Diabetes mellitus is a common endocrine disease in dogs, with the most frequent presentation being that of insulin deficiency with a life-long requirement for exogenous insulin . Contributing factors to canine diabetes pathogenesis may include autoimmunity, pancreatitis, insulin resistance related to endocrine disease or high progesterone, and rarely, congenital β-cell hypoplasia .
Canine diabetes is considered to be similar to human type 1 diabetes (T1D) ; however, some important unknowns persist with respect to the disease pathogenesis in dogs that are well established in the human form of the disease. Human T1D is considered a chronic autoimmune disease characterized by islet autoimmunity and insulin deficiency . Autoantibodies readily detectable in serum provide a marker of autoimmunity months to years before disease onset , with some 90–95% of patients positive for one or more autoantibodies at diagnosis . Hence, autoantibodies are well established biomarkers in T1D, especially those that target insulin, glutamic acid decarboxylase 65 (GAD65), insulinoma associated protein 2 (IA-2), and zinc transporter 8 (ZnT8) [3, 5]. In contrast, evidence for autoimmune mechanisms, including the presence of autoantibodies as biomarkers in canine diabetes are inconsistent [2, 6]. Studies to date have noted insulin autoantibodies in 3–12.5% of untreated diabetic dogs [7, 8]. GAD65 autoantibodies were detected in 0.8–13% of diabetic dogs using a canine specific assay [9, 10], and in 0% of diabetic dogs and 20% of control dogs using a human assay . Autoantibodies to IA-2 were observed in 10% of diabetic dogs using a canine specific assay  and 0% of diabetic dogs using a human assay ; the latter study also found no diabetic or control dogs to be positive for ZnT8 autoantibodies using a human assay.
The role of genetics in human T1D is well established, with human leukocyte antigen (HLA) haplotypes as the major genetic risk factor, along with over 60 non-HLA genes having lesser contributions . With respect to canine diabetes, a variety of breeds have been found to have a higher risk of diabetes in various geographic regions [13,14,15,16], suggesting a genetic component to the disease in this species as well. The Samoyed has repeatedly been identified as a high risk breed in the United States, United Kingdom, and Sweden [13,14,15,16]. Odds ratios for developing the disease in Samoyeds in the United States were reported as 3.3  and 11.8 , and in the United Kingdom as 35 . In addition, in one study in the United States, Australian Terriers were noted as being 32 times more likely to develop diabetes compared with mixed breed dogs . Additionally, Australian Terriers were also found to be at higher risk in Sweden  and Australia . A variety of studies have identified genetic risk factors associated with the disease in multiple dog breeds, including dog leukocyte antigen (DLA) haplotype , T-cell cytokine gene polymorphisms , and CTLA4 gene polymorphisms . These genetic associations often appear to be breed specific, and the degree of contribution of the identified genes to disease risk is currently unclear and may differ among breeds .
Hence, it has become increasingly apparent that canine diabetes is a heterogenous disease with multiple pathogenic factors [2, 6]. We have previously speculated that autoimmune mechanisms may be a component of the disease in a subset of diabetic dogs, potentially in certain breeds . Studies investigating immune system involvement in canine diabetes thus far have generally included a wide variety of breeds, whereas studies interrogating potential autoimmune mechanisms in a large number of dogs from a single breed are lacking. As noted earlier, the Australian Terrier and Samoyed are of particular interest due to their previously documented high risk for developing diabetes [13,14,15,16,17]. Therefore, the objective of this study was to evaluate the presence of GAD65, IA-2, and ZnT8 autoantibodies in diabetic and non-diabetic Australian Terriers and Samoyeds geographically located in the United States using human antigen sandwich enzyme-linked immunosorbent (ELISA) assays.