A. It's a genetic disease of the digestive system that's triggered by gluten, a protein found in wheat, as well as rye and barley. "Parents sometimes use the words allergy or intolerance to help other people understand celiac disease, but it's actually an autoimmune disease and not an allergy," says Nanci Pittman, MD, a pediatric gastroenterologist at Mount Sinai School of Medicine, in New York City. When a child with celiac disease eats foods containing gluten, her immune system attacks the lining of her small intestine so that she's unable to absorb all the nutrients in food. As a result, she may stop growing, become malnourished, and develop a variety of serious consequences such as anemia, chronic diarrhea, and osteoporosis.