Inflammatory bowel diseases represent a spectrum of disorders rather than distinct conditions, the results of a major genetic study suggest.

Researchers investigating genetic variation in patients with Crohn’s disease and ulcerative colitis found that many of the gene variants linked to these conditions are shared.

Their findings may prompt a rethink in the way inflammatory bowel diseases (IBD) are categorised and diagnosed, the researchers say.

International study

The team – which included researchers from the University’s Centre for Genomic & Experimental Medicine – analysed genetic information and clinical records from more than 30,000 people with IBD.

They found a few differences in genetic make-up to distinguish between patients with Crohn’s disease and ulcerative colitis. Subtle genetic differences were also associated with whereabouts in the bowel the disease occurred – whether in the small or large intestine.

Diagnosis

IBD is currently diagnosed based on symptoms reported by the patient and a series of tests.

Although the range of symptoms varies for each patient, diagnosis is only clinically categorised into either Crohn’s disease or ulcerative colitis.

Researchers say their findings suggest that IBD would be better classified into three distinct groups based on where the diseases manifests – small bowel (ileal) Crohn’s disease, large bowel (colonic) Crohn’s disease and ulcerative colitis.

Personalised treatments

In the majority of cases, genetic analysis may not be useful for confirming patients’ diagnoses. It may, however, help to identify which therapies are likely to work best for them.

Researchers will now study how patients respond to treatments over time, to try and work out the mechanisms underlying different forms of IBD.

While we can’t say yet what causes IBD, we know that there is a whole raft of genetic and environmental factors at work. In order to personalise treatments, we need to be open-minded about the clinical categories we have constructed by observing symptoms in isolation.

Dr Charlie LeesConsultant Gastroenterologist and Senior Lecturer, University of Edinburgh

Inflammatory bowel diseases

Crohn’s disease and ulcerative colitis affect around one in 200 people in the developed world. People with the conditions live with symptoms including abdominal pain, urgent diarrhoea, vomiting and profound tiredness.

Current therapies are limited to treating the symptoms rather than the cause of the conditions and many are associated with side effects. Major surgery is frequently required.

The study is published in The Lancet.