Towards an explanation for Crohn’s disease?

Twenty-five percent of Crohn’s disease patients have a mutation in what is called the NOD2 gene, but it is not precisely known how this mutation influences the disease. The latest study by Dr Marcel Behr, of the Research Institute of the McGill University Health Centre (MUHC) and McGill University, has provided new insight into how this might occur. The study is published in the Journal of Experimental Medicine.

When the NOD2 gene functions normally, it codes for a receptor that will recognize invading bacteria and then trigger the immune response. This study demonstrates that the NOD2 receptor preferentially recognises a peptide called N-glycolyl-MDP, which is only found in a specific family of bacteria called mycobacteria. When mycobacteria invade the human body, they cause an immediate and very strong immune response via the NOD2 receptor.

"Now that we have a better understanding of the normal role of NOD2, we think that a mutation in this gene prevents mycobacteria from being properly recognised by the immune system," explained Dr Behr. "If mycobacteria are not recognised, the body cannot effectively fight them off and then becomes persistently infected."

Researchers were already aware of the relationship between mycobacteria and Crohn’s disease, but they did not know whether the presence of bacteria was a cause or a consequence of the disease. This new discovery associates the predisposition for Crohn’s disease with both the NOD2 mutation and the presence of mycobacteria, but researchers must still determine the precise combination of these factors to understand how the disease develops.

More research is required to establish a complete explanation. From this, it is expected that new therapeutic approaches that fight the cause of Crohn’s disease may be developed.

(Source: McGill University Health Centre: Journal of Experimental Medicine: July 2009)