GERD is a common condition in the western world. In most cases, the diagnostic is established by good response to empiric proton pump inhibitor (PPI) therapy. When the patient symptoms are refractory to therapy, multiple invasive tests are available. The results of those tests (EGD, manometry, Ph monitoring and impedance) are clues that the physician use together to establish the diagnostic. No test however can be use alone because of their poor specificity and sensitivity. Recently, microscopy has been used to detect dilated intercellular space in between distal esophageal cells tissue; unfortunately this marker again failed to diagnose GERD.

In search of more sensitive and specific markers of GERD, we propose to assess if acid exposure affects: 1) gene and proteins expression in the esophageal/post-cricoid area tissue; and 2) local impedance of the mucosa. The secondary aim of this proposal is to determine if correlation exists between the two approaches.

Inclusion Criteria (GERD Cases):

• Male or female
• Ages 18 years or older
• Undergoing EGD as standard of care at Vanderbilt's Digestive Diseases Center
• Esophageal erosion detected at EGD
• Abnormal pH monitoring

Inclusion Criteria (Controls):

• Male or female
• Ages 18 years or older
• Undergoing EGD as standard of care at Vanderbilt's Digestive Diseases Center
• No complaints or history o heartburn or acid regurgitation
• No erosion at EGD
• Normal pH monitoring

Exclusion Criteria:

• Less than 18 years of age
• Unable to provide informed consent
• Use of acid suppressive therapy within last 14 days
• known history of Barrett's esophagus, gastric surgery, alcoholism, significant motility condition
• contraindications to biopsy such as taking anticoagulants other than aspirin (coumadin, plavix) or allergies to local anesthetic

Male and female volunteers ages 18 years and older; able to give informed consent; no use of acid suppressive therapy within 14 days prior to procedure; no history of Barret's esophagus, gastric surgery, alcoholism, or significant motility condition; no contraindications to biopsy, including taking anticoagulants or allergies to local anesthetic.