The study will involve subjects with endoscopically, laboratory and clinically confirmed diagnoses of organic and functional intestinal pathology or none of the above (healthy volunteers). All diagnoses are defined in accordance with the validated criteria presented in the clinical guidelines for the diagnosis and treatment of functional bowel pathology (Irritable Bowel Syndrome), 2020, Crohn's Disease (approved by the Ministry of Health of the Russian Federation, 2020), Ulcerative Colitis (approved by the Ministry of Health of the Russian Federation, 2020), in accordance with international criteria of ECCO-ESGAR Guidelines, 2018, 2019. After the initial screening and inclusion in the study, intestinal biopsy samples are taken in accordance with the applied endoscopic examination technique during the endoscopic examination. These biopsy samples will be further used for molecular and immunological diagnostics.

Procedure: Anorectal manometry (ARM) Studies are performed in the left lateral position with the hips and knees of the subject flexed. Manometric sensor records circumferential pressure. The base of the rectal balloon attached to the ARM catheter is sited 3-5 cm above the upper border of the anal canal, to prevent the balloon impinging upon the anal canal during inflation. The most distal recording sensor is external to anal verge. If any pain or discomfort is experienced, the probe is immediately withdrawn.

Procedure: Rectal sensory test (RST) The test is also performed in the left lateral position with hips and knees flexed. Studies are conducted with either an integrated balloon on the manometric probe or with a separate system. Balloon capacity is no less than 400 mls and all components are latex-free. Insufflation is always performed with air. For ramp distension, the rate should be between 1 and 5 mL/s, and for phasic distension, inflation rate should be set at 10 mL/s (C1).

Assessment of metabolome ( gas chromatographic analysis with vapor-phase extraction). Metabolic parameters (Tetradecanoic acid, Hydracinnamic acid, Hexadecanoic acid, Hexanoic acid, Indole, Pentanoic acid) will be measured in feces by gas chromatographic analysis with vapor-phase extraction method. Metabolite extraction methods are performed according to the standard metabolite isolation protocol.The above mentioned metabolites will be measured in intensity of the ion current of the analyzed metabolite, normalized to the total ion current according to the standardized methods.

Assessment of genetic profiling (risk polymorphism assessment). Assessment of risk polymorphisms: NOD2 (rs2066844, rs2066845, rs17221417), ATG16L1 (rs2241880), IL23R (rs2201841) will be performed in leukocyte fraction of blood samples according to the standardized methods. Resulting relative risk will be assessed according to the data on relative risks for each of the above mentioned polymorphisms.

Assessment of local cytokine profile by Human Cytokine Screening panel Bio-plex Pro (27 cytokines, concentrations measured in pg/ml). Local cytokine profile will be assessed in gut biopsy lyophilisate. All cytokine concentrations will be measured in pg/ml.

Assessment of systemic cytokine profile by Human Cytokine Screening panel Bio-plex Pro (27 cytokines, concentrations measured in pg/ml). Systemic cytokine profile will be assessed by serum analysis. All cytokine concentrations will be measured in pg/ml.