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Same, but different? Genetic analysis of five immune mediated diseases reveals molecular taxonomy of chronic inflammation

A newly published genetic analysis sheds new light on the high comorbidity between primary sclerosing cholangitis (PSC) and inflammatory bowel disease. Findings are consistent with a hypothesis in which the bowel disease in patients with PSC is a unique disease that shares some genetic factors with other forms of inflammatory bowel disease (ulcerative colitis and Crohn’s disease) but is distinct from “classical” inflammatory bowel disease phenotypes on important instances.

The frequent occurrence of diseases of the liver, skin or joints in patients with inflammatory bowel disease has previously led to the hypothesis that these conditions were somehow caused by the bowel disease. However, the findings in this study strongly suggest that this is not the case. Although some genetic overlap was detected, the results show that it is possible to distinguish distinct disease entities by a molecular taxonomy determined by the genetic findings.

The study, which was published in Nature Genetics in early online format on March 14th, is the largest systematic cross-disease genetic study for chronic immune-mediated diseases thus far, including the five diseases ankylosing spondylitis (Bechterew’s disease), Crohn’s disease, ulcerative colitis, psoriasis and PSC. Researchers from four large disease consortia, encompassing hundreds of researchers from 26 countries, joined forces to combine data from studies of their respective diseases, amounting to 52,262 patients and 34,213 healthy controls. The analysis enabled the researchers to delineate the genetic overlap between the conditions, as well as describe the molecular abnormities that were specific to each disease. In all, the analysis delineated 244 risk genes, describing the genetic susceptibility involving in chronic inflammation at an unprecedented level. .

“This study is important because it creates a platform for understanding the molecular make-up of each disease, in the future enabling more specified treatment of chronic inflammatory disease. That there is some genetic overlap means there may still be important opportunities for drug repurposing”, says Tom Hemming Karlsen, coordinator of one of the participating consortia, the International PSC Study Group (www.ipscsg.org), and professor at the University of Oslo.