Irritable bowel syndrome phenotypes: leading factors of genetics and epigenetics, mechanisms of formation

Aim. To develop individualized approaches to the treatment of irritable bowel syndrome (IBS) based on the interaction of genetic and epigenetic factors, to characterize the phenotypes of the disease. Materials and methods. According to the formulated concept of the authors, from the cohort of patients with IBS, subgroups were distinguished post-infectious IBS (n=45), IBS in overweight and obese people (n=49), comorbid IBS (n=75) and essential IBS (n=51). In each subgroup the prevalence of candidate gene polymorphisms associated with IBS (COMT, SLC6A4, FTO), nutritional habits, levels of anxiety and depression, secretion of cortisol, serotonin, dopamine and zonulin levels in feces were studied. Results. Patients with post-infectious IBS are characterized by the carriage of the S allele of the SLC6A4 gene, the val/val genotype of the COMT gene, the prevalence of diarrhea, a high level of anxiety and frequent refusal of milk and dairy products. The phenotype IBS in overweight and obese individuals is characterized by L/L genotypes of the SLC6A4 gene, met/met of the COMT gene and A/A of the FTO gene, constipation, low plasma dopamine levels, signs of depression, frequent episodes of overeating, addiction to fatty and sweet foods, excessive consumption of sugar, lack of vegetables in the diet. The comorbid IBS phenotype is characterized by more frequent detection of the val/val genotype of the COMT gene and the carriage of the S allele of the SLC6A4 gene, clinically pronounced anxiety and depression, early onset of the disease, severe course, significant food restrictions and significant increase in epithelial permeability. With the essential phenotype, there are no bright stigmas of the disease; it is not possible to identify distinctive genetic and epigenetic factors, as well as the leading pathogenetic mechanism. Conclusion. The analysis of genetic and epigenetic factors, the leading mechanisms of the formation and course of IBS allows us to identify additional (except for postinfectious) phenotypes of the disease: IBS in overweight and obese people, comorbid and essential.