Hunting Down Genetic Roles in IBD

Genome study showed two regions associated with ulcerative colitis found only in people of African-American descent.

Genetics plays a role in people's susceptibility to a number of diseases. And with new treatments being developed all the time, it is important to know those roles.

A new study of genetic risk factors for inflammatory bowel disease (IBD) found that people of African-American ancestry have two specific areas in the genes (loci) associated with ulcerative colitis.

IBD is an immune system disorder in which the immune system mistakenly attacks body tissues as if they were a dangerous invader. In inflammatory bowel diseases such as Crohn's disease and ulcerative colitis, the attack is centered on the intestines.

Previous research into IBD identified specific loci that made people more susceptible. In people of predominantly European ancestry, more than 200 loci have been identified, and in those of Asian ancestry at least 35 have been identified.

"Although most human gene mapping has been done in people of European background, inflammatory bowel disease is not race-specific," corresponding author Subra Kugathasan, MD, said in a press release. "Genome-wide studies lag behind in non-European populations, and African-Americans are the last group not to be studied specifically. As new therapies are developed it will be important to know the genotype of individuals we are treating."

Dr. Kugathasan is a professor of pediatrics at Emory University School of Medicine.

Researchers from 35 institutions in the US and Canada participated in the study under the direction of Dr. Kugathasan, Steven Brant, MD and Dermot McGovern, MD, PhD.

Dr. Brant, who is the study’s first author, is the director of the Johns Hopkins Meyerhoff Inflammatory Bowel Disease Center. Dr. McGovern is the director of the McGovern Laboratory at Cedars Sinai.

"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," Dr. Brant said in the press release.

This is the first major, in-depth analysis of genetic risk factors for inflammatory bowel disease in African-Americans.

The researchers evaluated genetic patterns in more than 1,500 African-Americans with IBD. In the study, 1,088 participants had Crohn’s disease and 361 had ulcerative colitis. They compared this data to 1,797 African-Americans without IBD.

The researchers found that three genetic variations associated with Crohn's disease in Caucasians are also important risk factors for African-Americans. However, they found some strong evidence for other gene variations that are present only in African-Americans.

They also found that the second-strongest pathway for IBD in whites, known as the Leishmania infection pathway, was not found in African-Americans with IBD.

Finally, the research showed that African trypanosomiasis infection—which causes African sleeping sickness—was a significant and unique pathway for ulcerative colitis in African-Americans.

The study was published in the September issue of Gastroenterology.

Information on study funding and conflict of interest was not available.