There is always a genetic component to the development of disease. Always. The dangerous thing about flaunting these correlations, however, is that it isn't always made clear to people what is meant by "genetic link", science writing in mainstream media being what it is.
Contrary to what the populace typically assumes, what is usually meant by "genetic link" is not an inherited DNA mutation causing a disorder. Most often, when scientistific media reports "genetic link" they are actually talking about mRNA. The critical difference here is that mRNA trascribes from DNA, making modifications as dictated by the dynamics of its cellular environment... such as an auto-immune disorder like Crohn's disease.
What I'm getting at here is that when you read about "genetic links" between genes and disease, keep in mind that they're talking about association, not cause.
Good. Now that we've cleared that up...
The Friedman et al PNAS article (Sept. 2009) found that in people who have Crohn's, a genetic marker for "low CD39 production" was significantly more common than in people who don't have any kind of IBD. Id est, a deficiency of CD39 mRNA is correlated with having Crohn's.
What I like about this study is that they also did the animals work, creating a knockout mouse model by silencing the expression of CD39. They found that eliminating the expression of CD39 in the mice made them more susceptible to Dextran sodium sulfate, a chemical that mimics IBD pathophysiology. It is very rare to see real-time translation between clinical and basic science studies, and I commend the authors for doing so. I suppose that's why they're on the cover of the September '09 volume.
What I don't like about this study is that it is not open access, so I will have to wait to go back to work on Monday to get some quotes from the actual paper...