Researchers report this in the advance online edition of The New England Journal of Medicine.
The scientists -- who included Deborah Smyth, BSc, of England's University of Cambridge -- studied the DNA of more than 22,000 Europeans, including 8,000 type 1 diabetes patients and 2,560 people with celiac disease.
Smyth's team focused on certain gene variants linked to type 1 diabetes and other gene variants tied to celiac disease. The goal was to see whether any of those gene variants overlapped between the two diseases.
The results: Four celiac disease variants were linked to type 1 diabetes, and two type 1 diabetes variants were tied to celiac disease.
Those variants didn't always behave the same way. Some made both celiac disease and type 1 diabetes more likely. But others had opposing effects, making one condition more likely and the other disease less likely, like two sides of the same coin.
"One can begin to imagine how combinations of these alleles lead to celiac disease and other combinations lead to type 1 diabetes, with multiple possible combinations for both diseases," writes editorialist Robert Plenge, MD, PhD, of the rheumatology division of Brigham and Women's Hospital in Boston.
Celiac disease and type 1 diabetes are both autoimmune diseases, and Plenge writes that for years, epidemiologic data have suggested a "common cause" between the two conditions.
The new study shows genetic overlap among celiac disease and type 1 diabetes. But Smyth and colleagues are also eyeing environmental factors -- especially exposure to gluten, which celiac disease patients can't tolerate.
Smyth's team calls for further studies to test the hypothesis that cereal and gluten might be an environmental factor in type 1 diabetes, leading to an alteration of the function of the gut immune system and its relationship with the pancreatic immune system."
Smyth's study doesn't prove that gluten hypothesis. Plenge points out that "some combination of alleles (together with environmental factors and chance) lead to celiac disease, and others lead to type 1 diabetes" and picking apart those patterns "should lead to new insights in disease."