Biomarkers are objectively measurable indicators of normal or pathological processes or pharmacological responses to a therapeutic intervention.1 Examples of biomarkers that unquestionably help physicians in their daily clinical practice include simple physiological indicators, like the assessment of blood pressure or heart rate, and more advanced markers, like anti-endomysial antibodies for celiac disease. The identification of reliable biomarkers represents a major step forward in the management of a disease because they can elucidate the aetiology, define the diagnosis, and predict the prognosis. Biomarkers may also speed up different phases of drug development and reduce disease-related costs. Thus, biomarkers are generating considerable interest in the pharmaceutical industry. A disease biomarker should be characterised by high sensitivity (ie, discriminate well between health and disease) and specificity (ie, be able to distinguish the disease from other pathological conditions). Biomarkers should also be reproducible, ideally non-invasive, and inexpensive to allow screening large numbers of patients in clinical or trial settings. For these reasons, biomarker discovery represents a significant challenge to basic and clinical researchers and has been a major initiative in the roadmaps of the European Medicines Agency (http://www.emea.europa.eu) and the U.S. Food and Drug Administration (http://www.fda.gov).

Abdominal pain, diarrhoea, constipation, bloating, nausea, and vomiting are common gastrointestinal complaints in the general population. Usually, patients seeking medical attention experience severe symptoms, have an impaired daily life, or worry that “it might be something serious”. Disappointingly, efforts to identify metabolic, biochemical, infectious, degenerative or neoplastic causes fail in a significant percentage of patients. This leads to a diagnosis of “functional bowel disorders”, among which, irritable bowel syndrome (IBS) is the most common. These diagnoses vanquish the patients’ expectations of finding a “cause” for their symptoms and generate frustration. Symptom-based criteria and Bristol stool score, in the absence of red flags, have been developed as …