Genetics of inflammatory bowel disease: scientific and clinical implications

Considerable progress has been made in the last decade in studies of the genetics of the inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Epidemiological data, notably concordance rates in twin pairs and sibling pairs, have provided strong evidence for the importance of the genetic contribution, particularly in Crohn's disease. These observations provided the catalyst for laboratory-based studies of the molecular genetics of Crohn's disease and ulcerative colitis around the world. The complementary strategies of genome-wide scanning and candidate gene-directed studies have led to the identification of a number of genetic markers which appear to predict disease susceptibility and behaviour. The identification of the IBD1 gene on chromosome 16 as NOD-2 is unquestionably an important scientific discovery. Although many issues with respect to gene function and expression remain to be resolved there is great optimism that important clinical applications will directly result.

Azathioprine and anti-TNF alpha therapies in Crohn's disease: a review of pharmacology, clinical efficacy and safety

Crohn's disease (CD), a chronic relapsing inflammatory condition of the intestines, is a common cause of gastrointestinal morbidity in young people. Although the aetiology of CD is unknown, host, genetic and environmental influences are clearly important. Glucocorticoids remain the mainstay of treatment for active CD, however only two-third of patients will respond and side effects are considerable. Surgery is often undesirable or impracticable and therefore alternative medical strategies have been sought. In recent years, there has been much interest in two areas of IBD therapy-the use of established immunomodulators, and the development of novel biological therapies. In this review, we have selected two areas of particular controversy-the use of purine analogues (azathioprine (AZA) and 6-mercaptopurine (6-MP)) and the introduction of anti-tumour necrosis factor alpha (TNFalpha) therapy and have examined the data for efficacy, safety and tolerability of these medications.

The genetic jigsaw of inflammatory bowel disease

Following a prolonged period of relative inertia, real progress has been made in the past few years in understanding the pathogenesis of the chronic inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Clinical experience, epidemiological studies, and molecular genetics have provided strong evidence that both genetic and environmental factors are important in disease pathogenesis, and gene-environmental interaction determines disease susceptibility and behaviour.

A functional polymorphism of the stromelysin gene (MMP-3) influences susceptibility to primary sclerosing cholangitis

BACKGROUND AND AIMS

We have investigated the influence of a biallelic polymorphism of the promoter region of stromelysin (matrix metalloproteinase 3) on susceptibility to primary sclerosing cholangitis (PSC). The 5A allele is associated with increased transcription, compared with wild-type (6A).

METHODS

An allelic association study was performed: in stage 1, 52 PSC patients (43 with inflammatory bowel disease [IBD]) and 99 healthy subjects (HS) were genotyped. In stage 2, 59 PSC patients (49 IBD), 84 patients with uncomplicated ulcerative colitis, and 72 HS were genotyped.

RESULTS

In stage 1, 5A carriage rate (90.4% vs. 72.7%; P = 0.012) and 5A allelic frequency (65.4% vs. 48.5%; P = 0.005) were increased, and 6A homozygosity was reduced in PSC (9.6% vs. 27.3%; P = 0.012). In stage 2, 5A allelic carriage was increased in PSC (93.2% vs. 76.4% in HS; P = 0.0092) and 6A homozygosity was reduced (6.8% vs. 23.8% in HS; P = 0.0092). Portal hypertension was associated with 5A homozygosity in PSC (P = 0.035; odds ratio [OR], 3.88). In the combined data set, 5A allelic frequencies (63.5% vs. 49.4%; P = 0.001; OR, 1.78) and 5A carriage rates (91.9% vs. 74.2%; P = 0.0002; OR, 3.92) were increased, and 6A homozygosity was reduced in PSC (8.1% vs. 25.7%; P = 0.0002; OR, 0.25). Overall, portal hypertension was associated with 5A homozygosity (P = 0.0192; OR, 3.12).

CONCLUSIONS

Stromelysin polymorphism may influence susceptibility and disease progression in PSC.

Genetics of inflammatory bowel disease: from bench to bedside?

Epidemiological data, particularly concordance rates in twin pairs and in multiply affected families, provide strong evidence that both genetic and environmental influences are important in the development of the chronic intestinal inflammation characteristic of Crohn disease and ulcerative colitis. Furthermore, supplementary data now suggest that not only susceptibility, but also disease behavior and response to therapy may have a strong genetic influence. The model of disease susceptibility most pertinent to the inflammatory bowel diseases is that Crohn disease and ulcerative colitis are related polygenic disorders. Recently, this model has received strong support from the results of genome-wide scanning and candidate gene studies carried out in European, North American and Australian populations. In spite of all potential difficulties related to disease and ethnic heterogeneity, consistent replication of linkage has been found with distinct regions on chromosomes 16, 12, 6 (the major histocompatibility complex) and most recently chromosome 14. Whereas the linkages on chromosome 16 and 14 appear strongest in Crohn disease, the chromosome 12 locus appears most pertinent to ulcerative colitis, and the HLA region appears more pertinent in all forms of inflammatory bowel disease. The current challenge is to narrow these regions of linkage and identify the susceptibility genes within the regions. The task may be greatly benefited by the recent successful sequence data available from the human genome project. Compelling data have emerged to suggest genetic markers that may allow prediction of disease severity, and efficacy and tolerability of immuno-suppressants commonly used in inflammatory bowel disease.

Review article: the genetics of inflammatory bowel disease

Recent epidemiological, clinical and molecular studies have provided strong evidence that inherited predisposition is important in the pathogenesis of chronic inflammatory bowel diseases. The model most consistent with the epidemiological data suggests that Crohn's disease and ulcerative colitis are related polygenic diseases, sharing some but not all susceptibility genes. Investigators throughout the world have applied the complementary techniques of genome-wide scanning and candidate gene analysis. Four areas of linkage have been widely replicated on chromosomes 16 (IBD1), 12 (IBD2), 6 (IBD3-the HLA region), and most recently on chromosome 14. Fine mapping of these regions is underway. Of the 'positional' candidate genes, most attention has centred on the genes of the major histocompatibility complex. Genes within this region may determine disease susceptibility, behaviour, complications and response to therapy. Hope continues that studies of inflammatory bowel disease genetics will provide fresh insight into disease pathogenesis and soon deliver clinical applications.

Effect of HLA class II genotype on T helper lymphocyte responses and viral control in hepatitis C virus infection

Hepatitis C virus (HCV) infection is very common worldwide, but has a broad range of outcomes. A minority of patients are able to clear infection spontaneously, and this is thought to be due to the emergence and maintenance of effective cell-mediated immunity, particularly CD4+ T lymphocyte responses. Furthermore, genetic studies have indicated that HLA class II genotype strongly influences the outcome of infection. We have therefore investigated the influence of the protective HLA class II haplotype (DQB1*0301, which is in tight linkage disequilibrium with DRB1*1101) on the CD4+ T lymphocyte responses to HCV. We observe a strong association between this genotype and maintenance of a multispecific CD4+ T helper response. The effect on T helper responses was also maintained after combination interferon-alpha/ribavirin therapy, although the latter influenced the pattern of viral antigens to which patients responded. This is the first disease in which an association of HLA genotype with clinical outcome has been linked to an alteration of the immunological phenotype. The selection of protective peptides in those with the favourable HLA class II genotype may point in the direction of suitable vaccine candidates.

Mapping MHC-encoded susceptibility and resistance in primary sclerosing cholangitis: the role of MICA polymorphism

BACKGROUND & AIMS

Recent studies suggest that major histocompatibility complex-encoded susceptibility to primary sclerosing cholangitis (PSC) maps to the HLA B-TNFA region on chromosome 6p21.3.

METHODS

The present study uses a standard polymerase chain reaction protocol to investigate the 16 common alleles of the MICA locus as candidates in 2 patient populations (King's College Hospital, London, and John Radcliffe Hospital, Oxford).

RESULTS

The MICA*002 allele was found in 4 of 62 (6.4%) patients and none of 50 patients vs. 41 of 118 (35%) controls (pc = 0.00018, odds ratio [OR] = 0.12, and P = 0.0000016, OR = 0.0, respectively). Overall, the MICA*008 allele was more common in PSC (gene frequency 66% vs. 48% of controls, P = 0.0023, OR = 2.11). However, unlike MICA*002 in which the difference was a result of the absence of MICA*002 heterozygotes, the MICA*008 association may be caused by an increased frequency of MICA*008 homozygosity in patients (58% vs. 22%, pc = 0.000015, OR = 5.01 and 58% vs. 22%, P = 0.0000056, OR = 4.51, respectively). Though MICA*008 is found on the ancestral 8.1 haplotype, stratification analysis indicates that this association is independent of B8 and other HLA haplotypes associated with PSC.

CONCLUSIONS

The MICA*002 allele has a strong dominant effect in reducing the risk of PSC, whereas the increased risk of disease associated with MICA*008 may be a recessive effect requiring 2 copies of the MICA*008 allele.

Evidence for inflammatory bowel disease of a susceptibility locus on the X chromosome

BACKGROUND & AIMS

The technique of genomewide scanning has been applied successfully in inflammatory bowel disease (IBD). A number of putative susceptibility loci have been identified through genomewide searches including replicated regions of linkage on chromosomes 12, 16, 6 (the HLA region), and 14. We have investigated the contribution of the X chromosome in 145 Belgian affected relative pairs.

METHODS

In the first stage of the study, 79 (68 CD, 11 mixed) sibling pairs were genotyped at 12 microsatellite markers covering the X chromosome. In the second stage, 10 additional markers in the X-pericentromeric region were studied in the families involved in stage 1 together with 62 additional families (52 sibling pairs, 14 second-degree relative pairs).

RESULTS

In the first stage, evidence for linkage was found over a 30-cM pericentromeric region spanning dXs991, dXs990, and dXs8096 (multipoint maximum LOD score in the CD subgroup, 2.5; P = 0.0003). The remainder of the X chromosome was excluded (exclusion under LOD-2) for a locus with lambda(s) = 2. Fine mapping in the second stage confirmed linkage, and narrowed and shifted the linked region to Xq21.3 around dXs1203 (nonparametric linkage [NPL], 2.90; P = 0.0017). The NPL-1 interval around the linkage peak comprises 19.7 cM.

CONCLUSIONS

These data provide suggestive evidence for the presence and chromosomal location of an X-linked susceptibility gene in IBD.

The IBD2 locus shows linkage heterogeneity between ulcerative colitis and Crohn disease

The IBD2 locus on chromosome 12 has been linked to both Crohn disease (CD) and ulcerative colitis (UC) but has not been detected in some CD-dominated data sets. In the present study, we genotyped 581 relative pairs with inflammatory bowel disease (252 from CD-only families, 138 from UC-only families, and 191 from mixed families containing cases of both CD and UC), using 12 markers spanning the IBD2 locus. A GENEHUNTER-PLUS multipoint LOD score of 3.91 was detected for pairs from UC-only families, compared with 1.66 for CD-only and 1.29 for mixed families. The difference between the LOD scores for UC and CD was significant in two different tests for heterogeneity (P=.0057 for one test and P=.0375 for the other). IBD2 thus appears to make a major contribution to UC susceptibility but to have only a relatively minor effect with regard to CD, for which there may be substantially more locus heterogeneity.

Exclusion of linkage of Crohn's disease to previously reported regions on chromosomes 12, 7, and 3 in the Belgian population indicates genetic heterogeneity

Susceptibility to inflammatory bowel disease (IBD) is significantly determined by genetic factors. Linkage data from genome-wide searches have identified regions on chromosomes 16, 12, 7, and 3. Our goal was to replicate these four regions in a Belgian population of IBD families. Fifty-four IBD families were studied (47 with Crohn's disease [CD] and 7 with mixed CD and ulcerative colitis, containing 79 affected sibpairs (68 CD only, 11 mixed) for the regions previously implicated to chromosomes 16, 12, 7, and 3. In this study, no evidence for linkage was found on any of the four chromosomal regions studied for either the whole IBD dataset or the CD subgroup. The multipoint maximum logarithm of odds scores were less than 0.7 for all four regions. Exclusion mapping could significantly exclude chromosomes 3, 7, and 12. Despite earlier findings, we could significantly exclude linkage of CD with previously reported regions on chromosomes 12, 7, and 3, and could not find evidence for linkage to chromosome 16. It is important to report these findings in light of the genetic heterogeneity of IBD. A genome-wide search on a larger group of affected siblings is being analyzed to detect other possible susceptibility loci in the Belgian population.

Inflammatory bowel disease: progress toward a gene

The pathogenesis of ulcerative colitis (UC) and Crohn's disease (CD) is still unknown, but the importance of genetic susceptibility has been clearly shown by epidemiological data from family and twin studies. Linkage studies have identified two susceptibility loci for inflammatory bowel disease (IBD) on chromosomes 12 and 16. Importantly, these linkages have been replicated by independent investigators, and studies of positional candidates within these regions continue, together with fine mapping strategies. Regions of 'suggestive' linkage on chromosomes 1, 3, 4, 6, 7, 10, 22 and X have also been reported in individual studies. Other important candidate genes investigated include the interleukin-1 receptor antagonist, MUC3 and genes of the human leukocyte antigen (HLA) system. The apparently conflicting data in different studies from around the world may be explained by ethnic differences, case mix and genetic heterogeneity. Replicated class II HLA associations include HLA DRB1*0103 and DR2 (DRB1*1502), involved in UC susceptibility, and HLA DRB1*03 and DR4 as resistance alleles for CD and UC respectively. Animal studies have provided insights from targeted mutations and quantitative trait locus analysis. The goals of continuing research include narrowing the regions of linkages and analysis of candidate genes, and possibly the application of newly developed methods using single nucleotide polymorphisms. Advances in IBD genetics hold the potential to provide knowledge about the disease pathogenesis at the molecular level, with ensuing benefits for clinical practice.

Cytokine (TNF alpha, LT alpha and IL-10) polymorphisms in inflammatory bowel diseases and normal controls: differential effects on production and allele frequencies

The influence of biallelic polymorphisms in the tumour necrosis factor-alpha (TNF alpha), lymphotoxin-alpha (LT alpha) and interleukin-10 (IL-10) genes on stimulated TNF alpha and IL-10 production was studied in ulcerative colitis (UC) patients, Crohn's disease (CD) patients and in healthy controls. A polymerase chain reaction sequence-specific primer (PCR-SSP) system was developed to type nine biallelic polymorphisms, three in each of the TNF alpha, LT alpha and IL-10 genes. Production of the TNF alpha and IL-10 was measured by ELISA in lipopolysaccharide (LPS) stimulated whole blood. Four haplotypes of the TNF alpha gene, three haplotypes of LT alpha and three haplotypes of IL-10 were identified. No significant differences in haplotype frequencies were found between patients and controls overall. On subgroup analysis however, haplotype TNF-2 was more frequent in women with extensive colitis compared to distal colitis (31% vs 12%; P = 0.028). This difference was even greater for the combined TNF-2-LT alpha-2 haplotype (56% vs 21%; P = 0.0007). The TNF-2 and LT alpha-2 haplotypes were associated with higher TNF alpha production in CD patients, and the TNF-4 haplotype was associated with lower TNF alpha production in UC patients. The A allele in the IL-10 promoter region at position -1082 was associated with decreased IL-10 production in CD patients and controls (P = 0.005, P = 0.015 respectively). These data provide evidence that the effect of TNF alpha, LT alpha and IL-10 gene polymorphisms on cytokine production differ in CD, UC patients and controls.

Is interleukin-6 important in inflammatory bowel disease?

The IL-6 gene maps to an area of chromosome 7 known to be significant for susceptibility to inflammatory bowel disease. The functional effects of interleukin-6 (IL-6) polymorphisms in the 4th intron and in the 3' flanking region of IL-6 gene were studied in 192 inflammatory bowel disease patients and healthy subjects. A polymerase chain reaction with sequence-specific primers (PCR-SSP) was used to determine a G to A polymorphism (* at position 4470 in intron 4 of IL-6 gene). Four alleles in the 3' flanking region were studied using a variable number of tandem repeats PCR (VNTR-PCR) amplification. Production of IL-6 was measured in lipopolysaccharide (LPS) stimulated whole blood samples by an enzyme-linked immunosorbent assay (ELISA). A modest increase in the frequency of the IL-6*G allele was noted in Crohn's disease (CD) patients (50%) and ulcerative colitis (UC) patients (46.1%) as compared to controls (39.8%, P = 0.025). We were unable to find any significant functional effect of the IL-6 polymorphisms tested on IL-6 protein production. We postulate that the IL-6 polymorphisms investigated here may be in linkage disequilibrium with a susceptibility gene and that they may be utilised as genetic markers.

Genetics of inflammatory bowel disease: a reappraisal

The advent of advanced molecular biological techniques in the last two decades has allowed the study of genetic factors in inflammatory bowel disease (IBD). A variety of techniques have been employed to elucidate the effects of genes, starting with the clinical observations that IBD is more common in the relatives of patients than the general population, and the consistency of clinical features within families. The situation is likely to be much more complicated than single gene disorders, and it is estimated that between 10 and 20 genes may be involved. Genome scanning techniques using microsatellite markers have been employed to highlight areas of chromosomes linked to disease such as those on chromosomes 12 and 16. In addition association studies of specific genes such as HLA and cytokine genes have been carried out on functional or positional grounds. It is likely that a combination of these techniques will be required to elucidate the role of individual genes. Recently much work has been focused on genes that may determine clinical phenotype such as disease extent or severity or the response to treatment. Identification of these genes may lead to better targeting of therapy and prognostication, and they are likely to be easier to identify than disease susceptibility genes.

Association of ulcerative colitis with rare VNTR alleles of the human intestinal mucin gene, MUC3

Ulcerative colitis (UC), a common form of inflammatory bowel disease, is a multifactorial disorder with significant genetic influence. Recently, evidence of linkage on chromosome 7q near the intestinal mucin gene MUC3 was reported by an affected sib-pair analysis. Previous reports indicate a possible mucin abnormality in UC patients, but whether genetic differences in a specific mucin gene are associated with UC is unknown. Here we analysed polymorphisms of variable number of tandem repeats (VNTRs) within this gene using DNAs obtained from 243 Japanese (75 patients with UC and 168 controls), and to confirm the result we undertook a two-stage examination using 328 Caucasian samples (72 and 85 with UC in the first and second stages, respectively, and 171 controls). When the frequency of patients carrying one or two rare VNTR alleles was compared with that of controls, a significant increase was found first in Japanese patients (odds ratio 2.72, 95% CI 1.17-6.32, P = 0. 0308). In Caucasians, the odds ratio was 2.80 (95% CI 1.36-5.75, P = 0.0079) in the first stage, 2.43 (95% CI 1.20-4.92, P = 0.0196) in the second stage and 2.60 (95% CI 1.41-4.80, P = 0.0024) in total. The overall odds ratio was 2.64 (95% CI 1.60-4.33, P = 0.0001). This result suggests that rare alleles of the MUC3 gene may confer genetic predisposition to UC.

Genetics of inflammatory bowel disease. A personal view on progress and prospects

Clinical, epidemiological and molecular data reported in the last 5 years have provided strong evidence that genetic factors are important in susceptibility to both Crohn's disease and ulcerative colitis. The model of disease inheritance which best fits the epidemiological data is that Crohn's disease and ulcerative colitis are related polygenic diseases. However, genetic heterogeneity is likely to be extensive, and may well underlie the variability in clinical presentation associated with inflammatory bowel disease. Considerable progress has already been made in identifying potential disease susceptibility loci using the technique of genome-wide scanning. There is optimism that international collaborative studies will allow fine mapping of the loci implicated on chromosomes 16 and 12. The identification of novel susceptibility genes has become a realistic goal for investigators. Once this has been achieved, there are likely to be immediate clinical benefits, both in understanding disease pathophysiology, and in disease management.

Contribution of the IL-2 and IL-10 genes to inflammatory bowel disease (IBD) susceptibility

Although the importance of genetic susceptibility to IBD has been established by epidemiological studies, the genes involved remain poorly characterized. Important candidate genes include those encoding the immunoregulatory cytokines IL-2 and IL-10. The aim of this study was to assess the contribution of the IL-2 and IL-10 genes to IBD susceptibility. One hundred and ninety-eight pairs of siblings with IBD were genotyped at dinucleotide repeat polymorphisms within the IL-2 and IL-10 genes, and data analysed by the affected sib-pair method of linkage analysis and the transmission disequilibrium test (TDT). A subset of 89 affected sibling pairs was genotyped at markers flanking the IL-2 gene as part of a genome-wide search. The IL-2 polymorphism showed no linkage to IBD overall, but modest evidence for linkage to the ulcerative colitis (UC) data set (P = 0.028). A microsatellite 4 cM distal to the IL-2 gene showed a similar distortion in the ulcerative colitis subgroup (P = 0.006). The TDT showed some distortion of allelic transmission for the IL-2 polymorphism in the UC group, but this did not reach statistical significance (P = 0.09). Results for the IL-10 polymorphism were not significant. Thus the gene encoding IL-2 may contribute to UC susceptibility, but the effect is modest and must await replication in other data sets. The IL-10 gene does not appear to contribute to the risk of developing UC or Crohn's disease.

Genetics of inflammatory bowel disease

1. The aetiology of the chronic inflammatory bowel diseases, Crohn's disease and ulcerative colitis, is uncertain. Studies of specific environmental factors and immune dysfunction have provided little insight into disease pathogenesis. 2. Concordance rates in twin pairs and siblings provide strong evidence that genetic factors are important in disease pathogenesis. In Oxford, information was obtained from 433 adult patients with Crohn's disease. Compared with the prevalence in the general population, the relative risks in siblings of patients with Crohn's disease calculated from these data were respectively 36.5 for Crohn's disease, 16.6 for ulcerative colitis and 24.7 for inflammatory bowel disease. 3. Clinical patterns of disease were compared in members of over 250 multiply affected families with inflammatory bowel disease. A high degree of concordance for many characteristics was noted (disease type, extent, extra-intestinal manifestations). However, in 77 affected parent-child pairs, the median age of onset in the parents was significantly higher than in offspring (P < 0.0001). These data reflect the results from other studies throughout the world, and are consistent with the phenomenon of genetic anticipation. 4. A detailed study investigating the contribution of the major histocompatibility complex was undertaken. Eighty-three affected sibling pairs were involved in a linkage analysis study; 348 patients with inflammatory bowel disease and 472 controls were involved in a detailed allelic association study. These data provide evidence that the major histocompatibility complex is an important determinant in ulcerative colitis, but not in Crohn's disease. 5. Cytokine genes are important candidate genes in inflammatory bowel disease. Allelic association study was performed to investigate the contribution of the gene encoding the interleukin-1 receptor antagonist and tumour necrosis factor-alpha. These data do not suggest that these genes encode important determinants of disease susceptibility in inflammatory bowel disease. 6. A two-stage genome-wide search for susceptibility loci in inflammatory bowel disease was performed involving 186 affected sibling pairs. The data provide strong evidence for the model of Crohn's disease and ulcerative colitis as related polygenic disorders. Loci on chromosomes 3, 7 and 12 were linked to inflammatory bowel disease overall, whereas loci on chromosomes 2 and 6 were linked only in ulcerative colitis. Linkage with chromosome 16 was noted in Crohn's disease only. Fine mapping of these susceptibility loci is in progress, and may lead to gene identification with attendant clinical benefits.

The presence of anti-neutrophil antibodies reflects clinical and genetic heterogeneity within inflammatory bowel disease

A detailed investigation of the relationship between anti-neutrophil cytoplasmic antibodies (ANCA) status, HLA genotype, and clinical patterns of inflammatory bowel disease was carried out, involving 236 European patients resident in the United Kingdom [120 had ulcerative colitis (UC), 116 had Crohn's disease (CD)]. ANCA status was determined on coded plasma samples in Los Angeles using a two-stage assay [fixed neutrophil enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence], and HLA genotyping was carried out by polymerase chain reaction. The results provide evidence that ANCA reflect clinical and genetic heterogeneity within the inflammatory bowel diseases. In the UC patients, 78.3% were ANCA positive [64.2 perinuclear (pANCA)], but only 46.5% CD patients were ANCA positive (19.3% pANCA). Furthermore, mean ELISA binding was significantly lower in CD (14.5% +/- 18.8% versus 40.5% +/- 41.0% in UC, p = 2.31 x 10(-9)). Only 15 CD samples, all from patients with colonic disease, displayed ELISA > 20%; and the six CD patients with highest ELISA binding had clinical features very similar to ulcerative colitis. Moreover, in UC, significant relationships between ANCA status and genotype were noted. Thus, 92.7% of patients with the DR3 DQ2 TNF2 haplotype were ANCA positive [p = 0.03 versus DR3 DQ2 TNF2-negative patients (73.9%)]. ELISA binding was increased in DR3 DQ2 TNF2-positive patients (56.0 versus 35.7%, p = 0.02). In this population of UC, ANCA was not associated with DR2, DR4, or clinical pattern. These data emphasize the many factors that need to be considered in genetic marker studies in inflammatory bowel disease. Extensive disease heterogeneity, ethnicity, and methodological differences in ANCA detection are all pertinent.

Mapping susceptibility loci in inflammatory bowel disease: why and how?

The cause of the inflammatory bowel diseases Crohn's disease and ulcerative colitis is unknown, but epidemiological evidence suggests that it is multifactorial with a strong genetic component. Several genetic loci probably contribute to disease susceptibility, accounting for the complex pattern of inheritance and heterogeneous clinical manifestations. The combination of candidate gene studies and, more recently, genome-wide searches has resulted in the identification of a number of putative susceptibility loci. With large-scale, fine-mapping studies under way, and accelerating progress in the physical mapping of the human genome, rapid progress is now being made towards the identification of the genes responsible for inflammatory bowel disease.

Genetic markers may predict disease behavior in patients with ulcerative colitis

BACKGROUND & AIMS

Recent studies have suggested that HLA DRB1*0103 and allele 2 of the interleukin 1 receptor antagonist (IL-1RA) gene predict severe and extensive ulcerative colitis, respectively. The aim of this study was to test these hypotheses in patients undergoing surgery for their colitis.

METHODS

HLA DRB1 and DQB1 genotyping was performed in 99 patients and 472 controls. Genotyping for polymorphisms of genes encoding tumor necrosis factor alpha and IL-1RA was performed in 107 patients and 89 controls. Measurement of antineutrophil cytoplasmic antibody (ANCA) was performed in 72 patients and 58 healthy subjects by fixed neutrophil enzyme-linked immunosorbent assay and indirect immunofluorescence.

RESULTS

The DRB1*0103 allele was increased in patients (14.1% vs. 3.2% in controls; P < 1 x 10[-5]). This association was greatest in patients with extensive disease (15.8%; P < 0.0001) or extraintestinal manifestations (22.8%; P < 0.0001): mouth ulcers (25.8%; P < 0.0001), arthritis (27.2%; P < 0.0001), and uveitis (35.7%; P < 0.0001). The DRB1*04 alleles were reduced in patients (P = 0.005). Differences were noted between extensive and distal disease in the frequency of allele 2 of IL-1RA (10.9% in distal vs. 28.6% in extensive; P = 0.01) and allele 2 homozygosity. ANCA was detected in 76.4% of patients. Carriage of IL-1RA allele 2 and tumor necrosis factor 2 allele was increased in ANCA-positive patients.

CONCLUSIONS

Genetic markers may predict disease behavior in ulcerative colitis.

Cytokine gene polymorphisms in inflammatory bowel disease

BACKGROUND

Concordance rates in siblings and twins provide strong evidence that genetic susceptibility is important in the pathogenesis of inflammatory bowel disease. The number and identity of susceptibility genes is largely uncertain. Cytokine genes are attractive candidate loci.

AIMS

To study allelic frequencies of polymorphisms of the interleukin-1 receptor antagonist (IL-1RA) gene and the tumour necrosis factor alpha gene in patients with inflammatory bowel disease.

SUBJECTS

One hundred and twenty nine North European caucasoid patients with ulcerative colitis, 120 patients with Crohn's disease, and 89 healthy controls.

METHODS

Genotyping was performed by polymerase chain reaction. A variable number of tandem repeats (VNTR) in the IL-1RA gene and a single base pair polymorphism in the TNF alpha gene promoter region (TNF-308) were analysed.

RESULTS

No significant differences in IL-1RA VNTR allelic frequencies were noted between Crohn's disease (allele 1: 72.6%, allele 2: 24.7%, allele 3: 2.6%), ulcerative colitis (72.6%, 24.3%, 3.1%, respectively), and controls (76.9%, 20.8% and 2.3%). Some 42.4% of patients with ulcerative colitis and 43.4% patients with Crohn's disease were carriers of allele 2, compared with 34.8% healthy subjects. The TNF2 allele was modestly reduced in Crohn's disease (13.2%), compared with healthy subjects (21.3%; p = 0.04), and ulcerative colitis (21.6%).

CONCLUSIONS

The associations demonstrated are modest: these polymorphisms are unlikely to be important determinants of overall disease susceptibility.

Two stage genome-wide search in inflammatory bowel disease provides evidence for susceptibility loci on chromosomes 3, 7 and 12

Crohn's disease (CD) and ulcerative colitis (UC), the chronic inflammatory bowel diseases (CIBD), are common causes of gastro-intestinal disease in the Western world, with a combined prevalence of 100-200/100,000 (ref. 1). Epidemiological studies, particularly concordance rates in twin pairs and siblings, strongly implicate genetic susceptibility in the pathogenesis of CIBD. In fact, the relative contribution of genetic factors to the pathogenesis of CD may be greater than in schizophrenia, asthma or hypertension, and at least equivalent to that in insulin-dependent diabetes. Systematic screening of the entire human genome now provides a strategy for the identification of susceptibility genes in complex polygenic disorders. We undertook a two-stage genome search for susceptibility genes in inflammatory bowel disease involving 186 affected sibling pairs from 160 nuclear families. We provide strong evidence for the presence of susceptibility loci for both CD and UC on chromosome 3, 7 and 12. We obtained the highest lod score (5.47; P = 2.66 x 10(-7) with the marker D12S83 and lod scores of 3.08 and 2.69 for D7S669 and D3S1573, respectively. Our data suggest that CD and UC are closely related, but distinct, polygenic disorders that share some, but not all, susceptibility genes.

Inflammatory bowel disease and the X chromosome

A review of documented cases demonstrates a significant association of Turner's syndrome with Crohn's disease and ulcerative colitis; this association relates particularly to genetic constitutions comprising an abnormal rather than an absent X chromosome. The karyotype 46XiXq, in pure or mosaic form, appears to be a significant susceptibility factor for inflammatory bowel disease. This karyotype often gives rise to relatively weak phenotypic characteristics of Turner's syndrome, which may be overlooked in short females with inflammatory bowel disease. The association of inflammatory bowel disease with Turner's syndrome may reflect the presence on the X chromosome of genes involved in disease pathogenesis. Linkage analysis studies, involving microsatellite markers on the X chromosome, are being performed.

Contribution of genes of the major histocompatibility complex to susceptibility and disease phenotype in inflammatory bowel disease

BACKGROUND

Despite strong evidence implicating immune dysfunction and genetic predisposition in the pathogenesis of the chronic inflammatory bowel diseases Crohn's disease and ulcerative colitis, the importance of the genes of the major histocompatibility complex remains uncertain. We have investigated the contribution of HLA DRB1 and DQB genes by the strategies of non-parametric linkage analysis (affected sibling pair method) as well as association study. The relation between genotype and phenotype was examined in detail.

METHODS

For linkage analysis 74 families in whom two or more siblings had inflammatory bowel disease were studied. A total of 83 affected sibling pairs were involved: in 42 pairs both siblings had Crohn's disease; in 29 both had ulcerative colitis; in 12 one sibling had Crohn's disease, the other ulcerative colitis. For the association study there were 175 patients with ulcerative colitis, 173 with Crohn's disease, and 472 controls. Details of sex, age of onset, disease extent, and family history were analysed. 24 patients with ulcerative colitis and 92 with Crohn's disease required surgery for refractory disease. HLA DRB1 and DQB1 gene-typing was performed by polymerase chain reaction with sequence-specific primers.

FINDINGS

In ulcerative colitis, the sharing of alleles among affected sibling pairs provided evidence for linkage with DRB1 locus (p = 0.017, chi2 = 5.32). Of 29 affected sibling pairs studied, only one pair shared no DRB1 DQB haplotypes. 15 shared two DRB DQB haplotypes. In contrast, no linkage was noted for Crohn's disease (42 sibling pairs; p = 0.30, chi2 = 0.16) or for inflammatory bowel disease overall (83 sibling pairs, p = 0.16, chi2 = 2.28). In the association study the rare DRB1*103 (8.3% vs 3.2% in controls) and DRB1*12 (8.6% vs 2.1% in controls) alleles were associated with ulcerative colitis (p = 0.0074, chi2 = 7.22, odds ratio OR = 2.9 [95% CI 1.3-6.4] and p = 0.0056, chi2 = 12.63, OR = 4.33 [1.8-11.0] respectively). No association with alleles representing DR2 (p = 0.55, chi2 = 0.34) was noted. No overall association was seen in Crohn's disease. In ulcerative colitis, the frequency of DRB1*0301 DQB*0201 (DR3 DQ2) was reduced in females (9.8% vs 26.3% in controls, p = 0.037, chi2 = 8.39 OR = 0.34 [0.15-0.71]), particularly in those with distal disease (2.3%, p = 0.001 vs controls, chi2 = 11.35, OR = 0.07 [0.00-0.39]). In both males and females, the DR3 DQ2 haplotype was predictive of extensive ulcerative colitis (32.9% vs 10.7% in distal disease, p < 0.01, chi2 = 10.94, OR 4.09 [1.70-10.6]) but not of need for surgery (p = 0.93, chi2 = 0.01).

INTERPRETATION

These data provide strong evidence for genetic heterogeneity in inflammatory bowel disease. Genes of the major histocompatibility complex are implicated as important inherited determinants of susceptibility to ulcerative colitis and may also influence the pattern of disease. In Crohn's disease, important susceptibility genes are likely to exist outside the HLA region.

Clinical patterns of familial inflammatory bowel disease

BACKGROUND

Although many recent studies have shown the increased risk of inflammatory bowel disease in relatives of patients with Crohn's disease and ulcerative colitis, clinical patterns of disease within families remain relatively poorly documented.

AIMS

In this study, clinical characteristics (disease type, extent, age on onset, need for surgery, and presence of extraintestinal manifestations) have been compared in affected subjects in multiply-affected families, with inflammatory bowel disease.

METHODS

54 families in whom one parent and at least one child were affected (a total of 77 parent-child pairs) and 155 families in whom at least two siblings were affected (a total of 190 affected sibling pairs) were involved.

RESULTS

In affected parent-child pairs, parent and child were concordant for disease type in 58 of 77 pairs (75.3%), for extent in 63.6%, extraintestinal manifestations in 70.1%, and smoking history in 85%. The median age of onset in parents was significantly higher than offspring (p < 0.0001). In 40 pairs, 60.6%, the parent was at least 10 years older than child. Siblings were concordant for disease type in 81.6% of the affected sibling pairs, extent in 76.0%, extraintestinal manifestations in 83.8%, and smoking history in 81.3%. In contrast with the parent-child pairs, 68.1% (111 sibling pairs) siblings were diagnosed within 10 years of each other. The median age of onset was 24.0 years.

CONCLUSIONS

This study has shown consistent clinical patterns in many families with inflammatory bowel disease. The differences in age of onset between parents and children are not readily explained by a simple cohort effect or ascertainment bias, and may reflect effects of genetic factors, producing anticipation between generations.

Ulcerative colitis complicated by renal cell carcinoma: a series of three patients

Three patients are described in whom renal cell carcinoma was diagnosed between seven months and 14 years after the onset of ulcerative colitis. All three had required treatment with corticosteroids and azathioprine, as well as maintenance therapy with 5-aminosalicylate derivatives, for chronic active colitis. One patient had coexisting polymyalgia rheumatica; one had primary biliary cirrhosis. It is uncertain whether this association, which has not previously been described, has pathogenetic importance or has arisen simply by chance. Genetic predisposition or the effect of drug treatment, particularly immunosuppression, may be pertinent to the co-occurrence of these diseases.

Are serum concentrations of nitric oxide metabolites useful for predicting the clinical outcome of severe ulcerative colitis?

OBJECTIVE

To determine serum concentrations of nitric oxide metabolites (NOX) in patients with severe ulcerative colitis and to assess whether these concentrations predict clinical outcome.

PATIENTS

Twenty-six patients (16 men and 10 women, mean age 46 years) with severe ulcerative colitis requiring hospitalization for parenteral steroid therapy. Thirteen patients had a complete clinical response and symptoms resolved after 5 days of parenteral steroid administration; 13 made an incomplete recovery and needed further treatment (six cyclosporin, seven colectomy).

METHODS

Serum concentrations of NOX and C-reactive protein (CRP) were measured daily for 3 days in all patients and as clinically indicated thereafter. The normal range for NOX was established by measuring the concentration in 25 healthy controls.

RESULTS

Mean serum NOX and CRP concentrations were significantly elevated in both the patients with a complete and those with an incomplete response compared with controls (P < 0.001) on day 1 and fell during the first 3 days of therapy. On day 3, mean serum concentrations of NOX and CRP were lower in the patients with a complete response, but only the difference in CRP attained statistical significance (P = 0.02). There was no correlation between NOX and CRP concentrations.

CONCLUSIONS

In the majority of patients with severe ulcerative colitis, circulating concentrations of NOX are increased at presentation and fall promptly during parenteral steroid therapy, irrespective of clinical outcome. However, in a small number of patients NOX concentrations do not fall during steroid treatment and such patients will probably require additional medical therapy or surgery.

Misuse of ecstasy

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Multifocal peripheral neuropathy in eosinophilic fasciitis

Polyneuropathy may complicate eosinophilia-associated connective tissue disease. We report a multi-focal neuropathy in a patient with eosinophilic fasciitis proven by demonstrating an eosinophilic cellular infiltrate in a fascial biopsy specimen from the forearm. Sural nerve biopsy revealed lymphocytic cuffing of epineural arterioles. Although described in the L-tryptophan-related eosinophilia-myalgia syndrome, peripheral neuropathy with these features has not been previously noted in a patient with eosinophilic fasciitis who had not consumed L-tryptophan.

Interleukin 1 in Crohn's disease

A number of the activities currently ascribed to the mediator interleukin 1 (IL-1) are relevant to chronic inflammatory bowel disease. Using the mouse thymocyte stimulation assay, lymphocyte-activating factor (LAF) activity was measured in plasma samples and supernatants from cultures of peripheral blood mononuclear cells from 16 patients with Crohn's disease, six with ulcerative colitis, and 10 healthy subjects. Results were compared with disease activity, drug therapy, granulocyte count, and plasma levels of zinc and C-reactive protein (CRP). Very low levels of LAF were detected in a few plasma samples from each of the subject groups. Mononuclear cells from healthy subjects produced LAF only when cultured with lipopolysaccharide, but stimulated cells from patients produced greater amounts. Moreover, cells from six patients with Crohn's disease, not receiving steroids, produced LAF spontaneously. Crohn's disease patients also had low plasma zinc but elevated levels of CRP and granulocytes. This enhanced production of LAF in vitro may reflect a primary cellular defect in Crohn's disease, or a secondary consequence of monocyte activation.