• willingness to participate (based on the signed informed consent form);

• presence of gastroesophageal reflux disease, based on the following: a) typical symptoms, like heartburn and/or regurgitation (for primary selection, symptoms should be present at least weekly, be actual for at least 3 months prior to the enrolment, and the patient should report the history of symptoms which lasts for at least 6 months); b) previous response to the intake of proton pump inhibitors; c) data of 24-hours oesophageal pH-impedance monitoring with detected pathological gastroesophageal reflux according to the Lyon consensus definitions;