Aim: to evaluate the effect of obstructive sleep apnea-hypopnea syndrome (OSAHS) on E-cadherin expression and epithelium histoarchitectonics of the lower third of the esophagus. Patients and Methods: 108 patients were included in a cross-sectional comparative study. According to the results of somnology, a mild severity of OSAHS was diagnosed in 49 patients (group 1), an average severity — in 29 (group 2). Group 3 included 30 people without OSAHS. All patients underwent esophagogastroduodenoscopy with a biopsy of the lower third of the esophagus. Morphometrics of epithelial thickness, height of connective tissue papillae, and internuclear distances in all epithelial layers was performed. To assess the E-cadherin expression, immunohistochemistry was performed using monoclonal antibodies to E-cadherin. Results: in contrast to the comparison group, patients with mild and moderate OSAHS were characterized by a higher epithelium thickness (273 (228; 372), 360 (312; 411), 186 (168; 192) μm, respectively, р1–3=0.000, р2–3=0.000), higher connective tissue papillae (108 (96; 120), 144 (120; 228), 72 (60; 84) μm, respectively, р1–3=0,001, р2–3=0,000), and larger internuclear distances in superficial layer (9 (7; 10), 8 (7; 9), 6 (5; 7) μm, respectively, р1–3=0.000, р2–3=0.002), spinous layer (8 (6; 9), 8 (7; 8), 6 (5; 7) μm, respectively, р1–3=0.000, р2–3=0.000), basal layer (4 (3; 5), 3 (3; 4), 2 (2; 3) μm, respectively, р1–3=0.000, р2–3=0,001) of epithelium. E-cadherin expression decreased in patients with both mild OSAHS (0.748 (0.623; 0.833) and 0.539 (0.263; 0.676), respectively, p=0.044) and moderate OSAHS (0.748 (0.623; 0.833) and 0.163 (0.026; 0.365), respectively, p=0.000) versus the comparison group. Correlations were found between respiratory monitoring indicators and E-cadherin expression in the esophageal epithelium. Conclusion: OSAHS negatively affects the lining condition of the lower third of the esophagus, contributes to the loss of E-cadherin, which creates conditions for disorganization of epithelial tissue and increases the risk of precancerous diseases and esophageal cancer. KEYWORDS: obstructive sleep apnea-hypopnea syndrome, E-cadherin, esophageal epithelium, histoarchitectonics, epithelial-mesenchymal transition, intermittent hypoxia, apnea-hypopnea index. FOR CITATION: Shelkovich Yu.Ya. Effect of obstructive sleep apnea-hypopnea syndrome on E-cadherin expression in esophageal epithelium. Russian Medical Inquiry. 2020;4(5):268–273. DOI: 10.32364/2587-6821-2020-4-5-268-273.