Certain hybrid grains such as triticale have been confirmed to contain proteins that trigger symptoms in people with celiac disease or gluten sensitivity.
"Hybrid grains" is a common catchall phrase used to describe any genetically engineered grain that combines traits or characteristics of more than one naturally occurring grain. Hybrid grains can be made using traits from any combination of natural grains, so it is always important to investigate what any specific hybrid grain is made from before attempting to determine if it is safe for people with celiac disease or gluten sensitivity. However, because this can be difficult to do hybrid grains are often lumped together and cited as potential triggers for those with celiac disease or gluten sensitivity because they can be produced using wheat, barley and rye.
One such example is triticale, which is a man-made hybrid of wheat and rye. Triticale is a recognized species within the grass family that also has its own USDA standard. Triticale is not considered safe for anyone with celiac disease or gluten sensitivity, and the FDA specifically references triticale in its inclusion of hybrid grains in its definition of gluten in its gluten-free labeling rule. Triticale is an example of a grain engineered for specific traits of its components. Wheat has long been preferred for its ability to provide a plentiful food source due to high crop yeilds and good quality, but it also suffers from greater susceptibility to certain plant disease than does rye. Triticale combines certain traits of wheat and rye in an attempt to produce a high-quality and plentiful source of plant-based protein that has enhanced resistance to disease, making it a more reliable (and thus less costly) crop to cultivate. While the goal is to produce an improved food source, triticale tends to suffer from poor performance compared to wheat when milled to make flour and baked to produce food such as bread. As a result triticale is typically only used in the U.S. as animal feed and in some breakfast cereals, but it is still an important ingredient for anyone with celiac disease or gluten sensitivity to look out for.
About the FDA Gluten-Free Labeling Rule ... Start with the FDA's guidance website
About the USDA's classification of Triticale ... Read the United States Standards for Triticale [PDF]
About Triticale ... Check out the USDA Commodity Image Gallery and its USDA profile