Irritable bowel syndrome (IBS) is a functional bowel disorder characterised by chronic or recurrent abdominal pain associated with either relief or exacerbation by defecation, or a change in bowel habit. IBS is one of the most widely recognised functional bowel disorders, with more than 10% of the global adult population reporting symptoms compatible with the condition in population-based surveys. A better understanding of the potential underlying mechanisms involved in the generation of symptoms is crucial for improving eff ectiveness of future treatments. IBS is divided into subgroups according to the predominant stool pattern because this categorisation defines treatment options and so, by definition, it is a heterogeneous disorder.
Underlying mechanisms that could lead to irritable bowel syndrome include genetic factors (most notably an identifi ed mutation of SCN5A); post-infectious changes, chronic infections and disturbances in the intestinal microbiota; low-grade mucosal infl ammation, immune activation, and altered intestinal permeability; disordered bile salt metabolism (in 10–20% of cases with diarrhoea); abnormalities in serotonin metabolism; and alterations in brain function, which could be primary or secondary factors.