The alternative serotonin transporter promoter P2 impacts gene function in females with irritable bowel syndrome

Genetics of irritable bowel syndrome: shifting gear via biobank-scale studies

The pathophysiology of irritable bowel syndrome (IBS) is multifactorial and probably involves genetic predisposition and the effect of environmental factors. Unlike other gastrointestinal diseases with a heritable component, genetic research in IBS has been scarce and mostly characterized by small underpowered studies, leading to inconclusive results. The availability of genomic and health-related data from large international cohorts and population-based biobanks offers unprecedented opportunities for long-awaited, well-powered genetic studies in IBS. This Review focuses on the latest advances that provide compelling evidence for the importance of genes involved in the digestion of carbohydrates, ion channel function, neurotransmitters and their receptors, neuronal pathways and the control of gut motility. These discoveries have generated novel information that might be further refined for the identification of predisposed individuals and selection of management strategies for patients. This Review presents a conceptual framework, the advantages and potential limitations of modern genetic research in IBS, and a summary of available evidence.

Temporal Relationships Between Abdominal Pain, Psychological Distress and Coping in Patients With IBS - A Time Series Approach

OBJECTIVE

Irritable bowel syndrome (IBS) is a chronic disease leading to abdominal pain that is often related to psychological distress. The aim of the study was to investigate the temporal relationships between abdominal pain and psychological variables in patients with IBS.

METHODS

This longitudinal diary study included eight patients from a waiting group, recruited in the frame of a pilot intervention study. During their waiting time of 3 months the patients answered questions daily regarding somatic and psychological variables using an online diary. All patients were considered and analyzed as single cases. The temporal dynamics between the time series of psycho-somatic variables were analyzed using a vector autoregressive (VAR) modeling approach.

RESULTS

For all patients, positive same-day correlations between somatic and psychological time series were observed. The highest same-day correlations were found between somatic symptoms and pain-related discomfort (r = 0.40 to r = 0.94). Altogether, n = 26 significant lagged relationships were identified; n = 17 (65%) indicated that somatic values were predictive of psychological complaints on the following days. N = 9 (35%) lagged relationships indicated an opposite relationship in that psychological complaints were predictive of somatic symptoms. Three patients showed a significant positive same-day correlation between abdominal pain and use of a positive coping strategy. However, significant lagged relationships in two patients showed that for these patients the use of positive thinking as a coping strategy was unhelpful in reducing pain on the following days.

CONCLUSIONS

In patients with IBS abdominal symptoms appear to be closely related to psychological symptoms. For some patients, somatic complaints predict psychological complaints, in other patients the directionality is opposite. The impact of coping strategies on somatic symptoms varies among patients, therefore their role for a possible reduction of pain should be further explored. The results suggest the need of characterizing patientsindividually for effective health interventions. Individual time series analyses provide helpful tools for finding reasonable person-level moderators.

Identification of gene candidates associated with Irritable bowel syndrome

Background/Aim: Irritable bowel syndrome (IBS) belongs to the gastrointestinal disorders characterised by abdominal discomfort and pain, altered constipation, diarrhoea and stomach distension. The aim was to assess relationship between the selected genetic polymorphisms with IBS, their combined genotype effect as well as to assess a difference in the distribution of allele and genotype frequencies of selected loci between case and control group. Methods: This was a prospective study which included 29 participants, 20 individuals diagnosed with IBS based on Rome III criteria and 9 healthy individuals. The study analysed the selected genetic polymorphisms as possible risk factors for IBS according to the model of the case-control study. Genotyping was performed for FKBP5, DRD2 and DAT polymorphisms qualified as risk factors for IBS in previous researches. Results: The results revealed a significant association between DAT polymorphism with IBS, both, at the allelic level (p = 0.006) and genotype level (p = 0.031). Individuals with 434 allelic variant in the genotype have six time higher probability for developing IBS, in comparison to the individuals without this allelic variant. The statistical association between other analysed polymorphism and IBS was not reached. The analysis of combined effects of selected polymorphisms revealed no association with IBS, except FKBP5 and DAT which result was at the level of statistical significance (p = 0.05). Conclusion: Further analysis which would include DAT polymorphism with larger sample size, as well as other genes involved in dopamine neurotransmitter system would be of great interest to define closer conclusion of IBS aetiology.

The alternative serotonin transporter promoter P2 impacts gene function in females with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a gut-brain disorder in which symptoms are shaped by serotonin acting centrally and peripherally. The serotonin transporter gene SLC6A4 has been implicated in IBS pathophysiology, but the underlying genetic mechanisms remain unclear. We sequenced the alternative P2 promoter driving intestinal SLC6A4 expression and identified single nucleotide polymorphisms (SNPs) that were associated with IBS in a discovery sample. Identified SNPs built different haplotypes, and the tagging SNP rs2020938 seems to associate with constipation-predominant IBS (IBS-C) in females. rs2020938 validation was performed in 1978 additional IBS patients and 6,038 controls from eight countries. Meta-analysis on data from 2,175 IBS patients and 6,128 controls confirmed the association with female IBS-C. Expression analyses revealed that the P2 promoter drives SLC6A4 expression primarily in the small intestine. Gene reporter assays showed a functional impact of SNPs in the P2 region. In silico analysis of the polymorphic promoter indicated differential expression regulation. Further follow-up revealed that the major allele of the tagging SNP rs2020938 correlates with differential SLC6A4 expression in the jejunum and with stool consistency, indicating functional relevance. Our data consolidate rs2020938 as a functional SNP associated with IBS-C risk in females, underlining the relevance of SLC6A4 in IBS pathogenesis.