Genetic analysis of inflammatory bowel disease in a large European cohort supports linkage to chromosomes 12 and 16

Additional evidence of linkage between Crohn's disease and a putative locus on chromosome 12

PURPOSE

The inflammatory bowel diseases (IBD), Crohn's disease (CD), and ulcerative colitis (UC) are chronic intestinal disorder of unknown etiology. Genetic factors play an important role in the pathogenesis of these diseases, but with a complex pattern of inheritance. A number of genome-wide scans have identified several putative susceptibility loci for both CD and UC, including a locus on chromosome 12 reported in a set of British families. We aim to evaluate the linkage between CD or UC and this chromosome 12 locus in an independent set of U.S. Caucasian families (36% being of Ashkenazi Jewish origin).

METHODS

Microsatellite markers along chromosome 12 spaced at approximately 10 cm intervals were used to test the putative loci in CD only families (65 sib pairs from 46 families). Regions with positive linkage for CD were then tested in a panel of UC and mixed families (44 sib pairs from 29 families). Two point linkage analysis was performed with SIBPAL. Multipoint linkage analysis was carried out with MAPMAKER/SIBS.

RESULTS

We observed evidence of linkage between the region on chromosome 12 and Crohn's disease, because there was a significant excess of allele sharing in CD sib pairs (pi = 0.62, p = 0.0004 from two-point linkage; and logarithm of the odds score (LOD) = 2.0 from multipoint linkage). However, we did not observe the same linkage in UC and mixed families (p = 0.48; not significant [ns]).

CONCLUSION

Our data provided further evidence that the region on chromosome 12 is likely to contain a gene predisposing to CD.

Genetics and inflammatory bowel disease

Genetic factors have a definite role in the etiology of inflammatory bowel disease (IBD). The mode of inheritance suggests a polygenic disease with the penetrance of the genetic factors being strongly influenced by the lifestyle of an industrialized society. Molecular techniques, which have become available through the progress of the human genome project, allowed a first series of linkage studies in pairs of affected siblings with IBD, which suggested multiple genomic susceptibility regions. These regions are still large, but considerable progress is being made toward the identification of actual disease genes. It is hoped that an understanding of the genetic etiology of IBD will lead to enhanced diagnostic procedures, more effective therapeutic interventions, and preventive strategies in the future.

Polymorphism of heat-shock protein gene HSP70-2 in Crohn disease: possible genetic marker for two forms of Crohn disease

BACKGROUND

Previous reports have shown that heat-shock protein 70 (HSP70) may be associated with Crohn disease. However, genetic analysis of the HSP70 gene in Crohn disease has not been done. The aim of this study is to investigate whether HSP70-2 gene polymorphism is involved in susceptibility to Crohn disease in the Japanese population and whether it correlates with clinical manifestation of the disease.

METHODS

A total of 108 genetically unrelated patients with Crohn disease and 108 healthy controls were typed for HSP70-2 PstI polymorphism by restriction fragment length polymorphism analysis (alleles A and B). Patients with Crohn disease were classified into two types: either perforating or non-perforating.

RESULTS

Genotype and allele frequency did not differ between patients and controls. In patients with Crohn disease, allele A frequency was significantly higher in the non-perforating than in the perforating type (P = 0.02). When patients with Crohn disease of more than 6.7 years' duration were assessed, the differences in genotype and allele frequency between the two groups became more significant (P < 0.001 and P < 0.001, respectively).

CONCLUSIONS

These data suggest that HSP70-2 gene polymorphic allele A is a possible genetic marker of less severe clinical phenotype in Japanese patients with Crohn disease.

A genomewide analysis provides evidence for novel linkages in inflammatory bowel disease in a large European cohort

Inflammatory bowel disease (IBD) is characterized by a chronic relapsing intestinal inflammation, typically starting in early adulthood. IBD is subdivided into two subtypes, on the basis of clinical and histologic features: Crohn disease and ulcerative colitis (UC). Previous genomewide searches identified regions harboring susceptibility loci on chromosomes 1, 3, 4, 7, 12, and 16. To expand our understanding of the genetic risk profile, we performed a 9-cM genomewide search for susceptibility loci in 268 families containing 353 affected sibling pairs. Previous linkages on chromosomes 12 and 16 were replicated, and the chromosome 4 linkage was extended in this sample. New suggestive evidence for autosomal linkages was observed on chromosomes 1, 6, 10, and 22, with LOD scores of 2.08, 2.07, 2.30, and 1.52, respectively. A maximum LOD score of 1.76 was observed on the X chromosome, for UC, which is consistent with the clinical association of IBD with Ullrich-Turner syndrome. The linkage finding on chromosome 6p is of interest, given the possible contribution of human leukocyte antigen and tumor necrosis-factor genes in IBD. This genomewide linkage scan, done with a large family cohort, has confirmed three previous IBD linkages and has provided evidence for five additional regions that may harbor IBD predisposition genes.