S. Bridger

A simple method for assessing intestinal inflammation in Crohn's disease

BACKGROUND AND AIMS Assessing the presence and degree of intestinal inflammation objectively, simply, and reliably is a significant problem in gastroenterology. We assessed faecal excretion of calprotectin, a stable neutrophil specific marker, as an index of intestinal inflammation and its potential use as a screening test to discriminate between patients with Crohns disease and those with irritable bowel syndrome. METHODS The validity of faecal calprotectin as a marker of intestinal inflammation was assessed in 22 patients with Crohns disease (35 studies) by comparing faecal excretions and concentrations using four day faecal excretion of111indium white cells. A cross sectional study assessed the sensitivity of faecal calprotectin concentration for the detection of established Crohns disease (n=116). A prospective study assessed the value of faecal calprotectin in discriminating between patients with Crohns disease and irritable bowel syndrome in 220 patients referred to a gastroenterology clinic. RESULTS Four day faecal excretion of 111indium (median 8.7%; 95% confidence interval (CI) 7–17%; normal <1.0%) correlated significantly (p<0.0001) with daily (median ranged from 39 to 47 mg; normal <3 mg; r=0.76–0.82) and four day faecal calprotectin excretion (median 101 mg; 95% CI 45–168 mg; normal <11 mg; r=0.80) and single stool calprotectin concentrations (median 118 mg/l; 95% CI 36–175 mg/l; normal <10 mg/l; r=0.70) in patients with Crohns disease. The cross sectional study showed a sensitivity of 96% for calprotectin in discriminating between normal subjects (2 mg/l; 95% CI 2–3 mg/l) and those with Crohns disease (91 mg/l; 95% CI 59–105 mg/l). With a cut off point of 30 mg/l faecal calprotectin has 100% sensitivity and 97% specificity in discriminating between active Crohns disease and irritable bowel syndrome. CONCLUSION The calprotectin method may be a useful adjuvant for discriminating between patients with Crohns disease and irritable bowel syndrome.

Genetic Analysis of Inflammatory Bowel Disease in a Large European Cohort Supports Linkage to Chromosomes 12 and 16

BACKGROUND & AIMS Inflammatory bowel disease (IBD) is a complex disorder of unknown etiology. Epidemiological investigations suggest a genetic basis for IBD. Recent genetic studies have identified several IBD linkages. The significance of these linkages will be determined by studies in large patient collections. The aim of this study was to replicate IBD linkages on chromosomes 12 and 16 in a large European cohort. METHODS Three hundred fifty-nine affected sibling pairs from 274 kindreds were genotyped using microsatellite markers spanning chromosomes 12 and 16. Affection status of the sibling pairs was defined as Crohns disease (CD) or ulcerative colitis (UC). RESULTS Nonparametric statistical analyses showed linkage for both chromosomes. Two-point results for chromosome 12 peaked at D12S303 (logarithm of odds [LOD], 2.15; P = 0.003) for CD and at D12S75 (LOD, 0.92; P = 0.03) for UC. Multipoint analyses produced a peak LOD of 1.8 for CD. Chromosome 16 showed linkage for CD at marker D16S415 (LOD, 1.52; P = 0.007). Multipoint support peaked above markers D16S409 and D16S411 (LOD, 1.7). CONCLUSIONS These data are consistent with linkage of IBD to chromosomes 12 and 16. The replication of genetic risk loci in a large independent family collection indicates important and common susceptibility genes in these regions and will facilitate identification of genes involved in IBD.

In siblings with similar genetic susceptibility for inflammatory bowel disease, smokers tend to develop Crohn's disease and non-smokers develop ulcerative colitis

Background and aims: Smoking tobacco has opposite effects on the different forms of inflammatory bowel disease (IBD). It predisposes to the development of Crohns disease (CD) yet is associated with a reduced incidence of ulcerative colitis (UC). We have studied sib pairs discordant for both smoking and IBD phenotype (UC or CD) to investigate whether smoking determines the type of IBD that develops in individuals with very similar genetic susceptibility. Patients: Smoking habits and disease characteristics were analysed in 242 IBD pedigrees (658 patients). Within this group there were 339 affected sibling pairs of whom 89 were discordant for smoking when diagnosed. Results: Smoking at diagnosis was associated with development of CD (odds ratio (OR) 3.55; 95% confidence limits 2.50–5.02; p<0.001) in all of the familial patients, with increases when analysed for ileocaecal disease, fibrostenosis, and intestinal resection. Smokers were also protected from UC (OR 0.28; 0.2–0.4; p<0.001). Of 89 sibling pairs discordant for smoking at diagnosis, 23 were also discordant for disease type—in 21 of these, CD occurred in the smoker and UC in the non-smoker (OR 10.5; 2.6–92; p<0.0001). Conclusions: Smoking is a strong environmental risk factor for Crohns disease and increases the likelihood of needing surgery. However, sib pairs who are discordant for both smoking and IBD type almost always show CD in the smoker and UC in the non-smoker, and so in some cases tobacco consumption acts on IBD genetic predisposition to shift the phenotype from UC towards CD. The explanation of part of the apparent “protective” effect of smoking on sporadic UC may be that the form of IBD that develops in a proportion of smokers is not UC but CD.

Why children with inflammatory bowel disease are diagnosed at a younger age than their affected parent

BACKGROUND Genetic anticipation has been proposed to explain observed age differences at diagnosis of Crohn’s disease in affected parents and offspring. AIMS To compare affected parent-child pairs with Crohn’s disease and ulcerative colitis with a control group of non-familial patients with inflammatory bowel disease (IBD) in order to quantify whether ascertainment bias could account for this effect. METHODS 137 affected parent-child pairs from 96 families and 214 patients with sporadic IBD were studied. Age at onset of symptoms and diagnosis were ascertained by interview and disease confirmed from clinical records. RESULTS Of the 137 affected parent-child pairs, 50 had Crohn’s disease only, 51 had ulcerative colitis only, and in 36, one had Crohn’s disease and the other ulcerative colitis. The median age of parents at diagnosis was 17.5 years older, 16 years older, and 18 years older in the Crohn’s disease, ulcerative colitis, and mixed disease families respectively (p<0.001 in each case). These observed age differences were compatible with those predicted from the regression lines of years of birth against age at diagnosis for the non-familial IBD patients. No evidence was found for an effect of parental sex on age at diagnosis or disease extent in offspring. CONCLUSIONS There was no evidence of genetic anticipation or genomic imprinting of age at diagnosis in this sample of IBD families. Ascertainment bias is responsible for the age differences at diagnosis between affected parents and children.

Analysis of single-nucleotide polymorphisms in the interleukin-4 receptor gene for association with inflammatory bowel disease.

Abstract Genetic linkage analysis in families with multiple cases of inflammatory bowel disease (IBD) has mapped a gene which confers susceptibility to IBD to the pericentromeric region of chromosome 16 (IBD1). The linked region includes the interleukin(IL)-4 receptor gene (IL4R). Since IL-4 regulation and expression are abnormal in IBD, the IL4R gene is thus both a positional and functional candidate for IBD1. We screened the gene for single-nucleotide polymorphisms (SNPs) by fluorescent chemical cleavage analysis, and tested a subset of known and novel SNPs for allelic association with IBD in 355 families, which included 435 cases of Crohns disease and 329 cases of ulcerative colitis. No association was observed between a haplotype of four SNPs (val50ile, gln576arg, A3044G, G3289A) and either the Crohns disease or ulcerative colitis phenotypes using the transmission disequilibrium test. There was also no evidence for association when the four markers were analyzed individually. The results indicate that these variants are not significant genetic determinants of IBD, and that the IL4R gene is unlikely to be IBD1. Linkage disequilibrium analyses showed that the val50ile and gln576arg variants are in complete equilibrium with each other, although they are separated by only about 21 kilobases of genomic DNA. This suggests that a very dense SNP map may be required to exclude or detect disease associations with some candidate genes.