Susceptibility Gene For Crohn's Disease Research Articles

Systematic Association Mapping Identifies NELL1 as a Novel IBD Disease Gene

Crohn disease (CD), a sub-entity of inflammatory bowel disease (IBD), is a complex polygenic disorder. Although recent studies have successfully identified CD-associated genetic variants, these susceptibility loci explain only a fraction of the heritability of the disease. Here, we report on a multi-stage genome-wide scan of 393 German CD cases and 399 controls. Among the 116,161 single-nucleotide polymorphisms tested, an association with the known CD susceptibility gene NOD2, the 5q31 haplotype, and the recently reported CD locus at 5p13.1 was confirmed. In addition, SNP rs1793004 in the gene encoding nel-like 1 precursor (NELL1, chromosome 11p15.1) showed a consistent disease-association in independent German population- and family-based samples (942 cases, 1082 controls, 375 trios). Subsequent fine mapping and replication in an independent sample of 454 French/Canadian CD trios supported the authenticity of the NELL1 association. Further confirmation in a large German ulcerative colitis (UC) sample indicated that NELL1 is a ubiquitous IBD susceptibility locus (combined p<10−6; OR = 1.66, 95% CI: 1.30–2.11). The novel 5p13.1 locus was also replicated in the French/Canadian sample and in an independent UK CD patient panel (453 cases, 521 controls, combined p<10−6 for SNP rs1992660). Several associations were replicated in at least one independent sample, point to an involvement of ITGB6 (upstream), GRM8 (downstream), OR5V1 (downstream), PPP3R2 (downstream), NM_152575 (upstream) and HNF4G (intron).

Protein-Tyrosine Phosphatase Sigma Is Associated with Ulcerative Colitis

Inflammatory bowel disease (IBD), a relatively common chronic debilitating intestinal illness, is composed of two broadly defined groups, Crohn's disease (CD) and ulcerative colitis (UC). Although several susceptibility genes for CD have been recently described, susceptibility genes exclusive for UC have not been forthcoming. Here, we show that receptor protein-tyrosine phosphatase sigma (PTPRS-encoding PTPsigma) knockout mice spontaneously develop mild colitis that becomes severe when challenged with two known inducers of colitis. We also demonstrate that E-cadherin and beta-catenin, two important adherens junction proteins involved in maintenance of barrier defense in the colon, act as colonic substrates for PTPsigma. Furthermore, we show that three SNPs (rs886936, rs17130, and rs8100586) that flank exon 8 in the human PTPRS gene are associated with UC. The presence of these SNPs is associated with novel splicing that removes the third immunoglobulin-like domain (exon 9) from the extracellular portion of PTPsigma, possibly altering dimerization or ligand recognition. We propose that polymorphisms in the human PTPRS gene lead to ulcerative colitis.

Polymorphisms in NFKBIA and ICAM-1 genes in New Zealand Caucasian Crohn's disease patients

Crohn's disease (CD) is a complex polygenetic inflammatory disease of the bowel. NFKBIA (IkappaBalpha) is a downstream regulator of NF-kappaB, which is an effector of the major Crohn's susceptibility gene CARD15/NOD2. ICAM-1 is an integrin ligand and vascular addressin, which contributes to the trafficking of pathogenic leukocytes into the inflamed bowel. Here we examined whether the NFKBIA 2758G/A and ICAM-1 K469E variants, recently shown to be CD susceptibility genes in Caucasian populations in Germany and the United Kingdom, are associated with CD in Caucasian patients in New Zealand. PCR-RFLP analysis was used to examine the frequency of gene polymorphisms in 182 CD patients and 188 ethnically matched controls. There was no significant evidence of a difference in the allele frequency of either the 2758G/A polymorphism in NFKBIA (0.38 vs 0.35, P = 0.47) or the K469E polymorphism in ICAM-1 (0.43 vs 0.37, P = 0.10) between CD patients and controls. Nevertheless, the ICAM-1 469E allele significantly (P = 0.016, Pc = 0.047) influenced the age of diagnosis of CD. Meta-analysis with five other studies confirmed a lack of association of the K469E polymorphism with Crohn's disease (P = 0.33; OR = 0.93; 95% CI, 0.82-1.07). The NFKBIA 2758G/A and ICAM-1 K469E polymorphisms are not significant risk factors for CD in New Zealand; however, there is evidence that the latter polymorphism influences the age of diagnosis.

Contribution of the novel inflammatory bowel disease gene IL23R to disease susceptibility and phenotype

A North American genome-wide single nucleotide polymorphism (SNP) association study identified IL23R as a novel inflammatory bowel disease (IBD) susceptibility gene. Association was reported with multiple risk variants in the centromeric portion of IL23R in 3 large independent cohorts. The aims of this study were to replicate the association of IL23R with Crohn's disease (CD), examine subphenotype relationships, and look for evidence of epistasis with the known CD susceptibility gene CARD15 and susceptibility haplotype IBD5 in a large collection of CD patients. We further investigated the relationship between IL23R and ulcerative colitis (UC). In all, 604 CD and 647 UC patients who had been rigorously phenotyped and who had been recruited from a single UK center were used in this study. Controls were either spouses of patients (141) or were recruited from well-person clinics (993). Eight SNPs were genotyped using MassArray (Sequenom). All 8 SNPs genotyped were significantly associated with CD. The association with the nonsynonymous SNP rs11209026 was confirmed (P=6.65x10(-6), odds ratio [OR], 0.43, 95% confidence interval [CI]: 0.29-0.64). The most significant SNP in our study was rs7517847 (P=4.9x10(-9), OR 0.65, 0.56-0.75), which is statistically independent of rs11209026. Preliminary evidence suggests an epistatic interaction with the IBD5 risk haplotype. The effects of mutations in this IL23R appear weaker in UC (P=0.008, OR 0.63, 0.45-0.89 and 0.005 OR, 0.81, 0.71-0.94, respectively). No subphenotype associations were identified. We confirmed the findings that IL23R is a susceptibility gene for IBD with suggestive epistasis with the IBD5 locus in the CD population.

Confirmation of the role of ATG16l1 as a Crohnʼs disease susceptibility gene

A German genome-wide nonsynonymous single nucleotide polymorphism (nsSNP) association study identified ATG16L1 as a Crohn's disease (CD) susceptibility gene. The association appeared to be confined to the nsSNP rs2,241,880 and was confirmed in 2 German independent case-control collections (combined P = 4.0 x 10(-8), odds ratio [OR] 1.45; 95% confidence interval [CI]: 1.21-1.74), a CD transmission disequilibrium test (TDT) collection, and an independent UK cohort. A weak statistical interaction with CARD15 was demonstrated. No association with ulcerative colitis (UC) was demonstrated. The aims of the study were to replicate the association with CD, examine subphenotype associations and statistical interactions with CARD15, IL23R, and the IBD5 risk haplotype, as well as explore the association with UC. The study included 645 CD and 676 UC rigorously phenotyped patients recruited from a single UK center. Unaffected controls comprised either spouses of patients (141) or individuals recruited from well-person clinics (1,049). The nsSNP rs2,241,880 was genotyped using MassArray (Sequenom). A strong association with CD was demonstrated (P = 2.33 x 10(-7), OR 1.45 [1.25-1.67]), but no significant association was demonstrated with any subphenotype. We failed to replicate the reported interaction between rs2,241,880 and the CARD15 low-risk haplotypes dd and Dd. No significant statistical interaction with the 3 known CD susceptibility genes was seen. No association with UC susceptibility (P = 0.37, OR 1.06 [0.93-1.22]), or any UC subphenotype was identified. We confirmed the findings that ATG16L1 is a CD susceptibility gene and found no evidence of interaction with CARD15, IL23R, or IBD5.

Lack of association of the 3′-UTR polymorphism in the NFKBIA gene with Crohn’s disease in an Israeli cohort

Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal tract associated with dysregulation of the immune response. It is caused by a combination of environmental and genetic factors. Patients with CD have a TH1-type inflammatory response characterized by nuclear factor kappa B (NFkappaB) activation. Mutations in the bacterial pattern recognition receptors NOD2/CARD15 and Toll-like receptor 4 (TLR4) genes, which lead to activation of NFkappaB under normal circumstances, have been associated with increased susceptibility for CD. NFkappaB plays a critical role in the immune response and is down-regulated by NFkappaB inhibitor alpha (NFKBIA). NFKBIA was found to be a susceptibility gene for German CD patients lacking NOD2/CARD15 mutations. A cohort of 231 Israeli CD patients previously genotyped for the single nucleotide polymorphisms (SNPs) in the CARD15, TLR4 susceptibility genes for CD, was analyzed for the 3'-untranslated region (UTR) SNP of the NFKBIA gene in comparison to 100 healthy ethnically matched controls. We evaluated the contribution of the 3'-UTR SNP in NFKBIA in patients with or without other SNPs in CARD15 to age of onset, disease location, and disease behavior (Vienna classification). We did not identify a significant difference in allele and genotype frequencies between either groups or an effect on phenotype. No interactions were found between NFKBIA and any NOD2. The contribution of population diversity to susceptibility genes for CD plays an important role in disease-associated variants and is important for better understanding of the pathologic mechanisms of the polymorphism.

Toll-Like Receptor 9 (TLR-9) Polymorphisms and CARD15/NOD-2 Mutations in Hispanics with Crohnʼs Disease

Purpose: Crohn's disease (CD) exhibits phenotypic heterogenicity. The pattern of inheritance is unknown. Variable penetrance and expression support a complex genetic predisposition. CARD15/NOD-2 was described as the first susceptibility gene for CD. TLR-9 is a toll-like intracellular receptor that recognizes muramyl dipeptide motifs derived from bacterial peptidoglycan and acts on the innate mucosal response. TLR-9 participates in the innate response, it controls the immune response to bacterial infections. Particular interest has evolved over the role of NOD-2 and TLR-9 polymorphisms in IBD patients. The aim of this study was to determine the prevalence of polymorphisms of CARD15 and TLR-9 in Puerto Ricans with Crohn's and describe possible phenotypic associations. Methods: Samples from 113 Puerto Ricans with Crohn's disease and 107 controls recruited for the IBD Genetics Consortium project were studied for the presence of mutations of, NOD-2_8, NOD-2_13, and TLR 9_rs352140. These polymorphisms were correlated with disease behavior, location and need for surgery. Results: Polymorphisms in NOD-2 were identified in 18.67% of CD as compared to 9.4% of controls (p= 0.049). The presence of NOD-2_13 was significant for the absence of colorectal disease (p= 0.02), the presence of stricturing disease (p= 0.02), and the absence of perianal disease (p= 0.01). The presence of NOD-2_8 and NOD-2_13 were significant for the absence of perianal disease (p= 0.00). TLR9_rs352140 was more frequent in subjects with no CD-related surgery (p= 0.04). Conclusions: NOD-2 was found to be more prevalent in Puerto Ricans with CD as compared to racially similar controls. Association of some mutations with specific disease behavior or location support the influence of genetic variants on clinical expression of the disease.

Ileal Lymphonular Hyperplasia Is Not Associated With NOD2/CARD15 Mutations

Lymphonodular hyperplasia (LNH) is a mass of lymphoid tissue that has been described in the terminal ileum, colon and duodenum mainly in children. Controversy exists regarding the benign nature of LNH. The combination of chronic abdominal pain and hematochezia leads many of these patients to undergo investigations for inflammatory bowel diseases. NOD2/CARD15 on chromosome 16 has been identified as a susceptibility gene for Crohn disease (CD). No study has yet examined the possible association of NOD2/CARD15 mutations with patients with LNH. The purpose of this study was to investigate the presence of NOD2/CARD15 mutations in patients with clinically proven LNH. Children and young adults with gastrointestinal symptoms diagnosed as having terminal ileum LNH were eligible for the study. The study group consisted of 32 patients (15 males and 17 females), age range 3-23 years, mean 13.1 +/- 5 years. Twenty-seven (84%) had abdominal pain, 3 (9%) had rectal bleeding. The duration of symptoms ranged from 1-60 months (17.9 +/- 14.5). Only 2 patients (6.2%) were found to be heterozygote for the NOD2/CARD15 mutation (1007 fs), whereas all of the others did not carry any of the 3 common mutant alleles. This number is significantly lower (P < 0.001) than the mutation prevalence demonstrated in both pediatric and adult Israeli CD patients. NOD2/CARD15 mutations are not associated with LNH. This may strengthen the lack of association between CD and LNH that has been previously reported. We suggest that genotyping NOD2/CARD15 may help to distinguish LNH from inflammatory bowel diseases in selected patients.

The Frameshift Mutation in Nod2 Results in Unresponsiveness Not Only to Nod2- but Also Nod1-activating Peptidoglycan Agonists

NOD2/CARD15 is the first characterized susceptibility gene in Crohn disease. The Nod2 1007fs (Nod2fs) frameshift mutation is the most prevalent in Crohn disease patients. Muramyl dipeptide from bacterial peptidoglycan is the minimal motif detected by Nod2 but not by Nod2fs. Here we investigated the response of human peripheral blood mononuclear cells (PBMCs) from Crohn disease patients not only to muramyl dipeptide but also to several other muramyl peptides. Most unexpectedly, we observed that patients homozygous for the Nod2fs mutation were totally unresponsive to MurNAc-L-Ala-D-Glu-meso-diaminopimelic acid (DAP) (M-Tri(DAP)), the specific agonist of Nod1, and to Gram-negative bacterial peptidoglycan. In contrast, PBMCs from a patient homozygous for the Nod2 R702W mutation, also associated with Crohn disease, displayed normal response to Gram-negative bacterial peptidoglycan. In addition, the blockage of the Nod1/M-Tri(DAP) pathway could be partially overcome by co-stimulation with the Toll-like receptors agonists lipoteichoic acid or lipopolysaccharide. Investigation into the mechanism of this finding revealed that Nod2fs did not act as a dominant-negative molecule for the Nod1/M-Tri(DAP) pathway, implying that the blockage is dependent upon the expression or activity of other factors. We demonstrated that PBMCs from Nod2fs patients express high levels of the peptidoglycan recognition protein S, a secreted protein known to interact with muramyl peptides. We proposed that through a scavenger function, peptidoglycan recognition protein S may dampen M-Tri(DAP)-dependent responses in Nod2fs patients. Together, our results identified a cross-talk between the Nod1 and Nod2 pathways and suggested that down-regulation of Nod1/M-Tri(DAP) pathway may be associated with Crohn disease.

Comparative Phenotypic and CARD15 Mutational Analysis Among African American, Hispanic, and White Children with Crohnʼs Disease

Despite a large body of literature on the subject of Crohn's disease (CD), very little information is available on racial/ethnic differences related to disease presentation, clinical course, and genetics. The first identified CD susceptibility gene, CARD15, seems to be present in up to 40% of white children with CD. However, the frequency of this gene among patients with CD of other racial/ethnic groups in the United States is not known. We conducted a multicenter study on African American and Hispanic children with CD to describe the phenotypic and genotypic (CARD15) features in comparison with white children with CD. We also analyzed the frequency of CARD15 mutations in large control samples from white, African American, and Hispanic children. The disease location and behavior were similar among all 3 groups, with inflammatory behavior and the ileocolonic location being the most frequent phenotype. However, significantly lower frequencies of CARD15 mutations were seen in African American (P < 0.0001) and Hispanic (P < 0.0001) children with CD compared with white children with CD. This lower CARD15 frequency among African American patients with CD was also mirrored in the general population. Phenotypic features of CD are similar among African American and Hispanic children compared with white children. CARD15 mutations are not increased among African American and Hispanic children with CD. CARD15 mutational frequencies among African American and Hispanic children within the general population are lower compared with white children within the general population. Future genetics studies will be required to determine the relationships between genotype and CD phenotype in various ethnic and racial groups.

GRIM-19 Interacts with Nucleotide Oligomerization Domain 2 and Serves as Downstream Effector of Anti-bacterial Function in Intestinal Epithelial Cells

Nucleotide oligomerization domain 2 (NOD2) functions as a mammalian cytosolic pathogen recognition molecule, and variants have been associated with risk for Crohn disease. We recently demonstrated that NOD2 functions as an anti-bacterial factor limiting survival of intracellular invasive bacteria. To gain further insight into the mechanism of NOD2 activation and signal transduction, we performed yeast two-hybrid screening. We demonstrate that GRIM-19, a protein with homology to the NADPH dehydrogenase complex, interacts with endogenous NOD2 in HT29 cells. GRIM-19 is required for NF-kappaB activation following NOD2-mediated recognition of bacterial muramyl dipeptide. GRIM-19 also controls pathogen invasion of intestinal epithelial cells. GRIM-19 expression is decreased in inflamed mucosa of patients with inflammatory bowel diseases. GRIM-19 may be a key component in NOD2-mediated innate mucosal responses and serve to regulate intestinal epithelial cell responses to microbes.

The Familial Mediterranean Fever (MEVF) Gene as a Modifier of Crohn's Disease

Crohn's disease (CD) has been reported to be more frequent among non-Ashkenazi Jewish patients suffering from familial Mediterranean fever (FMF). Interestingly, functional similarities between the CD susceptibility gene (NOD2/CARD15) and the FMF gene (MEFV) have been described: both belong to the death domain containing protein family, important in the regulation of apoptosis, cytokine processing and inflammation. To investigate the prevalence of MEFV mutations in Jewish non-Ashkenazi CD patients and its putative effect on CD presentation. Germline DNA of 105 Israeli CD patients of non-Ashkenazi and mixed Ashkenazi-non-Ashkenazi ethnic background was analyzed for three most common MEFV mutations: M694V, V726A, and E148Q. Five patients (4.7%) with a clinical diagnosis of FMF were included. Data obtained from each patient included: age of onset, disease location, and behavior, the presence of extraintestinal manifestations of CD and therapeutic regimens. The overall prevalence of mutation carriers among non-FMF-CD patients was 13% (13/100). A stricturing disease pattern was observed in 56% (10/18) of all carriers, FMF-CD, and non-FMF-CD patients, and in 25% (22/87) of noncarriers (OR: 3.7, 95% CI: 1.3-10.5, p= 0.015). The prevalence of fistulas was comparable in both groups. Extraintestinal manifestations were significantly more frequent among carriers than noncarriers (65%vs 32%, OR 3.9, 95% CI = 1.3-11.5, p= 0.015). No differences were observed in disease location and disease severity. MEFV mutations are not associated with CD susceptibility, yet the presence of these mutations appears to be associated with a stricturing disease pattern and extraintestinal disease manifestations of CD.

Update on the pathophysiology of inflammatory bowel disease

Crohn's disease (CD) and Ulcerative colitis (UC) comprise a series of inflammatory bowel disease (IBD) resulting from chronic up-regulation of the mucosal immune system. Although the pathogenesis of IBD remains elusive, it appears that there is chronic activation of the immune and inflammatory cascade in genetically susceptible individuals, which are directed by genetic factors, immunological factors, and environmental factors such as foods and enteric microbes. Regarding genetic factors, important new insights have been gained into the function of caspase-activating and recruitment domain-15 (CARD15)/NOD2, the first cloned susceptibility gene for CD. New data on CARD15/NOD2 function and nuclear factor-κB activation indicate that an inflammatory reaction of the intestinal mucosa as a response of the innate immune system may be necessary for the maintenance of gut homeostasis. CD may therefore be seen as a defective immune response, no longer only as hyperresponsiveness of the mucosal immune system. Data on CARD15/NOD2 expression suggest that macrophages and epithelial cells could be the site of a primary pathophysiologic defect, and T-cell activation might just be a secondary effect inducing chronification of the inflammation, perhaps as a backup mechanism to a defective innate immunity. In addition to CARD15/NOD2, there are additional “innate” pathways by which commensal and pathogenic bacteria can directly interact with cells of the intestinal mucosa (eg, toll-like receptors). The “germ concept” and the “genetic concept” of IBD pathophysiology are converging. The evidence continues to accumulate that CD is primarily due to a T helper cell-type 1 immune response in the gut wall. IL-12 and IL-18 appear to be the cytokines primarily responsible for Th1 polarization. T-cell resistance to apoptosis occurs in CD, and human and mouse studies indicate that the signaling molecule STAT3, which transduces signals from IL-6 and IL-10, is involved in mucosal T cell homeostasis. Progress in understanding the pathophysiology of UC remains slow, but IL-13 produced by natural killer T cells may be involved. There is a possibility that UC might be a sort of syndrome such as viral/bacterial infectious diseases and autoimmune disorders. Despite the evidence of a role for Th1 in CD, support for a Th2 pathogenesis in ulcerative colitis is much weaker. The presence of autoantibodies, such as anticolon antibody, antimucin antibody, or antitropomyosin antibody, is suggestive of a Th2 pathogenesis. There are several conflicting immunological findings, but some immunological abnormalities may induce colonic inflammation.

Crohn's disease—“Genes propose, environments dispose”

The pathogenesis of Crohn's disease (CD) eludes definition; the prevalent theories invoke a combination of genetic susceptibility and an environmental trigger. Recently susceptibility genes for CD have been identified; the one receiving the greatest interest is NOD2/CARD15, localized to chromosome 16. Mutations in NOD2/CARD15 have been variably noted in certain populations with CD and in certain clinical forms of CD. Weiss et al compared the NOD2/CARD15 genotype in Jewish Ashkenazi children with CD. The carrier rate for the three NOD2/CARD15 associated variants was 52%. There were no clear genotype-phenotype correlations. The finding of a specific allele variant of this susceptibility gene in children should aid in the quest to understand the precise pathogenesis of CD. Page 208

Update in inflammatory bowel disease pathogenesis

During the last few years, significant advances have been achieved in the understanding of the pathogenesis of inflammatory bowel disease (IBD). By gaining new insights, paradigms that seemed to be a safe basis of our knowledge on IBD pathogenesis have recently become doubtful. This review discusses and summarizes the most recent developments. Important new insights have been gained into the function of caspase-activating and recruitment domain-15 (CARD15)/NOD2, the first cloned susceptibility gene for Crohn disease (CD). New data on CARD15/NOD2 function and nuclear factor-kappaB activation indicate that an inflammatory reaction of the intestinal mucosa as a response of the innate immune system may be necessary for the maintenance of gut homeostasis. CD may therefore be seen as a defective immune response, no longer only as hyperresponsiveness of the mucosal immune system. Data on CARD15/NOD2 expression suggest that macrophages and epithelial cells could be the site of a primary pathophysiologic defect, and T-cell activation might just be a secondary effect inducing chronification of the inflammation, perhaps as a backup mechanism to a defective innate immunity. In addition to CARD15/NOD2, there are additional "innate" pathways by which commensal and pathogenic bacteria can directly interact with cells of the intestinal mucosa (eg, toll-like receptors). The "germ concept" and the "genetic concept" of IBD pathophysiology are converging. New findings are changing our concepts of the pathogenesis of IBD. The innate immune system, early responses to bacterial products, and the modulation of T-cell responses are important aspects that are reviewed.

Genetic and pathogenetic insights into inflammatory bowel disease.

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory disorders of the gastrointestinal tract that share clinical and pathologic characteristics. The most credible hypothesis is that CD and UC result from an inappropriate and exaggerated mucosal immune response to normal constituents of the mucosal microflora that is in part genetically determined. However, there is reason to believe that the main pathologic processes in these two diseases are distinct. For example, the CARD15/NOD2 gene has been identified as a susceptibility gene for CD but not for UC. Moreover, the study of patients and mouse models of inflammatory bowel disease has clearly shown that, in CD, the tissue-damaging inflammatory reaction is driven by interleukin-12-activated Th1 cells, whereas a humoral response predominates in UC.

Evidence for genetic heterogeneity in inflammatory bowel disease (IBD); HLA genes in the predisposition to suffer from ulcerative colitis (UC) and Crohn's disease (CD).

Family and epidemiological studies support a genetic susceptibility to UC and CD. Conflicting reports regarding associations between UC and HLA-DR2 and between CD and various HLA alleles have been published. The aim of this study was to determine whether molecularly defined HLA-DR genes are associated with these diseases in a Dutch group of patients. Fifty-nine unrelated Dutch UC patients and 89 CD patients were typed using DNA-based methods. A total of 2400 healthy local blood donors served as controls. The phenotype frequency of the HLA-DRB1*15 allele was increased in UC patients compared with controls (42% versus 26% in controls; P = 0.006; odds ratio (OR) = 2.1), and was predominantly found in female patients (53% versus 24%; P = 0.001; OR = 3.5). The DRB1*15 allele was increased in UC patients having a positive family history (P = 0.01; OR = 5.8). Among the 16 patients who showed an increase in extent of disease during follow up, 10 were DRB1*15+ (P = 0.002; OR = 4.8). The frequency of the DRB1*13 allele was decreased in patients with UC (15% versus 28% in controls; P = 0.04; OR = 0.5). In CD, no association was observed between disease or particular clinical subgroups and any allele tested. The present study provides additional evidence for the genetic association between UC and HLA-DRB1*15, and supports recent findings that the susceptibility gene(s) for CD is not located in the HLA class II region.

CARD15: a Pleiotropic Autoimmune Gene That Confers Susceptibility to Psoriatic Arthritis

A recent genomewide scan in psoriatic arthritis (PsA) revealed a susceptibility locus at 16q. This region overlaps CARD15, a susceptibility gene in Crohn disease. The possibility of a common susceptibility gene between PsA and Crohn disease is further supported by epidemiological studies that note an increased incidence of psoriasis in subjects with Crohn. We screened 187 patients with PsA and 136 healthy controls, all from Newfoundland, for the three common, independent sequence variants of CARD15 (R702W, leu1007fsinsC, and G908R), which were detected by polymerase chain reaction by use of allele-specific primers and visualized through gel electrophoresis. In total, 53/187 (28.3%) probands with PsA had at least one variant of the CARD15 gene, compared with 16/136 (11.8%) controls (odds ratio 2.97; 95% confidence interval 1.61-5.47; P=.0005). Allele frequencies of R702W, leu1007fsinsC, and G908R were 10.43%, 3.21%, and 1.61%, respectively, in patients with PsA, compared with 3.31%, 2.57%, and 0.37%, respectively, in the control patients. CARD15 conferred susceptibility to PsA independent of HLA-Cw*0602. Thus, CARD15 represents a pleiotropic autoimmune gene and is the first non-MHC gene to be associated with PsA.

Genetic Evidence for Interaction of the 5q31 Cytokine Locus and the CARD15 Gene in Crohn Disease

A common haplotype spanning 250 kb in the cytokine gene cluster on chromosome 5q31 has recently been reported to be strongly associated with Crohn disease (CD) in Canadian families. We have replicated this finding by both the transmission-disequilibrium test (TDT) (P=.016) and in a case-control association study (P=.008) in a large European cohort of patients with CD, although the increase in disease risk was small (odds ratio 1.49 for homozygotes, 95% CI 1.11-2.0). No association was detected in families or individuals with ulcerative colitis (UC). Stratification of offspring with CD in the TDT sample by mutation status in the CD susceptibility gene CARD15 showed that the association with the 5q31 risk haplotype was present only in offspring with at least one of the known CARD15 disease susceptibility alleles (P=.044). The 5q31 risk haplotype frequency was 53.1% in unrelated individuals with CD who had one or two CARD15 mutations versus 43.7% in control subjects (P=.0001) but was not significantly elevated in individuals with CD who had no CARD15 mutations (45.4%, P=.41). Kaplan-Meier survival analysis of age at disease onset showed a significantly earlier onset in homozygotes for the 5q31 risk haplotype (P=.0019). These findings suggest that genetic variants at the 5q31 (IBD5) locus may hasten the onset of Crohn disease and cooperate with CARD15 in disease causation.

Association of NOD2 with Crohn's disease in a homogenous Irish population.

Linkage of IBD to the pericentromeric region of chromosome 16 has been widely confirmed by analyses of multiple populations. The NOD2 gene is located in the peak region of linkage on chromosome 16 and thought to be involved in the activation of nuclear factor (NF) kappaB in response to bacterial components. Mutations in the NOD2 gene are found to be strongly associated with susceptibility to Crohn's disease (CD). A total of 65 Irish CD families were genotyped to determine if NOD2 mutations conferred susceptibility to CD and the prevalence of these mutations in sporadic and familial forms of the disease. The Irish population is relatively homogenous and thus may provide advantages in genetic studies of complex diseases. We confirmed the IBD1 locus as a susceptibility locus for IBD within the Irish population by linkage analysis followed by linkage disequilibrium studies. No significant evidence of linkage was observed to the previously identified regions on chromosomes 1, 12 and 14. In all, 131 CD affected families were then genotyped for seven of the previously published NOD2 single-nucleotide polymorphisms (SNPs). Allelic transmission distortion was investigated using the pedigree disequilibrium test (PDT). SNP13 (3020insC) was found to be associated with CD (P=0.0186). Patients who possessed a rare allele of SNP8, 12 or 13 presented earlier when compared to patients without rare variants (mean age, 20.1 vs 24 years, P=0.011) and the rare allele of SNP13 was observed to be predominantly linked to ileal disease (P=0.02). This report confirms the importance of NOD2 as a susceptibility gene for CD within the Irish population.