Here's a quick definition of Celiac Disease from a typical Google search:
Celiac disease: A disorder resulting from an immune reaction to gluten, a protein found in wheat and related grains, and present in many foods. Celiac disease causes impaired absorption and digestion of nutrients through the small intestine. Symptoms include frequent diarrhea and weight loss. A skin condition dermatitis herpetiformis can be associated with celiac disease. The most accurate test for celiac disease is a biopsy of the involved small bowel. Treatment is to avoid gluten in the diet.
That barely covers it. There is such a wide range of symptoms and medical problems from mild to serious that it boggles the mind. From what I've heard and read, most people are diagnosed after suffering for up to a decade or more of symptoms that do not seem to relate to a particular disease or serious health problem.
If I only had a hundred dollars for every time a doctor said "that's just how you were made" or "we tested you for _____, but it came back negative." Kind of surprising that a disease which is estimated to affect 1 in every 133 people is not considered a possibility more often.