HLA class II alleles associated with susceptibility and resistance to Crohn's disease in the Jewish population

Role of HLA typing on Crohn's disease pathogenesis

Crohn's disease (CD) is the main type of chronic inflammatory bowel disease of unknown etiology. Evidence from family and twin studies suggests that genetics plays a significant role in predisposing an individual to develop Crohn's disease. A susceptibility locus for Crohn's disease has been mapped 3 to chromosome 16: a frameshift variant and two missense variants of NOD2, encoding a member of the Apaf-1/Ced-4 superfamily of apoptosis regulators which is expressed in hematopoietic compartment cells and intestinal epithelial cells as well as in paneth cells, where NOD2 may play an important role in the pathogenesis of Crohn disease in the gastrointestinal system. This leads to alteration the structure of either the leucine-rich repeat domain of the protein or the adjacent region. NOD2 activates nuclear factor NF-kB; this activating function is regulated by the carboxy-terminal leucine-rich repeat domain, which has two functions, first an inhibitory role and also acts as an intracellular receptor for components of microbial pathogens. Thus, NOD2 gene product confers susceptibility to Crohn's disease by altering the recognition of these components and/or by over-activating NF-kB in intestinal epithelial cells as well as in paneth cells. Further confirmation of a genetic predisposition comes from studies of the association between the human leukocyte antigen (HLA) system and CD. The immunogenetic predisposition may be considered an important requirement for the development of CD, as several alleles of human major histocompatibility complex had an association with CD. Although it is difficult to estimate the importance of this region in determining overall genetic susceptibility in a population, studies of HLA allele sharing within families suggest that this region contributes between 10% and 33% of the total genetic risk of Crohn's disease.

Epidemiology and Disease Burden of Ulcerative Colitis in Taiwan: A Nationwide Population-Based Study

OBJECTIVES

A rising trend of incidence and prevalence of ulcerative colitis (UC) had been noticed in Asian countries. We conducted this study to investigate the epidemiology and medical burden of UC in Taiwan.

METHODS

In this 10-year retrospective database study, we identified cases of patients with UC during 1998 to 2008 from the Taiwan National Health Insurance Research Database. Patients who had a catastrophic illness certificate were included in epidemiology and medical burden calculation.

RESULTS

There were 1522 cases identified in our study period. The incidence increased twofold from 0.37 per 100,000 in 1998 to 0.78 per 100,000 in 2008. The incidence and prevalence had an increasing trend in our population. The cases onset age was 45.0 years on average. In our survey, most of the top 20 coexisting diseases were gastrointestinally relevant diseases, anemia (9.99%), and hypertension (7.69%). There were more than 70% patients using mesalamine, and the medical expenditure on mesalamine occupied the highest position in patients with UC. The average medical expenditure of patients with UC had a decreasing trend after 2001.

CONCLUSIONS

This study had the largest sample and the longest study period for the epidemiology and medical burden estimation of UC in Taiwan. The incidence rates and medicine use of patients with UC had a definite rising trend across the years in Taiwan. Patients with anemia or choric diseases were observed in our population. More surveillance of UC-related diseases and health care costs need to be conducted in the future.

Analysis of genetic variation in Ashkenazi Jews by high density SNP genotyping

BACKGROUND

Genetic isolates such as the Ashkenazi Jews (AJ) potentially offer advantages in mapping novel loci in whole genome disease association studies. To analyze patterns of genetic variation in AJ, genotypes of 101 healthy individuals were determined using the Affymetrix EAv3 500 K SNP array and compared to 60 CEPH-derived HapMap (CEU) individuals. 435,632 SNPs overlapped and met annotation criteria in the two groups.

RESULTS

A small but significant global difference in allele frequencies between AJ and CEU was demonstrated by a mean FST of 0.009 (P < 0.001); large regions that differed were found on chromosomes 2 and 6. Haplotype blocks inferred from pairwise linkage disequilibrium (LD) statistics (Haploview) as well as by expectation-maximization haplotype phase inference (HAP) showed a greater number of haplotype blocks in AJ compared to CEU by Haploview (50,397 vs. 44,169) or by HAP (59,269 vs. 54,457). Average haplotype blocks were smaller in AJ compared to CEU (e.g., 36.8 kb vs. 40.5 kb HAP). Analysis of global patterns of local LD decay for closely-spaced SNPs in CEU demonstrated more LD, while for SNPs further apart, LD was slightly greater in the AJ. A likelihood ratio approach showed that runs of homozygous SNPs were approximately 20% longer in AJ. A principal components analysis was sufficient to completely resolve the CEU from the AJ.

CONCLUSION

LD in the AJ versus was lower than expected by some measures and higher by others. Any putative advantage in whole genome association mapping using the AJ population will be highly dependent on regional LD structure.

Polymorphism of HLA-DRB1 gene shows no strong association with ulcerative colitis in Chinese patients

The genetic factors predisposing to ulcerative colitis (UC) have remained totally unclear to date. This study aimed to investigate the role of HLA-DRB1 genetic polymorphism in the susceptibility to develop UC in Chinese patients. HLA-DRB1 genotyping was carried out in 72 unrelated patients with UC and 314 healthy controls by using polymerase chain reaction-sequence-specific primers (PCR-SSP). All of the patients and healthy controls are Han people in China. The frequency of DRB1*07 allele was increased in UC patients compared with healthy controls (19.4% vs. 9.2%, P = 0.0229, OR = 2.372, 95%CI: 1.181-4.766), but the significance disappeared when given Bonferroni correction (P(C) = 0.2977). Furthermore, compared with healthy controls, although HLA-DRB1*07, DRB1*16/DRB1*09 and DRB1*07/DRB1*12 genotypes were increased in frequency in the patients with extensive colitis, and the patients without extraintestinal manifestations (EIMs) carried an increased frequency of HLA-DRB1*07 and DRB1*07/DRB1*12 genotypes, these differences did not reach statistical significance after Bonferroni correction. HLA-DRB1 alleles showed no strong association with UC, and no HLA-DRB1 alleles or genotypes were strongly associated with clinical subgroups of UC in Chinese patients.

Association of ulcerative colitis with the inflammatory bowel disease susceptibility locus IBD2 in non-Jewish Caucasians and evidence of genetic heterogeneity among racial and ethnic populations with Crohn disease

Genomewide scanning has been used to identify chromosomal regions encoding susceptibility loci to inflammatory bowel disease (IBD). The greatest evidence for linkage to IBD has been reported for a region of chromosome 12q14 surrounding the microsatellite marker D12S83, with a logarithm of odds score of 5.47 and a positive transmission disequilibrium test, and which was subsequently named IBD2. We wished to confirm this locus by genotyping the highly polymorphic microsatellites D12S1022, D12S1056, and D12S83, spanning a continuous region on chromosome 12 of 342 kb, in a cohort of nonrelated individuals with ulcerative colitis (89 patients), Crohn disease (121 patients), and population-based control subjects (100 patients). In non-Jewish Caucasians, one D12S1022 allele, one D12S1056 genotype, and three D12S83 alleles were found to have statistically significant differences in distribution between the two disease groups and the control population. These data support a significant association of IBD with the IBD2 locus in close vicinity to the three markers studied. The replication of genetic risk loci in a case control association study may indicate susceptibility genes in this region and may facilitate identification of candidate genes for IBD. Subgroup analysis revealed a notable difference in genotype distribution among Jewish Caucasian and African American patients affected with Crohn disease when compared with similarly affected non-Jewish Caucasians. Using Fisher exact test, statistically significant distribution differences were observed for D12S1022 and D12S83. These data indicate that there may be significant genetic heterogeneity between different ethnic and racial IBD populations or may simply reflect differences in marker allele frequencies among populations.