HLA antigens and ulcerative colitis in Japan

The contribution of HLA genes to IBD susceptibility and phenotype

The human leukocyte antigen (HLA) region located on chromosome 6p encodes the highly polymorphic, classical class I and II genes essential for normal lymphocyte function; it also encodes a further 224 genes. Many early studies investigating this region were limited by small sample size, poor statistical methodology, population stratification and variable disease definition. Although more recent studies have improved study design, investigators are still challenged by the complex patterns of linkage disequilibrium across this gene-dense region, and by the disease heterogeneity characteristic of all genetically complex disorders. However, a number of important observations have emerged from recent studies: (1) the HLA harbours gene(s) that determine susceptibility to colonic inflammation in both ulcerative colitis (UC) and Crohn's disease (CD); (2) most of the specific associations with UC and CD appear to differ; (3) associations between different ethnic groups differ; (4) markers in the HLA might predict the course of disease and the development of complications, notably the extraintestinal manifestations of disease.

Update on the genetics of inflammatory bowel disease

There is a general consensus that interplay of genetic and environmental factors leads to an overactive mucosal immune response, which mediates the tissue damage in inflammatory bowel disease. Ethnic aggregation of inflammatory bowel disease (particularly, increased incidence and prevalence in the Ashkenazim), familial aggregation of inflammatory bowel disease, and greater concordance for inflammatory bowel disease in monozygotic twins than dizygotic twins are 3 lines of evidence for a central role of genetic factors in the pathogenesis. The genetics of inflammatory bowel disease cannot be explained by simple Mendelian genetics; it is characterized by incomplete penetrance, multiple susceptibility loci and genetic heterogeneity. Unraveling the complex genetics of inflammatory bowel disease is a daunting challenge, but the perseverance of inflammatory bowel disease gene hunters has produced commendable results in recent years. Since 1996, the field of inflammatory bowel disease genetics has progressed from publication of the first systematic genome searches for inflammatory bowel disease susceptibility loci to the identification of Crohn disease-associated genetic variants in CARD15/NOD2. Strategies for finding additional inflammatory bowel disease genes include taking advantage of the greater resolution and power of linkage disequilibrium mapping, mapping by admixture disequilibrium in African-American and Hispanic-American populations, stratifying genetic analyses by genotypes at known inflammatory bowel disease loci, and refining inflammatory bowel disease phenotypes to reduce genetic heterogeneity and simplify the search for additional inflammatory bowel disease genes.

The genetics of inflammatory bowel disease

The complex genetics of IBD is characterized by more than one susceptibility locus, genetic heterogeneity, incomplete penetrance, and probable gene-gene and gene-environment interactions. Functional candidate gene association studies during the past few decades have revealed only modest associations between IBD and genetic variants in the HLA genes and a limited number of other genes that are involved in immune regulation and the inflammatory response. Important advances in IBD genetics research have come about from systematic genome searches for IBD loci. The identification of Crohn's disease-associated NOD2 genetic variants that appear to alter the innate immune response to bacteria is a seminal finding that perhaps is the greatest advance toward understanding the pathogenesis of IBD in decades. The future discovery of other IBD genetic risk factors, facilitated by the completion of the human genome sequencing and annotation, may allow the development of better therapies, possibly including preventive therapies, for patients with Crohn's disease and ulcerative colitis.

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.

Analysis of genes within the HLA region affecting susceptibility to ulcerative colitis

To clarify the molecular relationship between HLA loci and ulcerative colitis (UC) in Japanese patients, we performed HLA-DP genotyping by the PCR-RFLP method and studied tumor necrosis factor beta-chain genetic polymorphism by Southern hybridization, in addition to conventional serologic typing. Significant increase was observed in Bw52, DPw9 (DPB1*0901), and DR2 (DRB1*1502) in Japanese patients with UC. Linkage analysis indicated that A24-Bw52-DR2-DPw9 alleles constitute a common haplotype in Japanese UC patients. Among the patients not carrying Bw52, B13 was significantly increased and B44 was relatively increased. These Bw52, B13, and B44 alleles share the unique amino acids, serine and aspartic acid at positions 67 and 77, respectively. These positions are in the second hypervariable region of the alpha 1-domain of the HLA-B13, B44, Bw52, and B49 antigens (B49 is quite rare in the Japanese population). The inflammatory region in UC patients was found to vary depending on their HLA-B alleles. These results suggest that the HLA-B locus itself plays an important role in the susceptibility to Japanese UC.

Serum tumor necrosis factor activity in inflammatory bowel disease

Serum tumor necrosis factor (TNF) levels in 33 patients with inflammatory bowel disease (IBD) were measured by using a sensitive enzyme immunoassay. Four of five Crohn's diseases (CD) and nine of twenty eight ulcerative colitis (UC) had elevated levels of serum TNF. In active CD or UC, a greater fraction of patients studied had significantly increased serum TNF levels (3/3 for CD and 8/11 for UC). Production of TNF by peripheral blood monocytes when stimulated by lipopolysaccharide was also increased in these patients and correlated with their serum TNF levels. These results suggest that TNF may have some pathoetiological meaning in IBD.

Inflammatory bowel disease in Japan: studies of epidemiology and etiopathogenesis

The epidemiologic features of inflammatory bowel disease in Japan are somewhat different from the western features. Many immunologic abnormalities are observed, but without primary evidence for etiology. There are some differences regarding epidemiologic and immunologic aspects between ulcerative colitis and Crohn's disease. Bacteriovirological studies have not shown specific pathogens, but suggest that the enteric bacteria flora is significantly involved in the pathogenesis.

Prevalence and incidence of inflammatory bowel disease in family members

To determine the risk of having or developing inflammatory bowel disease (IBD) in a family member of an IBD patient, a population of 245 IBD probands was randomly selected from the University of Chicago IBD Registry and their family history was elucidated by questionnaire and follow-up telephone call. One hundred seventy-nine (73%) probands responded to the questionnaire. There were no demographic distinctions between those eligible for the study, those who were complete responders, those who were nonresponders, and those with a positive family history of IBD. Fifty-four family members from 40 proband families (22%) had confirmed IBD. Prevalence of IBD in family members at the time of diagnosis of the proband was highest for parents (4.6%), siblings (2.6%), and children (1.9%). Grandparents, aunts and uncles, and first cousins had prevalence of IBD of less than 1%. Incident case frequency was determined by dividing the number of cases incident after the diagnosis of the proband by all those ever at risk. The incident case frequency was highest for siblings (1.9%), parents (1.0%), and children (1.0%). There was concordance noted for type of disease in the proband and the relative. No association could be discerned between the familial risk of IBD and gender, race, or religion of the proband. Despite a high occurrence rate of proband families with IBD, the specific risk to first, second, or third degree family members is low.

HLA antigens and myasthenia gravis in Japan

Recent studies have noted an increased association of the histocompatibility antigen HLA-B8 with myasthenia gravis in Caucasian patients. The HLA types of 63 Japanese patients with myasthenia were compared to those of 271 controls. The present study was designed to assess correlations between HLA antigens, sex, age at onset, the presence of autoantibodies and thymic morphology. HLA-B12 was increased Japanese patients, especially females with early age at onset, and in addition it was significantly correlated with thymic hyperplasia. HLA-B5 was frequently found in the patients with thymoma. Statistically the most frequent haplotype found in this disease was HLA-A10-HLA-B12.