Familial and sporadic inflammatory bowel disease: different entities?

Genetics in diagnosing and managing inflammatory bowel disease

We believe the future clinical application of genomic information in IBD will lie in the use of a combination of “gene-chips” designed specifically for variation relevant to IBD and ultimately in the cataloging of an individual’s entire collection of genomic variation through whole-genome sequencing. In the short term, the expansion of pharmacogenomic tests and biomarker assessments are likely to have the most significant influence on prescribed IBD treatment therapies and disease management. Moreover, these pharmacogenomic and biomarker data are likely to benefit greatly from the ongoing genomic analyses, as they can begin to put these data in the proper genetic context as they relate to monitoring and assessing these effects across different ethnic and racial populations. Although mentioned only briefly in this review, a clearer understanding of environmental triggers of IBD will be of utmost importance to furthering our understanding of the genetic factors and the complex interactions that are likely to exist between genes and environment. The successful identification of genetic factors influencing IBD risk has been accelerating over the last few years and is likely to continue. Currently, these genetic factors provide no direct bearing on clinical treatments or therapies. Instead, these findings aid in our understanding of disease pathogenesis and indirectly to potential for development of novel therapeutics. In the near term, they may be able to provide some additional utility in distinguishing CD cases from UC cases. Future use of genomic information and its role in diagnosing and managing IBD patients is promising but not yet mature. The search for the so-called missing heritability in IBD will undoubtedly continue to uncover novel genes, biological pathways, and the likely interplay between genetic variation and environmental factors. The creation of a customized gene-chip (allowing for the creation of a patient-specific cataloging of IBD relevant genetic information), for use in clinical practice, is an almost certainty. Although this information will likely provide significant aid to diagnostics and treatment, it is doubtful that it could ever fully stand alone. It must be accompanied by thorough clinical evaluation and data, a more complete characterization of a patient’s potential environmental triggers, and integration with other known pharmacogenomic and molecular biomarker information.

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have been so far related to the diagnosis of Crohn's disease. Those genes are related to innate pattern recognition receptors, to epithelial barrier homeostasis and maintenance of epithelial barrier integrity, to autophagy and to lymphocyte differentiation. So far, the most strong and replicated associations with Crohn's disease have been done with NOD2, IL23R and ATG16L1 genes. Many genes have so far been implicated in prognosis of Crohn's disease and many attempts have been made to classify genetic profiles in Crohn's disease. CARD15 seems not only a susceptibility gene, but also a disease-modifier gene for Crohn's disease. Enriching our understanding on Crohn's disease genetics is important but when combining genetic data with functional data the outcome could be of major importance to clinicians.

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering the epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have so far been related to the diagnosis of Crohn's disease. These genes are related to innate pattern recognition receptors, to epithelial barrier homeostasis and maintenance of epithelial barrier integrity, to autophagy and to lymphocyte differentiation. So far, the strongest and most replicated associations with Crohn's disease have been demonstrated with NOD2, IL23R and ATG16L1 genes. Many genes have so far been implicated in the prognosis of Crohn's disease and many attempts have been made for classification of genetic profiles in Crohn's disease. CARD15 seems to be not only a susceptibility gene, but also a disease-modifier gene for Crohn's disease. Enriching our understanding of Crohn's disease genetics is of value, but when combining genetic data with functional data the outcome could be of major importance to clinicians.

Immune-related disorders in families of children with inflammatory bowel disease--a prospective cohort study

BACKGROUND

The aim of this paper was to examine the prevalence of immune-related disorders in families of children with inflammatory bowel disease (IBD) compared to those without IBD.

METHODS

Children ≤18 years of age presenting to the IBD clinic between September 2007 and August 2009 with an established diagnosis of IBD were recruited. Age and sex matched controls without IBD were recruited. The study was a single-centre prospective cohort study. Outcome measures were prevalence of immune-based/inflammatory diseases in families of both patients and controls.

RESULTS

One hundred and eight children in each group were recruited. Asthma was the most frequently reported disease in families of the IBD patients (52.8%) and controls (46.3%). The prevalence of IBD in families of IBD patients was significantly higher than in those without IBD (OR 2.03, 95% CI 1.04-3.95).

CONCLUSIONS

The prevalence of immune-based disorders, as a group, in families of children with IBD was not significantly higher when compared to children without IBD.

Inflammatory bowel disease: review from the aspect of genetics

Regardless of how inflammatory bowel disease (IBD) is defined, the term "genetic susceptibility" is always included. Due to substantial progress in the characterization of susceptible genes that interact with environmental influences, a number of review articles offering the latest insights continue to be presented. To date, more than 30 novel IBD susceptible loci have been found, while several promising associations between IBD and gene variants have also been identified and replicated effectively. The present review highlights recent insights regarding linkage analysis and genome-wide association presented in studies of IBD susceptible genes, which provide additional evidence supporting their involvement in disease pathogenesis, based on linking to innate immune systems as a result of interactions with intestinal microbial flora. An improved understanding of IBD genetics will promote the identification of novel therapeutic agents, making it possible to identify environmental factors related to intestinal inflammation.

What are the major arguments in favour of the genetic susceptibility for inflammatory bowel disease?

Epidemiological data, notably concordance rates in twin pairs and familial aggregation, have provided strong evidence for the importance of the genetic contribution in inflammatory bowel diseases. Genome wide scanning has been remarkably successful in identifying a number of susceptibility loci. The identification of the IBD1 gene on chromosome 16 as NOD2/CARD15 definitely establishes that a significant proportion of Crohn's disease has an underlying genetic cause. In addition, our knowledge of the clinical impact of other genes in modelling disease phenotypes has increased in parallel. These results have led to great optimism that important clinical applications will result from genetic research in the near future.

CARD15 genetic variation in a Quebec population: prevalence, genotype-phenotype relationship, and haplotype structure

The caspase recruitment domain gene (CARD15) was recently identified as the underlying gene associated with the IBD1 locus that confers susceptibility to Crohn disease (CD). CARD15 is related to the NOD1/Apaf-1 family of apoptosis regulators, and three sequence variants (Arg702Trp, Gly908Arg, and Leu1007fsinsC) in the gene were demonstrated to be associated with CD. We collected a cohort of 231 patients with CD and 71 healthy control individuals from the Canadian province of Quebec, to determine the prevalence of these sequence variants in an independent population. Clinical records of all patients were systematically reviewed, and detailed phenotypic information was obtained. All patient DNA samples were genotyped for the three variants, thus enabling an analysis of genotype-phenotype correlations. In this cohort, 45.0% of patients with CD carried at least one variant in the CARD15 gene, compared with 9.0% of control individuals (P<10-7). Allele frequencies of Arg702Trp, Gly908Arg, and Leu1007fsinsC were 12.9%, 5.2%, and 10.3% in patients with CD, compared with 4.2%, 0.7%, and 0.7% in control individuals, respectively. Importantly, CARD15 mutants were seen with equal frequency in patients with familial and sporadic CD. Analysis of the relationship between genotype and phenotype convincingly demonstrates that CARD15 variants are significantly associated with ileal disease involvement, as opposed to strictly colonic disease (P<.001). Moreover, we were able to determine the haplotype structure surrounding this disease gene by genotyping 45 single-nucleotide polymorphisms (SNPs) in a 177-kb region that contained the CARD15 gene. This structure helps clarify the history of these causal mutations. Finally, this analysis shows that CARD15 involvement with CD is detectable by use of publicly available SNPs alone.