Autoimmune polyglandular syndromes (APS) are rare and orphan diseases that are usually characterized by the presence of two or more endocrine gland disorders in the same patient, and in some cases by the combination of other non-endocrine gland autoimmune disorders (1). APS is characterized by a wide range of heterogeneity, which manifests itself sequentially over the time intervals of disease onset (2). Based on the different combinations of autoimmune endocrine diseases, APS has been classified into four types, APS-1, APS-2, APS-3, and APS-4 (2).

APS-1, also known as Autoimmune Poly-Endocrine-Candidiasis-Ectodermal-Dystrophy (APECED) or multiple autoimmune syndrome type 1 (MAS-1), is mainly caused by mutations in the autoimmune regulatory gene (AIRE) on chromosome 21 and is inherited in an autosomal recessive inheritance pattern (3). APS-1 is clinically characterized by chronic mucocutaneous candidiasis (CMC), chronic hypoparathyroidism, and Addison’s disease (AD), as well as ectodermal dystrophy and many other disorders affecting endocrine and non-endocrine organs. APS-1 is diagnosed when an individual has at least two of the three conditions: CMC, hypoparathyroidism, and AD. The diagnostic criteria for APS-1 also include serum interferon-ω1 (IFNω1), the hallmark antibody for APS-1, and interferon-alpha (IFN-α), in combination with mutations in the AIRE gene (4, 5). The prevalence of APS-1 typically ranges from 1:80,000 to 1:100,000, and it can be higher in some populations. For example, it is 1:9,000 among Iranian Jews, 1:14,500 in Sardinia, and 1:25,000 in the Finnish population (6).

APS-2 is defined as AD combined with type 1 diabetes mellitus (T1D) and/or autoimmune thyroid disease (AITD). AD is a mandatory component of APS-2, while T1D and AITD are not. Additionally, many other autoimmune diseases may also be associated with APS-2, including celiac disease (CeD), vitiligo, alopecia areata, myasthenia gravis, pernicious anemia, IgA deficiency, autoimmune liver disease, and hypogonadotropic hypogonadism (7, 8). It is also strongly associated with CeD. The prevalence of APS-2 is approximately 1:20,000, with a male-to-female ratio of 1:3. It has also been shown that APS-2 is more common in middle-aged women (9).APS-3 is the most common subtype, with an approximate prevalence of 1:20,000 in the general population. It also has a higher prevalence in women than in men (10). APS-3 is defined as an association of AITD with other autoimmune diseases, excluding Addison’s disease and hypoparathyroidism (11). APS-4 is a highly heterogeneous disease, and there are no clear and comprehensive diagnostic criteria for it. A study by Elisa Gatta et al. demonstrated a prevalence rate of 9:100,000 in the general population (12). APS-4 is defined as a condition that excludes the endocrine-organ-affecting diseases from the previous groups (11). It involves various clinical combinations of autoimmune diseases, where one endocrine organ (excluding AD, AITD, or hypoparathyroidism) is affected in combination with at least one other endocrine or non-endocrine organ (12).

CeD is a distinct intestinal autoimmune disorder triggered by the ingestion of gluten-containing foods among carriers of the genetically susceptible genes (HLA-DQ2/8), which may result in inflammation, villous atrophy, crypt hyperplasia, and malabsorption in the small intestine (13). When individuals consume gluten-containing foods, it initiates a T-cell-mediated self-destructive process in the small intestinal mucosa, which typically recovers when these grains and gluten are strictly excluded from the diet (14). Currently, a strict gluten-free diet (GFD) remains the sole effective treatment for CeD (15, 16). The prevalence of CeD in the general population varies from 0.5% to 2%, with an average prevalence of about 1%. The clinical manifestations of CeD are diverse (13, 17). Patients with CeD frequently experience gastrointestinal distress, weight loss, fatigue, bone hypomineralization, and hypocalcemia, while only a small proportion of patients present with anemia, weight loss, and infertility (18–20). Moreover, patients with CeD frequently have comorbidities with various extra-intestinal autoimmune diseases, mainly including AITD, T1D, systemic lupus erythematosus, and autoimmune liver disease (21). Deficiencies in iron, zinc, vitamin D, vitamin B12, or folate are the most common laboratory findings (18). Multiple studies have demonstrated that patients with CeD exhibit a high prevalence of glandular autoimmune diseases (22, 23). Autoimmune diseases frequently comorbid with CeD are also listed in the APS diagnostic guidelines. It has been suggested that there may be a high prevalence of APS in patients with CeD. However, the frequency of APS in patients with CeD remains unknown. Globally, there is a lack of epidemiological data on the comorbidity of APS in CeD, and its clinical features and staging distribution still need to be clarified.

In this study, by screening the clinical data and medical records of patients diagnosed with CeD in northwest China, we determined the prevalence of different types of APS in CeD and the clinical features of CeD combined with APS, aiming to provide a basis for the subsequent diagnosis and prevention of APS. This is the first systematic evaluation of the prevalence and typing characteristics of APS in CeD patients within the Chinese population, filling the data gap regarding APS prevalence in CeD.

Celiac disease (CeD) is an autoimmune enteropathy precipitated by gluten intake, and its pathogenesis encompasses genetic, environmental, and immune - microenvironment factors (17, 29). Patients with CeD frequently present with comorbidities involving various glandular autoimmune disorders, such as thyroid-associated Hashimoto’s thyroiditis (HT) and Graves’ disease (GD), pancreas-associated T1D, and adrenal - associated Addison’s disease (18, 26, 30). AITD, T1D, and AD are major components of APS. The diverse comorbidities of CeD suggest a potentially increased prevalence of APS in CeD patients. Furthermore, CeD shares a common genetic background with mono-and poly-glandular autoimmune diseases, where HLA-DQ2 and/or DQ8 are the predominant shared genetic susceptibility factors. However, to date, studies investigating the incidence of APS in CeD and their clinical features remain scarce. This study systematically assessed the prevalence and typing characteristics of APS in CeD within a Chinese population for the first time, thus filling a gap in the epidemiological data.

In the present study, through the analysis of the prevalence and typing characteristics of APS among 243 CeD patients, it was found that the overall prevalence of APS in CeD patients was 10.3% (25/243), and the male-to-female ratio was 1:4. The prevalence of different types of APS was as follows: APS-1, 0.4%; APS-2, 0.4%; APS-3, 8.2%; and APS-4, 1.2%. This finding suggests that the prevalence of APS among CeD patients is significantly higher than that in the general population.

Our screening for APS-1 was based on IFNω1 and IFN-α antibody positivity in combination with AIRE gene mutations as the primary diagnostic approach. Subsequently, we incorporated the patients’ clinical manifestations. Specifically, the presence of at least two of the three main features - chronic cutaneous mucocutaneous candidiasis, hypoparathyroidism, and AD was used to confirm the diagnosis of APS-1 (31, 32). The 243 enrolled CeD patients were screened for IFNω1 and IFN -α antibodies. After the screening process, one individual tested positive for both IFNω1 and IFN-α antibodies. We further screened this individual for AIRE gene mutations and detected multiple AIRE gene mutations in this individual. Based on the IFNω1 and IFN-α antibody results and the AIRE gene test results, the diagnosis of APS-1 for this patient was confirmed. In addition to AD and hypoparathyroidism, this patient’s clinical manifestations also included CeD, chronic atrophic gastritis, osteoporosis, and vitamin D deficiency.

We identified a 19-year-old female patient with APS-2. Her tTG-IgA level was 25.8 IU/mL, and her BMI was 18.37. The patient had AD, HT, and T1D, fulfilling the diagnostic criteria for APS-2. The patient had been previously diagnosed with APS MM during an earlier endocrinology consultation, yet the specific APS type remained undetermined. In addition to these disorders, the patient had a comorbid combination of CeD and vitamin D deficiency. CeD shares a common genetic and immunological basis with APS-2. Nearly all CeD patients carry the HLA-DQ2/DQ8 haplotype, and the central role of the HLA in autoimmunity is further evidenced by the high expression of HLA-DR3/DR4 in APS-2 patients (33, 34). Regarding Addison’s disease, whether occurring in isolation or as part of APS-2, the HLA genotypes conferring the highest risk are DR3/4 and DQ2/DQ8, especially in individuals carrying the DRB1*04:04 allele (35). Furthermore, the HLA-DQA1 and HLA-DQB1 genes are strongly associated with T1D, with DQ8.1 and DQ2.5 being the principal risk haplotypes for T1D. Previous studies have also demonstrated that polymorphisms in HLA class II molecules are associated with susceptibility to APS-2, APS-3, and APS-4.In the present study, we further investigated the HLA genotype of this patient and found that the patient’s HLA typing result was DQ7.5/DQ2.2 (DQA1*05:05-DQB1*03:01/DQA1*02:01-DQB1*02:02). The DQ7.5/DQ2.2 haplotype is associated with an increased risk of developing CeD, although this risk is substantially lower than that associated with the HLA-DQ2.5 and HLA-DQ8 haplotypes (36–38). To the best of our knowledge, there have been no direct investigations into the relationship between the HLA-DQ7.5/DQ2.2 haplotype and APS. However, several studies have demonstrated that HLA genes, especially the HLA class II locus, play a crucial role in the genetic susceptibility to APS. Different HLA alleles and haplotypes may be associated with different subtypes of APS or may be protective against certain autoimmune diseases (34).

In the present study, we screened and identified 20 patients with APS - 3. Among these patients, 13 had comorbid HT and 7 had comorbid GD. AITD is one of the most prevalent comorbid glandular autoimmune disorders in CeD, and thyroid antibodies are detected in approximately 10% to 30% of CeD patients (30, 39). A study of Italian CeD patients also found that the most common comorbid autoimmune glandular disease among CeD patients was AITD, with a comorbidity rate of approximately 24.2% (8). In the present study, we found that AITD had a comorbidity rate of 8.6% among CeD patients, which is in line with previous research findings (40). The coexistence of CeD and AITD can be attributed to shared genetic factors, such as HLA-DR3 or DR4 (which are associated with DQ2 and DQ8, respectively). HLA-associated genes, particularly DQA1*0501 and DQB1*0201, are associated with both CeD and AITD (41). Considering the high comorbidity rate of AITD in CeD, the prevalence of APS-3 among CeD patients may be significantly higher than that of other APS types, and this finding was also corroborated in the present study. Notably, the implementation of a gluten-free diet (GFD) in CeD patients with AITD facilitated a reduction in the dose of thyroid medication and decelerated the progression of AITD (42).

In addition, a total of three patients with APS-4 were identified through screening, and T1D was the predominant autoimmune glandular disease among APS-4. Given the extensive heterogeneity of APS-4, patients had varying comorbidities of other autoimmune disorders in addition to gland-associated autoimmune disorders. Previous studies have found that AITD and T1D are the most prevalent autoimmune glandular comorbidities in CeD (8). A single-center study involving 111 APS-4 patients revealed that T1D served as the primary diagnostic indicator in 78% of APS-4 patients, while 19% of the subjects reported T1D as a secondary clinical manifestation of APS-4. Moreover, their study also identified CeD as the most common comorbidity other than T1D (12). This could be attributed to the fact that both diseases share common HLA susceptibility alleles (43–45). There exists a genetic and immunological overlap between T1D and CeD, especially with respect to the HLA-DQ2 and HLA-DQ8 haplotypes. HLA-related genes play a pivotal role in the immune response, which might account for the shared susceptibility of these two diseases (46). Furthermore, patients with CeD have an elevated risk of developing T1D, and the risk of developing CeD is significantly higher in T1D patients (44, 45).

Among 25 patients with APS, vitamin D deficiency (13 cases, 52%) and H. pylori infection (8 cases, 32%) were the most prevalent comorbidities apart from CeD. Vitamin D deficiency is a common comorbidity in CeD. Intestinal inflammation and injury induced by CeD can cause vitamin D malabsorption, thereby resulting in vitamin D deficiency (47, 48). Conversely, as previous studies have reported, vitamin D deficiency may exacerbate the symptoms and comorbid conditions associated with CeD. Vitamin D deficiency might be implicated in the pathogenesis of APS via multiple mechanisms. It has the potential to affect the function of immune cells, modify cytokine production, and disrupt the establishment of immune tolerance (49). Bellastella et al., in a case - control study, demonstrated that 25 - hydroxyvitamin D (25 - OHD, vitamin D) levels were significantly lower in patients with APS than in healthy subjects (P < 0.001) (50). In the present study, 13 out of 25 patients with APS had concomitant vitamin D deficiency, suggesting that vitamin D deficiency could be one of the clinical manifestations of APS. However, it cannot be excluded that vitamin D deficiency is a consequence of a single autoimmune disease within the APS spectrum. H. pylori infection was positively correlated with the development of AITD(OR = 2.25, 95%;CI: 1.72 - 2.93). H. pylori infection may exacerbate AITD via molecular mimicry, immune response, and other mechanisms (51, 52). It has also been demonstrated that H. pylori infection can impact the host’s immune system, resulting in the disruption of immune tolerance and the activation of autoimmune responses. This immune dysregulation might promote the development of multiple autoimmune diseases within the APS context (53, 54).

We further analyzed the differences between patients with CeD co-occurring with APS and those with CeD alone. The results showed that there was no significant difference in age between patients with CeD co-morbid APS and those with CeD without APS (P = 0.238). However, further stratified analysis by age groups showed that the age of patients with middle-aged CeD co-morbid APS was significantly higher than that of patients with middle-aged CeD without APS (P < 0.05), which may be mainly attributed to the fact that the prevalence of APS-associated autoimmune diseases usually increases with age. A large-scale UK cohort study (22 million participants) on age- and sex-standardized incidence and prevalence of 19 autoimmune diseases showed that approximately 4.4% of individuals were newly diagnosed with at least one autoimmune disease, with a mean diagnosis age of 54 years, suggesting that middle age (30–60 years) may represent a high-prevalence age range for autoimmune disease development (55). In addition, the levels of tTG in patients with CeD co - occurring with APS were significantly lower than those in patients with CeD without APS comorbidity (P < 0.001), suggesting that the tTG level in CeD patients may not be associated with the incidence of autoimmune diseases. A prior study also indicated that not all patients with the highest anti - tTG antibody titers had concomitant autoimmune diseases (20). Besides age and tTG, no statistically significant differences were observed between the CeD with APS comorbidity group and the CeD without APS comorbidity group in terms of gender, ethnicity, and BMI (P > 0.05). Moreover, we discovered that patients with CeD co-occurring with APS were more prone to experience anxiety and depression compared to patients with CeD alone (P > 0.05). This might be related to several factors, such as the autoimmune processes of diverse autoimmune diseases, hormonal imbalances, and the reduced quality of life associated with chronic diseases (56, 57).

Although this study addresses a gap in data regarding the prevalence of APS among Chinese patients with CeD, it has several limitations. Firstly, the current study was a single-center retrospective investigation. The retrospective nature of the study design might have introduced sample selection bias. Secondly, the identification of comorbidities in CeD patients in the present study was derived from hospital-based medical records in the past. Since the patients were not followed up, the study cannot determine the sequence of occurrence of different autoimmune diseases. Moreover, the ethnic distribution of CeD patients included in the present study was concentrated in the Uyghur and Kazakh ethnic groups (79.8%). It is plausible that certain geographic or genetic factors might influence the prevalence of APS. Nevertheless, our meticulous diagnostic procedures for various types of APS and the analysis of patients’ clinical records enhanced the reliability of our results.

In conclusion, the overall prevalence of APS among CeD patients was 10.3%. The prevalence of different subtypes of APS was as follows: APS-1, 0.4%; APS-2, 0.4%; APS-3, 8.2%; and APS-4, 1.2%. To the best of our knowledge, this study is the first to report the prevalence of APS in CeD patients. The high prevalence of AITD among CeD patients might be the primary factor contributing to the co-occurrence of APS in these patients. Moreover, CeD and APS share a genetic background, and both are associated with major histocompatibility complex (MHC) class II molecules. This suggests the significance of screening for APS in CeD patients. Our study also revealed that CeD patients with concomitant APS were more likely to experience anxiety and depression. These findings not only disclose the unique association pattern between CeD and APS in the Chinese population but also offer a crucial foundation for clinical screening. In the future, large-scale cohort studies are required to further explore the association and shared pathogenesis between CeD and gland-related autoimmune diseases. Moreover, screening for APS in CeD patients is essential for the early detection and treatment of associated autoimmune diseases and the enhancement of patients’ quality of life.