Other diseases that may cause or contribute to GERD are hypothyroidism, Crohn's disease, cancer, and developmental and neurological disorders. In addition, some diseases of the stomach can cause or contribute GERD; for example, the stomach of patients who have gastrinoma (Zollinger-Ellison synodrome) generate copious quantities of hydrochloric acid that easily penetrate the LES and cause a reflux of food backwards from the stomach to the esophagus.
Now that you've got some knowledge of why people get GERD, the next question is how doctors figure out if you have GERD.