The genetics of Crohn’s disease decoded
“We’re not searching blindly through the three billion letters of the genome”, explains Emilie Theâtre, a Giga Research researcher. “The sequences tested by the chip are either genes that have already been identified for their role in Crohn’s disease, or genetic sequences that produce proteins known for their role in the inflammatory process of the digestive system, or genes associated with other inflammatory diseases such as diabetes or psoriasis.” The study published in Nature confirms the genetic relationship of several inflammatory immune diseases: Crohn’s, ulcerative colitis, diabetes, rheumatoid arthritis, psoriasis, etc. In some rare cases, patients can develop two or three of these diseases at the same time. And epidemiological studies show that some families are more affected than others by these inflammatory immune diseases: an uncle has diabetes, a nephew has Crohn’s, a first cousin, develops psoriasis, a great-aunt had ulcerative colitis, etc. For instance, there is extensive genetic overlap between diabetes and Crohn’s disease. Out of the 39 genetic variants identified in diabetes, 20 of them can also be found in Crohn’s disease. In that case, how can it be that the majority of people only develop one of these inflammatory diseases? In reality, genetics only rarely explains a single disease. The medical destiny of identical twins (who have exactly the same genetic heritage) provides a good example. In the case of Crohn’s disease, for instance, it is common for only one of the twins to develop the disease. The person’s environment and history must also be taken into account.