Some new, some familiar genetic risk factors found for inflammatory bowel disease in African-Americans

African-Americans have a slightly lower risk than white Americans for inflammatory bowel disease (IBD), yet cases of IBD in African-Americans have been steadily increasing in recent years. Also, little is known about African-Americans’ molecular genetic susceptibility to IBD.

To that end, more than 50 researchers from various sites—including Johns Hopkins University School of Medicine in Baltimore MD, Emory University School of Medicine in Atlanta, GA, Cedars-Sinai Medical Center in Los Angeles, CA, and many other centers in the U.S. and Canada—have published the first major, in-depth analysis of genetic risk factors of inflammatory bowel disease in African-Americans. Their results were published online August 13, 2015 in Gastroenterology.

In this comprehensive study, the researchers evaluated 1,511 African-American patients with IBD—including 1,088 with Crohn’s disease and 361 with ulcerative colitis—from 35 IBD centers across North America. For comparison, they also evaluated 1,797 African-Americans who did not have IBD. The researchers used genetic mapping to determine whether African-Americans share the same 163 loci of IBD susceptibility that have already been found in whites. Researchers also wanted to identify any new associated loci in African-Americans.

“We also studied whether there are regions of the genome that cause or protect IBD risk in African-Americans that arise from either their West African or European genetic ancestries,” said Steven Brant, MD, director of the Johns Hopkins Meyerhoff Inflammatory Bowel Disease Center and corresponding author of the study.

The researchers found that African-Americans have the same gene variants as whites for the most highly associated regions for Crohn’s disease: NOD2, IL23R, and 5p13.1.

The study also revealed that in African-Americans, as in whites and Asians, the dominant region for ulcerative colitis genetic risk is in the human leukocyte antigen (HLA) region. However, the specific variant associated with African-Americans in this region is the same as the variant most highly associated with Japanese and Korean ulcerative colitis, and to a lesser degree ulcerative colitis in Europeans. It also is the same major risk variant in HLA for lupus in African-Americans, whose lupus risk is 4 times greater than white Americans.

“The hope for genetic advances is that we will be able to develop new therapies and more personalized approaches to managing these chronic and potentially debilitating diseases,” said co-senior author Dermot McGovern, MD, PhD, Director of Translational Medicine for the Inflammatory Bowel Disease Center at Cedars-Sinai Medical Center. “These benefits should be available to all sections of society. This study is important, as it extends these possible advances to the African-American population, who may be at risk of more severe IBD.”