Association of trough serum infliximab to clinical outcome after scheduled maintenance treatment for Crohn's disease

BACKGROUND & AIMS

The effect of infliximab infused at scheduled intervals on antibody formation, preinfusion trough serum concentrations of infliximab, and their clinical significance was evaluated in patients with Crohn's disease.

METHODS

Antibodies to infliximab and trough serum infliximab were measured in 105 patients with Crohn's disease treated with 5 mg/kg infliximab for induction followed by maintenance episodic re-treatment (n = 23) or scheduled therapy at 6- to 8-week intervals (n = 82).

RESULTS

After a median of 14 infusions (range, 2-45), 21% of patients had detectable antibodies, 25% were antibody negative, and 54% were antibody inconclusive. Antibody formation was higher after episodic compared with scheduled treatment (39% vs 16%; P = .036) and was associated with a higher rate of infusion reactions (50% vs 21%; P = .018). Ninety patients continued maintenance scheduled therapy beyond 12 months including 12 converted episodic patients, with a median follow-up of 23 months (range, 16-68 months). The rate of clinical remission was higher for patients with a detectable trough serum infliximab compared with patients in whom serum infliximab was undetectable, including those without antibodies (82% vs 6%; P < .001). A detectable trough serum infliximab was also associated with a lower C-reactive protein (2.0 vs 11.8 mug/L; P < .001) and a higher rate of endoscopic improvement (88% vs 33%; P < .001). Concurrent immunomodulators did not alter outcomes.

CONCLUSIONS

For Crohn's disease patients treated with scheduled maintenance infusions of infliximab, the trough serum concentration of infliximab predicts clinical outcome. Factors in addition to antibody formation, likely pharmacokinetic, modulate serum infliximab and thus the response to infliximab therapy.

The Montreal classification of inflammatory bowel disease: controversies, consensus, and implications

In recent years, investigators have readdressed the complex issues involved in the classification of inflammatory bowel diseases. In 2003, a Working Party of investigators with an interest in the issues involved in disease subclassification was formed with the aim of summarising recent developments in disease classification and establishing an integrated clinical, molecular, and serological classification of inflammatory bowel disease. The results of the Working Party were reported at the 2005 Montreal World Congress of Gastroenterology. Here we highlight the key issues that have emerged from discussions of the Montreal Working Party and the relevance to clinical practice and research activities.

Inflammatory bowel disease characteristics among African Americans, Hispanics, and non-Hispanic Whites: characterization of a large North American cohort

OBJECTIVES

Inflammatory bowel disease (IBD), comprising primarily of Crohn's disease (CD) and ulcerative colitis (UC), is increasingly prevalent in racial and ethnic minorities. This study was undertaken to characterize racial differences in disease phenotype in a predominantly adult population.

METHODS

Phenotype data on 830 non-Hispanic white, 127 non-Hispanic African American, and 169 Hispanic IBD patients, recruited from six academic centers, were abstracted from medical records and compiled in the NIDDK-IBD Genetics Consortium repository. We characterized racial differences in family history, disease location and behavior, surgical history, and extraintestinal manifestations (EIMs) using standardized definitions.

RESULTS

African American CD patients were more likely than whites to develop esophagogastroduodenal CD (OR = 2.8; 95% CI: 1.4-5.5), colorectal disease (OR = 1.9; 95% CI: 1.1-3.4), perianal disease (OR = 1.7; 95% CI: 1.03-2.8), but less likely to have ileal involvement (OR = 0.55; 95% CI: 0.32-0.96). They were also at higher risk for uveitis (OR = 5.5; 95% CI: 2.3-13.0) and sacroiliitis (OR = 4.0; 95% CI: 1.55-10.1). Hispanics had higher prevalence of perianal CD (OR = 2.9; 95% CI: 1.8-4.6) and erythema nodosum (3.3; 95% CI: 1.7-6.4). Among UC patients, Hispanics had more proximal disease extent. Both African American and Hispanic CD patients, but not UC patients, had lower prevalences of family history of IBD than their white counterparts.

CONCLUSIONS

There are racial differences in IBD family history, disease location, and EIMs that may reflect underlying genetic variations and have important implications for diagnosis and management of disease. These findings underscore the need for further studies in minority populations.

Phenotype-stratified genetic linkage study demonstrates that IBD2 is an extensive ulcerative colitis locus

OBJECTIVES

The complete elucidation of genetic variants that contribute to inflammatory bowel disease (IBD) will likely include variants that increase risk to both Crohn's disease and ulcerative colitis as well as variants that increase risk for particular phenotypic subsets. The purpose of this study was to assess phenotypic subsets that contribute to the major IBD susceptibility loci.

METHODS

This linkage study encompassed 904 affected relative pairs, representing the largest combined phenotyped cohort to date, and allowing for meaningful subset analyses. Genetic linkage data were stratified by disease location and age at diagnosis.

RESULTS

We establish that some loci, notably the IBD3 and chromosome 3q linkage regions demonstrate contributions from both small intestine and colon cohorts, whereas others, notably the IBD1 (NOD2/CARD15) and IBD2 regions increase risk for small intestine or colon inflammation, respectively. The strongest linkage evidence in this study was for the subset of extensive ulcerative colitis in the region of IBD2 (lod 3.27; p < 0.001). Evidence for linkage in the region of NOD2/CARD15 (IBD1) was stronger for the subset of Crohn's patients with ileal disease (lod 2.56; p= 0.035) compared to the overall Crohn's group, consistent with previous findings that NOD2/CARD15 variants are associated with ileal disease.

CONCLUSIONS

Analyses incorporating disease location in IBD increase the power and enhance the accuracy of genomic localization. Our data provide strong evidence that extensive ulcerative colitis represents a pathophysiologic subset of IBD.

The IBD international genetics consortium provides further evidence for linkage to IBD4 and shows gene-environment interaction

BACKGROUND AND AIMS

The inflammatory bowel diseases (IBDs) Crohn's disease (CD) and ulcerative colitis are complex disorders with an important genetic determinant. One gene associated with CD has been identified: NOD2/CARD15. Two independent genome-wide scans found significant evidence (logarithm of odds [LOD] 3.6) and suggestive evidence (LOD 2.8) for linkage on locus 14q11-12, also known as the IBD4 locus. To further characterize this locus, we assessed gene-environment interaction (IBD4 x smoking) and phenotypic heterogeneity in a large cohort of IBD-affected sibling pairs as part of an ongoing international collaborative effort.

PATIENTS AND METHODS

A total of 733 IBD families, comprising 892 affected sibling pairs, were genotyped for microsatellites D14S261, D14S283, D14S972, and D14S275, spanning the IBD4 locus. Information on gender, ethnicity, age at onset, smoking at diagnosis, extraintestinal manifestations, and disease location was available.

RESULTS

A significant distortion in the mean allele sharing (MAS) between affected siblings was observed for CD patients only at each of the four markers (54.6%, 52.8%, 50.4%, and 53.3%, respectively). Maximum linkage for CD was observed at marker D14S261 (multipoint nonparametric linkage score 2.36; P </= 0.01; MAS 54.6%). MAS was higher in CD families in which all siblings or at least one sibling smoked compared with nonsmoking CD families (MAS, 58.90%, 57.50%, and 52.80%, respectively).

CONCLUSIONS

The IBD International Genetics Consortium replicated the IBD4 locus on chromosome 14q for CD and also showed evidence for a gene-environment interaction at this locus. Further studies are needed to explore the mechanism by which smoking influences IBD4.

CARD15 and HLA DRB1 alleles influence susceptibility and disease localization in Crohn's disease

OBJECTIVES

Crohn's disease (CD) is a chronic inflammatory disease of the gut associated with allelic variants of CARD15 and HLA-DRB1 genes. We investigated the prevalence and effects of these variants in a Canadian CD cohort.

METHODS

507 unrelated CD patients were genotyped for the three major CD-associated variants (Arg702Trp, Gly908Arg, and Leu1007fsinsC) and for thirteen HLA-DRB1 alleles.

RESULTS

At least one CARD15 variant was present in 32.5% of the CD patients compared with 20% of controls. The prevalence of CARD15 mutation was similar in both sporadic and familial and Jewish and non-Jewish CD patients. The Gly908Arg variant was significantly higher and the Arg702Trp variant significantly lower in Jewish compared to non-Jewish patients. A positive association between the HLA-DRB1*0103 allele and CD was detected in non-Jewish, familial cases (p = 0.0002), with risk for CD increased by 6.7 fold by the presence of an HLA-DRB1*0103 allele as compared to 1.9 fold and 19 fold by a single or two CARD15 variant alleles, respectively. We show a significant association of ileal involvement with CARD15 variants (OR = 1.8; p = 0.02), HLA-DRB1*0701 (OR = 1.9; p = 0.006) and DRB1*04 (OR = 1.7; p = 0.02) alleles and demonstrate the capacity of combined CARD15 and HLA-DRB1 genotyping to predict ileal disease in CD patients. By contrast, the HLA-DRB1*0103 allele was associated with later age of diagnosis (p = 0.02) and pure colonic disease (p = 0.000013).

CONCLUSIONS

These observations confirm the influence of CARD15 and HLA-DRB1 alleles on both CD susceptibility and site of disease and identify genotyping of these variants as a potential tool for improved diagnosis and risk prediction in CD.

Functional annotation of a novel NFKB1 promoter polymorphism that increases risk for ulcerative colitis

Nuclear Factor-kappaB (NF-kappaB) is a major transcription regulator of immune response, apoptosis and cell-growth control genes, and is upregulated in inflammatory bowel disease (IBD), both ulcerative colitis (UC) and Crohn's disease. The NFKB1 gene encodes the NF-kappaB p105/p50 isoforms. Genome-wide screens in IBD families show evidence for linkage on chromosome 4q where NFKB1 maps. We sequenced the NFKB1 promoter, exon 1 and all coding exons in 10 IBD probands and two controls, and identified six nucleotide variants, including a common insertion/deletion promoter polymorphism (-94ins/delATTG). Using pedigree-based transmission disequilibrium tests, we observed modest evidence for linkage disequilibrium (LD), independent of linkage, between the -94delATTG allele and UC in 131 out of 235 IBD pedigrees with UC offspring (P=0.047-0.052). This allele was also more frequent in the 156 non-Jewish UC probands from the 235 IBD pedigrees than in 149 non-Jewish controls (P=0.015). The -94delATTG association with UC was replicated in a second set of 258 unrelated, non-Jewish UC cases and 653 new, non-Jewish controls (P=0.021). Nuclear proteins from normal human colon tissue and colonic cell lines, but not ileal tissue, showed significant binding to -94insATTG but not to -94delATTG containing oligonucleotides. NFKB1 promoter/exon 1 luciferase reporter plasmid constructs containing the -94delATTG allele and transfected into either HeLa or HT-29 cell lines showed less promoter activity than comparable constructs containing the -94insATTG allele. Therefore, we have identified the first potentially functional polymorphism of NFKB1 and demonstrated its genetic association with a common human disease, ulcerative colitis.

A population- and family-based study of Canadian families reveals association of HLA DRB1*0103 with colonic involvement in inflammatory bowel disease

The aim of this study was to identify major histocompatibility complex alleles associated with the development and clinical features of inflammatory bowel disease (IBD). Genotyping at the human leukocyte antigen (HLA) DRB1 and DQB1 loci was performed on individuals from 118 Caucasian IBD sibling pair families and on 216 healthy controls. Both population- and family-based association tests were used to analyze data obtained on the entire study population and on clinical subgroups stratified by diagnosis, ethnicity, and disease distribution. HLA DRB1*0103 was significantly associated with IBD (OR = 6.0, p = 0.0001) in a case-control analysis of non-Jewish IBD-affected individuals. This association was apparent among both Crohn's disease (OR = 5.23, p = 0.0007) and ulcerative colitis (OR = 7.9, p = 0.0001) patients and was confirmed in the non-Jewish IBD population by results of family-based association analysis using the transmission disequilibrium test. HLA DQB1*0501 was also associated with IBD (OR = 1.64, p = 0.02) in the non-Jewish population. but statistically significant association of this allele with disease was not detected for Crohn's disease and ulcerative colitis separately. No significant associations were identified among the Jewish patients. In the non-Jewish IBD families, IBD was as strongly associated with the DRB1*0103 DQB1*0501 haplotype as with the DRB1*0103 allele alone. The carrier frequency of the DRB1*0103 allele was found to be 10-fold higher in Crohn's disease patients with pure colonic involvement than in healthy controls (38.5% vs. 3.2%; p = 0.0002). These data demonstrate the association of the HLA DRB1*0103 allele with both Crohn's disease and ulcerative colitis and with large intestine-restricted disease in non-Jewish IBD patients and therefore identify HLA DRB1*0103 as a potentially important contributor to disease susceptibility and to expression of colonic involvement in IBD.

Risk factors for low bone density in Crohn's disease

Osteopenia and osteoporosis are prevalent in patients with Crohn's disease (CD). We conducted a cross-sectional study on consecutive patients with CD to assess the prevalence and factors associated with low bone mass density (BMD). One hundred sixty-eight patients with CD were evaluated. Baseline demographics, medical and surgical history, calcium intake, physical activity, steroid use, Harvey Bradshaw Index, blood and urine tests, and dual-energy X-ray absorptiometry were obtained. Sixty-seven (40%) and seventy-five (45%) patients had osteopenia of the femur and spine, respectively. Ten to 11% of patients had osteoporosis. Of the 40 patients who never used steroids, 19 (48%) had osteopenia of the femur and 12 (30%) of the spine. Significant associations were found between BMD and age, body mass index, and serum magnesium. Lifetime steroid use was a weaker predictor of bone loss. Duration of disease did not correlate with BMD when adjusted for age. At follow-up at a mean of 2 years, BMD declined in the femur but not the spine. However, those with ongoing steroid use had lower spine BMD. A significant number of patients with CD have osteopenia. Age was the most important predictor of bone loss. Significant proportion of steroid naive patients had osteopenia, which implies that mechanisms other than steroid use are also involved in bone loss in CD. Disease activity, systemic inflammation, and hormonal and genetic factors may all be important determinants of bone loss in CD.

Diagnostic misclassification reduces the ability to detect linkage in inflammatory bowel disease genetic studies

BACKGROUND

Linkage data have now identified several inflammatory bowel disease (IBD) susceptibility loci but these data have not been consistently replicated in independent studies. One potential explanation for this is the possibility that patients enrolled in such studies may have been erroneously classified with respect to their diagnosis.

AIMS

To determine the rate and type of misclassification in a large population of individuals referred for participation in an IBD genetics study and to examine the effect of diagnostic misclassification on the power to detect linkage.

METHODS

The medical records of 1096 patients entered into an IBD genetics programme were reviewed using standardised diagnostic criteria. The original patient reported diagnoses were changed, if necessary, based on review, and the reasons for the change in diagnosis were recorded. To evaluate the effect of misclassification on linkage results, simulations were created with Gensim and analysed using Genehunter to evaluate a model for IBD inheritance.

RESULTS

Sixty eight of 1096 (6.2%) individuals had a change in diagnosis from that originally reported. The majority of changes were patients with either Crohn's disease or ulcerative colitis who were determined not to have IBD at all. The principal reasons for changes to the original diagnosis were discordance between the patients' subjective reports of diagnosis and actual clinical history, endoscopic, or pathological results; a change in disease pattern over time; and insufficient information available to confirm the original diagnosis. A 10% misclassification rate resulted in 28.4% and 40.2% loss of power to detect a true linkage when using a statistical model for a presumed IBD locus with lambda(s) values of 1.8 and 1.3, respectively.

CONCLUSIONS

Diagnostic misclassification occurs in patients enrolled in IBD genetic studies and frequently involves assigning the diagnosis of IBD to non-affected individuals. Even low rates of diagnostic misclassification can lead to significant loss of power to detect a true linkage, particularly for loci with modest effects as are likely to be found in IBD.

Genetic variation in the 5q31 cytokine gene cluster confers susceptibility to Crohn disease

Linkage disequilibrium (LD) mapping provides a powerful method for fine-structure localization of rare disease genes, but has not yet been widely applied to common disease. We sought to design a systematic approach for LD mapping and apply it to the localization of a gene (IBD5) conferring susceptibility to Crohn disease. The key issues are: (i) to detect a significant LD signal (ii) to rigorously bound the critical region and (iii) to identify the causal genetic variant within this region. We previously mapped the IBD5 locus to a large region spanning 18 cM of chromosome 5q31 (P<10(-4)). Using dense genetic maps of microsatellite markers and single-nucleotide polymorphisms (SNPs) across the entire region, we found strong evidence of LD. We bound the region to a common haplotype spanning 250 kb that shows strong association with the disease (P< 2 x 10(-7)) and contains the cytokine gene cluster. This finding provides overwhelming evidence that a specific common haplotype of the cytokine region in 5q31 confers susceptibility to Crohn disease. However, genetic evidence alone is not sufficient to identify the causal mutation within this region, as strong LD across the region results in multiple SNPs having equivalent genetic evidence-each consistent with the expected properties of the IBD5 locus. These results have important implications for Crohn disease in particular and LD mapping in general.

Carrier rate of APC I1307K is not increased in inflammatory bowel disease patients of Ashkenazi Jewish origin

Colorectal cancer (CRC) occurs with an increased incidence in individuals with chronic inflammatory bowel disease (IBD) of the colon. Recent data suggest that a family history of colorectal cancer is an independent risk factor for CRC in IBD, an observation that implies that genetic factors are relevant to the development of CRC in this context. Among the genetic defects associated with CRC, the APC I1307K mutation has been detected nearly exclusively in individuals of Ashkenazi Jewish (AJ) origin, occurring in 6%-7% of the AJ general population and in 10%-28% of AJ with a either a personal or family history of CRC or adenomatous polyps. These findings, together with the increased incidence of IBD in AJ, prompted the current analysis of the contribution of the APC I1307K variant of CRC in AJ IBD patients. APC I1307K carrier frequencies were determined in 306 AJ individuals affected with IBD and 308 of their unaffected relatives ascertained from a family collection obtained for the identification of IBD susceptibility genes. Prevalence of the I1307K variant was not significantly different among individuals with IBD, Crohn's disease, ulcerative colitis, and unaffected relatives (6.9%, 7.6%, 4.7%, and 6.2%, respectively), and the mutation was detected in only one of five IBD-affected individuals with a diagnosis of CRC. These results reveal that IBD patients of AJ origin carry the APC I1307K variant at the same rate as individuals within the general AJ population. Lack of an increased APC I1307K carrier rate suggests that this mutation does not account for the increased CRC susceptibility associated with IBD.

Genomewide search in Canadian families with inflammatory bowel disease reveals two novel susceptibility loci

The chronic inflammatory bowel diseases (IBDs)-Crohn disease (CD) and ulcerative colitis (UC)-are idiopathic, inflammatory disorders of the gastrointestinal tract. These conditions have a peak incidence in early adulthood and a combined prevalence of approximately 100-200/100,000. Although the etiology of IBD is multifactorial, a significant genetic contribution to disease susceptibility is implied by epidemiological data revealing a sibling risk of approximately 35-fold for CD and approximately 15-fold for UC. To elucidate the genetic basis for these disorders, we undertook a genomewide scan in 158 Canadian sib-pair families and identified three regions of suggestive linkage (3p, 5q31-33, and 6p) and one region of significant linkage to 19p13 (LOD score 4.6). Higher-density mapping in the 5q31-q33 region revealed a locus of genomewide significance (LOD score 3.9) that contributes to CD susceptibility in families with early-onset disease. Both of these genomic regions contain numerous genes that are important to the immune and inflammatory systems and that provide good targets for future candidate-gene studies.