Smoking is a strong environmental factor leading to adverse outcomes in Crohn's disease, but a more benign course in ulcerative colitis.
Several single nucleotide polymorphisms are associated with smoking quantity and behavior.
Dr Misselwitz and colleagues from Switzerland assessed whether smoking-associated single nucleotide polymorphisms interact with smoking to influence the clinical course of inflammatory bowel diseases.
Genetic and prospectively obtained clinical data from 1434 Swiss inflammatory bowel disease cohort patients were analyzed.
The team found that 6 single nucleotide polymorphisms were associated with smoking quantity and behavior were combined to form a risk score by adding the number of risk alleles.
We calculated multivariate models for smoking, risk of surgery, fistula, Crohn's disease location and ulcerative colitis disease extent.
|Patients with a risk score >7 had a significantly shorter time to first intestinal surgery|
|Alimentary Pharmacology & Therapeutics|
In Crohn's disease patients who smoke, the researchers found that the number of surgeries was associated with the genetic risk score.
This translates to a predicted 3.5-fold higher number of surgical procedures in smokers with 12 risk alleles than individuals with the lowest risk.
Patients with a risk score >7 had a significantly shorter time to first intestinal surgery.
The researchers found that the genetic risk score did not predict surgery in ulcerative colitis or occurrence of fistulae in Crohn's disease.
The team observed that single nucleotide polymorphism rs6265 was associated with ileal disease in Crohn's disease and proctitis in ulcerative colitis.
Dr Misselwitz's team comments, "Single nucleotide polymorphisms associated with smoking quantity is associated with an increased risk for surgery in Crohn's disease patients who smoke."
"Our data provide an example of genetics interacting with the environment to influence the disease course of inflammatory bowel disease."