Hla-B genotype in Japanese patients with Crohn's disease

The HLA-B gene is one of the susceptibility genes for inflammatory bowel disease. Previous association studies of HLA-B showed several associated alleles and haplotypes of HLA-B in patients with ulcerative colitis, and among the associated alleles HLA-B*52 is well known to be strongly associated with ulcerative colitis in Japanese patients. However, there are no convincing reports about HLA-B including the B*52 allele in patients with Crohn's disease. The purpose of this study was to determine if HLA-B, especially the B*52 allele, confers susceptibility to Crohn's disease or determines the disease phenotype of Crohn's disease.

A total of 195 patients with Crohn's disease (49 ileitis, 106 ileocolitis, 34 colitis, 6 uncertain) and 185 healthy controls were studied in this case-controlled study. All patients and healthy controls were Japanese. Genotyping of the HLA-B gene was performed by a polymerase chain reaction, sequence-specific primer that can classify the gene into 23 allele groups. Allele frequencies were compared between patients with Crohn's disease and healthy controls with chi-squared test using a 2 x 2 contingency table. P value was corrected by the number of allele groups (n = 23) observed in the Japanese population or the number of clinical subgroups. Corrected P values of <0.05 were considered to be statistically significant.

Before the correction for multiple testing, B*4001 and B*44 were associated with patients with Crohn's disease, positively and negatively, respectively. However, after the correction there were no significant differences in any HLA-B alleles between patients with Crohn's disease and healthy controls. In the subgroup analysis according to clinical phenotypes (disease location, anal lesion, age at diagnosis, need for surgery), none of the HLA-B alleles except B*52 showed any disease phenotype-genotype associations. The allele frequency of B*52 in the colitis type (16.2 percent; corrected P = 0.011) was significantly higher than that in the combined group of the ileitis (7.1 percent) and ileocolitis (5.2 percent) types.

These results demonstrated that HLA-B did not confer overall susceptibility to Crohn's disease in Japan, but the B*52 allele may affect the location of the disease.