Type 1 diabetes is an autoimmune disease. People with type 1 have higher rates of some other autoimmune diseases than the general population, especially thyroid disease, celiac disease, autoimmune gastritis, and Addison's disease. Of patients with type 1 diabetes, perhaps 25% will have thyroid disease (the most common other autoimmune disease associated with type 1), around 7% will have celiac disease, up to 20% will have markers of pernicious anemia (associated with autoimmune gastritis), and about 2% will have markers of Addison's disease (Narendran et al. 2005). One clinic screened patients for thyroid, celiac, and Addison's disease association antibodies when they were diagnosed with type 1, and found that one-third of new type 1s had autoantibodies for these other autoimmune diseases (Triolo et al. 2011).

 

There are two main categories of autoimmune diseases: systemic autoimmune diseases, that target multiple organs or tissues; and organ-specific autoimmune diseases, that target one organ (such as the pancreas in type 1 diabetes). Some researchers propose that many autoimmune diseases may share a common mechanism, especially organ-specific autoimmune diseases. They hypothesize that the development of autoimmune disease is determined in part by genetic susceptibility, and in part by a deficiency or dysfunction in certain immune system cells called regulatory T cells (discussed on the autoimmunity page). Under this hypothesis, a single environmental factor may lead to the occurrence of different autoimmune diseases, frequently more than one, in a single individual. Also, different environmental factors might lead to a single type of autoimmune disease in individuals genetically susceptible to that disease (Sakaguchi 2004). Thus, the role that environmental exposures may play in other autoimmune diseases may be relevant for type 1 diabetes.

 

A number of genes that increase the risk of type 1 diabetes have been identified (Concannon et al. 2009), so genetic susceptibility does play a role in the development of type 1 diabetes. Various differing autoimmune diseases have also been found to have common susceptibility genes (e.g., see Maiti et al. 2010). Type 1 diabetes and celiac disease, for example, are both associated with some of the same susceptibility genes (Smyth et al. 2008).

 

Like type 1 diabetes incidence, the incidence of many immune disorders, including many other autoimmune diseases, is rising (Bach 2002).

The role of environmental factors in various autoimmune diseases is a growing area of research. The current state of this research is summarized nicely for the public in this article, "Questions Persist: Environmental Factors in Autoimmune Disease," published in the peer-reviewed journal, Environmental Health Perspectives (Schmidt 2011).