Scientists Zoom In on Genetic Causes of Inflammatory Bowel Disease

Study by study, researchers are pushing ever closer toward identifying the gene variants to blame for inflammatory bowel disease (IBD). The latest and most promising findings were published in the journal Nature.

There are two forms of IBD: ulcerative colitis, which affects only the colon and is more common in women; and Crohn's disease, which can affect any part of the gastrointestinal tract and is slightly more common in men. Today, IBD affects between 1 and 1.3 million Americans, yet we understand very little about why it happens or why some groups of people are more susceptible than others.

It's possible and even likely, scientists say, that the root of the illness could lie in our genes. Previous studies have linked IBD to hundreds of different genetic variants, but that's as specific as they could get.

To take a closer look, researchers at three institutions collaborated to build a massive, high-resolution genetic map. They collected the genomes of 67,852 different people—18,967 with Crohn's disease, 14,628 with ulcerative colitis, and 34,257 healthy people for a control group—and combed through, looking for variants unique to the folks with IBD.

Like previous researchers, they found plenty. But the new map was so detailed that its creators could zoom in further and further down, checking how likely it was that any given variant could actually cause the disease. From hundreds, they narrowed it down to just 18 variants, and had at least 95 percent certainty that these were the ones responsible. Some of these gene variants were related to processing amino acids; some seemed to interfere with healthy molecule binding; and some were tied to the switching on and off of immune or gut cells.

"We need to be careful in deciding when we are sure we have the right variant," first author Hailiang Huang, of Massachusetts General Hospital and the Broad Institute, said in a statement. "This new technique helps us to pinpoint which genetic variants are implicated in IBD with greater confidence."

The authors say that isolating IBD-related gene variants will help develop new drugs, and could someday even aid in personalized medicine by helping doctors identify which existing drugs will be most effective for their patients.