Van gen naar ziekte; 'frame shift'-mutatie in het CARD15-gen en de ziekte van Crohn

A pericentromeric region on chromosome 16 (IBD1 locus) has been linked with Crohn's disease (CD). Very recently, three genetic variants in the CARD15 gene within the IBD1 locus have been identified which were highly associated with CD. Carriage increases the relative risk of developing CD. One specific mutation (302oinsC) leads to a stop codon and truncation of the C-terminal tandem leucinerich repeats (LRR) of the CARD15 protein. Of all patients with Crohn's disease, 11-19% are heterozygous and 3-7% homozygous for this frameshift mutation. The CARD15 gene is expressed in monocytes. The LRR-domain is thought to be involved in the binding of bacterial lipopolysaccharide and subsequent activation of nuclear factor kappa-B (NFκB). NFκB plays a central role in the regulation of the expression of other genes involved in the inflammatory response. In vitro, embryonic kidney cells transfected with the CARD15 302oinsC mutant showed a reduced activity of NFκB after exposure to lipopolysaccharide compared to cells transfected with the wildtype CARD15 gene. How the reduced response to lipopolysaccharide contributes to CD is not yet clear.