ARTICLE: Genome-wide Association Study Identifies African-Specific Susceptibility Loci in African Americans with Inflammatory Bowel Disease

AUTHORS: Steven R. Brant, David T. Okou, Claire L. Simpson, David J. Cutler, Talin Haritunians, Jonathan P. Bradfield, Pankaj Chopra, Jarod Prince, Ferdouse Begum, Archana Kumar, Chengrui Huang, Suresh Venkateswaran, Lisa W. Datta, Zhi Wei, Kelly Thomas, Lisa J. Herrinton, Jan-Micheal A. Klapproth, Antonio J. Quiros, Jenifer Seminerio, Zhenqiu Liu, Jonathan S. Alexander, Robert N. Baldassano, Sharon Dudley-Brown, Raymond K. Cross, Themistocles Dassopoulos, Lee A. Denson, Tanvi A. Dhere, Gerald W. Dryden, John S. Hanson, Jason K. Hou, Sunny Z. Hussain, Jeffrey S. Hyams, Kim L. Isaacs, Howard Kader, Michael D. Kappelman, Jeffry Katz, Richard Kellermayer, Barbara S. Kirschner, John F. Kuemmerle, John H. Kwon, Mark Lazarev, Ellen Li, David Mack, Peter Mannon, Dedrick E. Moulton, Rodney D. Newberry, Bankole O. Osuntokun, Ashish S. Patel, Shehzad A. Saeed, Stephan R. Targan, John F. Valentine, Ming-Hsi Wang, Martin Zonca, John D. Rioux, Richard H. Duerr, Mark S. Silverberg, Judy H. Cho, Hakon Hakonarson, Michael E. Zwick, Dermot P.B. McGovern, Subra Kugathasan

JOURNAL: Gastroenterology. 2016 Sep 28. pii: S0016-5085(16)35127-7. doi: 10.1053/j.gastro.2016.09.032. [Epub ahead of print]

Abstract

BACKGROUND & AIMS: The inflammatory bowel diseases (IBD) ulcerative colitis (UC) and Crohn's disease (CD) cause significant morbidity and are increasing in prevalence among all populations, including African Americans. More than 200 susceptibility loci have been identified in populations of predominantly European ancestry, but few loci have been associated with IBD in other ethnicities.

METHODS: We performed 2 high-density, genome-wide scans comprising 2345 cases of African Americans with IBD (1646 with CD, 583 with UC, and 116 inflammatory bowel disease unclassified [IBD-U]) and 5002 individuals without IBD (controls, identified from the Health Retirement Study and Kaiser Permanente database). Single-nucleotide polymorphisms (SNPs) associated at P<5.0x10-8 in meta-analysis with a nominal evidence (P<.05) in each scan were considered to have genome-wide significance.

RESULTS: We detected SNPs at HLA-DRB1, and African-specific SNPs at ZNF649 and LSAMP, with associations of genome-wide significance for UC. We detected SNPs at USP25 with associations of genome-wide significance associations for IBD. No associations of genome-wide significance were detected for CD. In addition, 9 genes previously associated with IBD contained SNPs with significant evidence for replication (P<1.6x10-6): ADCY3, CXCR6, HLA-DRB1 to HLA-DQA1 (genome-wide significance on conditioning), IL12B, PTGER4, and TNC for IBD; IL23R, PTGER4, and SNX20 (in strong linkage disequilibrium with NOD2) for CD; and KCNQ2 (near TNFRSF6B) for UC. Several of these genes, such as TNC (near TNFSF15), CXCR6, and genes associated with IBD at the HLA locus, contained SNPs with unique association patterns with African-specific alleles.

CONCLUSIONS: We performed a genome-wide association study of African Americans with IBD and identified loci associated with CD and UC in only this population; we also replicated loci identified in European populations. The detection of variants associated with IBD risk in only people of African descent demonstrates the importance of studying the genetics of IBD and other complex diseases in populations beyond those of European ancestry.

For a link to the full article, click here: http://www.sciencedirect.com/science/article/pii/S0016508516351277

Link to abstract online: https://www.ncbi.nlm.nih.gov/pubmed/27693347

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