Determining the progression of reflux disease in the esophagus of a patient includes identifying the location of an endoscopic gastroesophageal junction in the esophagus, removing a length of tissue of the esophagus that includes a portion of the endoscopic gastroesophageal junction, and identifying the proximal limit of tissue containing cardiac epithelium. Determining the length of the squamo-oxyntic gap of the biopsied tissue can involve measuring the length of tissue extending between the proximal limit of tissue containing gastric oxyntic epithelium to the proximal limit of tissue containing cardiac epithelium. A linear relationship can be determined from a slope of a line extending between a first data point and a second data point that can determine a target age of the patient when the lower esophageal sphincter will have a certain length.
