Genes and irritable bowel syndrome: is there a link?

Evolutionary medicine approaches to chronic disease: The case of irritable bowel syndrome

Irritable bowel syndrome (IBS), a gastrointestinal disease, is a global phenomenon correlated with industrialization. We propose that an evolutionary medicine approach is useful to understand this disease from an ultimate perspective and conducted a scoping literature review to synthesize the IBS literature within this framework. Our review suggests five potential evolutionary hypotheses for the cause of IBS, including (a) a dietary mismatch accompanying a nutritional transition, (b) an early hygienic life environment leading to the immune system and microbiotic changes, (c) an outcome of decreased physical activity, (d) a response to changes in environmental light-dark cycles, and (e) an artifact of an evolved fight or flight response. We find key limitations in the available data needed to understand early life, nutritional, and socioeconomic experiences that would allow us to understand evolutionarily relevant risk factors and identify a need for further empirical research to distinguish potential causes and test evolutionary hypotheses.

Genetic studies in irritable bowel syndrome-status quo

AIM

To evaluate the most common studied genetic polymorphisms that may have an etiological role in irritable bowel syndrome (IBS).

METHODS

The data base PubMed was searched for studies analyzing the association between gene polymorphisms and IBS. All original full papers, written in English, were retained for further analysis. The retrieved papers were further systematized according to those polymorphisms that have been detected in IBS.

RESULTS

Considering these criteria, our literature search found 12 polymorphisms, residing in 10 genes, which were reported to be consistently associated with IBS. The initial search identified 189 articles, out of which 48 potentially appropriate articles were reviewed. Of these 48 articles, 41 articles were included in the review. These articles were published between 2002 and 2016. Out of these 41 studies, 17 reported analysis of the serotonin transporter (SERT) gene (SLC6A4), eight on guanine nucleotide-binding protein subunit beta-3 (GNbeta3), six on the serotonin type 3 receptor genes (HTR3A), four on (HTR3E), three on (HTR2A), three the tumor necrosis factor superfamily member TL1A gene (TNFSF15), and ten on genetic polymorphisms with limited evidence.

CONCLUSION

Current evidence for the relation between genetic polymorphisms and IBS is limited owing to the fact that high-quality prospective studies and detailed phenotyping of patients suffering from IBS and matched controls were lacking in the past.

The possible role of gastrointestinal endocrine cells in the pathophysiology of irritable bowel syndrome

The etiology of irritable bowel syndrome (IBS) is unknown, but several factors appear to play a role in its pathophysiology, including abnormalities of the gastrointestinal endocrine cells. The present review illuminates the possible role of gastrointestinal hormones in the pathophysiology of IBS and the possibility of utilizing the current knowledge in treating the disease. Areas covered: Research into the intestinal endocrine cells and their possible role in the pathophysiology of IBS is discussed. Furthermore, the mechanisms underlying the abnormalities in the gastrointestinal endocrine cells in IBS patients are revealed. Expert commentary: The abnormalities observed in the gastrointestinal endocrine cells in IBS patients explains their visceral hypersensitivity, gastrointestinal dysmotility, and abnormal intestinal secretion, as well as the interchangeability of symptoms over time. Clarifying the role of the intestinal stem cells in the pathophysiology of IBS may lead to new treatment methods for IBS.

Irritable bowel syndrome: an integrated explanatory model for clinical practice

BACKGROUND

Although irritable bowel syndrome (IBS) is a symptom-based diagnosis, clinicians' management of and communication about the disorder is often hampered by an unclear conceptual understanding of the nature of the problem. We aimed to elucidate an integrated explanatory model (EM) for IBS from the existing literature for pragmatic use in the clinical setting.

METHODS

Systematic and exploratory literature searches were performed in PubMed to identify publications on IBS and EMs.

KEY RESULTS

The searches did not identify a single, integrated EM for IBS. However, three main hypotheses were elucidated that could provide components with which to develop an IBS EM: (i) altered peripheral regulation of gut function (including sensory and secretory mechanisms); (ii) altered brain-gut signaling (including visceral hypersensitivity); and (iii) psychological distress. Genetic polymorphisms and epigenetic changes may, to some degree, underlie the etiology and pathophysiology of IBS and could increase the susceptibility to developing the disorder. The three model components also fit into one integrated explanation for abdominal symptoms and changes in stool habit. Additionally, IBS may share a common pathophysiological mechanism with other associated functional syndromes.

CONCLUSIONS & INFERENCES

It was possible to elucidate an integrated, three-component EM as a basis for clinicians to conceptualize the nature of IBS, with the potential to contribute to better diagnosis and management, and dialog with sufferers.

Early-life stress selectively affects gastrointestinal but not behavioral responses in a genetic model of brain-gut axis dysfunction

BACKGROUND

Early-life stress and a genetic predisposition to display an anxiety- and depressive-like phenotype are associated with behavioral and gastrointestinal (GI) dysfunction. Animals exposed to early-life stress, and those genetically predisposed to display anxiety or depressive behaviors, have proven useful tools in which to study stress-related GI disorders, such as irritable bowel syndrome (IBS). IBS is a heterogeneous disorder, and likely a consequence of both genetic and environmental factors. However, the combined effects of early-life stress and a genetic predisposition to display anxiety- and depression-like behaviors on GI function have not been investigated.

METHODS

We assessed the effect of maternal separation (MS) on behavioral and GI responses in WKY animals relative to a normo-anxious reference strain.

KEY RESULTS

Both non-separated (NS) WKY and WKY-MS animals displayed anxiety-like responses in the open-field test and depressive-like behaviors in the forced swim test relative to Sprague-Dawley rats. However, MS had no further influence on anxiety- and depressive-like behaviors exhibited by this stress-prone rat strain. Similarly, corticosterone levels measured after the OFT were insensitive to MS in WKY animals. However, WKY-MS displayed significantly increased colonic visceral hypersensitivity, fecal output, and altered colonic cholinergic sensitivity.

CONCLUSIONS & INFERENCES

Our data suggest that early-life stress, on the background of a genetic predisposition to display an anxiety- and depressive-like phenotype, selectively influences GI function rather than stress-related behaviors. Thus, our findings highlight the importance of genetic predisposition on the outcome of early-life adversity on GI function.

Neuropeptide S receptor induces neuropeptide expression and associates with intermediate phenotypes of functional gastrointestinal disorders

BACKGROUND & AIMS

NPSR1, the receptor for neuropeptide S (NPS), is expressed by gastrointestinal (GI) enteroendocrine cells, and is involved in inflammation, anxiety, and nociception. NPSR1 polymorphisms are associated with asthma and inflammatory bowel disease. We aimed to determine whether NPS induces expression of GI neuropeptides; and to associate NPSR1 single nucleotide polymorphisms (SNPs) with symptom phenotype and GI functions in health and functional GI disorders (FGID).

METHODS

The effect of NPS on messenger RNA expression of neuropeptides was assessed using real-time polymerase chain reaction in NPSR1-tranfected HEK293 cells. Seventeen NPSR1 SNPs were successfully genotyped in 699 subjects from a regional cohort of 466 FGID patients and 233 healthy controls. Associations were sought using gender-adjusted regression analysis and false discovery rate correction.

RESULTS

NPS-NPSR1 signaling induced increased expression of cholecystokinin, vasoactive intestinal peptide, peptide YY, and somatostatin. There were no significant associations with phenotypes of FGID symptoms. There were several NPSR1 SNPs associated with individual motor or sensory functions; the associations of SNPs rs2609234, rs6972158, and rs1379928 with colonic transit rate remained significant after false discovery rate correction. The rs1379928 polymorphism was also associated with pain, gas, and urgency sensory ratings at 36 mm Hg distention, the level prespecified for formal testing. Associations with rectal sensory ratings were not significant after false discovery rate correction.

CONCLUSIONS

Expression of several neuropeptides is induced upon NPS-NPSR1 signaling; NPSR1 variants are associated with colonic transit in FGID. The role of the NPS system in FGID deserves further study.