An Intergenic Variant rs9268877 Between HLA-DRA and HLA-DRB Contributes to the Clinical Course and Long-term Outcome of Ulcerative Colitis.

BACKGROUND AND AIMS:The genetic contribution to the prognosis of ulcerative colitis [UC] is poorly understood, and most currently known susceptibility loci are not associated with prognosis. To identify genetic variants influencing the prognosis of UC, we performed an Immunochip-based study using an extreme phenotype approach. METHODS:Based on the finding that the only association, Pdiscovery-meta <1 × 10-4, was located in the human leukocyte antigen [HLA], we focused our analyses on the HLA region. We performed the analysis using HLA imputation data from three independent discovery cohorts of 607 UC patients [243 poor-prognosis and 364 good-prognosis], followed by replication in 274 UC patients [145 poor-prognosis and 129 good-prognosis]. RESULTS:We found that rs9268877, located between HLA-DRA and HLA-DRB, was associated with poor-prognosis of UC at genome-wide significance (odds ratio [ORdiscovery] = 1.82; ORreplication = 1.55; ORcombined-meta = 1.72, pcombined-meta = 1.04 × 10-8), with effect size [OR] increasing incrementally according to worsening of prognosis in each of the three independent discovery cohorts and the replication cohort. However, rs9268877 showed no association with UC susceptibility [ORcombined-meta = 1.07, pcombined-meta = 0.135]; rs9268877 influenced 30-year clinical outcomes, and the presence of the rs9268877 risk allele had a sensitivity of 80.0% and specificity of 38.1% for colectomy. CONCLUSIONS:Our results provide new insights into prognosis-associated genetic variation in UC, which appears to be distinct from the genetic contribution to disease susceptibility. These findings could be useful in identifying poor-prognosis patients who might benefit from early aggressive therapy.

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