How do we know that there's a genetic component to IBD?
There have been a number of clues. One strong clue is that we have observed families that have more than one family member with the disease. In fact, having parents or a sibling with inflammatory bowel disease is the strongest risk factor for developing the disease. The risks are sometimes quoted as high as thirty times that of the (general) population if you have a sibling with IBD, and a risk that's possibly as high as 50% chance that you're going to get IBD if both your parents have it.
A second clue comes from the study of twins. It was found that identical twins, who are genetically identical, are far more likely to both have IBD than fraternal twins.
Third, there are certain populations or ethnic groups that have higher incidence of Crohn's disease than others. The Ashkenazi Jewish population is the most well-studied, and incidence of Crohn's disease is five times greater in this population than in non-Ashkenazi populations.
We do know that inflammatory bowel disease genetics is complex. But, there's no doubt that there's a genetic component to IBD. The question is how much of a genetic component. And it may be different for each person. For example, two people with the same genetic makeup may have different expressions of disease. Likewise, two people who have Crohn's disease may have a completely different genetic makeup.
