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Genetics of Inflammatory Bowel Diseases

Gastroenterology, In Press, Accepted Manuscript, Available online 7 August 2015, January 1970

Abstract

In this Review, we provide an update on genome-wide association studies (GWAS) in inflammatory bowel disease (IBD). In addition, we summarize progress in defining the functional consequences of associated alleles for coding and non-coding genetic variation. In the small minority of loci where major association signals correspond to non-synonymous variation, we summarize studies defining their functional effects and implications for therapeutic targeting. Importantly, the large majority of GWAS-associated loci involve non-coding variation, many of which modulate levels of gene expression. Recent expression quantitative trait loci (eQTL) studies have established that expression of the large majority of human genes is regulated by non-coding genetic variation. Significant advances in defining the epigenetic landscape have demonstrated that IBD GWAS signals are highly enriched within cell-specific active enhancer marks. Studies in European ancestry populations have dominated the landscape of IBD genetics studies, but increasingly, studies in Asian and African-American populations are being reported. Common variation accounts for only a modest fraction of the predicted heritability and the role of rare genetic variation of higher effects (i.e. odds ratios markedly deviating from one) is increasingly being identified through sequencing efforts. These sequencing studies have been particularly productive in very-early onset, more severe cases. A major challenge in IBD genetics will be harnessing the vast array of genetic discovery for clinical utility, through emerging precision medicine initiatives. We discuss the rapidly evolving area of direct to consumer genetic testing, as well as the current utility of clinical exome sequencing, especially in very early onset, severe IBD cases. We summarize recent progress in the pharmacogenetics of IBD with respect of partitioning patient responses to anti-TNF and thiopurine therapies. Highly collaborative studies across research centers and across subspecialties and disciplines will be required to fully realize the promise of genetic discovery in IBD.

Keywords: Crohn's disease, Ulcerative Colitis, Epigenetics, Autophagy.

Footnotes

1 F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute, Medical Genetics Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA

2 Department of Pediatrics and Human Genetics, Emory University School of Medicine, and Children’s Healthcare of Atlanta, Atlanta, GA

3 Departments of Genetics and Medicine, Division of Gastroenterology, Icahn School of Medicine at Mount Sinai, New York, NY

No conflict of interest.