X Chromosome-wide Association Study Identifies a Susceptibility Locus for Inflammatory Bowel Disease in Koreans

Background and aims: Genome-wide association studies of inflammatory bowel disease identified > 200 susceptibility loci only in autosomes. This study aimed to identify inflammatory bowel disease susceptibility loci on the X chromosome.

Methods: We performed an X chromosome-wide association study in Korean patients with inflammatory bowel disease. We analysed X chromosome data from our recent genome-wide association studies, including 1505 cases [922 Crohn's disease and 583 ulcerative colitis] and 4041 controls during the discovery phase, followed by replication in additional 1989 cases [993 Crohn's disease, 996 ulcerative colitis] and 3491 controls. Sex-related differential effects of single nucleotide polymorphisms on disease were also evaluated.

Results: We confirmed a significant association of a previously reported inflammatory bowel disease susceptibility locus at chromosome Xq26.3 [CD40LG-ARHGEF6; odds ratio, 1.22; 95% confidence interval, 1.16-1.28; combined p = 3.79 × 10-15]. This locus accounted for 0.18% and 0.12% of genetic variance in Crohn's disease and ulcerative colitis, respectively, and increased the total autosomal chromosome genetic variance from 6.65% to 6.83% and from 5.47% to 5.59% for Crohn's disease and ulcerative colitis risk, respectively, in the Korean population. Sex-stratified analyses did not reveal sex-related differences in effect sizes.

Conclusions: We confirmed the association of rs2427870 at the CD40LG-ARHGEF6 locus with an inflammatory bowel disease through an X chromosome-wide association study in a Korean population. Our data suggest that the CD40LG-ARHGEF6 locus on the X chromosome might play a role in inflammatory bowel disease pathogenesis in the Korean population.