Upper endoscopy will be arranged within 2 weeks of baseline assessment in order to exclude organic pathology such as peptic ulcer, esophagitis and neoplasm. The position and morphology of gastroesophageal junction is assessed during withdrawal of endoscope after deflation of stomach at end-expiratory of the patient in left lateral body position. The morphology of gastroesophageal junction will be graded according to the "flap valve" concept. In order to avoid the confounding effect of gross anatomical disruption of gastroesophageal junction on acid exposure at SCJ, patients with grade IV disruption of gastroesophageal junction, which refers to patulous hiatus with axial displacement of SCJ, will be excluded.