Updates & Features

1. Early life influencers

i) Genetics

Two studies have reported higher concordance rates for diagnosed functional bowel disorders among monozygotic twins, suggesting a genetic contribution to IBS.^7,8 However, Levy et al. noted that among dizygotic twins, parent–child concordance was greater than concordance between the twins.⁸ As a parent and child share a similar number of genes to a pair of dizygotic twins, this strongly suggests that parent–child interactions are more important than genetic influences. Gene hunt efforts, so far, have explored several potential candidate genes and shown association between polymorphic gene loci and different IBS phenotypes. While studies so far have been less than emphatic in their results due to small sample sizes, varying criteria used to diagnose IBS, heterogeneity of methods used and ethnic differences of the participants tested, there is convincing evidence that a proportion of IBS diagnoses are due to additive genetic effects. As an alternative to current gene specific candidate driven approach, larger and non-candidate gene driven studies in the form of genome-wide association study (GWAS) are needed to understand this common and complex disorder.⁹

ii) Environmental factors

A large Norwegian population-based twin study (of 12,700 twins) assessed the influence of nutrition in foetal life on the development of IBS, using birth weight as an indicator.¹⁰ The twins with a birth weight below 2,500 g were significantly more likely to develop IBS, and IBS was significantly associated with anxiety and depression.

Parental reinforcement of illness behavior and children modelling their parents’ behavior are likely to contribute to the development of IBS. Children of IBS patients make more healthcare visits,¹¹ complain of more gastrointestinal and non-gastrointestinal symptoms, and have more school absences.¹²

The role of abuse, especially when this occurs during childhood, is still unclear in IBS. Nevertheless, abused individuals express higher level of psychological distress ¹³ and higher level of somatisation.¹⁴ In a recent study, an association has been found between psychological states and different readouts of visceral sensitivity in IBS, which are mediated through somatisation. Based on these findings, the psychobiological processes underlying these associations are likely to include central sensitisation/pain amplification processes driven by dysregulations in emotional arousal circuitry.¹⁵

2. During life psychosocial factors

i) Stressors

The most recent etiopathological model for IBS combines the classical observation of high levels of anxiety in IBS patients and the demographic similarity between patients with IBS and other functional disorders (such as fibromyalgia and chronic fatigue syndrome). Altered central stress circuits, should be triggered by external stressors, in predisposed individuals resulting in the development of gut and/or extraintestinal symptoms. Already at the end of the 80s, Creed showed that the most frequent events reported by patients with functional abdominal pain (including IBS patients) during 38 weeks prior to onset of symptoms, were a major disruption of close relationships, a marital separation, a family member leaving home, or break-up of a serious romantic relationship.¹⁶

ii) Personality traits

The majority of studies on personality traits and IBS highlight the idea that IBS patients have higher levels of neuroticism, conscientiousness and alexithymia, both when compared with the general population¹⁷ and with patients suffering from inflammatory bowel diseases.¹⁸ Most patients with IBS believe that their gut symptoms indicate a serious illness or even cancer. Patients with IBS have high scores on bodily preoccupation, hypochondriacal beliefs and disease phobia.¹⁹ Also, these patients adopt different coping strategies when compared to patients with organic diseases or healthy controls. Patients with IBS and other functional gastrointestinal diseases, do not use positive reappraisal as often as patients with organic disorders, and have a high emotional-oriented coping style.^20,21

iii) Psychiatric comorbidities

The most frequent psychiatric diagnosis in IBS is mood disorders (e.g. major depression and dysthymic disorder), anxiety disorders and somatoform disorders. Depression is the most common psychiatric diagnosis in IBS patients.^22,23 Patients with IBS have higher scores of depression than healthy controls,^24,25 but lower than the psychiatric population.²⁴ Depressive disorders are more common in clinic patients with IBS compared to healthy controls.²³ However, although the prevalence of comorbid depression is similar between IBS and patients with similar symptoms and organic GI diseases, IBS patients had more severe comorbid depressive and anxiety symptoms compared to IBD.²⁶ Anxiety and anxiety disorders, such as panic disorder (PD), generalised anxiety disorder (GAD) and post-traumatic stress disorder (PTSD) are also often observed in IBS patients. Anxiety tends to precede IBS onset, particularly if diarrhoea predominates. A study has reported that 12% of IBS patients have PD, 14% GAD and 29% depressive disorder.²² PTSD represents an independent risk factor for IBS.²⁷ Somatisation has been found to be a risk factor for comorbid IBS in patients with other functional GI disorders and an independent risk factor to develop IBS in subjects previously free of it.^28,29

The University of Maastricht is developing a disease-targeted patient-reported outcome measure (PROM) suitable for real-time assessment of abdominal pain and other gastrointestinal symptoms, and daily life factors that may influence IBS symptoms. A smartphone application has been specifically developed to implement this PROM and future research will comprise further, multicentre validation of this instrument with regard to the different languages and cross-cultural aspects. The experience sampling method (ESM) appears particularly suitable for the evaluation of individual symptom patterns over the course of a predefined period of time and the identification of specific triggers of gastrointestinal symptoms in daily life. It can thereby function in supporting diagnostic and therapeutic trajectories in clinical practice. Moreover, once the ESM is demonstrated to be a valid and reliable PRO instrument in this particular context, it can be implemented in clinical research to assess the effect of therapeutic interventions in IBS and to stratify IBS patients based on their symptoms.³⁰