Hypothesis driven research and molecular mechanisms in functional dyspepsia: the beginning of a beautiful friendship in research and practice?

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.

Polymorphisms of 5-HTT LPR and GNβ3 825C>T and Response to Antidepressant Treatment in Functional Dyspepsia: A Study from The Functional Dyspepsia Treatment Trial

OBJECTIVES

The Functional Dyspepsia Treatment Trial reported that amitriptyline (AMI) was associated with adequate relief of functional dyspepsia (FD) symptoms, but the pharmacogenetics of antidepressant response in FD are not known. GNβ3 825C>T CC genotype has been previously linked to FD and TT genotype to antidepressant response in depression. The ss genotype of the 5-HTT LPR variant of the serotonin transporter gene (SLC6A4) has been linked to selective serotonin reuptake inhibitor (SSRI) response. We aimed to examine whether GNβ3 825C>T and 5-HTT LPR polymorphisms result in differential treatment effects in FD patients receiving antidepressant therapy.

METHODS

Participants were randomized to receive placebo, 50 mg AMI, or 10 mg escitalopram (ESC). The primary end point was adequate relief for ≥5 weeks of the last 10 weeks. Genotyping of GNβ3 825C>T and 5-HTT LPR was performed utilizing PCR-based methods.

RESULTS

GNβ3 825C>T and 5-HTT LPR genotype data were available for 256 (88%) and 246 (84%) patients, respectively. Both polymorphisms were in Hardy-Weinberg equilibrium. In tests for differential treatment, neither 5-HTT LPR nor GNβ3 825C>T genotype influenced response to therapy (P=0.89 and P=0.54, respectively). Although there was a tendency for a more favorable response to ESC in the SS/LS genotype compared to the LL genotype groups (40% vs. 31% reporting adequate relief of FD symptoms) among those in the ESC treatment arm, this was not significant (P=0.43).

CONCLUSIONS

GNβ3 825C>T and 5-HTT LPR genetic variants do not alter treatment response to tricyclic and SSRI antidepressants in FD.

Functional dyspepsia: new insights into pathogenesis and therapy

One in 10 people suffer from functional dyspepsia (FD), a clinical syndrome comprising chronic bothersome early satiety, or postprandial fullness, or epigastric pain or burning. Postprandial distress syndrome (PDS, comprising early satiety and/or postprandial fullness) and epigastric pain syndrome (EPS) are increasingly accepted as valid clinical entities, based on new insights into the pathophysiology and the results of clinical trials. Diagnosis is based on the clinical history, and exclusion of peptic ulcer and cancer by endoscopy. Evidence is accumulating FD and gastroesophageal ref lux disease are part of the same disease spectrum in a major subset. The causes of FD remain to be established, but accumulating data suggest infections and possibly food may play an important role in subsets. FD does not equate with no pathology; duodenal eosinophilia is now an accepted association, and Helicobacter pylori infection is considered to be causally linked to dyspepsia although only a minority will respond to eradication. In those with EPS, acid suppression therapy is a first line therapy; consider a H2 blocker even if proton pump inhibitor fails. In PDS, a prokinetic is preferred. Second line therapy includes administration of a tricyclic antidepressant in low doses, or mirtazapine, but not a selective serotonin reuptake inhibitor.

Evidence-based clinical practice guidelines for functional dyspepsia

General interest in functional gastrointestinal disorders is increasing among Japanese doctors as well as patients. This increase can be attributed to a number of factors, including recent increased interest in quality of life and advances in our understanding of the pathophysiology of gastrointestinal disease. Japan recently became the world's first country to list "functional dyspepsia" as a disease name for national insurance billing purposes. However, recognition and understanding of functional dyspepsia (FD) remain poor, and no standard treatment strategy has yet been established. Accordingly, the Japanese Society of Gastroenterology (JSGE) developed an evidence-based clinical practice guideline for FD, consisting of five sections: concept, definition, and epidemiology; pathophysiology; diagnosis; treatment; and prognosis and complications. This article summarizes the Japanese guideline, with particular focus on the treatment section. Once a patient is diagnosed with FD, the doctor should carefully explain the pathophysiology and benign nature of this condition, establish a good doctor-patient relationship, and then provide advice for daily living (diet and lifestyle modifications, explanations, and reassurance). The proposed pharmacological treatment is divided into two steps: initial treatment including an acid inhibitory drug (H2RA or PPI) or prokinetics, (strong recommendation); second-line treatment including anxiolytics, antidepressants, and Japanese traditional medicine (weak recommendation). H. pylori eradication, strongly recommended with a high evidence level, is positioned separately from other treatment flows. Conditions that do not respond to these treatment regimens are regarded as refractory FD. Patients will be further examined for other organic disorders or will be referred to specialists using other approaches such as psychosomatic treatment.

Genetic contribution to motility disorders of the upper gastrointestinal tract

Motility disorders of the upper gastrointestinal tract encompass a wide range of different diseases. Esophageal achalasia and functional dyspepsia are representative disorders of impaired motility of the esophagus and stomach, respectively. In spite of their variable prevalence, what both diseases have in common is poor knowledge of their etiology and pathophysiology. There is some evidence showing that there is a genetic predisposition towards these diseases, especially for achalasia. Many authors have investigated the possible genes involved, stressing the autoimmune or the neurological hypothesis, but there is very little data available. Similarly, studies supporting a post-infective etiology, based on an altered immune response in susceptible individuals, need to be validated. Further association studies can help to explain this complex picture and find new therapeutic targets. The aim of this review is to summarize current knowledge of genetics in motility disorders of the upper gastrointestinal tract, addressing how genetics contributes to the development of achalasia and functional dyspepsia respectively.

Overlap between functional GI disorders and other functional syndromes: what are the underlying mechanisms?

BACKGROUND

Irritable bowel syndrome and other gastrointestinal (GI) and non-GI disorders such as functional dyspepsia, fibromyalgia, temporomandibular joint disorder, interstitial cystitis/painful bladder syndrome, and chronic fatigue syndrome are known as functional pain syndromes. They commonly coexist within the same individual. The pathophysiologic mechanisms of these disorders are not well understood, but it has been hypothesized that they share a common pathogenesis.

PURPOSE

The objective of this review is to discuss the proposed pathophysiologic mechanisms, which have been similarly studied in these conditions. These mechanisms include enhanced pain perception, altered regional brain activation, infectious etiologies, dysregulations in immune and neuroendocrine function, and genetic susceptibility. Studies suggest that these functional disorders are multifactorial, but factors which increase the vulnerability of developing these conditions are shared.

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.

Whither dyspepsia? A historical perspective of functional dyspepsia, and concepts of pathogenesis and therapy in 2009

Functional dyspepsia is a highly prevalent but heterogeneous disorder; multiple pathogenetic mechanisms are likely involved but the underlying causal pathways in functional dyspepsia remain obscure. The term functional dyspepsia was popularized by the famed Walter Alvarez at the Mayo Clinic early last century. Prominent Australian gastroenterologists who have contributed to our understanding of functional dyspepsia include Peter Baume, Barry Marshall, Douglas Piper, Nick Talley, John Kellow, and Gerald Holtmann. Specific dyspeptic symptoms have not generally correlated very well with any particular physiologic disturbance, although gastric disaccommodation and duodenal eosinophilia have been linked to early satiety in this condition. Genetic markers have been tentatively identified, and functional dyspepsia can follow bacterial gastroenteritis. No objective diagnostic tools for functional dyspepsia are currently agreed upon, although meal induction of symptoms appears reproducible and may have diagnostic utility. The symptomatic criteria for functional dyspepsia (Rome III criteria) are based on expert consensus and the exclusion of organic causes. Various therapeutic modalities for functional dyspepsia have been explored; however, empirical approaches are still employed for the treatment of functional dyspepsia. Better approaches for functional dyspepsia are likely to follow an improved understanding of the underlying pathophysiological abnormalities.

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.

Functional gastrointestinal disorders and the potential role of eosinophils

The eosinophil-mast cell-neural pathway may be important in the pathophysiology of functional gastrointestinal disorders characterized by unexplained abdominal pain, disordered defecation, or meal-related discomfort. There is evidence that duodenal eosinophils are increased in functional dyspepsia, whereas mast cells are increased in the lower gut in irritable bowel syndrome, directly supporting a role for a hypersensitivity-type reaction in these disorders. The trigger may be a pathogen, food, or other allergen in the gut mucosa. This trigger may evoke eosinophils, mast cells, and other components to cascade to up-regulate serotonin release, with modulation of the enteric and central nervous systems, creating a vicious cycle. If correct, this theory suggests treatment should specifically target the eosinophil-mast cell pathway.

Quality of life in patients with functional dyspepsia: Short- and long-term effect of Helicobacter pylori eradication with pantoprazole, amoxicillin, and clarithromycin or cisapride therapy: A prospective, parallel-group study

BACKGROUND

Quality of life (QOL) is impaired in functional dyspepsia (FD). Little is known about the effects of different therapies on the QOL profile in patients with this condition.

OBJECTIVES

The aims of this study were to measure baseline QOL in patients with FD and to assess changes in QOL over time associated with Helicobacter pylori eradication and prokinetic treatment. The primary and secondary end points were the improvement in QOL 6 weeks and 1 year after successful eradication of the infection or prokinetic therapy.

METHODS

This 1-year, single-center, prospective, open-label, controlled, parallel-group trial was conducted at the Department of Gastroenterology, Ferencvdros Health Centre, Budapest, Hungary. The Functional Digestive Disorder Quality of Life (FDDQoL) Questionnaire (MAPI Research Institute, Lyon, France) was translated and validated previously in Hungarian. Male and female subjects aged 20 to 60 years were enrolled and classified as H pylori positive (HP+), H pylori negative (HP-) with FD, or healthy (control group). The HP+ patients received pantoprazole 40 mg BID + amoxicillin 1000 mg BID + clarithromycin 500 mg BID for 7 days, followed by on-demand ranitidine (150-300 mg/d) for 1 year. The HP- patients received the prokinetic cisapride 10 mg TID for 1 month, followed by on-demand cisapride (10-20 mg/d) for 1 year. The FDDQoL questionnaire was completed by all 3 groups on enrollment, at 6 weeks, and 1 year.

RESULTS

A total of 101 HP+ patients, 98 HP- patients, and 123 healthy controls were included in the study (185 women, 137 men; mean age, 39.0 ears). The mean (SD) baseline QOL scores were significantly lower in the HP+ group (53.3 [9.6]; 95% CI, 54.4-58.2) and the HP- groups (50.0 [9.8]; 95% CI, 58.0-62.0) compared with that in healthy controls (76.2 [8.7]; 95% CI, 74.6-77.8) (both, P < 0.001). Analysis of the short-term domain scores found that the HP+ group had significantly decreased scores in 6 of 8 domains: daily activities (P = 0.005), anxiety level (P = 0.02), diet (P = 0.008), sleep (P < 0.001), discomfort (P = 0.004), and disease control (P = 0.02); the HP- group had significantly decreased scores in 5 of 8 domains: daily activities (P < 0.001), diet (P = 0.004), sleep (P = 0.005), discomfort (P < 0.001), and disease control (P = 0.02). Eradication of the infection was successful in 77/101 (76.2%) of the patients on intent-to-treat analysis and 77/94 (81.9%) on per-protocol analysis. Eradication was associated with an increase in mean (SD) QOL score to 70.8 (10.7) at 6 weeks (95% CI, 63.3-73.2; P < 0.001 vs baseline) and to 75.3 (9.3) at 1 year (95% CI, 73.2-77.5; P= 0.05 vs 6 weeks). In the HP- group, the QOL score increased to 73.3 (9.7) (95% CI, 71.3-75.4; P < 0.001 vs baseline) at 6 weeks of cisapride treatment and to 76.5 (8.5) at 1 year (95% CI, 74.5-78.4; P = 0.06 vs 6 weeks). Most of the impaired domain scores improved significantly after both treatments. The short-term effect size was 1.48 in HP+ and 1.35 in HP- patients. Adverse events (AEs) occurred in 22 (21.8%) patients in the HP+ group (nausea, 8 [7.9%] patients; diarrhea, 5 [5.0%]; loss of appetite, 5 [5.0%]; stomatitis, 5 [5.0%]; abdominal pain, 4 [4.0%]; bloating, 4 [4.0%]; headache, 4 [4.0%]; vomiting, 4 [4.0%]; constipation, 3 [3.0%]; and vaginitis, 3 [3.0%]). In HP- cases, AEs occurred in 9 (9.2%) patients (abdominal cramps, 7 [7.1%]; diarrhea, 4 [4.1%]; and nausea, 3 [3.1%]).

CONCLUSION

In this study in patients with FD and healthy controls, eradication of H pylori infection in infected patients and cisapride treatment in uninfected patients reversed low QOL scores during the 1-year follow-up period.