No abstract

SUMMARY BackgroundAlthough thiopurines have a proven role in maintenance therapy for Crohn's disease, an alternative therapy is needed for patients intolerant or resistant to thiopurines.

The efficacy of thiopurines, including azathioprine (AZA) and 6-mercaptopurine (6MP), has been demonstrated for the treatment of inflammatory bowel disease (IBD). The most common and serious adverse event of treatment with thiopurines altered by doctors is leukopenia. Hair loss is also a serious event that could be a critical reason for patients to decline thiopurine treatment. Thiopurine-induced severe hair loss causes cosmetic problems, and it takes a long time to recover. In a recent study, NUDT15 R139C was strongly associated with thiopurine-induced leukopenia in Korean and Caucasian populations. In this study, we performed an association study to investigate and replicate the association of R139C with adverse events of thiopurines in Japanese patients. A total of 142 Japanese patients with IBD, with histories of thiopurine treatment, were examined. NUDT15 R139C was genotyped using a custom TaqMan genotyping assay. Adverse events including leukopenia were reviewed from medical records. The 6MP dose was adjusted to AZA equivalents by multiplying with 2 as a thiopurine dose. Five patients developed severe hair loss and all of them were risk homozygous (T/T) for R139C. No early severe hair loss was observed in patients with the C/T or C/C genotype (P=3.82 × 10(-16), odds ratio=212). The association of R139C with early (<8 weeks) leukopenia (white blood cells<3000 mm(-3)), which was previously reported in Korean patients, was replicated in our Japanese IBD cohort (P=1.92 × 10(-16), odds ratio=28.4). However, we could not confirm the association with late leukopenia in the Japanese subjects. Patients with the C/T genotype discontinued treatment or required thiopurine dose reduction significantly earlier than patients with the C/C genotype (P=1.45 × 10(-4)); however, on manipulating the doses, there was no significant difference in the thiopurine continuation rates between the groups. In the maintenance period, the frequencies of 6MP usage were higher, and the doses of thiopurines were significantly lower in patients with the C/T genotype than in those with the C/C genotype (0.574±0.316 mg kg(-1) per day vs 1.03±0.425 mg kg(-1) per day, P=6.21 × 10(-4)). NUDT R139C was significantly associated with early severe hair loss in Japanese patients with IBD. We also verified the previously reported association of R139C with early leukopenia in a different East Asian population. It is recommended that treatment with thiopurines should be avoided for patients with the T/T genotype. Low-dose 6MP (0.2-0.3 mg kg(-1) per day) could be used rather than AZA for the patients with C/T genotype to continue thiopurine treatments. However, late leukopenia and other several adverse events could not be completely predicted by R139C genotypes.

Ulcerative colitis is one of the principal forms of inflammatory bowel disease with complex manifestations. Although previous studies have indicated that there is a genetic contribution to the pathogenesis of ulcerative colitis, the genes influencing susceptibility to the disease have not been fully determined. To identify genetic factors conferring risk of ulcerative colitis, here we conducted a two-stage genome-wide association study and subsequent replication study using 1,384 Japanese individuals with ulcerative colitis and 3,057 control subjects. In addition to the expected strong association with the major histocompatibility complex (MHC) region, we identified three new susceptibility loci: the immunoglobulin receptor gene FCGR2A (rs1801274, P = 1.56 x 10(-12)), a locus on chromosome 13q12 (rs17085007, P = 6.64 x 10(-8)) and the glycoprotein gene SLC26A3 (rs2108225, P = 9.50 x 10(-8)). rs1801274 is a nonsynonymous SNP of FCGR2A that is reported to have a critical effect on receptor binding affinity for IgG and to be associated with other autoimmune diseases. Our findings provide insight into the molecular pathogenesis of ulcerative colitis.

Tumour necrosis factor-alpha (TNF) expression is increased in inflammatory bowel disease (IBD), and TNF maps to the IBD3 susceptibility locus. Transmission disequilibrium and case-control analyses, in two independent Caucasian cohorts, showed a novel association of the TNF(-857C) promoter polymorphism with IBD (overall P=0.001 in 587 IBD families). Further genetic associations of TNF(-857C) with IBD sub-phenotypes were seen for ulcerative colitis and for Crohn's disease, but only in patients not carrying common NOD2 mutations. The genetic data suggest a recessive model of inheritance, and we observed ex vivo lipopolysaccharide-stimulated whole-blood TNF production to be higher in healthy TNF(-857C) homozygotes. We show the transcription factor OCT1 binds TNF(-857T) but not TNF(-857C), and interacts in vitro and in vivo with the pro-inflammatory NF(-kappa)B transcription factor p65 subunit at an adjacent binding site. Detailed functional analyses of these interactions in gut macrophages, in addition to further genetic mapping of this gene-dense region, will be critical to understand the significance of the observed association of TNF(-857C) with IBD.