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Type 1 diabetes (T1D) is an autoimmune disorder caused by inflammatory destruction of the pancreatic tissue. The etiopathogenesis and characteristics of the pathologic process of pancreatic destruction are well described. In addition, the putative susceptibility genes for T1D as a monoglandular disease and the relation to polyglandular autoimmune syndrome (PAS) have also been well explored. The incidence of T1D has steadily increased in most parts of the world, especially in industrialized nations. T1D is frequently associated with autoimmune endocrine and non-endocrine diseases and patients with T1D are at a higher risk for developing several glandular autoimmune diseases. Familial clustering is observed, which suggests that there is a genetic predisposition. Various hypotheses pertaining to viral- and bacterial-induced pancreatic autoimmunity have been proposed, however a definitive delineation of the autoimmune pathomechanism is still lacking. In patients with PAS, pancreatic and endocrine autoantigens either colocalize on one antigen-presenting cell or are expressed on two/various target cells sharing a common amino acid, which facilitates binding to and activation of T cells. The most prevalent PAS phenotype is the adult type 3 variant or PAS type III, which encompasses T1D and autoimmune thyroid disease. This review discusses the findings of recent studies showing noticeable differences in the genetic background and clinical phenotype of T1D either as an isolated autoimmune endocrinopathy or within the scope of polyglandular autoimmune syndrome.

The autoimmune polyglandular syndrome (APS) is defined as the manifestation of at least two endocrine autoimmune diseases. In order to take the wide spectrum of components and the variations of the disease fully into account, APS is usually divided up into the rare juvenile type (APS I) and the more common adult type (APS II-IV). APS I is caused by a monogenetic mutation whereas APS II-IV has a multifactorial genesis with combination related subgroups. Early diagnosis, individual adjustment of therapy and screening of high risk patients in particular are regarded as clinically relevant. In addition to the patient's history, the diagnosis of APS encompasses serologic measurement of organ-specific autoantibodies as well as a clinical examination and functional tests. However, the analysis of immunological modificating, zytokine-coding and tissue-specific genes could also be important within a screening. Although APS is a rather rare disease with an incidence of 1:100 000 (juvenile APS) and 1:20 000 (adult APS), the possibility of an autoimmune polyglandular syndrome should be timely considered. By this means, severe complications can be avoided to some extent and the patients' physical as well as psychological quality of life can be ensured.

The HLA class II genes are susceptibility genes for autoimmune endocrine diseases; however, scarce data are available pertaining to the determinants of genetic susceptibility to polyglandular autoimmunity (PGA). A total of 300 consecutive and unselected patients with either PGA or monoglandular autoimmune thyroid disease (AITD) and 100 healthy control subjects were genotyped for the HLA class II DRB1, -DQA1, and -DQB1 alleles. Compared to patients with AITD and controls, the HLA-DRB1*03 (pc =0.001), *04 (pc<0.001), -DQA1*03 (pc<0.001), and -DQB1*02 (pc =0.001) alleles were increased in patients with PGA. When dividing patients with Hashimoto's thyroiditis (HT) into those with PGA (PGA-HT) vs. those with HT as monoglandular disease, significant differences for the DRB1*03 (pc=0.001) and DQA1*03 (pc=0.001) alleles were observed. In contrast, the DQB1*02 allele was more prevalent in PGA patients with Graves' disease (PGA-GD) vs. those with monoglandular GD (pc=0.002). The HLA-DRB1*15 (pc =0.001), -DQA1*01 (pc =0.001), -DQB1*05 (pc =0.002) and -DQB1*06 (pc =0.002) alleles were significantly less present in PGA compared to monoglandular AITD and controls, thus indicating protective alleles. The HLA class II alleles differentiate between mono- and polyglandular autoimmunity in patients with autoimmune thyroid disease.

Context The major histocompatibility complex (MHC) strongly contributes to the development of polyglandular autoimmunity (PGA). Objective To evaluate the impact of sex on human leukocyte antigen (HLA) association with PGA for the first time. Design Cross-sectional immunogenetic study. Setting Academic tertiary referral Orphan Disease Center for PGA (ORPHA 282196) and immunogenetics laboratory. Subjects Patients (158) with coexistent type 1 diabetes and autoimmune thyroid disease (adult type 3 PGA, ORPHA 227982) and 479 unrelated healthy controls. Interventions All 637 white subjects were typed for HLA-A, -B, -DRB1, -DQA1, and -DQB1 alleles at a two-field level. Main Outcome Measures Modification of the gene-disease association by sex. Results MHC class I HLA-A association was sex related to both the total white adult type 3 PGA collective (n = 158, P = 0.0065), as well as in PGA patients with autoimmune Hashimoto thyroiditis (n = 91, P = 0.010). Compared with HLA-A*02:01, A*11:01 was over-represented in male patients, yet under-represented in women (OR 1.49, 95% CI 0.55 to 3.88 vs 0.42, 0.12 to 1.17). A*24:02 was under-represented in male but not in female patients (OR 0.37, 95% CI 0.11 to 1.04 vs 1.19, 0.65 to 2.15). With the exclusion of the five most frequent alleles (A*01:01, A*02:01, A*03:01, A*11:01, and A*24:02), the sum of all other identified alleles was under-represented in male patients (OR 0.37, 0.18 to 0.72, P = 0.0046). The strong MHC HLA-B association with PGA (P &lt; 0.0001) was not sex related (P = 0.55). Furthermore, no interaction with sex was observed for the MHC class II HLA-DRB1, -DQA1, and -DQB1 alleles. Conclusion MHC class I HLA-A association with type 3 PGA is significantly affected by sex.

Familial clustering is high in patients with PGA. Quality of life and psychosocial status are poor in patients and involved relatives. Multidisciplinary management of the multiplex families in specialized centers is warranted.

Polyglandular autoimmune syndromes encompass several endocrine and nonendocrine autoimmune disorders with variable onset and phenotype. Rheumatoid and gastroenterological symptoms in patients with autoimmune polyglandular syndromes are suggestive of additional rheumatoid gastrointestinal and hepatological autoimmune diseases. Autoimmune gastritis, celiac disease, autoimmune hepatitis, rheumatoid arthritis, Sjögren syndrome, and systemic Lupus erythematodus are of particular clinical relevance. In addition, unspecific rheumatoid and gastrointestinal attendant symptoms of the existing autoimmune endocrinopathy must be considered. Furthermore, certain disorders of polyglandular autoimmune syndromes, e. g., type 1 diabetes are frequently associated with particular gastrointestinal diseases such as small bowel bacterial overgrowth. An optimal patient-centered care of subjects with autoimmune diseases requires a comprehensive differential diagnostic work up and emphasizes the importance of an interdisciplinary cooperation.

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