Association Between SLC6A4 Serotonin Transporter Gene Lainked Polymorphic Region and ADRA2A -1291C>G and Irritable Bowel Syndrome in Korea

Identifying Novel Subtypes of Functional Gastrointestinal Disorder by Analyzing Nonlinear Structure in Integrative Biopsychosocial Questionnaire Data

Background/Objectives: Given the limited success in treating functional gastrointestinal disorders (FGIDs) through conventional methods, there is a pressing need for tailored treatments that account for the heterogeneity and biopsychosocial factors associated with FGIDs. Here, we considered the potential of novel subtypes of FGIDs based on biopsychosocial information. Methods: We collected data from 198 FGID patients utilizing an integrative approach that included the traditional Korean medicine diagnosis questionnaire for digestive symptoms (KM), as well as the 36-item Short Form Health Survey (SF-36), alongside the conventional Rome-criteria-based Korean Bowel Disease Questionnaire (K-BDQ). Multivariate analyses were conducted to assess whether KM or SF-36 provided additional information beyond the K-BDQ and its statistical relevance to symptom severity. Questions related to symptom severity were selected using an extremely randomized trees (ERT) regressor to develop an integrative questionnaire. For the identification of novel subtypes, Uniform Manifold Approximation and Projection and spectral clustering were used for nonlinear dimensionality reduction and clustering, respectively. The validity of the clusters was assessed using certain metrics, such as trustworthiness, silhouette coefficient, and accordance rate. An ERT classifier was employed to further validate the clustered result. Results: The multivariate analyses revealed that SF-36 and KM supplemented the psychosocial aspects lacking in K-BDQ. Through the application of nonlinear clustering using the integrative questionnaire data, four subtypes of FGID were identified: mild, severe, mind-symptom predominance, and body-symptom predominance. Conclusions: The identification of these subtypes offers a framework for personalized treatment strategies, thus potentially enhancing therapeutic outcomes by tailoring interventions to the unique biopsychosocial profiles of FGID patients.

Association of serotonin transporter promoter polymorphism (5-HTTLPR) with orocecal transit time in irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a multifactorial disorder with altered intestinal motility, secretion, and sensation. Serotonin (5-HT) stimulates gut motility and alters serotonin signaling that may lead to both intestinal and extraintestinal symptoms in IBS.

AIM

The aim of this study was to examine the association of serotonin transporter gene promoter polymorphism (5-HTTLPR) in IBS with orocecal transit time (OCTT) measured by lactulose hydrogen breath test.

METHOD

This prospective case-control study included 151 IBS patients (mean±SD 37.4±11.6 years, median 36, range 19-68). Ninety-two patients were diarrhea-predominant IBS (D-IBS), 44 constipation-predominant IBS (C-IBS), 15 alternating diarrhea and constipation IBS (M-IBS), and 100 healthy controls (mean±SD 37.2±11.4 years, median 36, range 20-64 years). 5-HTTLPR gene polymorphism was studied by polymerase chain reaction-based method. 5-HT levels were measured by enzyme-linked immunosorbent assay (ELISA). Orocecal transit time (OCTT) was measured by a non-invasive lactulose hydrogen breath test. OCTT was also compared with respect to 5-HTTLPR genotypes in different IBS phenotypes.

RESULTS

Serum serotonin levels were significantly higher in overall IBS patients (152±77 ng/mL, p<0.001), D-IBS (184±76 ng/mL, p<0.001), compared to healthy controls (129±56 ng/mL). There was no difference in 5-HT levels between C-IBS (124±53 ng/mL) and controls. In the case of M-IBS, 5-HT levels were (88±49 ng/mL p<0.05) significantly lower than that of controls. OCTT was significantly shorter in D-IBS patients (95±36 min) as compared to controls (112±41 min). In contrast, C-IBS showed significantly prolonged OCTT (136±54 min). There was a significant difference in OCTT between D-IBS and C-IBS patients (p<0.001). There was no significant association found between OCTT and 5-HTTLPR.

CONCLUSIONS

Serum serotonin concentrations were increased in D-IBS compared to controls and C-IBS. OCTT was shorter in D-IBS and delayed in C-IBS patients. There was no association of 5-HTLPR polymorphism with OCTT.

Engineered 5-HT producing gut probiotic improves gastrointestinal motility and behavior disorder

Slow transit constipation is an intractable constipation with unknown aetiology and uncertain pathogenesis. The gut microbiota maintains a symbiotic relationship with the host and has an impact on host metabolism. Previous studies have reported that some gut microbes have the ability to produce 5-hydroxytryptamine (5-HT), an important neurotransmitter. However, there are scarce data exploiting the effects of gut microbiota-derived 5-HT in constipation-related disease. We genetically engineered the probiotic Escherichia coli Nissle 1917 (EcN-5-HT) for synthesizing 5-HT in situ. The ability of EcN-5-HT to secrete 5-HT in vitro and in vivo was confirmed. Then, we examined the effects of EcN-5-HT on intestinal motility in a loperamide-induced constipation mouse model. After two weeks of EcN-5-HT oral gavage, the constipation-related symptoms were relieved and gastrointestinal motility were enhanced. Meanwhile, administration of EcN-5-HT alleviated the constipation related depressive-like behaviors. We also observed improved microbiota composition during EcN-5-HT treatment. This work suggests that gut microbiota-derived 5-HT might promise a potential therapeutic strategy for constipation and related behavioral disorders.

Sex and Gender Differences in Overlap Syndrome of Functional Gastrointestinal Disorder and Effect of Genetic Polymorphisms in South Korea: A Long-term Follow-up Study

BACKGROUND/AIMS

Overlap functional gastrointestinal disorder (FGID) is associated with more severe gastrointestinal symptoms and lower quality of life. The aim of this study is to evaluate clinical features of non-erosive reflux disease (NERD), functional dyspepsia, irritable bowel syndrome, their overlap in terms of sex and gender, and to assess the risk factors, including genetic polymorphisms.

METHODS

A total of 494 FGIDs and 239 controls were prospectively enrolled between 2004 and 2020. FGIDs were diagnosed based on the Rome III criteria and symptoms were evaluated using a questionnaire. Follow-up questionnaires were conducted to determine the change of symptoms during the 75.8-month mean observation period. Risk factors including genetic polymorphisms in neurotransmitter receptor (SLC6A4 5-HTTLPR, GNB3, ADRA2A, CCKAR, and TRPV1) and cytokine (TNFA and IL10) genes.

RESULTS

NERD was more prevalent in men, and functional dyspepsia in women. Overlap FGIDs (n = 239) were more prevalent than nonoverlap FGIDs (n = 255) in women (P = 0.019). Anxiety and depression scores were higher in the overlaps (P = 0.012 and P < 0.001, respectively). Symptoms were more frequent and severe in the overlap FGIDs than in the non-overlaps (P < 0.001). During followup, symptoms progressed more frequently in the overlap FGIDs, especially in patients with the L/S genotype of SLC6A4 5-HTTLPR and anxiety/depression.

CONCLUSIONS

Overlap FGID patients need attention given their association with anxiety/depression and more severe symptoms, especially in women. Genetic polymorphisms also may be associated with certain symptoms of overlap FGIDs.

Sex and Gender Differences in Overlap Syndrome of Functional Gastrointestinal Disorder and Effect of Genetic Polymorphisms in South Korea: A Long-term Follow-up Study

Background/Aims

Overlap functional gastrointestinal disorder (FGID) is associated with more severe gastrointestinal symptoms and lower quality of life. The aim of this study is to evaluate clinical features of non-erosive reflux disease (NERD), functional dyspepsia, irritable bowel syndrome, their overlap in terms of sex and gender, and to assess the risk factors, including genetic polymorphisms.

Methods

A total of 494 FGIDs and 239 controls were prospectively enrolled between 2004 and 2020. FGIDs were diagnosed based on the Rome III criteria and symptoms were evaluated using a questionnaire. Follow-up questionnaires were conducted to determine the change of symptoms during the 75.8-month mean observation period. Risk factors including genetic polymorphisms in neurotransmitter receptor (SLC6A4 5-HTTLPR, GNB3, ADRA2A, CCKAR, and TRPV1) and cytokine (TNFA and IL10) genes.

Results

NERD was more prevalent in men, and functional dyspepsia in women. Overlap FGIDs (n = 239) were more prevalent than non-overlap FGIDs (n = 255) in women (P = 0.019). Anxiety and depression scores were higher in the overlaps (P = 0.012 and P < 0.001, respectively). Symptoms were more frequent and severe in the overlap FGIDs than in the non-overlaps (P < 0.001). During follow-up, symptoms progressed more frequently in the overlap FGIDs, especially in patients with the L/S genotype of SLC6A4 5-HTTLPR and anxiety/depression.

Conclusions

Overlap FGID patients need attention given their association with anxiety/depression and more severe symptoms, especially in women. Genetic polymorphisms also may be associated with certain symptoms of overlap FGIDs.

Compositional and Functional Changes in the Gut Microbiota in Irritable Bowel Syndrome Patients

Background/Aims

This study aimed to characterize the changes in the gut microbiota of irritable bowel syndrome (IBS) patients and to investigate the consequent alterations in bacterial functions.

Methods

We performed 16S rRNA metagenomic sequencing and a phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analyses using fecal samples from control (n=12) and diarrhea-dominant IBS patients (n=7).

Results

The samples were clustered by the principal coordinates analysis depending on the presence of IBS (p=0.003). In the IBS patients, the abundances of Acidaminococcaceae, Sutterellaceae, and Desulfovibrionaceae were significantly increased, while those of Enterococcaceae, Leuconostocaceae, Clostridiaceae, Peptostreptococcaceae, and Lachnospiraceae were significantly decreased. The PICRUSt results indicated that two orthologues involved in secondary bile acid biosynthesis were significantly decreased in IBS patients. Modules involved in multidrug resistance, lipopolysaccharide biosynthesis, the reductive citrate cycle, and the citrate cycle were significantly increased in the IBS patients. In contrast, modules involved in cationic antimicrobial peptide resistance, and some transport systems were more abundant in controls than in IBS patients.

Conclusions

Changes in the gut microbiota composition in IBS patients lead to alterations in bacterial functions, such as bile acid transformation and the induction of inflammation, which is a known pathophysiological mechanism of IBS.

Ethnic differences in genetic polymorphism associated with irritable bowel syndrome

Genetic polymorphism is associated with irritable bowel syndrome (IBS) in terms of susceptibility and clinical manifestations. Previous studies have shown that genetic polymorphism might play a key role in the onset and progression of IBS by modulating components of its pathogenesis such as the gut-brain axis, gastrointestinal motility, inflammatory activity, and immune status. Although underlying pathophysiological mechanisms have not been fully clarified, the potential ethnic differences that are present in worldwide genetic studies of IBS deserve attention. This review surveyed numerous studies focusing on IBS-associated single nucleotide polymorphisms, and investigated the ethnic disparities revealed by them. The results demonstrate the need for more attention on ethnic factors in IBS-related genetic studies. Taking ethnic backgrounds into accounts and placing emphasis on disparities potentially ascribed to ethnicity could help lay a solid and generalized foundation for transcultural, multi-ethnic, or secondary analyses in IBS, for example, a meta-analysis. Broader genetic studies considering ethnic factors are greatly needed to obtain a better understanding of the pathophysiological mechanisms of IBS and to improve the prevention, intervention, and treatment of this disease.

Expression of Neurotrophic Factors, Tight Junction Proteins, and Cytokines According to the Irritable Bowel Syndrome Subtype and Sex

Background/Aims

Emerging evidence shows that the mechanism of irritable bowel syndrome (IBS) is associated with neurotrophic factors and tight junction proteins (TJPs). It is known that there are sex differences in the pathophysiology of IBS. The aim of the present study is to determine expression levels of neurotrophic factors, TJPs, and cytokines according to IBS subtype and sex.

Methods

From 59 IBS (33 IBS-constipation, 21 IBS-diarrhea, and 5 IBS-mixed) and 36 control patients, colonic mucosa mRNA expression levels of transient receptor potential vanilloid-1 (TRPV1), nerve growth factor (NGF), glial cell-derived neurotrophic factor (GDNF), and various TJPs were assessed by real-time polymerase chain reaction. Western blot was performed to determine levels of zonular occludens-1 (ZO-1). Serum levels of cytokines were measured by enzyme-linked immunosorbent assay.

Results

TRPV1, GDNF, and NGF mRNA levels were significantly increased in those with IBS-constipation compared to those in controls (all P < 0.05). However, they showed no significant difference between those with IBS-diarrhea and controls. Expression level of TRPV1 correlated with that of GDNF (r = 0.741, P < 0.001) and NGF (r = 0.935, P < 0.001). ZO-1 RNA expression levels were lower (P = 0.021) in female IBS-diarrhea than those in controls, although they showed no significant differences between male IBS-diarrhea and controls. Serum IL-1β levels in female IBS were significantly higher than those of male IBS, especially in IBS-constipation (P < 0.001).

Conclusions

Our results suggest that neurotrophic factors and IL-1β are closely related to IBS-constipation and that decrease of ZO-1 is an important factor in female with IBS-diarrhea.

Functional polymorphism of the serotonin reuptake transporter SLC6A4 gene in various clinical variants of irritable bowel syndrome

Rationale:Irritable bowel syndrome (IBS) is a multifactorial disease, the genetic aspect of which is being actively studied.

Aim:To investigate functional polymorphism of the serotonin reuptake transporter (SERT)SLC6A4gene of various clinical variants of IBS.

Materials and methods:We performed a cross-sectional single center study in 79 Caucasian patients with IBS (according to the Rome criteria IV). The patients were divided into two groups: group 1, IBS with diarrhea (IBS-D, n = 45) and group 2, IBS with constipation (IBS-C, n = 34). The control group included 59 Caucasian patients with gastrointestinal disorders without IBS. Polymorphism5-HTTLPRof theSLC6A4gene was assessed in all subjects. In group 1 patients, blood serotonin levels were measured and psychological tests were performed, including Spielberger's State / Trait Anxiety Inventory, quality of life by SF36 and GSRS, Asthenia scale, VAS scores for pain intensity.

Results:Thirty-five of 45 (77.8%) patients with IBS-D carried the mutantSallele, which was significantly more frequent than in the IBS-C group (p = 0.002) and in the control group (p = 0.005). There were no statistically significant differences (p = 0.54) in the frequency of detection of the homozygousLLgenotype (normal allele) and the heteroand homozygous mutant alleles (SLandSS) genotype between the IBS-C and control patients. In the IBS-D group, a gender difference for the mutantSSallele of5-HTTLPRwas found, with significantly higher frequency in female patients (p = 0.0147). No significant gender differences in the genotype distribution between the patients with IBS-C and the control group were found. There were also no differences in blood serotonin levels in the IBS patients with various5-HTTLPRtypes (p = 0.086); they were all in the reference range. However, there was a trend towards lower serotonin levels in theLLgenotype carriers compared to those with theSS/SLpolymorphisms. The Gastroenterological inventoryGSRSdemonstrated significantly higher total score for the constipation syndrome in the patients with homozygousLL 5-HTTLPRpolymorphism, compared to that in the patients with theSS/SLgenotype (p = 0.013).

Conclusion:The results may be related to lower expression of theSLC6A4gene in the carriers of the mutant allele in the5-HTTLPRpromoter and subsequent decreased rate of serotonin uptake, with resulting stimulation of the gastrointestinal tract. TheSERTpolymorphism of theSLC6A4gene is worth further investigation as a potential candidate gene in the IBS pathophysiology.

Candidate single nucleotide polymorphisms of irritable bowel syndrome: a systemic review and meta-analysis

Background

Genetic factors increase the risk of irritable bowel syndrome (IBS). Analysis of single nucleotide polymorphisms (SNPs) has been used in IBS patients, but the findings are inconsistent. The goal of this review was to synthesize all the published SNPs studies of IBS through meta-analysis to objectively evaluate the relevance of SNPs to IBS risks.

Methods

IBS - related polymorphisms studies from 2000 to 2018 were searched. Pooled odds ratios with a 95% confidence interval for each SNP were evaluated through five genetic models. Ethnicity, ROME criteria and IBS subtypes were defined for subgroup analyze.

Results

Ten relevant genes were evaluated. SNPs rs4263839 and rs6478108 of TNFSF15 associated with an increased risk of IBS; IL6 rs1800795 increased the risk for Caucasian IBS patients which diagnosed by Rome III criteria; and IL23R rs11465804 increased the risk for IBS-C patients. IL10 rs1800896 GG genotype associated with a decreased risk of IBS. No evidence supported the association of GNβ3 rs5443, TNFα rs1800629, and IL10 rs1800871 to IBS in this study.

Conclusions

This meta-analysis presents an in-depth overview for IBS SNPs analysis. It was confirmed that polymorphisms of TNFSF15 associated with increased IBS risk, while IL10 rs1800896 associated with decreased IBS risk. It might offer some insights into polymorphisms of inflammation factors which might affect IBS susceptibility. Moreover, the analysis also emphasizes the importance of diagnostic criteria and phenotype homogeneity in IBS genetic studies.

Sex-Gender Differences in Irritable Bowel Syndrome

Because of the sex-gender differences that are shown in a diversity of physiological and psychological factors, it can be speculated that the clinical presentation of symptoms as well as treatment strategies in women and men with irritable bowel syndrome (IBS) may differ. Studies have revealed that IBS is more common in women than men. As for the IBS subtype, IBS with constipation is significantly more prevalent among women than men. Sex hormones and gender differences may play important roles in the pathophysiology of IBS. However, its pathophysiologic mechanisms still remain largely unknown, and therapeutic implications are limited. Moreover, women IBS patients have been reported to feel more fatigue, depression, anxiety, and lower quality of life than men IBS patients. Furthermore, there has been evidence of differences in the appropriate treatment efficacy to IBS in men and women, although relatively few men are enrolled in most relevant clinical trials. A more sex-gender-oriented approach in the medical care setting could improve understanding of heterogeneous patients suffering from IBS. An individualized and multicomponent approach including sex and gender issues might help improve the treatment of IBS.

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.

Effect of Lactobacillus rhamnosus GG supernatant on serotonin transporter expression in rats with post-infectious irritable bowel syndrome

AIM

To evaluate the effect of Lactobacillus rhamnosus GG supernatant (LGG-s) on the expression of serotonin transporter (SERT) in rats with post-infectious irritable bowel syndrome (PI-IBS).

METHODS

Campylobacter jejuni 81-176 (10¹⁰ CFU/mL) was used to induce intestinal infection to develop a PI-IBS model. After evaluation of the post-infectious phase by biochemical tests, DNA agarose gel electrophoresis, abdominal withdrawal reflex (AWR) test, and the intestinal motility test, four PI-IBS groups received different concentrations of LGG-s for 4 wk. The treatments were maintained for 1.0, 2.0, 3.0 or 4.0 wk during the experiment, and the colons and brains were removed for later use each week. SERT mRNA and protein levels were detected by real-time PCR and Western blot, respectively.

RESULTS

The levels of SERT mRNA and protein in intestinal tissue were higher in rats treated with LGG-s than in control rats and PI-IBS rats gavaged with PBS during the whole study. Undiluted LGG-s up-regulated SERT mRNA level by 2.67 times compared with the control group by week 2, and SERT mRNA expression kept increasing later. Double-diluted LGG-s was similar to undiluted-LGG-s, resulting in high levels of SERT mRNA. Triple-diluted LGG-s up-regulated SERT mRNA expression level by 6.9-times compared with the control group, but SERT mRNA expression decreased rapidly at the end of the second week. At the first week, SERT protein levels were basically comparable in rats treated with undiluted LGG-s, double-diluted LGG-s, and triple-diluted LGG-s, which were higher than those in the control group and PBS-treated PI-IBS group. SERT protein levels in the intestine were also comparable in rats treated with undiluted LGG-s, double-diluted LGG-s, and triple-diluted LGG-s by the second and third weeks. SERT mRNA and protein levels in the brain had no statistical difference in the groups during the experiment.

CONCLUSION

LGG-s can up-regulate SERT mRNA and protein levels in intestinal tissue but has no influence in brain tissue in rats with PI-IBS.

G protein beta 3(GNβ3) C825T polymorphism and irritable bowel syndrome susceptibility: an updated meta-analysis based on eleven case-control studies

Several studies have reported an association between GNβ3 C825T polymorphism and irritable bowel syndrome (IBS). However, the results remain inconclusive and controversial, particularly for the data derived from different ethnicities and IBS subtypes. Therefore, we performed an updated meta-analysis to evaluate this association. All eligible case-control studies that met the search criteria were retrieved from multiple databases, and eleven case-control studies were included for detailed evaluation. The pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated to assess the strengths of the association between GNβ3 C825T polymorphism and susceptibility to IBS and its subtypes. Our meta-analysis found no significantly associations of GNβ3 C825T polymorphism with IBS risk in all populations. Whereas the C allele was demonstrated to be a decreased risk factor for constipation predominant IBS (IBS-C) in allele model. Additionally, the CC genotype was found to be associated with increased diarrhea predominant IBS (IBS-D) risk in recessive model. Subgroup analysis by ethnicity revealed that these associations held true for the Asian subpopulation. In conclusion, this meta-analysis suggests the C allele of GNβ3 C825T might be associated with a decreased risk of IBS-C, and the CC genotype of GNβ3 might be associated with increased IBS-D risk.

Overlap between irritable bowel syndrome and functional dyspepsia including subtype analyses

BACKGROUND AND AIM

Coexistent gastrointestinal symptom profiles and prevalence or associated factors for the overlap between each functional dyspepsia (FD) and irritable bowel syndrome (IBS) group remain unclear. Thus, the aim of the present study was to evaluate the clinicodemographic features of FD, IBS, and IBS-FD overlap and assess the risk factors thereof, including subtype and genetic polymorphisms for IBS-FD.

METHODS

Consecutive patients were enrolled from the outpatient Gastroenterology clinics of Bundang Seoul National University Hospitals in Korea. All gastrointestinal symptoms occurring at least once per week in the previous 3 months were recorded. Diagnostic criteria of functional gastrointestinal disorders were based on the Rome III criteria. Risk factors including genetic polymorphisms of 5-HTTLPR and ADRA2A 1291 G alleles and CCK-1R intron 779T>C were assessed using a multivariate logistic regression model.

RESULTS

A total of 632 subjects (278 control subjects, 308 FD, 156 IBS, and 110 who met the criteria for both FD and IBS) were included in this study. Patients with IBS-FD overlap had more severe symptoms (such as bloating, nausea, vomiting, hard or lumpy stools, defecation straining, and a feeling of incomplete bowel movement) and higher depression scores compared with non-overlap patients. Single/divorced or widowed marital status, nausea, bloating, and a feeling of incomplete emptying after bowel movements were independent risk factors for IBS-FD overlap among IBS patients. In contrast, young age, depression, bloating, and postprandial distress syndrome were positively associated with IBS-FD overlap among FD patients. 5-HTTLPR L/L was a risk factor for the co-occurrence of IBS-C among FD patients (OR: 12.47; 95% CI: 2.00-77.75; P = 0.007).

CONCLUSIONS

Bloating was a risk factor for IBS-FD overlap. Patients with postprandial distress syndrome have a higher risk of coexisting IBS, particularly constipation-dominant IBS.

Lessons learned--resolving the enigma of genetic factors in IBS

IBS is the most prevalent functional gastrointestinal disorder and phenotypically characterized by chronic abdominal discomfort, pain and altered defecation patterns. The pathophysiology of IBS is multifactorial, albeit with a substantial genetic component. To date, studies using various methodologies, ranging from family and twin studies to candidate gene approaches and genome-wide association studies, have identified several genetic variants in the context of IBS. Yet, despite enlarged sample sizes, increased statistical power and meta-analyses in the past 7 years, positive associations are still scarce and/or have not been reproduced. In addition, epigenetic and pharmacogenetic approaches remain in their infancy. A major hurdle is the lack of large homogenized case-control cohorts recruited according to standardized and harmonized criteria. The COST Action BM1106 GENIEUR (GENes in Irritable Bowel Syndrome Research Network EURope) has been established to address these obstacles. In this Review, the (epi)genetic working group of GENIEUR reports on the current state-of-the-art in the field, highlights fundamental flaws and pitfalls in current IBS (epi)genetic research and provides a vision on how to address and improve (epi)genetic approaches in this complex disorder in the future.

Genetics and pharmacogenetics of aminergic transmitter pathways in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) are highly prevalent syndromes, without evident underlying organic causes. Their pathogenesis is multifactorial in nature, with a combination of environmental and genetic factors contributing to their clinical manifestations, for which most of current treatments are not satisfactory. It is acknowledged that amine mediators (noradrenaline, dopamine and serotonin) play pivotal regulatory actions on gut functions and visceral sensation. In addition, drugs of therapeutic interest for FGIDs act on these transmitter pathways. The present article reviews current knowledge on the impact of genetics and pharmacogenetics of aminergic pathways on FGID pathophysiology, clinical presentations, symptom severity and medical management, in an attempt of highlighting the most relevant evidence and point out issues that should be addressed in future investigations.

Genetic epidemiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder characterized by presence of abdominal pain or discomfort associated with altered bowel habits. It has three main subtypes - constipation predominant IBS (C-IBS), diarrhea predominant IBS (D-IBS) and IBS with mixed features of both diarrhea as well as constipation (M-IBS). Its pathophysiology and underlying mechanisms remain elusive. It is traditionally believed that IBS is a result of multiple factors including hypersensitivity of the bowel, altered bowel motility, inflammation and stress. Initial studies have shown familial aggregation of IBS suggesting shared genetic or environmental factors. Twin studies of IBS from different parts of world have shown higher concordance rates among monozygotic twins than dizygotic twins, and thus suggesting a genetic component to this disorder. Multiple studies have tried to link single-nucleotide polymorphisms (SNPs) to IBS but there is little evidence that these SNPs are functional. Various molecules have been studied and investigated by the researchers. Serotonin, a known neurotransmitter and a local hormone in the enteric nervous system, has been most extensively explored. At this time, the underlying gene pathways, genes and functional variants linked with IBS remain unknown and the promise of genetically-determined risk prediction and personalize medicine remain unfulfilled. However, molecular biological technologies continue to evolve rapidly and genetic investigations offer much promise in the intervention, treatment and prevention of IBS.

Genetic polymorphism in pathogenesis of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a complex symptom-based disorder without established biomarkers or putative pathophysiology. IBS is a common functional gastrointestinal disorder which is defined as recurrent abdominal pain or discomfort that has at least two of the following symptoms for 3 d per month in the past 3 mo according to ROME III: relief by defecation, onset associated with a change in stool frequency or onset with change in appearance or form of stool. Recent discoveries revealed genetic polymorphisms in specific cytokines and neuropeptides may possibly influence the frequencies and severity of symptoms, as well as the therapeutic responses in treating IBS patients. This review gives new insights on how genetic determinations influence in clinical manifestations, treatment responses and potential biomarkers of IBS.