (OR: 1.39; P<0.004). An 8-marker P2 promoter haplotype containing rs1884613 was also found associated with CD (P<2.09 × 10(-4) for combined cohorts). This is the first report showing that the HNF4A locus may be a common genetic determinant of childhood-onset CD. These findings highlight the importance of the intestinal epithelium and oxidative protection in the pathogenesis of CD.

The putative role of endoplasmic reticulum aminopeptidases in autoimmunity: insights from genomic-wide association studies

Autoimmune diseases represent a heterogeneous group of conditions whose incidence is increasing worldwide. This has stimulated studies on their etiopathogenesis, derived from a complex interaction between genetic and environmental factors, aimed at finally improving prevention and treatment of these diseases. In the autoimmune process, immune responses are generated against self antigens presented by Major Histocompatibility Complex (MHC) class I on the cell surface. These peptide/MHC class I complexes are generated and assembled through MHC class I antigen processing and presentation machinery. In the endoplasmic reticulum (ER), aminopeptidases ERAP1 and ERAP2 display distinct trimming activity before antigenic peptides are loaded onto MHC class I molecules. The advent of new tools such as genome-wide association studies (GWAS) has provided evidence for new susceptibility loci and candidate genes playing a role in the autoimmune process for the recognized immune function of their transcripts. Genetic linkage has been discovered with MHC antigens and various autoimmune conditions. Recent GWAS showed the importance of ERAP1 and ERAP2 in several autoimmune diseases, including ankylosing spondylitis, insulin-dependent diabetes mellitus, psoriasis, multiple sclerosis, Crohn's disease. In this review, we first provide a general overview of ERAP1 and ERAP2 genes, their biological functions and their relevancy in autoimmunity. We then discuss the importance of GWAS and the case-control studies that confirm the relevancy of ERAP single-nucleotide polymorphism associations and their linkage with particular MHC class I haplotypes, supporting a putative functional role in the autoimmune process.