In this issue of Gut, Weersma et al (see page 388) report the results of their study on molecular prediction of disease risk and severity in a large Crohn’s disease cohort.1 This study, performed by the Dutch initiative on Crohn’s disease and colitis (ICC), assessed the risk for disease development and severity by combining information from five Crohn’s disease susceptibility genes. A total of 1684 patients with Crohn’s disease from seven university hospitals were included. The odds ratio for Crohn’s disease susceptibility progressively increased with increasing number of risk alleles and genotypes, a finding that is not unexpected and has also been shown for other common diseases, such as type 2 diabetes, breast cancer and atherosclerosis.2 3 Second, and probably more interesting, was the finding that patients with a more severe disease, patients needing surgery or patients in whom the age at onset of disease was below 40 years carried, on average, more risk alleles compared to patients not meeting these characteristics.

With the identification of several susceptibility genes through genome-wide association scanning, the research on molecular markers in common disorders has gained more attention and comes at a time where the introduction of biological therapies has opened the debate on which therapy to choose for a given patient.

There are several clinical situations where molecular markers are proposed, a first being prediction of disease. Identifying individuals at risk and hence preventing disease is an important strategy for reducing the overall burden of common complex disorders. However, most of the reported genes and risk alleles have a very low …