Prevalence and clinical associations of calcium-sensing receptor and NALP5 autoantibodies in Finnish APECED patients

Calcium-sensing receptor-mediated NLRP3 inflammasome activation in rheumatoid arthritis and autoinflammation

The calcium-sensing receptor (CaSR) is expressed in many cell types - including immune cells and in particular circulating monocytes. Here, the receptor plays an important physiological role as a regulator of constitutive macropinocytosis. This review article provides an overview of the literature on the role of the calcium sensing receptor in the context of inflammatory processes. Special emphasis is laid upon the importance for monocytes in the context of rheumatoid arthritis. We have shown previously, that stimulation of the receptor by increased extracellular Ca²⁺ ([Ca²⁺]_ex) triggers a pro-inflammatory response due to NLRP3 inflammasome assembly and interleukin (IL)-1β release. The underlying mechanism includes macropinocytosis of calciprotein particles (CPPs), which are taken up in a [Ca²⁺]_ex-induced, CaSR dependent manner, and leads to strong IL-1β release. In rheumatoid arthritis (RA), this uptake and the resulting IL-1β release is significantly increased due to increased expression of the receptor. Moreover, increased [Ca²⁺]_ex-induced CPP uptake and IL-1β release is associated with more active disease, while CaSR overexpression has been reported to be associated with cardiovascular complications of RA. Most importantly, however, in animal experiments with arthritic mice, increased local calcium concentrations are present, which in combination with release of fetuin-A from eroded bone could contribute to formation of CPPs. We propose, that increased [Ca²⁺]_ex, CPPs and pro-inflammatory cytokines drive a vicious cycle of inflammation and bone destruction which in turn offers new potential therapeutic approaches.

The study on the risk of other endocrine glands autoimmune diseases in patients with type 1 diabetes mellitus

To study the changes of pancreas, thyroid, adrenal, parathyroid and gonadal organ-specific antibodies in patients with type 1 diabetic patients and to explore the risk of development to other endocrine gland autoimmune diseases.Fifty one patients with type 1 diabetes mellitus were selected. ELISA was used to detect islet, adrenal gland, Parathyroid, gonadal organ-specific antibody levels, the level of thyroid-related antibodies by lectrochemiluminescence.Compared with the healthy control group, the levels of the 17-α-OHAb, 21-OHAb, NALP5Ab, P450sccAb, and CaSRAb in the T1DM group were significantly higher. GADAb-positive patients were more likely to have TPOAb-positive patients than GADAb-negative patients, and the positive rate of 2 thyroid antibodies in GADAb-positive patients was significantly higher than that in GADAb-negative patients. The presence of these antibodies is related to the age of onset of type 1 diabetes or Patient age. In combination with 1 or 2 islet antibody-positive patients, the combined non-islet antibody positive rate was higher than that of islet antibody-negative patients.Patients with type 1 diabetes with other autoimmune diseases at risk significantly increased compared with normal, of which the most common thyroid autoimmune disease, thyroid antibodies and hormone levels should be routinely detected at the first visit and long-term follow-up.

Epidemiology, pathogenesis, and diagnosis of Addison's disease in adults

BACKGROUND

Addison's disease (AD) is a rare disorder and among adult population in developed countries is most commonly caused by autoimmunity. In contrast, in children genetic causes are responsible for AD in the majority of patients.

PURPOSE

This review describes epidemiology, pathogenesis, genetics, natural history, clinical manifestations, immunological markers and diagnostic strategies in patients with AD. Standard care treatments including the management of patients during pregnancy and adrenal crises consistent with the recent consensus statement of the European Consortium and the Endocrine Society Clinical Practice Guideline are described. In addition, emerging therapies designed to improve the quality of life and new strategies to modify the natural history of autoimmune AD are discussed.

CONCLUSIONS

Progress in optimizing replacement therapy for patients with AD has allowed the patients to lead a normal life. However, continuous education of patients and health care professionals of ever-present danger of adrenal crisis is essential to save lives of patients with AD.

Calcium-Sensing Receptor Autoantibodies in Patients with Autoimmune Polyendocrine Syndrome Type 1: Epitopes, Specificity, Functional Affinity, IgG Subclass, and Effects on Receptor Activity

A major manifestation of autoimmune polyendocrine syndrome type 1 (APS1) is hypoparathyroidism, which is suggested to result from aberrant immune responses against the parathyroid glands. The calcium-sensing receptor (CaSR), which plays a pivotal role in maintaining calcium homeostasis by sensing blood calcium levels and regulating release of parathyroid hormone (PTH), is an autoantibody target in APS1. In this study, the aim was to characterize the binding sites, specificity, functional affinity, IgG subclass, and functional effects of CaSR autoantibodies using phage-display technology, ELISA, and bioassays. The results indicated that CaSR autoantibody binding sites were at aa 41-69, 114-126, 171-195, and 260-340 in the extracellular domain of the receptor. Autoantibodies against CaSR epitopes 41-69, 171-195, and 260-340 were exclusively of the IgG1 subclass. Autoantibody responses against CaSR epitope 114-126 were predominantly of the IgG1 with a minority of the IgG3 subclass. Only autoantibodies recognizing CaSR epitopes 114-126 and 171-195 affected receptor activity; inositol-phosphate accumulation was increased significantly in HEK293-CaSR cells, and PTH secretion from PTH-C1 cells was reduced significantly when either were incubated with purified Ab and Ca2+ compared with Ca2+ alone. In conclusion, although the majority of APS1 patients do not have CaSR-stimulating autoantibodies, the hypoparathyroid state in a small minority of patients is the result of functional suppression of the parathyroid glands.

Causes and pathophysiology of hypoparathyroidism

Hypoparathyroidism, a disorder characterized by hypocalcemia ensuing from inadequate parathyroid hormone secretion, is a rather rare disorder caused by multiple etiologies. When not caused by inadvertent damage or removal of the parathyroids during neck surgery, it is usually genetically determined. Epidemiological figures of this disease are still scarce and mainly limited to countries where non-anonymous databases are available and to surgical case series. Both the surgical and non-surgical forms pose diagnostic challenges. For surgical hypoparathyroidism, transient forms have to be ruled out even in the long term, in order to avoid unnecessary chronic replacement therapy with calcium and calcitriol. Regarding non-surgical hypoparathyroidism, once referred to as idiopathic, a systematic clinically and genetically-driven approach to define the precise diagnosis have to be pursued. In the case of syndromic hypoparathyroidism, patients have to be screened for associated abnormalities. Autoimmune, non-genetic hypoparathyroidism is still a diagnosis of exclusion, since no specific autoantibodies are specific for this condition.

Severe Symptomatic Hypocalcemia from HIV Related Hypoparathyroidism

We report the case of a 54-year-old Caucasian female who presented with a two-year history of persistent hypocalcemia requiring multiple hospitalizations. Her medical history was significant for HIV diagnosed four years ago. She denied any history of prior neck surgery or radiation. Her vital signs were stable with an unremarkable physical exam. Pertinent medications included calcium carbonate, vitamin D3, calcitriol, efavirenz, emtricitabine, tenofovir disoproxil, hydrochlorothiazide, and inhaled budesonide/formoterol. Laboratory testing showed total calcium of 5.7 mg/dL (normal range: 8.4-10.2 mg/dL), ionized calcium of 2.7 mg/dL (normal range: 4.5-5.5 mg/dL), serum phosphate of 6.3 mg/dL (normal range: 2.7-4.5 mg/dL), and intact PTH of 7.6 pg/mL (normal range: 15-65 pg/mL). She was diagnosed with primary hypoparathyroidism. Anti-calcium-sensing receptor antibodies and NALP5 antibodies were tested and found to be negative. During subsequent clinic visits, doses of calcium supplements and calcitriol were titrated. Last corrected serum calcium level was 9.18 mg/dL. She was subsequently lost to follow-up. This case gives insight into severe symptomatic hypocalcemia from primary hypoparathyroidism attributed to HIV infection. We suggest that calcium levels should be closely monitored in patients with HIV infection.

APECED in Turkey: A case report and insights on genetic and phenotypic variability

APECED is a rare monogenic recessive disorder caused by mutations in the AIRE gene. In this manuscript, we report a male Turkish patient with APECED syndrome who presented with chronic mucocutaneous candidiasis associated with other autoimmune manifestations developed over the years. The presence of the homozygous R257X mutation of the AIRE gene confirmed the diagnosis of APECED syndrome. We further performed literature review in 23 published Turkish APECED patients and noted that Finnish major mutation R257X is common in Turks. In particular, we assessed retrospectively how often the Ferre/Lionakis criteria would have resulted in earlier diagnosis in Finns, Sardinians and Turks in respect to the classic criteria. Since an earlier diagnosis could have been possible in 18.8% of Turkish, in 23.8% of Sardinian and 38.55% of Finnish patients we reviewed from literature, Ferre/Lionakis criteria could indeed allow in future earlier initiation of immunomodulatory treatments, if found effective in future studies.

Autoantibodies against the calcium-sensing receptor and cytokines in autoimmune polyglandular syndromes types 2, 3 and 4

OBJECTIVE

The frequency of autoimmunity against the parathyroid glands in patients with polyglandular autoimmunity that is not due to autoimmune polyendocrine syndrome type 1 (APS1) is unclear. To investigate this, this study aimed to determine the prevalence of autoantibodies against parathyroid autoantigens, calcium-sensing receptor (CaSR) and NACHT leucine-rich-repeat protein 5 (NALP5), in a large group of patients with non-APS1 polyendocrine autoimmunity. Possible occult APS1 was investigated by cytokine autoantibody measurement and AIRE gene analysis.

DESIGN, SUBJECTS AND MEASUREMENTS

Subjects were 178 patients with APS2, 3 or 4, and 80 healthy blood donors. Autoantibodies against the CaSR, NALP5 and cytokines were measured by immunoprecipitation, radioligand binding assays or ELISA, respectively.

RESULTS

Four patient samples (2.2%), but none of the controls, were positive for CaSR autoantibodies. NALP5 autoantibodies were not detected in any participant. Eleven patients (6.2%) had cytokine autoantibodies, but none of the control samples was positive. None of the patients with cytokine autoantibodies had any known or novel mutations in the AIRE gene.

CONCLUSIONS

The low prevalence of CaSR autoantibodies indicate a very low level of subclinical parathyroid autoimmunity in APS types 2, 3 and 4. In addition, autoantibodies against cytokines constitute an uncommon feature of non-APS1 polyglandular autoimmunity.

Exome Sequencing Reveals Mutations in AIRE as a Cause of Isolated Hypoparathyroidism

Context

Most cases of autosomal recessive hypoparathyroidism (HYPO) are caused by loss-of-function mutations in GCM2 or PTH.

Objective

The objective of this study was to identify the underlying genetic basis for isolated HYPO in a kindred in which 3 of 10 siblings were affected.

Subjects

We studied the parents and the three adult affected subjects, each of whom was diagnosed with HYPO in the first decade of life.

Methods

We collected clinical and biochemical data and performed whole exome sequencing analysis on DNA from the three affected subjects after negative genetic testing for known causes of HYPO.

Results

Whole exome sequencing followed by Sanger sequencing revealed that all three affected subjects were compound heterozygous for two previously reported mutations, c.967_979delCTGTCCCCTCCGC:p.(L323SfsX51) and c.995+(3_5)delGAGinsTAT, in AIRE, which encodes the autoimmune regulator protein that is defective in autoimmune polyglandular syndrome type 1 (APS-1). Each parent carries one mutation, and all of the children of the patients are either heterozygous for one mutation or wild type. The affected sister developed premature ovarian failure, but the two affected brothers have no other features of APS-1 despite elevated serum levels of anti-interferon-α antibodies.

Conclusions

Our findings indicate that biallelic mutations in AIRE can cause isolated HYPO as well as syndromic APS-1. The presence of antibodies to interferon-α provides a highly sensitive indicator for loss of AIRE function and represents a useful marker for isolated HYPO due to AIRE mutations.

Diseases associated with calcium-sensing receptor

The calcium-sensing receptor (CaSR) plays a pivotal role in systemic calcium metabolism by regulating parathyroid hormone secretion and urinary calcium excretion. The diseases caused by an abnormality of the CaSR are genetically determined or are more rarely acquired. The genetic diseases consist of hyper- or hypocalcemia disorders. Hypercalcaemia disorders are related to inactivating mutations of the CASR gene either heterozygous (autosomal dominant familial benign hypercalcaemia, still named hypocalciuric hypercalcaemia syndrome type 1) or homozygous (severe neonatal hyperparathyroidism). The A986S, R990G and Q1011E variants of the CASR gene are associated with higher serum calcium levels than in the general population, hypercalciuria being also associated with the R990G variant. The differential diagnosis consists in the hypocalciuric hypercalcaemia syndrome, types 2 (involving GNA11 gene) and 3 (involving AP2S1 gene); hyperparathyroidism; abnormalities of vitamin D metabolism, involving CYP24A1 and SLC34A1 genes; and reduced GFR. Hypocalcemia disorders, which are more rare, are related to heterozygous activating mutations of the CASR gene (type 1), consisting of autosomal dominant hypocalcemia disorders, sometimes with a presentation of pseudo-Bartter’s syndrome. The differential diagnosis consists of the hypercalciuric hypocalcaemia syndrome type 2, involving GNA11 gene and other hypoparathyroidism aetiologies. The acquired diseases are related to the presence of anti-CaSR antibodies, which can cause hyper- or especially hypocalcemia disorders (for instance in APECED syndromes), determined by their functionality. Finally, the role of CaSR in digestive, respiratory, cardiovascular and neoplastic diseases is gradually coming to light, providing new therapeutic possibilities. Two types of CaSR modulators are known: CaSR agonists (or activators, still named calcimimetics) and calcilytic antagonists (or inhibitors of the CasR). CaSR agonists, such as cinacalcet, are indicated in secondary and primary hyperparathyroidism. Calcilytics have no efficacy in osteoporosis, but could be useful in the treatment of hypercalciuric hypocalcaemia syndromes.

Pathogenic and Protective Autoantibodies in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED)

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare disorder caused by mutations in the autoimmune regulator (AIRE) gene, leading to defects in T cell selection. The disease manifestations include both autoimmune tissue destruction and immunodeficiency, with specific susceptibility to chronic mucocutaneous candidiasis. Studies have demonstrated a wide repertoire of high affinity tissue- and cytokine-specific antibodies in patients with APECED. Here, we review the antigenic targets and function of these disease-causing and disease-ameliorating antibodies.

Epidemiology and Health-Related Quality of Life in Hypoparathyroidism in Norway

OBJECTIVE

The epidemiology of hypoparathyroidism (HP) is largely unknown. We aimed to determine prevalence, etiologies, health related quality of life (HRQOL) and treatment pattern of HP.

METHODS

Patients with HP and 22q11 deletion syndrome (DiGeorge syndrome) were identified in electronic hospital registries. All identified patients were invited to participate in a survey. Among patients who responded, HRQOL was determined by Short Form 36 and Hospital Anxiety and Depression scale. Autoantibodies were measured and candidate genes (CaSR, AIRE, GATA3, and 22q11-deletion) were sequenced for classification of etiology.

RESULTS

We identified 522 patients (511 alive) and estimated overall prevalence at 102 per million divided among postsurgical HP (64 per million), nonsurgical HP (30 per million), and pseudo-HP (8 per million). Nonsurgical HP comprised autosomal dominant hypocalcemia (21%), autoimmune polyendocrine syndrome type 1 (17%), DiGeorge/22q11 deletion syndrome (15%), idiopathic HP (44%), and others (4%). Among the 283 respondents (median age, 53 years [range, 9-89], 75% females), seven formerly classified as idiopathic were reclassified after genetic and immunological analyses, whereas 26 (37% of nonsurgical HP) remained idiopathic. Most were treated with vitamin D (94%) and calcium (70%), and 10 received PTH. HP patients scored significantly worse than the normative population on Short Form 36 and Hospital Anxiety and Depression scale; patients with postsurgical scored worse than those with nonsurgical HP and pseudo-HP, especially on physical health.

CONCLUSIONS

We found higher prevalence of nonsurgical HP in Norway than reported elsewhere. Genetic testing and autoimmunity screening of idiopathic HP identified a specific cause in 21%. Further research is necessary to unravel the causes of idiopathic HP and to improve the reduced HRQOL reported by HP patients.

Serological proteome analysis reveals new specific biases in the IgM and IgG autoantibody repertoires in autoimmune polyendocrine syndrome type 1

OBJECTIVE

Autoimmune polyendocrine syndrome type 1 (APS 1) is caused by mutations in the AIRE gene that induce intrathymic T-cell tolerance breakdown, which results in tissue-specific autoimmune diseases.

DESIGN

To evaluate the effect of a well-defined T-cell repertoire impairment on humoral self-reactive fingerprints, comparative serum self-IgG and self-IgM reactivities were analyzed using both one- and two-dimensional western blotting approaches against a broad spectrum of peripheral tissue antigens.

METHODS

Autoantibody patterns of APS 1 patients were compared with those of subjects affected by other autoimmune endocrinopathies (OAE) and healthy controls.

RESULTS

Using a Chi-square test, significant changes in the Ab repertoire were found when intergroup patterns were compared. A singular distortion of both serum self-IgG and self-IgM repertoires was noted in APS 1 patients. The molecular characterization of these antigenic targets was conducted using a proteomic approach. In this context, autoantibodies recognized more significantly either tissue-specific antigens, such as pancreatic amylase, pancreatic triacylglycerol lipase and pancreatic regenerating protein 1α, or widely distributed antigens, such as peroxiredoxin-2, heat shock cognate 71-kDa protein and aldose reductase. As expected, a well-defined self-reactive T-cell repertoire impairment, as described in APS 1 patients, affected the tissue-specific self-IgG repertoire. Interestingly, discriminant IgM reactivities targeting both tissue-specific and more widely expressed antigens were also specifically observed in APS 1 patients. Using recombinant targets, we observed that post translational modifications of these specific antigens impacted upon their recognition.

CONCLUSIONS

The data suggest that T-cell-dependent but also T-cell-independent mechanisms are involved in the dynamic evolution of autoimmunity in APS 1.

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is an autosomal recessive disease caused by mutations in the autoimmune regulator (AIRE) gene. This review focuses on the clinical and immunological features of APECED, summarizes the current knowledge on the function of AIRE and discusses the importance of autoantibodies in disease diagnosis and prognosis. Additionally, we review the outcome of recent immunomodulatory treatments in APECED patients.

Normocalcaemic hypoparathyroidism: prevalence and effect on bone status in older women. The OPUS study

OBJECTIVE

There are no consistent data on the prevalence and bone status of normocalcaemic hypoparathyroidism (NHYPO) as defined by normal adjusted calcium and low PTH level. Our aim was to determine the prevalence and the metabolic bone profile of NHYPO in older women, assessing its evolution over time. The second objective was to evaluate the prevalence of other calcium metabolic disorders.

DESIGN

The Osteoporosis and Ultrasound Study (OPUS) is a 6-yr prospective study of fracture-related factors.

PARTICIPANTS

A total of 2419 older women (age 55-79 yrs) and 258 younger women (age 30-40 yrs) participated. Complete follow-up data were available in 1416 subjects.

MEASUREMENTS

After calculating the adjusted calcium according to James' formula, we identified 'abnormal' calcium and PTH using Mahalanobis distances and allocated older women into different pathological categories using reference intervals from the healthy young women.

RESULTS

We identified 57 subjects with NHYPO (2·4%). These women had lower than expected bone turnover as assessed by bone alkaline phosphatase (-14·5%, 95% CI: -26·2 to -3·0, P = 0·007), CTX (-66·3%, 95% CI: -74·0 to -56·4, P < 0·001) and osteocalcin (-36·8%, 95% CI: -45·6 to -26·6, P < 0·001). After 6 years, of the 35 NHYPO subjects with follow-up data, none developed overt hypoparathyroidism and only 15 (0·6%) subjects had persistent evidence of NHYPO. We also identified 86 subjects (3·6%) affected by hyperparathyroid hypercalcaemia.

CONCLUSION

This is the first large population-based study to investigate NHYPO in older women. NHYPO is fairly common, not always persistent and is characterized by low bone turnover.

Autoantibody response against NALP5/MATER in primary ovarian insufficiency and in autoimmune Addison's disease

CONTEXT

NACHT leucine-rich-repeat protein 5 (NALP5)/maternal antigen that embryo requires (MATER) is an autoantigen in hypoparathyroidism associated with autoimmune polyendocrine syndrome type 1 (APS1) but is also expressed in the ovary. Mater is an autoantigen in experimental autoimmune oophoritis.

OBJECTIVES

The objectives of the study were to determine the frequency of NALP5/MATER autoantibodies (NALP5/MATER-Ab) in women with premature ovarian insufficiency (POI) and in patients with autoimmune Addison's disease (AAD) and to evaluate whether inhibin chains are a target for autoantibodies in POI.

METHODS

Autoantibodies against NALP5/MATER and inhibin chains-α and -βA were determined by radiobinding assays in 172 patients with AAD without clinical signs of gonadal insufficiency, 41 women with both AAD and autoimmune POI [steroidogenic cell autoimmune POI (SCA-POI)], 119 women with idiopathic POI, 19 patients with APS1, and 211 healthy control subjects.

RESULTS

NALP5/MATER-Ab were detected in 11 of 19 (58%) sera from APS1 patients, 12 of 172 (7%) AAD sera, 5 of 41 (12%) SCA-POI sera, 0 of 119 idiopathic POI sera and 1 of 211 healthy control sera (P < .001). None of 160 POI sera, including 41 sera from women with SCA-POI and 119 women with idiopathic POI, and none of 211 healthy control sera were positive for inhibin chain-α/βA autoantibodies.

CONCLUSIONS

NALP5/MATER-Ab are associated with hypoparathyroidism in APS1 but are present also in patients with AAD and in women with SCA-POI without hypoparathyroidism. Inhibin chains do not appear to be likely candidate targets of autoantibodies in human POI.