Association of the -1438 G/A and 102 T/C polymorphism of the 5-Ht2A receptor gene with irritable bowel syndrome 5-Ht2A gene polymorphism in irritable bowel syndrome

Risk factors for irritable bowel syndrome: A review

Irritable bowel syndrome (IBS) is one of the most common diseases of the digestive tract from the group of disorders of interaction in the gut-brain axis. IBS has a negative impact of on patients' quality of life and the significant social and economic burden of the disease due to the low effectiveness of available treatment strategies, which are only symptomatic, without impacting factors and mechanisms of intestinal dysfunction. From this perspective, it is critical to study the factors contributing to the onset and persistence of IBS symptoms to improve the early diagnosis of the disease and implement targeted prevention technology in at-risk groups. The objective of this paper is to systematize data on the main risk factors for IBS, including hereditary predisposition, stress and psycho-emotional state, diet and eating habits, and acute intestinal infections.

The serotonin receptor 2A (HTR2A) rs6313 variant is associated with higher ongoing pain and signs of central sensitization in neuropathic pain patients

BACKGROUND

The serotonin receptor 2A (HTR2A) has been described as an important facilitation mediator of spinal nociceptive processing leading to central sensitization (CS) in animal models of chronic pain. However, whether HTR2A single nucleotide variants (SNVs) modulate neuropathic pain states in patients has not been investigated so far. The aim of this study was to elucidate the potential association of HTR2A variants with sensory abnormalities or ongoing pain in neuropathic pain patients.

METHODS

At total of 240 neuropathic pain patients and 253 healthy volunteers were included. Patients were phenotypically characterized using standardized quantitative sensory testing (QST). Patients and controls were genotyped for HTR2A g.-1438G > A (rs6311) and c.102C > T (rs6313). Genotype-related differences in QST parameters were assessed considering QST profile clusters, principal somatosensory components and sex.

RESULTS

There was an equal distribution of rs6313 and linked rs6311 between patients and controls. However, the rs6313 variant was significantly associated with a principal component of pinprick hyperalgesia and dynamic mechanical allodynia, indicating enhanced CS in patients with sensory loss (-0.34 ± 0.15 vs. +0.31 ± 0.11 vs., p < .001). In this cluster, the variant allele was also associated with single QST parameters of pinprick hyperalgesia (MPT, +0.64 ± 0.18 vs. -0.34 ± 0.23 p = .002; MPS, +0.66 ± 0.17 vs. -0.09 ± 0.23, p = .009) and ongoing pain was increased by 30%.

CONCLUSIONS

The specific association of the rs6313 variant with pinprick hyperalgesia and increased levels of ongoing pain suggests that the HTR2A receptor might be an important modulator in the development of CS in neuropathic pain.

SIGNIFICANCE

This article presents new insights into serotonin receptor 2A-mediating mechanisms of central sensitization in neuropathic pain patients. The rs6313 variant allele was associated with increased mechanical pinprick sensitivity and increased levels of ongoing pain supporting a contribution of central sensitization in the genesis of ongoing pain providing a possible route for mechanism-based therapies.

The trace aminergic system: a gender-sensitive therapeutic target for IBS?

Due to a lack of specific or sensitive biomarkers, drug discovery advances have been limited for individuals suffering from irritable bowel syndrome (IBS). While current therapies provide symptomatic relief, inflammation itself is relatively neglected, despite the presence of chronic immune activation and innate immune system dysfunction. Moreover, considering the microgenderome concept, gender is a significant aetiological risk factor. We believe that we have pinpointed a "missing link" that connects gender, dysbiosis, diet, and inflammation in the context of IBS, which may be manipulated as therapeutic target. The trace aminergic system is conveniently positioned at the interface of the gut microbiome, dietary nutrients and by-products, and mucosal immunity. Almost all leukocyte populations express trace amine associated receptors and significant amounts of trace amines originate from both food and the gut microbiota. Additionally, although IBS-specific data are sparse, existing data supports an interpretation in favour of a gender dependence in trace aminergic signalling. As such, trace aminergic signalling may be altered by fluctuations of especially female reproductive hormones. Utilizing a multidisciplinary approach, this review discusses potential mechanisms of actions, which include hyperreactivity of the immune system and aberrant serotonin signalling, and links outcomes to the symptomology clinically prevalent in IBS. Taken together, it is feasible that the additional level of regulation by the trace aminergic system in IBS has been overlooked, until now. As such, we suggest that components of the trace aminergic system be considered targets for future therapeutic action, with the specific focus of reducing oxidative stress and inflammation.

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.

A machine-learned analysis of human gene polymorphisms modulating persisting pain points to major roles of neuroimmune processes

Background

Human genetic research has implicated functional variants of more than one hundred genes in the modulation of persisting pain. Artificial intelligence and machine‐learning techniques may combine this knowledge with results of genetic research gathered in any context, which permits the identification of the key biological processes involved in chronic sensitization to pain.

Methods

Based on published evidence, a set of 110 genes carrying variants reported to be associated with modulation of the clinical phenotype of persisting pain in eight different clinical settings was submitted to unsupervised machine‐learning aimed at functional clustering. Subsequently, a mathematically supported subset of genes, comprising those most consistently involved in persisting pain, was analysed by means of computational functional genomics in the Gene Ontology knowledgebase.

Results

Clustering of genes with evidence for a modulation of persisting pain elucidated a functionally heterogeneous set. The situation cleared when the focus was narrowed to a genetic modulation consistently observed throughout several clinical settings. On this basis, two groups of biological processes, the immune system and nitric oxide signalling, emerged as major players in sensitization to persisting pain, which is biologically highly plausible and in agreement with other lines of pain research.

Conclusions

The present computational functional genomics‐based approach provided a computational systems‐biology perspective on chronic sensitization to pain. Human genetic control of persisting pain points to the immune system as a source of potential future targets for drugs directed against persisting pain. Contemporary machine‐learned methods provide innovative approaches to knowledge discovery from previous evidence.

Significance

We show that knowledge discovery in genetic databases and contemporary machine‐learned techniques can identify relevant biological processes involved in Persitent pain.

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.

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.

Pharmacogenetics and the treatment of functional gastrointestinal disorders

The diagnosis and management of functional gastrointestinal disorders (FGIDs) remain very challenging. In the era of precision medicine, it is important to individualize the treatment of these conditions by providing targeted and effective therapies while minimizing the risk of medication side effects. By using genetic information that predicts and affects the responses to specific medications, it is anticipated that the science of pharmacogenetics in FGIDs will advance the practice of precision medicine. The pathophysiology of FGIDs is complex, involving the interaction between predisposing genetic and environmental factors. Studies have shown that genetic polymorphisms may contribute to the variable responses to specific medications among individuals with FGIDs. Genetic variations in the CYP450 system can affect the metabolism and, hence, the pharmacokinetics of drugs used to treat FGIDs. Polymorphisms in the genes controlling proteins that are involved in the direct action of medications targeting the serotonergic, cannabinoid, adrenergic and bile acid pathways can affect the pharmacologic effects of the medications. In this review, we summarize the published literature on the pharmacogenetics of FGIDs and address the potential clinical utility and future challenges in this field. Since it was the dominant topic in the majority of the articles relevant to FGIDs, our review will focus on irritable bowel syndrome.

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.

Association of 5-HT2A receptor gene polymorphisms with gastrointestinal disorders in Egyptian children with autistic disorder

Gastrointestinal disturbances (GID) are frequently reported in children with autism spectrum disorders (ASD). Recently, mounting evidence suggests that there may be a genetic link for autism with gastrointestinal disturbances. We aimed to investigate whether there were any association between the -1438A/G, 102T/C and His452Tyr polymorphisms of the serotonin 2A receptor gene (5-HT2A) in Egyptian children with ASD and GID. Eighty children with autistic disorder and 100 healthy control children were examined. -1438A/G, 102T/C and His452Tyr polymorphisms of 5-HT2A were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Significant increase of the G allele and the GG genotype of the -1438A/G polymorphism was observed in children with autism than control, but there were no significant differences in the frequencies either of the 102T/C genotype or His452Tyr genotype between the two groups. There was a significant increase of homozygote A allele of the -1438A/G and CC genotype of the 102T/C polymorphism in ASD children with GID. This study supports the possible involvement of the 5-HT2A receptor in the development of ASD and associated GID.

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: 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.

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 increases the functional activity of capsaicin-sensitive rat trigeminal nociceptors via peripheral serotonin receptors

Peripheral serotonin (5HT) has been implicated in migraine and temporomandibular pain disorders in humans and animal models and yet the mechanism(s) by which 5HT evokes pain remains unclear. Trigeminal pain can be triggered by activation of the transient receptor potential V1 channel (TRPV1), expressed by a subset of nociceptive trigeminal ganglia (TG) neurons and gated by capsaicin, noxious heat, and other noxious stimuli. As 5HT is released in the periphery during inflammation and evokes thermal hyperalgesia, and TRPV1 is essential for thermal hyperalgesia, we hypothesized that 5HT increases the activity of capsaicin-sensitive trigeminal neurons and that this increase can be attenuated by pharmacologically targeting peripheral 5HT receptors. TG cultures were pretreated with 5HT (10 nM-100 μM), sumatriptan (5HT(1B/1D) agonist), ketanserin (5HT(2A) antagonist), granisetron (5HT(3) antagonist), or vehicle prior to capsaicin (30-50 nM). Single-cell accumulation of intracellular calcium was recorded or calcitonin gene-related peptide (CGRP) release was measured following each treatment. In addition, using in situ hybridization and immunohistochemistry, we detected the colocalization of 5HT(1B), 5HT(1D), 5HT(2A), and 5HT(3A), but not 5HT(2C) mRNA with TRPV1 in TG cells. 5HT pretreatment evoked a significant increase in calcium accumulation in capsaicin-sensitive trigeminal neurons and enhanced capsaicin-evoked CGRP release, but had no significant effect when given alone. Sumatriptan, ketanserin, and granisetron treatment attenuated calcium accumulation and 5HT enhancement of capsaicin-evoked CGRP release. Together these results indicate that 5HT increases the activity of capsaicin-sensitive peripheral nociceptors, which can be attenuated by pharmacologically targeting peripheral 5HT receptors, thereby providing a mechanistic basis for peripheral craniofacial pain therapy.

Gene, environment, and brain-gut interactions in irritable bowel syndrome

The genetic predisposition and influence of environment may underlie in the pathogenesis and/or pathophysiology of irritable bowel syndrome (IBS). This phenomenon, gene x environment interaction together with brain-gut interactions is emerging area to be clarified in IBS research. Earlier studies focused on candidate genes of neurotransmitters, cytokines, and growth factors. Among them, some studies but not all studies revealed association between phenotypes of IBS and 5-hydroxytryptamine (5-HT)-related genes, noradrenaline-related genes, and cytokine genes. Recent prospective cohort study showed that genes encoding immune and adhesion molecules were associated with post-infectious etiology of IBS. Psychosocial stressors and intraluminal factors especially microbiota are keys to develop IBS. IBS patients may have abnormal gut microbiota as well as increased organic acids. IBS is disorder that relates to brain-gut interactions, emotional dysregulation, and illness behaviors. Brain imaging with or without combination of visceral stimulation enables us to depict the detailed information of brain-gut interactions. In IBS patients, thalamus, insula, anterior cingulate cortex, amygdala, and brainstem were more activated in response to visceral stimulation than controls. Corticotropin-releasing hormone and 5-HT are the candidate substances which regulate exaggerated brain-gut response. In conclusion, gene x environment interaction together with brain-gut interactions may play crucial roles in IBS development. Further fundamental research on this issue is warranted.

Existing and emerging therapies for irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome is a common disorder that is associated with a significant impact on both affected individuals and society. While the pathophysiology of irritable bowel syndrome remains unknown, knowledge regarding the normal and abnormal functions of the gut and its complex interaction with the body's nervous systems continues to shed light on the multifactorial origins of irritable bowel syndrome symptoms. This article provides an overview of the current knowledge of the therapeutic approaches to irritable bowel syndrome.

AREAS COVERED

A search of the online bibliographic databases MEDLINE and EMBASE was performed in order to identify all relevant articles published between 1980 and 2010. The search was enhanced with the use of a medical librarian. Bibliographies from potentially relevant articles were manually searched.

EXPERT OPINION

The therapeutic options for irritable bowel syndrome are rapidly evolving beyond traditional symptom-based therapies, such as fiber, antispasmodics, antidiarrheals and laxatives, and are moving toward agents with organ-specific receptor selectivity directed, in many cases, at specific gastrointestinal functions.

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.

Treatment of irritable bowel syndrome: beyond fiber and antispasmodic agents

Irritable bowel syndrome (IBS) is a chronic functional disorder of the gastrointestinal tract of unknown etiology. The diagnosis of IBS is made clinically, using symptom-based criteria such as the Manning or Rome criteria. Medical therapy for this condition has traditionally been directed towards symptom relief, using fiber or antispasmodic agents. In recent years, emerging data have confirmed the efficacy of antidepressants, psychological therapies, 5-HT(3) antagonists, 5-HT(4) agonists, and probiotics in the short-term treatment of IBS, although whether these therapies influence the long-term course of the disease is unknown. Increasing knowledge regarding the pathophysiological mechanisms underlying IBS has resulted in a number of novel molecular treatments, which show promise. These include therapies targeting gastrointestinal mucosal chloride channels and guanylate cyclase-C receptors, as well as highly selective agents influencing serotonergic transmission that, at the time of writing, do not appear to have any severe deleterious effects. In this article we provide a summary of current and emerging therapies in this field.

A pronociceptive role for the 5-HT2 receptor on spinal nociceptive transmission: an in vivo electrophysiological study in the rat

Serotonin (5-HT) plays a major yet complex role in modulating spinal nociceptive transmission as a consequence of the number of 5-HT receptor subtypes. These include the 5-HT2 receptor, which is further sub classified into 5-HT2A, B and C. Studies have described both a pro- and antinociceptive action following 5-HT2A-receptor activation; therefore, to shed light on the directional nature of spinal 5-HT2A receptor activity, we investigated the effects of spinal administration of the 5-HT2A receptor antagonist, ketanserin, on the evoked responses of dorsal horn neurones to electrical, mechanical and thermal stimulation. We also assessed the effects of systemic administration of ritanserin, a 5-HT2A/2C receptor antagonist and spinal application of (±)-2,5-Dimethoxy-4-iodoamphetamine hydrochloride (DOI) (3.6 and 17.8 μg/50 μl), a 5-HT2A/2C agonist, on the same evoked neuronal responses. Ketanserin (1, 10 and 100 μg/50 μl) produced a dose related inhibition of the evoked responses to noxious mechanical punctate and thermal stimuli only. Ritanserin (2 mg/kg) replicated the inhibitory effects seen with ketanserin on the natural evoked neuronal responses and also potently inhibited the C-fibre, post discharge, input and wind-up evoked responses. DOI increased the mechanical and thermal evoked responses, an effect reversed by ketanserin. Thus, our findings show that spinal ketanserin (1–100 μg/50 μl) and systemic ritanserin (2 mg/kg), at these doses, have similar antinociceptive effects, whereas the agonist, DOI, produced excitatory effects, on spinal neuronal activity. Our data, therefore, supports a pronociceptive role for 5-HT2 receptors, most likely through modulation of 5-HT2A receptor activity, on spinal nociceptive transmission under normal conditions.

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.

Association between 5-hydroxytryptamine 2A receptor gene polymorphism and postoperative analgesic requirements after major abdominal surgery

Although the serotonin (5-hydroxytryptamine (5-HT)) 2A receptor has been reported to be associated with pain, no relationship has been found between single nucleotide polymorphisms in the 5-HT2A receptor gene and analgesic requirements. To clarify the mechanism of individual differences in analgesic requirements, we investigated the relationship between the 5-HT2A 102T/C gene polymorphism and analgesic requirements in 135 patients who underwent major open abdominal surgery and were managed with continuous epidural analgesia with opioids after surgery. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism. We found that the 102T/C polymorphism had significant main effects with regard to analgesic requirements. In addition, significant interaction effects were found between the 102T/C polymorphism and sex in terms of analgesic requirements. Among female subjects, patients with the T/T genotype of the 102T/C polymorphism had more analgesic requirements than those with the other genotypes. This finding suggests that the linkage disequilibrium block, which includes the 102T/C polymorphism of the 5-HT2A receptor gene, is involved in individual differences in analgesic requirements in women.

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.

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.

Progress in genetic studies of pain and analgesia

Interindividual variability in pain sensitivity and the response to analgesic manipulations remains a considerable clinical challenge as well as an area of intense scientific investigation. Techniques in this field have matured rapidly so that much relevant data have emerged only in the past few years. Our increasing understanding of the genetic mediation of these biological phenomena have nonetheless revealed their surprising complexity. This review provides a comprehensive picture and critical analysis of the field and its prospects.

The many faces of the genetics contribution to temporomandibular joint disorder

OBJECTIVES

Review the literature on candidate genes for temporomandibular joint disorder (TMD). Setting and Sample Population - Literature review.

MATERIALS AND METHODS

Two basic approaches were used to obtain literature in any language regarding genes and TMD. First, Medline, Embase, and Science Citation Index databases were searched using the keywords 'temporomandibular joint disorder' and 'temporomandibular joint dysfunction' for studies published from 1966 to 2007. Then, the references list of the studies obtained in the database was also considered.

RESULTS

Candidate genes for TMD include genes for individual variations in pain perception, gender and ethnicity, proinflammatory cytokines, female hormones, breakdown of extracellular matrix, and syndromic forms of TMD.

CONCLUSION

Most of the studies on genetic variation contributing to TMD are approaching the disease mainly from an immune-inflammatory perspective. Recent investigations of the genetic variables which may predict identifiable levels of pain perception may uncover new approaches to our traditional treatment modalities for the chronic pain patient.

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.

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.

Genetics of chronic pain states

Chronic pain states are common in the general population. Genetic factors can explain a significant amount of the variability in the perception of pain. Fibromyalgia syndrome (FMS) and related conditions are syndromes characterized by generalized pain sensitivity as well as a constellation of other symptoms. Family studies show a strong familial aggregation of FMS and related conditions, suggesting the importance of genetic factors in the development of these conditions. Recent evidence suggests a role for polymorphisms of genes in the serotoninergic, dopaminergic and catecholaminergic systems in the pathogenesis of FMS and related conditions. Environmental factors may trigger the development of these disorders in genetically predisposed individuals. Future large well-designed studies are needed to further clarify the role of genetic factors in FMS and related conditions. The knowledge of these gene polymorphisms may help with better subgrouping of FMS patients and in designing a more specific pharmacologic treatment approach.

Fibromyalgia and Overlapping Disorders: The Unifying Concept of Central Sensitivity Syndromes

OBJECTIVES

To discuss fibromyalgia syndrome (FMS) and overlapping conditions, eg, irritable bowel syndrome, headaches, and chronic fatigue syndrome, within the concept of central sensitivity syndromes (CSS).

METHODS

A critical overview of the literature and incorporation of the author's own views.

RESULTS

The concept of CSS seems viable. It is based on mutual associations among the CSS conditions as well as the evidence for central sensitization (CS) among several CSS members. However, such evidence is weak or not available in other members at this time, requiring further studies. The biology of CSS is based on neuroendocrine aberrations, including CS, that interact with psychosocial factors to cause a number of symptoms.

CONCLUSIONS

CSS is an important new concept that embraces the biopsychosocial model of disease. Further critical studies are warranted to fully test this concept. However, it seems to have important significance for new directions for research and patient care involving physician and patient education. Each patient, irrespective of diagnosis, should be treated as an individual considering both the biological and psychosocial contributions to his or her symptoms and suffering.

The genetics of fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a common chronic widespread pain syndrome mainly affecting women. Although the etiology of FMS is not completely understood, varieties of neuroendocrine disturbances, as well as abnormalities of autonomic function, have been implicated in its pathogenesis. The exposure of a genetically predisposed individual to a host of environmental stressors is presumed to lead to the development of FMS. Fibromyalgia overlaps with several related syndromes, collectively compromising the spectrum of the functional somatic disorder. FMS is characterized by a strong familial aggregation. Recent evidence suggests a role for polymorphisms of genes in the serotoninergic, dopaminergic and catecholaminergic systems in the etiopathogenesis of FMS. These polymorphisms are not specific for FMS and are similarly associated with additional comorbid conditions. The mode of inheritance in FMS is unknown, but it is most probably polygenic. Recognition of these gene polymorphisms may help to better subgroup FMS patients and to guide a more rational pharmacological approach. Future genetic studies conducted in larger cohorts of FMS patients and matched control groups may further illuminate the role of genetics in FMS.

Irritable Bowel Syndrome: A Practical Review

The epidemiology and current understanding of the pathophysiology of irritable bowel syndrome is reviewed, beginning with a historical perspective. The roles of genetics, environment, allergy, infection and inflammation, bacterial overgrowth, hormones and motility abnormalities are discussed. Using the current evidence-based literature, the practical approach of diagnosis and treatment is outlined, including traditional modalities and newer therapeutic agents such as serotonin modulators.

The genetics of irritable bowel syndrome

Because of the heterogeneity in symptoms and diagnostic findings, patients with irritable bowel syndrome (IBS) remain a challenge to treat and to study. This difficulty stems from lack of understanding of the pathophysiology of this disorder. Environmental factors likely play an important role in the pathogenesis and clinical manifestations of IBS. Several recent studies suggest a genetic basis for IBS, either in etiology or predicting response to therapy. Because of interest in studying the genetic contributors to this and other functional gastrointestinal disorders, we review the literature on genetic risk factors that might explain the familial clustering of IBS. Familial aggregation studies and twin studies suggest a modest contribution of genetics to the development of IBS. Pharmacogenomic and association studies provide stronger, although far from conclusive, evidence for genetic variants that affect expression of IBS. Together, these studies suggest that a multidisciplinary approach with clinical and psychological tools, epidemiologic methods, and genetic techniques might help elucidate the molecular components leading to the common symptoms of IBS and result in better treatments for those with IBS.

Irritable bowel syndrome: a syndrome in evolution

As a group, functional gastrointestinal disorders are the most common gastrointestinal disorder seen by both generalists and specialists. These disorders can be frustrating to both patients and physicians as they are usually chronic in nature and difficult to treat. These disorders are associated with frequent healthcare visits, the scheduling of multiple, expensive diagnostic tests, and the use of both over-the-counter and prescription medications. All of these factors lead to a significant economic burden to society. In addition, functional gastrointestinal disorders are associated with a reduction in quality of life for the patient. Irritable bowel syndrome (IBS) is the most common of the functional gastrointestinal disorders. This syndrome has been the focus of a large number of research studies over the past two decades. These studies have resulted in a number of significant changes in our definition of IBS. In addition, these research studies have produced considerable changes in our understanding of the etiology and pathogenesis of IBS. In this section, we will review some of the evolutionary changes that have occurred in IBS. We will discuss how the definition of IBS has changed, consider our evolving strategies to evaluate and diagnose IBS, and finally, provide a brief overview of treatment options for this common disorder.