A genetic association study of 5-HTT LPR and GNbeta3 C825T polymorphisms with irritable bowel syndrome

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.

Serotonin-Related Gene Variants in Patients with Irritable Bowel Syndrome and Depressive or Anxiety Disorders

AIM

To assess the association of six polymorphisms in serotonin-related genes with depressive or anxiety disorders in patients with irritable bowel syndrome (IBS).

METHODS

The lifetime prevalence of depressive and anxiety disorders was assessed in 95 IBS patients (85% women) using the Munich version of the Composite International Diagnostic Interview (CIDI). IBS was diagnosed according to the Rome III criteria. SCL6A4 HTTLPR polymorphism (rs4795541) was determined using PCR-based method. Single-nucleotide polymorphisms in HTR1A (rs6295), HTR2A (rs6313 and rs6311), HTR2C (rs6318), and TPH1 (rs1800532) were detected by minisequencing method.

RESULTS

IBS patients with depressive disorders were characterized by higher frequency of 5-HTTLPR L allele in comparison to IBS patients with anxiety disorders. The lower frequency of 1438 A allele in HTR2A was found in IBS patients with depressive disorders in comparison to IBS patients without mental disorders. The lower G allele frequency in HTR2C rs6318 polymorphism among IBS patients with anxiety disorders was also observed.

CONCLUSIONS

Our results provide further evidence for the involvement of SLC6A4 rs4795541 and HTR2A rs6311 polymorphisms in the pathophysiology of depressive disorders in IBS patients. The new findings indicate that HTR2C rs6318 polymorphism may be associated with the susceptibility to anxiety disorders in IBS patients.

Serotonin Transporter Gene (SLC6A4) Polymorphism and Mucosal Serotonin Levels in Southeastern Iranian Patients with Irritable Bowel Syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a digestive system disorder with an unknown etiology. Serotonin has a key role in the secretion and motility of the intestine. Polymorphism in serotonin re-uptake transporter (SERT or SLC6A4) gene may have a functional role in the gut of patients with IBS. The aims of the present study were to investigate the association between SLC6A4 gene polymorphism and IBS and to detect the correlation between rectal serotonin levels and IBS sub-types.

METHODS

SLC6A4 gene polymorphism in 131 patients with IBS and 211 healthy controls were analysed using the quantitative polymerase chain reaction high-resolution melting (qPCR-HRM) curve technique. Serotonin was measured in rectal biopsies of patients with IBS using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The patients were categorized into three groups: IBS with diarrhoea (IBS-D): 70 patients, IBS with constipation (IBS-C): 18 patients, and IBS with mixed symptoms (IBS-M): 43 patients. The frequency of SLC6A4 s/s and l/s genotypes was significantly higher in IBS-C than IBS-D, IBS-M, and controls (p=0.036). Serotonin levels were similar in IBS sub-types.

CONCLUSION

SLC6A4 polymorphism is a possible candidate gene associated with the pathogenesis of IBS-C. Although serotonin levels did not differ in rectal biopsies of IBS sub-types, further investigation is recommended.

[Current Status of Translational Research on Irritable Bowel Syndrome]

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder. The pathophysiology of IBS is not completely understood. Genetic, immune, environmental, inflammatory, neurological and psychological factors contribute to the risk of this condition. Traditional research explored gastrointestinal motor abnormalities, central neural dysregulation, abnormal psychological features, and visceral hypersensitivity. More recent investigations consider bacterial overgrowth, abnormal serotonin pathways, altered gut flora, immune activation and mucosal inflammation. The purpose of this article is to review recent translational research concerning the pathophysiology, biomarker and genetic factors of IBS and to encourage IBS research in Korea.

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.

Gene polymorphisms associated with functional dyspepsia

Functional dyspepsia (FD) is a constellation of functional upper abdominal complaints with poorly elucidated pathophysiology. However, there is increasing evidence that susceptibility to FD is influenced by hereditary factors. Genetic association studies in FD have examined genotypes related to gastrointestinal motility or sensation, as well as those related to inflammation or immune response. G-protein b3 subunit gene polymorphisms were first reported as being associated with FD. Thereafter, several gene polymorphisms including serotonin transporter promoter, interlukin-17F, migration inhibitory factor, cholecystocynine-1 intron 1, cyclooxygenase-1, catechol-o-methyltransferase, transient receptor potential vanilloid 1 receptor, regulated upon activation normal T cell expressed and secreted, p22PHOX, Toll like receptor 2, SCN10A, CD14 and adrenoreceptors have been investigated in relation to FD; however, the results are contradictory. Several limitations underscore the value of current studies. Among others, inconsistencies in the definitions of FD and controls, subject composition differences regarding FD subtypes, inadequate samples, geographical and ethnical differences, as well as unadjusted environmental factors. Further well-designed studies are necessary to determine how targeted genes polymorphisms, influence the clinical manifestations and potentially the therapeutic response in FD.

Stomach antral endocrine cells in patients with irritable bowel syndrome

To the best of our knowledge, stomach antral endocrine cells have not previously been investigated in patients with irritable bowel syndrome (IBS). Thus, in the present study, 76 patients with IBS were examined (designated as IBS-total). Diarrhoea was the predominant symptom in 26 of these patients (IBS-D), while in 21 patients, the predominant symptoms were both diarrhoea and constipation (IBS-M) and in 29 patients the predominant symptom was constipation (IBS-C). Forty-three healthy subjects were enrolled as the controls. Stomach antral biopsy samples obtained from all of the subjects were immunostained using the avidin-biotin-complex method for serotonin, gastrin, somatostatin and serotonin transporter (SERT). The immunopositive cell densities and immunoreactivity intensities were determined by computer-aided image analysis. The density of the serotonin-immunoreactive cells was significantly decreased in the IBS-M patients and increased in the IBS-C patients relative to the controls. The immunoreactivity intensity did not differ significantly between the controls and IBS-total. The density of the gastrin-immunoreactive cells was significantly greater in the IBS-D, IBS-M and IBS-C patients than in the controls. The immunoreactivity intensity of gastrin was significantly greater in the IBS-D patients than in the controls. The density of the somatostatin-immunoreactive cells cells was significantly lower in the IBS-total, IBS-D, IBS-M and IBS-C patients than in the controls. The immunoreactivity intensities of both somatostatin and SERT did not differ significantly between the controls and IBS-total. The increase in gastrin cell density and the decrease in somatostatin cell density in all IBS subtypes may cause high levels of gastric secretion, which may in turn contribute to the high incidence of dyspepsia and gastro-oesophageal reflux observed in patients with IBS.

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

Background/Aims

Despite numerous studies on the relation of genetic polymorphisms with irritable bowel syndrome (IBS), the results still remain inconclusive. The aim of this study was to assess the possible association between SLC6A4 serotonin transporter gene linked polymorphic region (5-HTTLPR), ADRA2A −1291C>G, GNB3 825C>T, CCK1R intron 779T>C and TRPV1 945G>C polymorphisms and IBS based on Rome III criteria in Korea.

Methods

Study subjects were prospectively recruited from visitors to Seoul National University Bundang Hospital between July 2009 and January 2014. Ninety-nine IBS patients and 171 healthy controls were enrolled. Polymorphisms of above-mentioned 5 genes were genotyped. Serum serotonin from 101 participants was measured by ELISA and compared according to SLC6A4 5-HTTLPR polymorphisms and IBS subtypes.

Results

Regarding SLC6A4 5-HTTLPR polymorphism, L/L genotype was significantly associated with the total IBS, constipation predominant IBS (IBS-C) and mixture of diarrhea and constipation IBS (IBS-M) (adjusted OR: 4.35, 95% CI: 1.04–16.67; adjusted OR: 11.11, 95% CI: 1.69–50.00 and adjusted OR: 5.56, 95% CI: 1.05–33.33, respectively). Carrying ADRA2A −1291G allele was significantly associated with total IBS and diarrhea predominant IBS (adjusted OR: 3.37, 95% CI: 1.16–9.77 and adjusted OR: 5.64, 95% CI: 1.18–27.01, respectively). IBS-C patients showed reduced level of serum serotonin compared to controls and patients with diarrhea predominant IBS (50.2 ng/mL vs. 69.0 ng/mL and 92.9 ng/mL, P = 0.017 and P = 0.001, respectively).

Conclusions

Genetic polymorphisms of SLC6A4 5-HTTLPR and ADRA2A −1291C>G could be one of the pathophysiological factors of IBS in Korea. Reduced serum serotonin shown in the IBS-C group suggested a role of serotonin in IBS, but large study is needed for confirming genotypic difference in serum serotonin level.

A genetic association study of single nucleotide polymorphisms in GNβ3 and COMT in elderly patients with irritable bowel syndrome

Background

Several polymorphisms have been reported to be associated with irritable bowel syndrome (IBS), including C825T, the single nucleotide polymorphism (SNP), responsible for a truncated G protein β3 subunit (GNβ3), and the Vall158Met substitution in catechol-O-methyltransferase (COMT). We investigated the association between these mutations and the prevalence of IBS in 66 elderly Chinese patients.

Material/Methods

Sixty-six patients (over age 60 years) were diagnosed with IBS according to the Rome III criteria, and divided into 3 groups based on symptom presentation. The groups consisted of 7 patients with constipation, 46 patients with diarrhea, and 13 patients with both or neither symptoms. We enrolled 115 age-matched individuals without IBS as the control group. All patients were evaluated by using the Geriatric Depression Scale, disease progression was recorded, and GNβ3 and COMT were genotyped by PCR.

Results

There was no significant difference in GNβ3 C825T genotype distribution and allele frequency between the 2 groups. In contrast, compared with control subjects, COMT 158Met was significantly more prevalent in the IBS group (P=0.040) and significantly more prevalent in patients with diarrhea (P=0.029). 158Met was also more prevalent in those patients who had experienced symptoms for over 5 years (P=0.022).

Conclusions

In elderly Chinese patients, the 158Met SNP in COMT is associated with IBS pathogenesis, but the GNβ3-C825T SNP is not associated with IBS pathogenesis.

Genetic variants in CDC42 and NXPH1 as susceptibility factors for constipation and diarrhoea predominant irritable bowel syndrome

OBJECTIVE

The complex genetic aetiology underlying irritable bowel syndrome (IBS) needs to be assessed in large-scale genetic studies. Two independent IBS cohorts were genotyped to assess whether genetic variability in immune, neuronal and barrier integrity genes is associated with IBS.

DESIGN

384 single nucleotide polymorphisms (SNPs) covering 270 genes were genotyped in an exploratory cohort (935 IBS patients, 639 controls). 33 SNPs with Puncorrected<0.05 were validated in an independent set of 497 patients and 887 controls. Genotype distributions of single SNPs were assessed using an additive genetic model in IBS and clinical subtypes, IBS-C and IBS-D, both in individual and combined cohorts. Trait anxiety (N=614 patients, 533 controls), lifetime depression (N=654 patients, 533 controls) and mRNA expression in rectal biopsies (N=22 patients, 29 controls) were correlated with SNP genotypes.

RESULTS

Two SNPs associated independently in the exploratory and validation cohort: rs17837965-CDC42 with IBS-C (ORexploratory=1.59 (1.05 to 1.76); ORvalidation=1.76 (1.03 to 3.01)) and rs2349775-NXPH1 with IBS-D (ORexploratory=1.28 (1.06 to 1.56); ORvalidation=1.42 (1.08 to 1.88)). When combining both cohorts, the association of rs2349775 withstood post hoc correction for multiple testing in the IBS-D subgroup. Additionally, three SNPs in immune-related genes (rs1464510-LPP, rs1881457-IL13, rs2104286-IL2RA), one SNP in a neuronal gene (rs2349775-NXPH1) and two SNPs in epithelial genes (rs245051-SLC26A2, rs17837965-CDC42) were weakly associated with total-IBS (Puncorrected<0.05). At the functional level, rs1881457 increased IL13 mRNA levels, whereas anxiety and depression scores did not correlate with rs2349775-NXPH1.

CONCLUSIONS

Rs2349775 (NXPH1) and rs17837965 (CDC42) were associated with IBS-D and IBS-C, respectively, in two independent cohorts. Further studies are warranted to validate our findings and to determine the mechanisms underlying IBS pathophysiology.

Irritable bowel syndrome: Emerging paradigm in pathophysiology

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, characterized by abdominal pain, bloating, and changes in bowel habits. These symptoms cannot be explained by structural abnormalities and there is no specific laboratory test or biomarker for IBS. Therefore, IBS is classified as a functional disorder with diagnosis dependent on the history taking about manifested symptoms and careful physical examination. Although a great deal of research has been carried out in this area, the pathophysiology of IBS is complex and not completely understood. Multiple factors are thought to contribute to the symptoms in IBS patients; altered gastrointestinal motility, visceral hypersensitivity, and the brain-gut interaction are important classical concepts in IBS pathophysiology. New areas of research in this arena include inflammation, postinfectious low-grade inflammation, genetic and immunologic factors, an altered microbiota, dietary factors, and enteroendocrine cells. These emerging studies have not shown consistent results, provoking controversy in the IBS field. However, certain lines of evidence suggest that these mechanisms are important at least a subset of IBS patients, confirming that IBS symptoms cannot be explained by a single etiological mechanism. Therefore, it is important to keep in mind that IBS requires a more holistic approach to determining effective treatment and understanding the underlying mechanisms.

The serotonin transporter gene polymorphism (5-HTTLPR) and irritable bowel syndrome: a meta-analysis of 25 studies

Background

The results of previous studies assessing the association between the 5-HTTLPR polymorphism of serotonin transporter gene and irritable bowel syndrome (IBS) are inconsistent. The aim of this study was to clarify the association between the 5-HTTLPR mutation and the presence of IBS and its subtypes with a meta-analysis of 25 studies.

Methods

A thorough search for case–control studies evaluating the association between the 5-HTTLPR polymorphism of serotonin transporter gene and the presence of IBS was carried out in four electronic databases. A meta-analysis was performed in accordance with the Cochrane Handbook for systemic reviews.

Results

A total of 25 articles with 3443 IBS cases and 3359 controls were included into our meta-analysis. No significant association was found between this polymorphism and IBS in all populations. Whereas the LL genotype was demonstrated to be a risk factor for constipation predominant IBS (IBS-C) development in the overall population (LL vs SS: OR = 1.570, 95% CI = 1.147-2.148, P = 0.005, Bon = 0.030; LL vs LS: OR = 1.658, 95% CI = 1.180-2.331, P = 0.004, Bon = 0.024; LL vs LS/SS: OR = 1.545, 95% CI = 1.187-2.012, P = 0.001, Bon = 0.006). In the analysis of different ethnicities, L allele and LL genotype were significantly associated with increased IBS-C risk in the East Asian population (L vs S: OR = 1.487, 95% CI = 1.139-1.941, P = 0.003, Bon = 0.018; LL vs SS: OR = 2.575, 95% CI = 1.741-3.808, P = 0.000, Bon = 0.000; LL vs LS: OR = 3.084, 95% CI = 2.017-4.715, P = 0.000, Bon = 0.000; LL vs LS/SS: OR = 2.759, 95% CI = 1.933-3.938, P = 0.000, Bon = 0.000), but not in the Caucasian population.

Conclusions

Different from the conclusions of the earlier meta-analyses, the 5-HTTLPR mutation affects IBS-C but not IBS-D and IBS-M development and this effect only exists in the East Asian population but not other populations.

Serotonin and serotonin transporter in the rectum of patients with irritable bowel disease

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder, which considerably reduces the quality of life of patients and represents an economic burden to society. In previous studies, the density of serotonin‑expressing cells in the rectum of IBS patients did not differ from that of control subjects. The present study was undertaken to investigate the immunoreactivity intensity of serotonin and serotonin‑selective reuptake transporter (SERT) in the rectum of IBS patients. A cohort of 50 patients with IBS (41 females and 9 males) were included in the study. Thirty patients had diarrhoea (IBS‑D) and 20 had constipation (IBS‑C) as the predominant symptom. Twenty‑seven subjects were included as controls (19 females and 8 males). Rectal biopsy specimens were immunostained using the avidin‑biotin complex method for serotonin and SERT. The immunoreactivity intensity was quantified by computerised image analysis using Olympus cell Sens imaging software. There was no statistical difference of serotonin immunoreactivity intensity in multiple comparisons between controls, IBS‑total, IBS‑D and IBS‑C. Dunn's post test did not reveal any statistical differences among the four groups. There was a significant statistical difference in multiple comparisons between controls, IBS‑total, IBS‑D and IBS‑C regarding the SERT immunoreactivity intensity. SERT immunoreactivity intensity of IBS‑total, IBS‑D and IBS‑C differed significantly from that of controls. It was concluded that the reduced rectal SERT in the IBS patients could be one of the factors contribu-ting to the development of both diarrhoea and constipation in these patients, and that the increasing body of evidence of a genetic abnormality involving SERT underlines the importance of the role of SERT in the pathophysiology of IBS.

Serotonin transporter gene polymorphisms in Southwestern Iranian patients with irritable bowel syndrome

BACKGROUND AND STUDY AIMS

Irritable bowel syndrome is a common chronic functional gastrointestinal disorder of unknown etiology. Serotonin is an important factor in sensory signaling in the brain-gut axis, which plays a key role in intestinal motility and secretion. Serotonin clearance is mediated by a specific protein called the serotonin reuptake transporter. Transcription activity of the serotonin transporter gene is affected by some polymorphisms in this gene. The aim of this study was to investigate the relationship between serotonin transporter gene polymorphisms and irritable bowel syndrome.

PATIENTS/MATERIAL AND METHODS

The 5-HTTLPR, rs25531 and STin2VNTR polymorphisms of the serotonin transporter gene were analyzed by PCR-based methods in 50 patients with irritable bowel syndrome and 100 healthy controls.

RESULTS

Serotonin transporter polymorphisms were similar in patients and healthy controls. There were no significant differences in allele or genotype frequencies between the two groups.

CONCLUSION

Our findings suggest that polymorphisms in the gene encoding for the serotonin transporter are not associated with irritable bowel syndrome. Interactions between environmental factors and predisposing genetic factors are important in the pathophysiology of irritable bowel syndrome, and further genetic and epigenetic research may provide novel insights into the mechanisms contributing to this disease.

Influence of the serotonin transporter 5HTTLPR polymorphism on symptom severity in irritable bowel syndrome

5HTTLPR polymorphism of serotonin transporter yields short (S) and long (L) alleles. SS and LS genotypes are associated with reduced expression of serotonin transporter. This cross-sectional study investigated the association of 5HTTLPR with symptom severity of irritable bowel syndrome (IBS). Patients with IBS (Rome III) and healthy controls were included. Genomic DNA was extracted from saliva, and 5HTTLPR alleles were assessed by polymerase chain reaction. IBS symptom severity was evaluated by means of IBS-SSS questionnaire. Two hundreds and four IBS patients (159 females; mean age: 39.6±12.3 years; 106 with constipation: C-IBS; 98 with diarrhea: D-IBS) and 200 healthy controls (154 females; mean age: 40.4±15.8 years) were enrolled. The overall IBS-SSS value was higher in LS/SS than LL patients (319.0±71.5 versus 283.8±62.3; P = 0.0006). LS/SS patients had also higher values of abdominal pain (59.7±21.0 versus 51.0±18.8; P = 0.020) and bowel dissatisfaction (80.1±23.9 versus 70.5±22.8; P = 0.035). The overall IBS-SSS values in C-IBS and D-IBS patients were 317.2±68.3 and 296.1±71.4, respectively (P = 0.192), with significantly higher values for abdominal distension (65.0±24.4 versus 51.4±24.8; P = 0.0006), but not for bowel dissatisfaction (80.5±21.7 versus 72.9±25.7; P = 0.138). Frequencies of 5HTTLPR genotypes did not differ significantly when comparing IBS patients (overall or upon stratification in C-IBS and D-IBS) with healthy controls. In conclusion, the LS and SS genotypes are significantly correlated with IBS symptom severity, although their possible direct causal role remains to be proven. In addition, the present findings do not support an association of 5HTTLPR with IBS or its clinical presentation in terms of bowel habit predominance.

A serotonin transporter gene (SLC6A4) polymorphism is associated with reduced risk of irritable bowel syndrome in American and Asian population: a meta-analysis

AIM

Association studies of serotonin transporter gene SLC6A4 I/S polymorphism and irritable bowel syndrome (IBS) have shown inconsistent and contradictory results among different populations. In the present study, meta-analysis was performed to evaluate the association between SLC6A4 I/S polymorphism and IBS susceptibility.

METHODOLOGY

Systemic assessment was performed for the published studies based on the association of SLC6A4 I/S polymorphism and IBS risk from PubMed (Medline), EMBASE search. A meta-analysis was done to appraise the said association. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for allele contrast, homozygous, heterozygous, dominant and recessive genetic model.

RESULTS

A total of twelve studies comprising 2068 IBS cases and 2076 controls were included in this meta-analysis. Overall, no significant results were obtained for S allele carrier (S vs. I: p=0.488; OR=1.073, 95% CI=0.879 to 1.311) Co-dominant (SS vs. II; p=0.587; OR=1.112, 95% CI=0.758 to 1.631), (IS vs. II; p=0.361; OR=0.878, 95% CI=0.665 to 1.160). Similarly, dominant (SS+IS vs. II: p=0.853; OR=0.974, 95% CI=0.736 to 1.288) and recessive (SS vs. II+IS: p=0.267; OR=1.172, 95% CI=0.886 to 1.522) genetic models did not demonstrate risk. In the subgroup population based analysis, reduced risks were found in American (IS vs. II: p=0.009; OR=0.685, 95% CI=0.516 to 0.908) and Asian (SS+IS vs. II; p=0.001; OR=0.116, 95% CI=0.068 to 0.197) population. However, no risk was observed in European population.

CONCLUSIONS

This investigation clearly demonstrates that SLC6A4 (Ins/Del) polymorphism is associated with reduced risk of IBS in American and Asian population. However, future well-designed studies with stratified case control and biological characterization will be needed to validate this finding.

Genetic polymorphism of pri-microRNA 325, targeting SLC6A4 3'-UTR, is closely associated with the risk of functional dyspepsia in Japan

BACKGROUND

The role of genetics in the susceptibility to functional dyspepsia (FD) remains unclear. We attempted to clarify the association between FD and polymorphisms in SLC6A4. In addition, rs5981521 (C>T) in the pri-microRNA 325 (pri-miR-325) coding region was also investigated.

METHODS

The study was performed in 395 subjects (172 with no upper abdominal symptoms and 223 with FD, including medication-resistant FD). We employed a polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) method to detect gene polymorphisms.

RESULTS

Neither SLC6A4 -185 A>C nor *463 G>T was associated with susceptibility to FD. The number of rs5981521 T alleles was significantly correlated with an increased risk for FD (odds ratio [OR] 1.45, 95 % confidence interval [CI] 1.05-1.98; p = 0.022) and the TT homozygote was more closely associated with the risk for FD (OR 3.01, 95 % CI 1.41-6.42; p = 0.0043). The TT homozygote also had significantly increased risks for both the epigastric pain syndrome (EPS) and postprandial distress syndrome (PDS) subtypes of FD (OR 3.04, 95 % CI 1.25-7.42; p = 0.014 and OR 3.05, 95 % CI 1.14-8.13; p = 0.026, respectively). In addition, Helicobacter pylori-negative TT homozygotes had a greater risk for FD (OR 8.37, 95 % CI 1.78-39.5; p = 0.0072). In subjects with the SLC6A4 5'-untranslated region (UTR) wild homozygote, the number of rs5981521 T alleles was significantly correlated to an increased risk for FD (OR 1.45, 95 % CI 1.03-2.04, p = 0.033). Of note, in subjects who were SLC6A4 3'-UTR mutant carriers, the number of rs5981521 T alleles was also significantly correlated with an increased risk for FD (OR 2.07, 95 % CI 1.08-3.98; p = 0.029).

CONCLUSIONS

Our results suggest that the genetic polymorphism pri-miR-325 is associated with FD and interacts with SLC6A4 polymorphisms in increasing susceptibility to FD in Japanese.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Genetic epidemiology and pharmacogenetics in irritable bowel syndrome

The objectives of this review are twofold. Our first objective is to evaluate the evidence supporting a role for genetics in irritable bowel syndrome (IBS). Specific examples of the associations of genetic variation and symptoms, syndromes, and intermediate phenotypes, including neurotransmitter (serotonergic, α(2)-adrenergic, and cannabinoid) mechanisms, inflammatory pathways (IL-10, TNFα, GNβ3, and susceptibility loci involved in Crohn's disease), and bile acid metabolism, are explored. The second objective is to review pharmacogenetics in IBS, with the focus on cytochrome P-450 metabolism of drugs used in IBS, modulation of motor and sensory responses to serotonergic agents based on the 5-hydroxytryptamine (5-HT) transporter-linked polymorphic region (5-HTTLPR) and 5-HT(3) genetic variants, responses to a nonselective cannabinoid agonist (dronabinol) based on cannabinoid receptor (CNR1) and fatty acid amide hydrolase (FAAH) variation, and responses to a bile acid (sodium chenodeoxycholate) and bile acid binding (colesevelam) based on klothoβ (KLB) and fibroblast growth factor receptor 4 (FGFR4) variation. Overall, there is limited evidence of a genetic association with IBS; the most frequently studied association is with 5-HTTLPR, and the most replicated association is with TNF superfamily member 15. Most of the pharmacogenetic associations are reported with intermediate phenotypes in relatively small trials, and confirmation in large clinical trials using validated clinical end points is still required. No published genome-wide association studies in functional gastrointestinal or motility disorders have been published.

Polymorphisms of the Serotonin Transporter Gene and G-Protein β3 Subunit Gene in Korean Children with Irritable Bowel Syndrome and Functional Dyspepsia

BACKGROUND/AIMS

Many candidate gene studies have revealed that polymorphisms of the 5'-flanking controlled SERT gene linked polymorphic region (5HTT-LPR) gene and G-protein β3 C825T gene might be associated with functional dyspepsia (FD) and irritable bowel syndrome (IBS). This study was performed to investigate polymorphisms of the 5HTT-LPR gene and G-protein β3 C825T gene in FD and IBS in Korean children.

METHODS

In total, 102 patients with FD, 72 patients with IBS based on the Rome III criteria and 148 healthy controls without gastrointestinal symptoms were included in the study to analyze 5HTT-LPR and G-protein β3 C825T polymorphisms.

RESULTS

5HTT-LPR genotype analysis revealed no signifi cant differences in FD and IBS patients compared with controls. The GNβ3 C825T genotype distribution for CC, CT, and TT was 23.6%, 53.4%, and 23.0% in controls, 36.3%, 38.2%, and 25.5% in FD and 37.5%, 38.9%, and 23.6% in IBS, respectively. The CC genotype was more common in FD and IBS patients than controls (p<0.05). When the IBS patients were grouped according to IBS subtypes, CC genotype GNβ3 C825T was common in diarrhea-dominant IBS, and the TT genotype was common in constipation-dominant IBS (p<0.05).

CONCLUSIONS

The CC genotype of G-protein β3 C825T may be associated with FD and diarrhea-predominant IBS. The TT genotype may be associated with constipation-predominant IBS.

Serotonin transporter and G protein beta 3 subunit gene polymorphisms in Greeks with irritable bowel syndrome

BACKGROUND

Polymorphisms in the serotonin transporter (SERT) and G protein β3 subunit (GNB3) genes might contribute to the pathophysiology of irritable bowel syndrome (IBS). Association studies of SERT and GNB3 polymorphisms and IBS have shown diverse results among different populations, which might be due to subject composition differences.

AIMS

The aim of the study was to assess the potential association between SERT and GNB3 polymorphisms and IBS in Greeks.

METHODS

A total of 124 patients with IBS diagnosed according to the Rome III criteria and 238 healthy individuals were included in the study. SERT and GNB3 gene polymorphisms were genotyped using polymerase chain reaction-based methods.

RESULTS

It was shown that the frequencies of the SS genotype and S allele of the serotonin transporter polymorphism were significantly associated with IBS (P = 0.0314 and P = 0.019, respectively). TT genotype and T allele frequencies of G protein β3 subunit showed also significant difference between the IBS patients and healthy controls IBS (P = 0.0163 and P = 0.0001, respectively). None of the clinical symptoms analyzed was significantly associated with the polymorphisms tested.

CONCLUSIONS

The results suggest that SERT and GNB3 gene polymorphisms might be associated with irritable bowel syndrome predisposition in Greeks.

New insight in the pathogenesis of functional gastrointestinal disorders: association between genetics and colonic transit

Genome wide association studies and meta-analyses identified risk factors related to epithelial integrity of the intestinal barrier, innate immune responses and autophagy in inflammatory bowel disorder (IBD) and celiac disease. Irritable bowel syndrome (IBS), the most common functional gastrointestinal disorder (FGID), coexists and shares common, although milder, features with IBD and celiac disease. Although our knowledge on genetic variability in IBS symptom generation is very limited, smaller scale studies attempt to provide insight in the mechanisms underlying IBS. Camilleri et al. identified associations for susceptibility loci in inflammatory and epithelial barrier genes with colonic transit in lower FGID. Their report is the first descriptive study to assess potential genetic factors involved in motor function. Further exploration of genetic variation in IBS will be crucial to unravel its' pathogenesis.

Serotonin transporter gene polymorphism may be associated with functional dyspepsia in a Japanese population

Background

Although familial clustering of functional dyspepsia (FD) has been reported, the role of genetics in the susceptibility to FD is still not well understood. In the present study, the association between serotonin transporter (SERT) gene (SLC6A4) polymorphism and FD was explored.

Methods

Subjects were divided into either a postprandial distress syndrome (PDS) group or an epigastric pain syndrome (EPS) group according to the Rome III criteria. The healthy controls were those who had visited a hospital for an annual health check-up. The presence of the SLC6A4 promoter polymorphism, 5-hydroxytryptamin transporter gene linked polymorphic region (5-HTTLPR), was then evaluated, and logistic regression analysis was used to test all variables.

Results

The 5-HTTLPR genotype distribution was 448 SS, 174 SL, and 24 LL in controls and 30 SS, 20 SL, and 3 LL in FD subjects. No significant correlation was found between the 5-HTTLPR genotype and FD. When the genotypes and subtypes of FD were exploratory evaluated, the SL genotype was significantly associated with PDS [odds ratio (OR) = 2.24, 95% confidence interval (CI); 1.16-4.32, P = 0.034 after Bonferroni correction] compared to the SS genotype adjusted for sex and age. Comparison of the SS genotype with the SL/LL genotype also showed a significant association of genotype with PDS (OR = 2.32, 95% CI; 1.23-4.37, P = 0.009).

Conclusion

The present results suggest that 5-HTTLPR L allele may influence the susceptibility to PDS.

Genetic factors for functional dyspepsia

BACKGROUND

Although familial clustering of functional dyspepsia (FD) has been reported, the role of genetics in the susceptibility to FD is still not well established. Several reports indicate the associations between FD and gene polymorphisms, however the data are inconsistent. This review summarized the evidence of genetics in FD based on genetic epidemiology.

RESULTS

Genetic association studies with FD symptom phenotype have limited for several candidate genes investigated. There have been no genome wide association studies in FD. G-protein beta3 (GNB3) subunit C825T was first reported as a candidate gene for FD susceptibility. However, the data are inconsistent in countries. Significant link between homozygous 825C allele of GNB3 protein and dyspepsia was reported from Germany and the USA. On the other hand, the association between T allele of GNB3 C825T polymorphism and dyspepsia was reported from Japan and Netherlands. Association of serotonin transporter promoter (SERT-P) gene polymorphism and FD was reported negatively from a USA community and Netherlands. However we found that SERT SL genotype was significantly associated with PDS. Involvement of IL-17F, migration inhibitory factor (MIF), catechol-o-methyltransferase (COMT) gene val158met, 779 TC of CCK-1 intron 1, cyclooxygenase-1 (COX-1), transient receptor potential cation channel, subfamily V, member 1 (TRPV1) 315C and regulated upon activation normal T cell expressed and secreted (RANTES) polymorphisms was reported in Japanese studies.

CONCLUSIONS

Genetic factors are associated with the development of dyspeptic symptoms. Further studies are needed to confirm these data and to determine how genetic factors influence the clinical manifestation of FD patients.

The role of genetics in IBS

Irritable bowel syndrome (IBS) is a common disorder that has been shown to aggregate in families and to affect multiple generations, but not in a manner consistent with a major Mendelian effect. Relatives of an individual with IBS are 2 to 3 times as likely to have IBS, with both genders being affected. To date, more than 100 genetic variants in more than 60 genes from various pathways have been studied in a number of candidate gene studies, with several positive associations reported. These findings suggest that there may be distinct, as well as shared, molecular underpinnings for IBS and its subtypes.

An update on irritable bowel syndrome: from diagnosis to emerging therapies

PURPOSE OF REVIEW

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder characterized by abdominal discomfort or pain that is accompanied by a disturbance in defecation. Although the exact etiopathogenesis is not completely understood, recent advances in the understanding of the biochemical, physiologic, and biopsychosocial mechanisms of IBS have resulted in exciting new insights as well as therapies. This article will review the recent developments in pathogenesis, diagnosis, and treatment.

RECENT FINDINGS

IBS may be the product of various pathogenic mechanisms which include IBS as a serotonergic disorder; the role of genetics; IBS as an inflammatory state and the potential role of mast cells; IBS as a result of bacterial overgrowth and altered gastrointestinal microbiome; and abnormal pain processing and pain memory. Emerging therapies have developed targeting these mechanisms.

SUMMARY

IBS remains a symptom-based diagnosis that can usually be made comfortably based on clinical history without testing in the absence of alarm features. Novel and emerging therapies that are based upon the evolving understanding of the pathophysiology of IBS hold significant promise and for the first time there are potential therapies that may alter the natural history of this disorder.

Association of serotonin transporter gene polymorphisms with the development of functional dyspepsia and accompanying psychiatric symptoms

AIM: To investigate the association of serotonin transporter (SERT) gene polymorphisms with the development of functional dyspepsia (FD) and accompanying psychiatric symptoms.

METHODS: Polymerase chain reaction (PCR) was used to detect the SERT gene-linked polymorphic region (5-HTTLPR) and the variable number tandem repeats (VNTRs) in intron 2 of the SERT gene in 60 patients with FD and 80 healthy subjects.

RESULTS: There are significant differences in 5-HTTLPR S allele frequencies among groups classified according to FD subtype and those according to psychiatric symptoms (all P < 0.05). No significant differences were noted in genotype distribution or allele frequency of VNTRs between controls and FD patient.

CONCLUSION: The S allele of 5-HTTLPR may be associated with the development of FD-PDS subtype and FD-associated psychiatric symptoms.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.

Trauma history and risk of the irritable bowel syndrome in women veterans

BACKGROUND

Over 1.8 million women in the U.S. are veterans of the armed services. They are at increased risk of occupational traumas, including military sexual trauma.

AIM

To evaluate the association between major traumas and irritable bowel syndrome among women veterans accessing Veteran Affairs (VA) healthcare.

METHODS

We administered questionnaires to assess trauma history as well as IBS, post-traumatic stress disorder (PTSD) and depression symptoms to 337 women veterans seen for primary care at VA Women's Clinic between 2006 and 2007. Logistic regression was used to evaluate the association between individual traumas and IBS risk after adjustment for age, ethnicity, PTSD and depression.

RESULTS

Irritable bowel syndrome prevalence was 33.5%. The most frequently reported trauma was sexual assault (38.9%). Seventeen of eighteen traumas were associated with increased IBS risk after adjusting for age, ethnicity, PTSD and depression, with six statistically significant [range of adjusted odds ratios (OR) between 1.85 (95% CI, 1.08-3.16) and 2.6 (95% CI, 1.28-3.67)]. Depression and PTSD were significantly more common in IBS cases than controls, but neither substantially explained the association between trauma and increased IBS risk.

CONCLUSIONS

Women veterans report high frequency of physical and sexual traumas. A lifetime history of a broad range of traumas is independently associated with an elevated risk of the irritable bowel syndrome.

5-HTTLPR and STin2 polymorphisms in the serotonin transporter gene and irritable bowel syndrome: effect of bowel habit and sex

BACKGROUND

Conflicting data exist on the association between functional polymorphisms in the serotonin reuptake transporter (SERT) gene (SLC6A4) and irritable bowel syndrome (IBS). This may be partly because of small participant numbers and varying ethnic origin and sex within the cohorts studied.

AIM

To reassess the potential association between the SERT polymorphisms 5-HTTLPR and STin2 in both male and female IBS patients with diarrhoea (IBS-D) and constipation (IBS-C) compared with healthy volunteers.

METHODS

In this case-control study, 196 Caucasian Rome II IBS patients [97 IBS-D (aged 18-66 years; 67 female) and 99 IBS-C (aged 18-65 years; 95 female)] and 92 Caucasian healthy volunteers (aged 18-63 years; 60 female) from the UK had genomic DNA extracted from peripheral blood and the 5-HTTLPR and STin2 polymorphisms genotyped.

RESULTS

The frequency of the 5-HTTLPR (ss) genotype was slightly lower in both IBS-D (16.5%) and IBS-C (14.3%) patients compared with controls (23.9%), although not significantly (P<or=0.191). This seemed to be related to a reduction in the frequency of the 5-HTTLPR (ss) genotype in male patients, particularly those with IBS-D [IBS-D 10%, IBS-C 25%, controls 37.5%; P=0.01 for IBS-D vs. controls; odds ratio (95% confidence interval) for 5-HTTLPR (ss) vs. 5-HTTLPR (non-ss)=0.185 (0.046-0.744)] than in female patients (IBS-D 19.4%, IBS-C 13.8%, controls 16.7%). There were no differences in the frequencies of either the 5-HTTLPR (ll) or (ls), or STin2 genotypes between any of the three groups.

CONCLUSION

Our finding that male IBS-D patients have a reduced frequency of the 5-HTTLPR (ss) genotype contradicts three earlier studies of a similar size, which did not take sex into account. Therefore, replication studies in even larger cohorts, stratifying for sex and endophenotypes, after assessing physiological and psychological traits, are required to unravel the contribution of SERT polymorphisms to the IBS phenotype.

G protein beta3 subunit, interleukin-10, and tumor necrosis factor-alpha gene polymorphisms in Koreans with irritable bowel syndrome

BACKGROUND

The association between irritable bowel syndrome (IBS) based on Rome III criteria and G protein beta3 subunit (GNB3), interleukin (IL)-10, and tumor necrosis factor (TNF)-alpha gene polymorphisms is uncertain.

METHODS

Case and control subjects were recruited from Korean visitors to the Health Promotion Center and Digestive Disease Center for gastrointestinal endoscopy. G protein beta3 subunit, IL-10, and TNF-alpha gene polymorphisms were genotyped using a polymerase chain reaction-based method. Multifactor dimensionality reduction (MDR) analysis was used to assess gene-gene interactions.

KEY RESULTS

Genotype and allele frequencies of GNB3 showed marginal significance between the healthy controls and IBS patients (chi(2) = 5.92, P = 0.052; chi(2) = 3.76, P = 0.053). G protein beta3 subunit T allele was more strongly correlated with IBS with constipation (12 of constipation-dominant type and 31 of mixed type) than with 51 diarrhea-dominant type and 88 normal subjects (chi(2) = 13.91, P = 0.008). Multifactor dimensionality reduction analysis revealed that there were no significant interactions of GNB3, IL-10, and TNF-alpha gene variants with susceptibility to IBS (P > 0.05).

CONCLUSIONS & INFERENCES

The results suggest that GNB3 825T allele might be associated with IBS with constipation in Koreans.

Genetic approaches to functional gastrointestinal disorders

Functional gastrointestinal disorders are complex symptom-based disorders without agreed upon biomarkers or pathophysiology. A better understanding of the genetic architecture of these disorders would help to better identify their complex biology and explain the common comorbidity with other disorders of persistent pain, mood, and affect, as well as possibly make it possible to identify subgroups of patients who respond to customized therapies. In contrast to monogenic diseases, polygenic diseases and traits are characterized by the contribution of common variants in a large number of genes, as well as environmental factors, to the vulnerability of an individual. Family and twin studies have clearly established a genetic component in irritable bowel syndrome. Although candidate gene studies have identified a few gene polymorphisms that may be correlated with the syndrome, small sample size, lack of reproducibility in large data sets, and the unreliability of the clinical phenotype require caution when extrapolating to a major role of any of the reported polymorphisms in the pathophysiology of irritable bowel syndrome. Future progress in this area will require better characterization of intermediate phenotypes with large effect size for the clinical phenotype, as well as consideration of gene-gene, environment-gene (epigenetics), and sex-gene interactions, genome-wide association, and whole genome sequencing approaches in large data sets.

Relationship between TRPV1 gene polymorphism and irritable bowel syndrome

AIM: To investigate the relationship between transient receptor potential vanilloid 1 (TRPV1) gene polymorphism and irritable bowel syndrome (IBS).

METHODS: Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and direct sequence analysis were used to comparatively analyze the polymorphism of the TRPV1 gene in patients with IBS (n = 73) fulfilling the Rome III criteria and healthy controls (n = 65).

RESULTS: A total of three genotypes were detected in IBS patients and healthy controls: CC, CT and TT. The frequencies of CC genotype and C allele in IBS patients were significantly higher than those in healthy controls (genotype: χ² = 6.858, P = 0.032; allele: χ² = 4.174, P = 0.041). A significant difference was found in TRPV1 gene polymorphism between IBS and healthy controls (P < 0.05).

CONCLUSION: The TRPV1 gene polymorphism is associated with the development of IBS. The presence of CC genotype and C allele probably increases the susceptibility of individuals to IBS. TRPV1 may be a novel therapeutic target for IBS.

The serotonin transporter polymorphism rs25531 is associated with irritable bowel syndrome

Irritable bowel syndrome is a frequent gastrointestinal disorder of unknown etiology. The serotonin transporter regulates the intensity and duration of serotonin signaling in the gut and is, therefore, an attractive candidate gene for irritable bowel syndrome. Previous studies investigating the 5-HTTLPR and Stin2 VNTR polymorphisms of the serotonin transporter have proved inconclusive. In this exploratory study we therefore expanded the search for a possible association of the serotonin transporter with irritable bowel syndrome to include not only the 5-HTTLPR and Stin2 VNTR length polymorphisms, but also the functional single nucleotide polymorphism rs25531. We genotyped 186 patients with irritable bowel syndrome and 50 healthy control subjects raging in age from 18 to 70 years. Carriers of the rare G allele of rs25531 had approximately threefold increased odds of irritable bowel syndrome compared with healthy controls (OR 3.3, 95% CI 1.1-9.6). Our findings suggest that further investigation of the possible role of the serotonin transporter in the etiology of IBS is warranted.

The interleukin-6, serotonin transporter, and monoamine oxidase A genes and endurance performance during the South African Ironman Triathlon

Previous studies have identified an association of genetic variants believed to alter physiological and biochemical processes locally within the skeletal muscle and therefore performance in the Ironman triathlon. There is growing evidence that the serotonergic system and circulating interleukin (IL)-6 levels are also involved in mediating endurance capacity. Investigators have demonstrated that recombinant human IL-6 administration and serotonergic neurotransmission manipulation, with 5-hydroxytryptamine transporter (5-HTT) and monoamine oxidase A (MAO-A) inhibitors, prior to exercise, can alter running performance, consistent with a central governor hypothesis. The aim of this study was to investigate possible associations of functional polymorphisms within the IL-6, 5-HTT, and MAO-A genes with endurance performance of Ironman triathletes. Four hundred sixty-eight male Caucasian triathletes who completed the 2000 and (or) 2001 South African Ironman Triathlon and 200 healthy Caucasian male controls were genotyped for the -174 IL-6 G/C, 5-HTT 40 base pair (bp) insertion-deletion and 30 bp variable number of tandem repeats (VNTR) MAO-A gene polymorphisms. There were no significant differences in the relative genotype distributions within the IL-6 (p = 0.636), 5-HTT (p = 0.659), and MOA-A (p = 0.227) polymorphisms when the fastest-fnishing, middle-finishing, and slowest-finishing triathletes, as well as the control groups, were compared. There were no direct associations between the IL-6 -174 G/C, 5-HTT 44 bp insertion-deletion, and MAO-A 30 bp VNTR gene polymorphisms and endurance performance in the 2000 and (or) 2001 South African Ironman Triathlons. The neurogenetic basis of the central governor requires further investigation.

5-hydroxytryptamine signalling in irritable bowel syndrome with diarrhoea: effects of gender and menstrual status

BACKGROUND

Symptomatology and physiology differ between men and women and across the menstrual cycle in irritable bowel syndrome (IBS). Ovarian hormones influence 5-hydroxytryptamine (5-HT), an amine known to play a role in gut motor-sensory function.

AIM

To assess the effects of gender and menstrual status on platelet-depleted plasma (PDP) 5-HT concentration in IBS patients with diarrhoea (IBS-D) patients compared with healthy volunteers (HV).

METHODS

Platelet-depleted plasma 5-HT concentrations were assessed under fasting and fed conditions in 73 IBS-D patients (aged 18-58 years; 18 men) and 64 HV (aged 18-50 years; 24 men). Women were divided into those with low or high progesterone/oestrogen (P/O) levels.

RESULTS

Irritable bowel syndrome patients with diarrhoea had higher PDP 5-HT concentrations than HV under fasting (P = 0.002) and fed (P = 0.049) conditions. This was particularly related to IBS-D men having higher PDP 5-HT concentrations than healthy controls (P = 0.002). Moreover, PDP 5-HT concentrations in IBS-D women with low P/O levels were similar to healthy controls.

CONCLUSIONS

Similar to IBS-D women with high P/O levels, IBS-D men also have raised PDP 5-HT concentrations. 5-HT concentration normalizes at menses in IBS-D women, suggesting a shift in the mechanisms responsible for abnormal 5-HT signalling in these patients.

Genetics and irritable bowel syndrome: from genomics to intermediate phenotype and pharmacogenetics

PURPOSE

Familial aggregation and sibling pair studies suggest there is a genetic contribution to the development of irritable bowel syndrome (IBS). The aim of this study was to review the evidence of genetics in IBS based on genetic epidemiology, studies of association with intermediate phenotypes and pharmacogenetics.

RESULTS

Genetic association studies with IBS symptom phenotype have generally provided inconsistent results for many candidate genes investigated, such as SLC6A4, GNB3, and IL-10. There have been no genome-wide association studies in IBS to date. Studies of associations of candidate genes with intermediate phenotypes suggest associations with pathophysiological mechanisms of motor and sensory functions; however, these results also require replication. Pharmacogenetics studies illustrate the potential of genetics to impact on response to therapy, as observed with SLC6A4 and responses to the 5-HT3 antagonist alosetron and the 5-HT4 agonist, tegaserod.

CONCLUSIONS

While the heritable component and genetics in the complex disorder of IBS are still poorly understood, studies of the associations of spontaneous genetic variations and altered functions may provide novel insights of the mechanisms contributing to the disease.

Serotonin transporter promoter variant: Analysis in Indian IBS patients and control population

BACKGROUND

Studies of serotonin reuptake transporter (SERT-P) polymorphism and irritable bowel syndrome (IBS) have shown diverse results among different populations, which might be due to racial and ethnic difference.

AIM

This study was to investigate the potential association between the SERT-P polymorphism and clinical subtypes of IBS patients in the Indian population.

METHOD

This prospective case-control study included 151 IBS patients. Ninety-two patients were diarrhea-predominant IBS, 44 were constipation-predominant IBS (C-IBS), 15 were alternating diarrhea and constipation IBS, and 100 were healthy controls. SERT gene polymorphism was studied by polymerase chain reaction.

RESULT

A genotypic association was observed between SS genotype of SERT-P polymorphism and C-IBS (P<0.05). When the L/S and L/L genotypes were combined into one group, the frequency of the S/S genotype was significantly higher than that of the non-S/S genotype between C-IBS and the control group (P<0.05). There was no significant difference in the SERT-P genotype and allele frequency between c-ibs, alternating diarrhea and constipation IBS, all types of IBS cases, and controls.

CONCLUSIONS

A significant association was observed between the SS genotype of SERT-P polymorphism and C-IBS in the Indian population.

Dissecting GI phenotype-genotype relationships in GERD and dyspepsia: an SNP here and an SNP there!

It is known that the predisposition to human disease is a mixture of inherited susceptibility and acquired exposure to environmental factors. Understanding gastrointestinal disease has indicated that germline adenomatous polyposis coli mutations predispose with a 99% certainty to colorectal cancer, whereas squamous esophageal cancer is caused by a combination of environmental exposures (including alcohol consumption, cigarette smoke, ingestion of contaminated preserved food) and/or infection (specifically with human papilloma virus), in most cases. Until now, despite the reasonably strong evidence for genetic risk from monozygotic twin studies for gastro-esophageal reflux disease (GERD), there have been no documented genetic targets in GERD. In this edition of the Journal, there is intriguing evidence that a common, single base-pair change in the secondary messenger gene GNbeta3 (i.e., a single-nucleotide polymorphism) may be important, perhaps through promoting abnormal perception of visceral pain in the esophagus. Other works link this genetic factor to functional dyspepsia, and these exciting preliminary lines of evidence are reviewed.

Genes and irritable bowel syndrome: is there a link?

Advances in genetics and genomics during the past decade, including sequencing of the human genome and DNA sequencing technologies, have made it possible to discover the genetic basis for many diseases. With the discovery of multiple genetic loci for gastrointestinal diseases such as Crohn's disease, some have begun to wonder-Could there be a genetic basis for irritable bowel syndrome (IBS)? This article summarizes the evidence for and against a link between genes and IBS. In addition, a gene-environment paradigm is presented to combine the two opposing hypotheses, as IBS may represent a complex genetic disorder that results from the interaction of several genes and environmental risk factors.

Impact of serotonin transporter and catechol-O-methyl transferase genes polymorphism on gastrointestinal dysfunction in Swedish and Japanese familial amyloidotic polyneuropathy patients

BACKGROUND

Differences in the gastrointestinal manifestations have emerged between Swedish and Japanese familial amyloidotic polyneuropathy amyloidogenic transthyretin Valine30Methionine (FAP ATTR Val30Met) patients. To elucidate the cause of the differences, we investigated the associations between serotonin transporter gene-linked polymorphic region (5-HTTLPR) and/or catechol-O-methyl transferase (COMT) gene polymorphism and their gastrointestinal in these patients.

METHODS

Twenty-six Swedish and 24 Japanese patients with gastrointestinal disturbances, in whom genetic material was available, were included in the study. The initial gastrointestinal manifestations of the disease were classified as constipation, constipation alternating with diarrhoea, continuous diarrhoea, and nausea/vomiting. 5-HTTLPR and COMT gene polymorphism were assessed by polymerase chain reaction and enzymatic digestion.

RESULTS

A significantly higher LA allele frequency of 5-HTTLPR was noted in the Swedish population compared with that of the Japanese. Moreover, the LA allele frequency tended to be lower in the continuous diarrhoea group than in that of the remaining groups of both Swedish and Japanese patients. No association between COMT genotype and initial gastrointestinal symptoms was noted.

CONCLUSION

A high expression of serotonin transporter induced by LA allele of 5-HTTLPR may be one of the factors implicated with the inhibition of severe diarrhoea in early stages of Swedish FAP ATTR Val30Met patients.

Genetics of irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common diagnoses made by gastroenterologists and primary care providers alike, and yet the underlying mechanism remains poorly understood. Family and twin studies suggest that IBS may have a genetic basis. Several candidate gene association studies have been performed, but thus far, they have failed to clearly identify an "IBS gene." Epidemiological studies are needed to facilitate phenotype definition and identify relevant environment risk factors that will need to factor in gene and environment interactions in all future genetic studies. As genetic research in IBS is relatively nascent, much opportunity, as well as many challenges, exists in identifying the genes responsible for IBS.

Irritable bowel syndrome aggregates strongly in families: a family-based case-control study

Irritable bowel syndrome (IBS) runs in families. Prior family studies surveyed patients inquiring about family history without surveying family members. The stigma associated with IBS may lead relatives to not share information with others,resulting in underestimates of familial aggregation of IBS. The aim of the study was to evaluate the accuracy of patient-report of family history of IBS in cases and controls, and to estimate familial aggregation of IBS using both a case-control and a family-study design. Fifty cases and 53 controls completed symptom questionnaires and provided contact information for first-degree relatives. Questionnaires were mailed to relatives. Relatives were considered to have IBS if they met Rome criteria and did not have an alternate GI diagnosis. Cases and controls identified 573 relatives in their families. A total of 202 (51%) of 396 living relatives participated. The kappa statistics between proband- and relative-reported IBS for case- and control-relatives were 0.27 and 0.04. Cases reported 21%of relatives had IBS; relative-reports showed 37%(P = 0.003). Controls reported 4% of relatives had IBS;relative-reports showed 16% (P = 0.013). Regardless of whether the proband or the relative themselves were the information source, case-relatives were three fold as likely to have IBS than control-relatives (P < 0.05).However, overall rates were higher when data collected from relatives were used. Regardless of approach, strong familial aggregation of IBS was observed. Cases and controls underestimated the frequency of IBS in their relatives and agreement between proband- and relative-report of IBS status was extremely poor, thus emphasizing the need for direct data collection from relatives in IBS family studies.

The genetics of the serotonin transporter and irritable bowel syndrome

Serotonin transporter (SERT) mediates the intracellular reuptake of released serotonin, thus regulating its biological functions. Abnormalities in serotonin reuptake can alter enteric serotonergic signalling, leading to sensory, motor and secretory gut dysfunctions, which contribute to the pathophysiology of irritable bowel syndrome (IBS). This relationship has fostered the use of selective serotonin reuptake inhibitors (SSRIs) in the treatment of IBS. Current data on the efficacy of SSRIs in IBS, association of the SERT gene promoter polymorphism 5-HTTLPR with IBS and the expression pattern of SERT in the intestinal mucosa of IBS patients are conflicting. Recent molecular studies have raised critical questions about multiple SERT mRNA transcripts in the human gut, the role of polymorphic SERT promoter in the regulation of enteric SERT expression and the ability of 5-HTTLPR to affect human SERT gene transcription. The present review highlights recent advances in SERT genetics, discusses their implications for potential therapeutic applications of SSRIs in IBS and presents original suggestions for future investigations.

Relationship between genetic polymorphism and irritable bowel syndrome pathogenesis

Irritable bowel syndrome is a common functional disorder, whose etiology remains unknown. Previous researches indicated that its pathogenesis might be associated such factors as gastrointestinal motor abnormality, altered visceral sensation, psychological factors, neurotransmitter and imbalance of gastrointestinal flora, intestinal infection and food intolerance, etc. Besides, recent research has touched on relationship between genetics and IBS. This paper reviewed relationship between the inheritance, gene-linked polymorphism and irritable bowel syndrome pathogenesis.