Characterization of mutations in patients with autoimmune polyglandular syndrome type 1 (APS1)

Autoimmune polyglandular syndrome type 1 (APS1), also known as autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), is an autosomal recessive disorder characterized by the failure of several endocrine glands as well as nonendocrine organs. The autoimmune regulator (AIRE) gene responsible for APS1 on chromosome 21q22.3 has recently been identified. Here, we have characterized mutations in the AIRE gene by direct DNA sequencing in 16 unrelated APS1 families ascertained mainly from the USA. Our analyses identified four different mutations (a 13-bp deletion, a 2-bp insertion, one nonsense mutation, and one potential splice/donor site mutation) that are likely to be pathogenic. Fifty-six percent (9/16) of the patients contained at least one copy of a 13-bp deletion (1094–1106del) in exon 8 (seven homozygotes and two compound heterozygotes). A nonsense mutation (R257X) in exon 6 was also found in 31.3% (5/16) of the USA patients. These data are important for genetic diagnosis and counseling for families with autoimmune endocrine syndromes. Received: 24 August 1998 / Accepted: 29 September 1998     

Effector mechanisms of the autoimmune syndrome in the murine model of autoimmune polyglandular syndrome type 1

Mutations in the Aire gene result in a clinical phenomenon known as Autoimmune Polyglandular Syndrome (APS) Type I, which classically manifests as a triad of adrenal insufficiency, hypoparathyroidism, and chronic mucocutaneous infections. In addition to this triad, a number of other autoimmune diseases have been observed in APS1 patients including Sj?gren's syndrome, vitiligo, alopecia, uveitis, and others. Aire-deficient mice, the animal model for APS1, have highlighted the role of the thymus in the disease process and demonstrated a failure in central tolerance in aire-deficient mice. However, autoantibodies have been observed against multiple organs in both mice and humans, making it unclear what the specific role of B and T cells are in the pathogenesis of disease. Using the aire-deficient mouse as a preclinical model for APS1, we have investigated the relative contribution of specific lymphocyte populations, with the goal of identifying the cell populations which may be targeted for rational therapeutic design. In this study, we show that T cells are indispensable to the breakdown of self-tolerance, in contrast to B cells which play a more limited role in autoimmunity. Th1 polarized CD4(+) T cells, in particular, are major contributors to the autoimmune response. With this knowledge, we go on to use therapies targeted at T cells to investigate their ability to modulate disease in vivo. Depletion of CD4(+) T cells using a neutralizing Ab ameliorated the disease process. Thus, therapies targeted specifically at the CD4(+) T cell subset may help control autoimmune disease in patients with APS1.     

Subcellular location and expression pattern of autoimmune regulator (Aire), the mouse orthologue for human gene defective in autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED).

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), also known as autoimmune polyglandular syndrome Type I (APS1), is an autosomal recessive autoimmune disease caused by mutations in a gene designated as AIRE (autoimmune regulator). Here we have studied the expression of Aire in transfected cell lines and in adult mouse tissues. Our results show that Aire has a dual subcellular location and that it is expressed in multiple immunologically relevant tissues such as the thymus, spleen, lymph nodes, and bone marrow. In addition, Aire expression was detected in various other tissues such as kidney, testis, adrenal glands, liver, and ovary. These findings suggest that APECED protein might also have a function(s) outside the immune system.(J Histochem Cytochem 49:197-208, 2001)     

The role of autoimmune regulator (Aire) in the development of the immune system

AIRE is the gene responsible for a rather rare hereditary type of autoimmune disease. The mechanism underlying the autoimmune pathogenesis caused by AIRE deficiency is a focus of intense research because it could provide clues to the fundamental question of how the immune system discriminates between self and non-self within the thymic microenvironment.     

NMR structure of the first PHD finger of autoimmune regulator protein (AIRE1). Insights into autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) disease

Mutations in the autoimmune regulator protein AIRE1 cause a monogenic autosomal recessively inherited disease: autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). AIRE1 is a multidomain protein that harbors two plant homeodomain (PHD)-type zinc fingers. The first PHD finger of AIRE1 is a mutational hot spot, to which several pathological point mutations have been mapped. Using heteronuclear NMR spectroscopy, we determined the solution structure of the first PHD finger of AIRE1 (AIRE1-PHD1), and characterized the peptide backbone mobility of the domain. We performed a conformational analysis of pathological AIRE1-PHD1 mutants that allowed us to rationalize the structural impact of APECED-causing mutations and to identify an interaction site with putative protein ligands of the AIRE1-PHD1 domain. The structure unequivocally exhibits the canonical PHD finger fold, with a highly conserved tryptophan buried inside the structure. The PHD finger is stabilized by two zinc ions coordinated in an interleaved (cross-brace) scheme. This zinc coordination resembles RING finger domains, which can function as E3 ligases in the ubiquitination pathway. Based on this fold similarity, it has been suggested that PHD fingers might also function as E3 ligases, although this hypothesis is controversial. At variance to a previous report, we could not find any evidence that AIRE1-PHD1 has an intrinsic E3 ubiquitin ligase activity, nor detect any direct interaction between AIRE1-PHD1 and its putative cognate E2. Consistently, we show that the AIRE1-PHD1 structure is clearly distinct from the RING finger fold. Our results point to a function of the AIRE1-PHD1 domain in protein-protein interactions, which is impaired in some APECED mutations.     

HLA-DQA1*0301-associated susceptibility for autoimmune polyglandular syndrome type II and III.

No significant differences were reported for the frequency of DR3-DQ2 and DR4-DQ8 haplotypes in a recent study of one of the largest cohorts worldwide of patients with isolated Addison's disease compared to patients with APS II. However, previous studies had suggested that the HLA-DQ genes, especially DQA1*0102, may be a genetic marker for resistance to autoimmune thyroid disease, which is the most frequent disease in APS II or III. Until now, HLA-DQA1 alleles have not been systematically investigated in APS. We determined the HLA-DR and HLA-DQA1 association in 112 unrelated patients with APS II (n = 29), APS III (n = 83) and 184 unrelated patients with single-component diseases without further manifestations of APS: Graves' disease (n = 70), Hashimoto's thyroiditis (n = 53), autoimmune Addison's disease (n = 15), vitiligo (n = 16) and alopecia (n = 30), and 72 healthy controls - German Caucasians - to identify possible predisposing and protective HLA class II alleles in APS. In agreement with previous studies, we detected a significantly higher frequency of DR 3 and/or DR 4 in patients with APS II and III compared to controls. In patients with APS II, we detected a significantly higher frequency of DQA1*0301 and *0501 compared to controls confirming the increased frequency of an extended HLA DRB1-*04-DQA1-*03-DQB-*03 haplotype as previously described. In contrast, only DQA1*0301 was increased in our patients with APS III compared to controls. Moreover, we detected an increased frequency of DQA1*0301 in patients with APS, whereas DQA1*0301 was only significantly elevated in alopecia in patients with single-component diseases without APS. Therefore, our results indicate an association between DQA1*0301 and APS II or III since this allele was otherwise not significantly associated with any of its component diseases except alopecia. Moreover, our data imply that the allele DQA1*0301 is a marker of increased risk for further APS manifestations in patients who suffer from an organ-specific autoimmune disease.     

Cloning and developmental expression analysis of ltd-1, the Caenorhabditis elegans homologue of the mouse kyphoscoliosis (ky) gene

We have characterized the developmental expression pattern of the Caenorhabditis elegans homologue of the mouse ky gene. The Ky protein has a putative key function in muscle development and has homologues in invertebrates, fungi and a cyanobacterium. The C. elegans Ky homologue gene has been named ltd-1 for LIM and transglutaminase domains gene. The LTD-1::GFP construct is expressed in developing hypodermal cells from the twofold stage embryo through adulthood. These data define the ltd-1 gene as a novel marker for C. elegans epithelial cell development.     

Susceptibility alleles and haplotypes of human leukocyte antigen DRB1, DQA1, and DQB1 in autoimmune polyglandular syndrome type III in Japanese population

BACKGROUND: It has been reported that HLA class II haplotypes DRB1*0405-DQA1*0303-DQB1*0401 and DRB1*0901-DQA1*0302-DQB1*0303 are major susceptibility haplotypes for type 1 diabetes mellitus (DM) in Japanese population. However, little has been reported on the susceptibility HLA class II haplotypes in Japanese patients with autoimmune polyglandular syndrome type II and type III (APS III). PATIENTS AND METHODS: HLA class II haplotypes of DRB1-DQA1-DQB1 in 31 patients with APS III, 14 patients with Hashimoto's thyroiditis alone, and 15 patients with Graves' disease alone were examined in Japanese population. APS III patients were divided into three groups (A, B, and C) depending on the combination of autoimmune endocrine diseases. RESULTS: In 13 APS III patients with both Hashimoto's thyroiditis and type 1 DM (group A), the haplotype frequencies of the HLA DRB1*0802-DQA1*0401-DQB1*0402 and DRB1*0901-DQA1*0302-DQB1*0303 were significantly higher than in the controls. In patients with Hashimoto's thyroiditis alone, the haplotype frequency of DRB1*0901-DQA1*0302-DQB1*0303 was significantly higher than in controls, whereas the frequency of DRB1*0802-DQA1*0401-DQB1*0402 did not differ significantly from those in the controls. In 11 APS III patients with both Graves' disease and type 1 DM (group B), the haplotype frequencies of HLA DRB1*0405-DQA1*0303-DQB1*0401 and DRB1*0802-DQA1*0301-DQB1*0302 were significantly higher than in controls. In patients with Graves' disease alone, the haplotype frequency of DRB1*0803-DQA1*0103-DQB1*0601 were significantly higher than those in controls, suggesting that the susceptibility haplotypes for group B APS III differed from those for Graves' disease alone. In 7 APS III patients with both autoimmune thyroid diseases and pituitary disorders (group C), the haplotype frequency of HLA DRB1*0405-DQA1*0303-DQB1*0401 was significantly higher than in controls. CONCLUSIONS: Susceptible HLA class II haplotypes of DRB1-DQA1-DQB1 for APS III differ between the Japanese and Caucasian populations. More interestingly, the susceptible HLA class II haplotypes differ among the three types of Japanese APS III and are not merely a combination of susceptibility haplotypes of each endocrine disease.     

An intragenic TaqI polymorphism in the faciogenital dysplasia (FGD1) locus,the gene responsible for Aarskog syndrome

A TaqI polymorphism, located in intron 4 of the faciogenital dysplasia (FGD1) gene, the gene responsible for Aarskog syndrome, is described. FGD1 encodes a putative Rho/Rac guanine nucleotide exchange factor involved in mammalian morphogenesis. The identification of an intragenic polymorphism will facilitate the accurate carrier detection of individuals at risk for Aarskog syndrome.     

Fine-scale mapping of the gene responsible for multiple endocrine neoplasia type 1 (MEN 1).

We have constructed a high-resolution genetic linkage map in the vicinity of the gene responsible for multiple endocrine neoplasia type 1 (MEN1). The mutation causing this disease, inherited as an autosomal dominant, predisposes carriers to development of neoplastic tumors in the parathyroid, the endocrine pancreas, and the anterior lobe of the pituitary. The 12 markers on the genetic linkage map reported here span nearly 20 cM, and linkage analysis of MEN1 pedigrees has placed the MEN1 locus within the 8-cM region between D11S480 and D11S546. The markers on this map will be useful for prenatal or presymptomatic diagnosis of individuals in families that segregate a mutant allele of the MEN1 gene.     

Cloning, chromosome mapping and functional characterization of a human homologue of murine gtse-1 (B99) gene

Murine Gtse-1 (G(2) and S phase expressed protein), previously named B99, is a wt-p53 inducible gene that encodes a microtubule-localized protein which is able to induce G(2)/M phase accumulation when ectopically expressed. Here we report the cloning and characterization of a new cDNA (GTSE-1) encoding a human homologue of the mouse Gtse-1 protein. Chromosome mapping of mouse and human genes assigned Gtse-1 to chromosome 15 and GTSE-1 to chromosome 22q13.2-q13.3 in a region with conserved synteny to that where Gtse-1 mapped. Analysis of the genomic structure revealed that GTSE-1 contains at least 11 exons and 10 introns, spanning approximately 33kb of genomic DNA. Similar to murine Gtse-1, the product of GTSE-1 localized to the microtubules, was able to delay G(2)/M progression when ectopically expressed and was cell cycle regulated. Taken together, these results indicate GTSE-1 as the human functional homologue of murine Gtse-1.