In 1996, genetic linkage of inflammatory bowel disease (IBD) to chromosome 16 was established. The recently identified NOD2 gene is a possible candidate. This is because it is located in the region of linkage on chromosome 16q12, and activates nuclear factor (NF) kappa-B in response to bacterial lipopolysaccharides.
Stefan Schreiber and coworkers from Kiel University, Germany, sequenced the coding region of the NOD2 gene and genotyped an insertion polymorphism (alteration) in 512 individuals with IBD, from 309 German or British families. They also did this in 369 German trios (German patients with sporadic IBD and their unaffected parents), and 272 normal controls.
The researchers then tested for association with Crohn's disease and ulcerative colitis.
Family-based association analyses were consistently positive in 95 British and 99 German affected sibling pairs with Crohn's disease. The association was confirmed in the 304 German trios with Crohn's disease.
However, no association was seen in the 115 sibling pairs and 65 trios with ulcerative colitis.
|Enhanced risk of developing Crohn's disease:|
Heterozygous NOD2 mutation: 2.6 times
Homozygous mutation: 45 times
Heterozygous carriers of the mutation were estimated to be 2.6 times more likely to be at risk of disease. Homozygous carriers were 42 times more likely.
Stefan Schreiber comments 'Important future implications of gene discovery in IBD will include insights into the etiology of related diseases, including irritable bowel syndrome, a condition which affects about 30% of the adult population.'
'In addition, gene defects responsible for IBD may be useful to direct therapies and to predict the natural course of disease progression.'
In an accompanying Commentary, David van Heel and coworkers from the Wellcome Trust Centre for Human Genetics and Gastroenterology Unit, University of Oxford, England, comment, 'About a fifth of cases of Crohn's disease are attributable to NOD2 mutations. Other IBD genes must exist.'
'Nonetheless, this finding is an important proof of principle that positional cloning and the candidate-gene approach can be successfully applied to polygenic disorders.'