Analysis of the autoimmune regulator gene in patients with autoimmune non-APECED polyendocrinopathies

Analysis of the AIRE Gene Promoter in Patients Affected by Autoimmune Polyendocrine Syndromes

Autoimmune polyglandular syndromes (APS) are classified into four main categories, APS1-APS4. APS1 is caused by AIRE gene loss of function mutations, while the genetic background of the other APS remains to be clarified. Here, we investigated the potential association between AIRE gene promoter Single Nucleotide Polymorphisms (SNPs) and susceptibility to APS. We sequenced the AIRE gene promoter of 74 APS patients, also analyzing their clinical and autoantibody profile, and we further conducted molecular modeling studies on the identified SNPs. Overall, we found 6 SNPs (-230Y, -655R, -261M, -380S, -191M, -402S) of the AIRE promoter in patients' DNA. Interestingly, folding free energy calculations highlighted that all identified SNPs, except for -261M, modify the stability of the nucleic acid structure. A rather similar percentage of APS3 and APS4 patients had polymorphisms in the AIRE promoter. Conversely, there was no association between APS2 and AIRE promoter polymorphisms. Further AIRE promoter SNPs were found in 4 out of 5 patients with APS1 clinical diagnosis that did not harbor AIRE loss of function mutations. We hypothesize that AIRE promoter polymorphisms could contribute to APS predisposition, although this should be validated through genetic screening in larger patient cohorts and in vitro and in vivo functional studies.

Analysis of a series of Italian APECED patients with autoimmune hepatitis and gastro-enteropathies

Introduction

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) syndrome is a rare monogenic disease determined by biallelic mutations in AIRE gene, which encodes a transcription factor essential for central immune tolerance. Classic diagnosis is determined by the presence of two of the main APECED clinical diseases: chronic mucocutaneous candidiasis, chronic hypoparathyroidism, and Addison's disease. Non-endocrine autoimmunity, involving the liver, intestine, eyes, and kidneys, is generally reported in a minority of European patients, while American APECED patients have a higher tendency of developing organ-specific non-endocrine manifestations early in life. This observation led to the revision of the diagnostic criteria to permit earlier diagnosis based on the appearance of one classic triad symptom or one non-classical manifestation at a young age in the presence of IFNωAbs or AIRE mutations (Ferre-Lionakis criteria).

Patients and methods

We analyzed the clinical, genetic, and autoantibody (Ab) profiles in a series of 14 pediatric Italian APECED patients with gastrointestinal manifestations (seven male and seven female patients). Ten patients presented hepatitis (APECED-associated hepatitis (APAH)), while seven were affected by constipation, diarrhea, and malabsorption. Four patients had developed APAH before classic triad symptoms.

Results

Based on the age of appearance of non-endocrine manifestations including APAH and gastro-enteropathy, the Ferre-Lionakis criteria would have allowed an expedited diagnosis in 11/14 patients. Abs to tryptophan hydroxylase (TPHAb) and hepatic aromatic l-amino acid decarboxylase (AADC) were significantly associated with APECED patients of the present series. Abs to cP4501A2 were detectable in the serum of 4/8 patients with APAH, and Abs to cP4502A6 were detectable in 3/8 patients. AADC Abs tested positive in 5/7 patients, which is indicative of gastrointestinal dysfunction in APECED and TPHAb in 5/7 patients with gastrointestinal dysfunction. IFNAb was significantly associated with the syndrome.

Conclusion

Although Ferre-Lionakis expanded criteria applied to the American cohorts of APECED patients would require validation in independent large cohorts of European patients, the results of this study emphasize the importance to evaluate the presence and the age of appearance of APAH and autoimmune enteropathy even in European cohorts for an earlier APECED diagnosis. An earlier APECED diagnosis would also allow the prevention of episodes of life-threatening hypocalcemic seizures and adrenal crisis, which are the main manifestations of undiagnosed APECED.

In Search for the Missing Link in APECED-like Conditions: Analysis of the AIRE Gene in a Series of 48 Patients

Autoimmune diseases are a heterogeneous group of disorders of the immune system. They can cluster in the same individual, revealing various preferential associations for polyendocrine autoimmune syndromes. Clinical observation, together with advances in genetics and the understanding of pathophysiological processes, has further highlighted that autoimmunity can be associated with immunodeficiency; autoimmunity may even be the first primary immunodeficiency manifestation. Analysis of susceptibility genes for the development of these complex phenotypes is a fundamental issue. In this manuscript, we revised the clinical and immunologic features and the presence of AIRE gene variations in a cohort of 48 patients affected by high polyautoimmunity complexity, i.e., APECED-like conditions, also including patients affected by primary immunodeficiency. Our results evidenced a significant association of the S278R polymorphism of the AIRE gene with APECED-like conditions, including both patients affected by autoimmunity and immunodeficiency and patients with polyautoimmunity compared to healthy controls. A trend of association was also observed with the IVS9+6 G>A polymorphism. The results of this genetic analysis emphasize the need to look for additional genetic determinants playing in concert with AIRE polymorphisms. This will help to improve the diagnostic workup and ensure a precision medicine approach to targeted therapies in APECED-like patients.

Novel Gene Mutations Regulating Immune Responses in Autoimmune Polyglandular Syndrome With an Atypical Course

Context

Autoimmune polyglandular syndrome (APS) is a cluster of endocrine disorders arising from immune dysregulation, often combined with damage to nonendocrine organs. There are 2 types of APS: type 1 and type 2 (APS-1 and APS-2, respectively). In clinical practice, an atypical course of APS is often observed.

Objective

This work aims to find a novel genetic predictor of APS.

Methods

We performed exome sequencing in 2 patients with an atypical clinical APS picture and members of their families. Patient A presented with a manifestation of APS-2 in early childhood and patient B with a late manifestation of the main components of APS-1.

Results

In patient B, we identified inherited compound mutations as a novel combination of the c.769C > T and c.821delG alleles of AIRE and genetic variation in the CIITA gene. No homozygous or compound mutations in AIRE were found in patient A, but we did reveal mutations in genes encoding regulatory proteins of innate and acquired immunity in this patient.

Conclusion

Our data revealed novel combination of mutations in the AIRE gene in atypical APS and imply that mutations in immune-related genes may modify the clinical manifestation of APS in AIRE-mutation carriers and contribute to the development of autoimmune pathology in non-AIRE carriers with atypical APS.

Twenty Years of AIRE

About two decades ago, cloning of the autoimmune regulator (AIRE) gene materialized one of the most important actors on the scene of self-tolerance. Thymic transcription of genes encoding tissue-specific antigens (ts-ags) is activated by AIRE protein and embodies the essence of thymic self-representation. Pathogenic AIRE variants cause the autoimmune polyglandular syndrome type 1, which is a rare and complex disease that is gaining attention in research on autoimmunity. The animal models of disease, although not identically reproducing the human picture, supply fundamental information on mechanisms and extent of AIRE action: thanks to its multidomain structure, AIRE localizes to chromatin enclosing the target genes, binds to histones, and offers an anchorage to multimolecular complexes involved in initiation and post-initiation events of gene transcription. In addition, AIRE enhances mRNA diversity by favoring alternative mRNA splicing. Once synthesized, ts-ags are presented to, and cause deletion of the self-reactive thymocyte clones. However, AIRE function is not restricted to the activation of gene transcription. AIRE would control presentation and transfer of self-antigens for thymic cellular interplay: such mechanism is aimed at increasing the likelihood of engagement of the thymocytes that carry the corresponding T-cell receptors. Another fundamental role of AIRE in promoting self-tolerance is related to the development of thymocyte anergy, as thymic self-representation shapes at the same time the repertoire of regulatory T cells. Finally, AIRE seems to replicate its action in the secondary lymphoid organs, albeit the cell lineage detaining such property has not been fully characterized. Delineation of AIRE functions adds interesting data to the knowledge of the mechanisms of self-tolerance and introduces exciting perspectives of therapeutic interventions against the related diseases.

AIRE genetic variants and predisposition to polygenic autoimmune disease: The case of Graves' disease and a systematic literature review

Autoimmune Regulator (AIRE) is a transcriptional regulator that is crucial for establishing central tolerance as illustrated by the Mendelian Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED) syndrome associated with AIRE-inactivating recessive or dominant mutations. Polymorphisms in AIRE have been proposed to be implicated in genetic susceptibility to non-Mendelian organ specific autoimmune diseases. Because there is evidence that in predisposition to Graves' disease (GD) central tolerance is crucial, we investigated whether AIRE polymorphisms could modulate risk of GD. A case-control association study using 29 variants and conducted in 150 GD patients and 200 controls did not detect any significant association. This result is not exceptional: a systematic review of the literature, including GWAS, on the association of AIRE variants with organ specific autoimmune diseases did not show clear associations; similarly heterozygous recessive mutations are not associated to non-Mendelian autoimmunity. Dominant negative mutations of AIRE are associated to autoimmunity but as mild forms of APECED rather than to non-Mendelian organ specific autoimmunity. The lack of association of common AIRE polymorphisms with polygenic autoimmune diseases is counterintuitive as many other genes less relevant for immunological tolerance have been found to be associated. These findings give rise to the intriguing possibility that evolution has excluded functionally modifying polymorphisms in AIRE.

The putative role of proteolytic pathways in the pathogenesis of Type 1 diabetes mellitus: the 'autophagy' hypothesis

Autoimmune diseases are a heterogeneous group of disorders affecting different organs and tissues. New tools, such as genome-wide association studies, have provided evidence for new susceptibility loci and candidate genes in the disease process including common susceptibility genes involved in the immunological synapse and T cell activation. Close linkages have been found in a number of diseases, including ankylosing spondylitis, multiple sclerosis, Crohn's disease and insulin-dependent diabetes mellitus (Type 1 diabetes mellitus). Evidence for some association with Type 1 diabetes was previously found in the region containing 5q15/ERAP1 (endoplasmic reticulum aminopeptidase 1) (rs30187, ARTS1). Recent data suggest that in eukaryotic cells in addition to the ubiquitin/proteasome system another proteolytic pathway may have a significant role in the autoimmunity process, i.e. the autophagic pathway which constitutes the principal regulated catabolic process mediated by lysosomes. Autophagy could play a role in MHC class I and class II self-antigen presentation at the basis of the autoimmunity process. Furthermore cross-talk among different proteolytic pathways was recently highlighted i.e. components processed in the ubiquitin/proteasome system possibly engaged in autophagic pathways. T1D is an autoimmune disease characterised by the destruction of pancreatic beta cells by autoreactive T cells. Immunological abnormalities can precede months to years the initial symptoms and clinical diagnosis. Our hypothesis suggests that in the autoimmune process autophagy can intervene at different levels, during the thymic selection process of T lymphocytes causing escape of autoreactive T cells, at the initiation stage of the disease, in the preclinical period or subsequently to the disease onset having a role at the level of perpetuation of the autoimmunity process. Supporting evidence derives from the already reported discovery of polymorphisms in autophagy-related genes in patients affected by several autoimmune conditions such as Systemic Lupus Erithematosus. In addition deregulated autophagy was detected in T cells from lupus-prone mice and also found in T cells from patients. Autophagy was found activated in osteoclasts from RA patients as demonstrated by the increased expression of Atg7 and Beclin-1. Our hypothesis to be unraveled could have, if correct, relevant implications for the management of autoimmune conditions such as Type 1 diabetes. In principle, novel therapeutic approaches could be established by targeting deregulated autophagy offering novel opportunities to personalized medicine in patients affected by the disease.

Human APECED; a Sick Thymus Syndrome?

Loss-of-function mutations in the Autoimmune Regulator (AIRE) gene cause a rare inherited form of autoimmune disease, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, also known as autoimmune polyglandular syndrome type 1. The patients suffer from multiple endocrine deficiencies, the most common manifestations being hypoparathyroidism, Addison’s disease, hypogonadism, and secondary amenorrhea, usually accompanied by typical autoantibodies against the target tissues. Chronic mucocutaneous candidiasis is also a prominent part of the disease. The highest expression of AIRE is found in medullary thymic epithelial cells (mTECs). Murine studies suggest that it promotes ectopic transcription of self antigens in mTECs and is thus important for negative selection. However, failed negative selection alone is not enough to explain key findings in human patients, necessitating the search for alternative or additional pathogenetic mechanisms. A striking feature of the human AIRE-deficient phenotype is that all patients develop high titers of neutralizing autoantibodies against type I interferons, which have been shown to downregulate the expression of interferon-controlled genes. These autoantibodies often precede clinical symptoms and other autoantibodies, suggesting that they are a reflection of the pathogenetic process. Other cytokines are targeted as well, notably those produced by Th17 cells; these autoantibodies have been linked to the defect in anti-candida defenses. A defect in regulatory T cells has also been reported in several studies and seems to affect already the recent thymic emigrant population. Taken together, these findings in human patients point to a widespread disruption of T cell development and regulation, which is likely to have its origins in an abnormal thymic milieu. The absence of functional AIRE in peripheral lymphoid tissues may also contribute to the pathogenesis of the disease.