A former Navy Medical Officer, Mark Johnston, MD, FACP, FACG, AGAF, has treated Members of Congress and served as Gastroenterologist to the White House. Dr. Johnston is a noted medical inventor, having patented a device to treat Barrett’s Esophagus and early esophageal cancer. Dr. Johnston is board certified in Internal Medicine and Gastroenterology and earned his medical degree at Hahnemann University. He completed his residency and GI fellowship at the National Naval Medical Center.