Toward A Better Understanding of IBD

A new study has uncovered how genetics affect exactly where gut inflammation is located in inflammatory bowel disease patients. The discovery has implication for the diagnosis and treatment of IBD patients.

The study, from an international team headed by researchers at the nonprofit Wellcome Institute in the UK, drew on genetic and clinical data from more than 30,000 patients. The research was published in the British medical journal The Lancet.

The largest study of its kind, this research uncovers a continuum of inflammatory bowel diseases, and shows that genetic information could be used to reveal misdiagnoses. The research demonstrates the importance of worldwide clinical collaborations and using information about symptoms to better understand the genetics of complex diseases.

Inflammatory bowel disease (IBD) is an umbrella term for two related immune diseases: Crohn’s disease, which can affect any part of the digestive tract, and ulcerative colitis, which affects only the colon, or large bowel. However this research shows that it’s oversimplifying to see IBD as just two disorders.

Genetic data indicate that IBD is a complex continuum of disorders heavily influenced by the site of inflammation. While disease location in Crohn’s has long been recognized as important, the new observation that large bowel Crohn’s disease is half-way between ulcerative colitis and small bowel Crohn’s disease on this genetic spectrum suggests that important aspects of disease biology are associated with location.

Previous research on IBD had shown that the genes involved are largely shared between Crohn’s disease and ulcerative colitis, with only a small number of genes specific to each disease. The new study married this genetic information with clinical symptoms to try to understand the biology behind the disease.

Diagnosis is based on clinical evidence and symptoms, with different medication and surgery indicated for Crohn’s and ulcerative colitis. For some patients, clinicians find it difficult to diagnose which of these two diseases is presented. The genetic continuum between the two ends of the spectrum explains some of this difficulty in diagnosis and patients could benefit from re-classification.

According to a news release from the Wellcome Trust, at extreme ends of the continuum, genetic markers may have some diagnostic usefulness. In the study, clinicians reassessed the records of outlier patients, who had genetic factors that strongly pointed to Crohn’s disease but had been originally diagnosed with ulcerative colitis, or vice-versa. They found that doctors had raised doubts about the diagnosis three times more often than for randomly chosen patients.

To treat complex diseases, physicians need to understand the underlying biology. Genetic information could be used to inform treatment guidelines, or which patients to include in a clinical trial to obtain the clearest results. It is possible that certain trials may be appropriate for colonic Crohn’s disease and ulcerative colitis patients. Genetics could also be used as another piece of evidence to catch rare mistakes in diagnosis, which could prevent unnecessary surgery.

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