The different phenotypes in these mouse lines could be attributed to the potential low expression levels of RIG-I truncation proteins generated by the targeted disruption of the RIG-I gene at different structural locations (the RIG-I −/− mouse displaying the colitis phenotype could possibly express truncated RIG-I with one of the 2 CARD domains, while the embryonic lethal RIG-I −/− knockout mouse would only express a truncated domain containing both CARDs). This evidence concerns the gene RIGI and colitis.