Homozygous Ser-1 to Pro-1 mutation in parathyroid hormone identified in hypocalcemic patients results in secretion of a biologically inactive pro-hormone.

Like other secreted peptides, nascent parathyroid hormone (PTH) is synthesized with a pre- and a pro-sequence (25 and 6 amino acids, respectively). These precursor segments are sequentially removed in parathyroid cells before packaging into secretory granules. Three patients from two unrelated families who presented during infancy with symptomatic hypocalcemia were found to have a homozygous serine (S) to proline (P) change affecting the first amino acid of the mature PTH. Unexpectedly, biological activity of synthetic [P1]PTH(1-34) was indistinguishable from that of unmodified [S1]PTH(1-34). However, in contrast to conditioned medium from COS-7 cells expressing prepro[S1]PTH(1-84), medium from cells expressing prepro[P1]PTH(1-84) failed to stimulate cAMP production despite similar PTH levels when measured by an intact assay that detects PTH(1-84) and large amino-terminally truncated fragments thereof. Analysis of the secreted, but inactive PTH variant led to the identification of pro[P1]PTH(-6 to +84). Synthetic pro[P1]PTH(-6 to +34) and pro[S1]PTH(-6 to +34) had much less bioactivity than the corresponding PTH(1-34) analogs. Unlike pro[S1]PTH(-6 to +34), pro[P1]PTH(-6 to +34) was resistant to cleavage by furin suggesting that the amino acid variant impairs preproPTH processing. Consistent with this conclusion, plasma of patients with the homozygous P1 mutation had elevated proPTH levels, as determined with an in-house assay specific for pro[P1]PTH(-6 to +84). In fact, a large fraction of PTH detected by the commercial intact assay represented the secreted pro[P1]PTH. In contrast, two commercial biointact assays that use antibodies directed against the first few amino acid residues of PTH(1-84) for capture or detection failed to detect pro[P1]PTH.

In vivo treatment with calcilytic of CaSR knock-in mice ameliorates renal phenotype reversing downregulation of the vasopressin-AQP2 pathway.

High concentrations of urinary calcium counteract vasopressin action via the activation of the Calcium-Sensing Receptor (CaSR) expressed in the luminal membrane of the collecting duct cells, which impairs the trafficking of aquaporin-2 (AQP2). In line with these findings, we provide evidence that, with respect to wild-type mice, CaSR knock-in (KI) mice mimicking autosomal dominant hypocalcaemia, display a significant decrease in the total content of AQP2 associated with significantly higher levels of AQP2 phosphorylation at Ser261, a phosphorylation site involved in AQP2 degradation. Interestingly, KI mice also had significantly higher levels of phosphorylated p38MAPK, a downstream effector of CaSR and known to phosphorylate AQP2 at Ser261. Moreover, ATF1 phosphorylated at Ser63, a transcription factor downstream of p38MAPK, was significantly higher in KI. In addition, KI mice had significantly higher levels of AQP2-targeting miRNA137 consistent with a post-transcriptional downregulation of AQP2. In vivo treatment of KI mice with the calcilytic JTT-305, a CaSR antagonist, increased AQP2 expression and reduced AQP2-targeting miRNA137 levels in KI mice. Together, these results provide direct evidence for a critical role of CaSR in impairing both short-term vasopressin response by increasing AQP2-pS261, as well as AQP2 abundance, via the p38MAPK-ATF1-miR137 pathway. KEY POINTS: Calcium-Sensing Receptor (CaSR) activating mutations are the main cause of autosomal dominant hypocalcaemia (ADH) characterized by inappropriate renal calcium excretion leading to hypocalcaemia and hypercalciuria. Current treatments of ADH patients with parathyroid hormone, although improving hypocalcaemia, do not improve hypercalciuria or nephrocalcinosis. In vivo treatment with calcilytic JTT-305/MK-5442 ameliorates most of the ADH phenotypes of the CaSR knock-in mice including hypercalciuria or nephrocalcinosis and reverses the downregulation of the vasopressin-sensitive aquaporin-2 (AQP2) expression, providing direct evidence for a critical role of CaSR in impairing vasopressin response. The beneficial effect of calcilytic in reducing the risk of renal calcification may occur in a parathyroid hormone-independent action through vasopressin-dependent inhibition of cAMP synthesis in the thick ascending limb and in the collecting duct. The amelioration of most of the abnormalities in calcium metabolism including hypercalciuria, renal calcification, and AQP2-mediated osmotic water reabsorption makes calcilytic a good candidate as a novel therapeutic agent for ADH.

Parathyroid Hormone Resistance and Autoantibodies to the PTH1 Receptor.

We describe two cases of acquired parathyroid hormone (PTH) resistance consequent to the development of serum PTH type 1 receptor (PTH1R) autoantibodies, which block PTH binding and signaling. Both cases were associated with other autoimmune manifestations, and one case was associated with atypical membranous glomerulonephritis. In vitro binding and signaling assays identified the presence of PTH1R-blocking IgG autoantibodies, which were not present in serum samples from patients with other renal or autoimmune disorders. (Funded by the Intramural Research Programs of the National Institute of Diabetes and Digestive and Kidney Diseases and others.).

Nanobodies as negative allosteric modulators for human calcium sensing receptor.

Human calcium sensing receptor (CaSR) senses calcium ion concentrations in vivo and is an important class of drug targets. Mutations in the receptor can lead to disorders of calcium homeostasis, including hypercalcemia and hypocalcemia. Here, 127 CaSR-targeted nanobodies were generated from camels, and four nanobodies with inhibitory function were further identified. Among these nanobodies, NB32 can effectively inhibit the mobilization of intracellular calcium ions (Ca2+i) and suppress the G12/13 and ERK1/2 signaling pathways downstream of CaSR. Moreover, it enhanced the inhibitory effect of the calcilytics as a negative allosteric modulator (NAM). We determined the structure of complex and found NB32 bound to LB2 (Ligand-binding 2) domain of CaSR to prevent the interaction of LB2 domains of two protomers to stabilize the inactive state of CaSR.

Let's stop talking about 'citrate toxicity'.

PURPOSE OF REVIEW: Continuous renal replacement therapy (CRRT) is a vital medical intervention used in critically ill patients with acute kidney injury (AKI). One of the key components of adequate clearance with CRRT is the use of anticoagulants to prevent clotting of the extracorporeal circuit. Regional citrate anticoagulation is the most often recommended modality. The term 'citrate toxicity' is used to describe potential adverse effects of accumulation of citrate and subsequent hypocalcemia. However, citrate is itself not inherently toxic. The term and diagnosis of citrate toxicity are questioned in this review. RECENT FINDINGS: Citrate is being increasingly used for regional anticoagulation of the CRRT circuit. Citrate accumulation is infrequent and can cause hypocalcemia and metabolic alkalosis, which are potential adverse effects. Citrate itself, however, is not a toxic molecule. The term 'citrate toxicity' has been used to denote hypocalcemia and metabolic acidosis. However, citrate administration is well known to cause systemic and urinary alkalinization and under certain circumstances, metabolic alkalosis, but is not associated itself with any 'toxic' effects.We review the existing literature and debunk the perceived toxicity of citrate. We delve into the metabolism and clearance of citrate and question current data suggesting metabolic acidosis occurs as the result of citrate accumulation. SUMMARY: In conclusion, this article calls into question prevailing concerns about 'citrate toxicity'. We emphasize the need for a more nuanced understanding of its safety profile. We recommend discarding the term 'citrate toxicity' in favor of another frequently used, but more meaningful term: 'citrate accumulation'.

New insights into renal calcium-sensing receptor activation.

PURPOSE OF REVIEW: Activation of the calcium-sensing receptor (CASR) in the parathyroid gland suppresses the release of parathyroid hormone (PTH). Furthermore, activation of the renal CASR directly increases the urinary excretion of calcium, by inhibiting transepithelial calcium transport in the nephron. Gain-of-function mutations in the CASR gene lead to autosomal dominant hypocalcemia 1 (ADH1), with inappropriately low PTH levels and hypocalcemia, indicative of excessive activation of the parathyroid CASR. However, hypercalciuria is not always observed. The reason why the manifestation of hypercalciuria is not uniform among ADH1 patients is not well understood. RECENT FINDINGS: Direct activation of the CASR in the kidney has been cumbersome to study, and an indirect measure to effectively estimate the degree of CASR activation following chronic hypercalcemia or genetic gain-of-function CASR activation has been lacking. Studies have shown that expression of the pore-blocking claudin-14 is strongly stimulated by the CASR in a dose-dependent manner. This stimulatory effect is abolished after renal Casr ablation in hypercalcemic mice, suggesting that claudin-14 abundance may gauge renal CASR activation. Using this marker has led to unexpected discoveries regarding renal CASR activation. SUMMARY: These new studies have informed on renal CASR activation thresholds and the downstream CASR-regulated calcium transport mechanisms.

Prevalence of denosumab-induced hypocalcemia: a retrospective observational study of patients routinely monitored with ionized calcium post-injection.

We assessed the prevalence of hypocalcemia after denosumab injections in a real-world cohort routinely monitored for calcium during up to 7.5 years of treatment. Among 1096 injections in 242 patients, 6.3% resulted in hypocalcemia, and was independent of the injection number. Severe hypocalcemia was rare (1%). PURPOSE: To assess the prevalence of and risk factors for hypocalcemia after administration of denosumab in a patient cohort routinely monitored for ionized calcium after each dose. METHODS: In this retrospective observational study, we analyzed denosumab-induced hypocalcemia in a real-world cohort who were routinely followed up with ionized calcium pre- and post-injection (within 31 days after injection) during the period 2011 to 2020. RESULTS: In total, we included data from 1096 denosumab injections in 242 individuals (1-15 injections per patient). The mean age for the first injection was 74 ± 10 years, and 88% were female. Post-injection hypocalcemia occurred after 6.3% of all injections (4.6% mild, 0.6% moderate, and 1.1% severe) and was independent of the number of injections (rate of hypocalcemia varied from 3-8%). Risk factors for hypocalcemia were male sex, severe renal failure, pre-injection hypocalcemia, hypomagnesemia, hypophosphatemia, and vitamin D insufficiency. Furthermore, older age was not associated with an increased hypocalcemia risk. CONCLUSIONS: Denosumab-induced hypocalcemia is a prevalent adverse event, which occurs independently of the number of injections. However, severe hypocalcemia is a rare occurrence, and severe renal failure and nutritional status appear to be important predictive factors. Magnesium and phosphate might add value in the pre-injection risk assessment; however, this observation needs to be confirmed in larger cohorts.

Denosumab-induced hypocalcemia in patients with solid tumors and renal dysfunction: a multicenter, retrospective, observational study.

BACKGROUND: Bone metastases are frequently observed in advanced cancer, and bone modifying agents are used to prevent or treat skeletal-related events. Zoledronic acid is contraindicated in patients with severe renal impairment (Ccr < 30 mL/min), but it is not completely known whether denosumab can be used in them. We aimed to determine the association between renal function and hypocalcemia development during denosumab treatment. METHODS: We included patients with solid cancer and bone metastases who started denosumab treatment between April 2017 and March 2019. They were classified into four groups based on creatinine clearance (Ccr; mL/min): normal (Ccr ≥ 80), mild (50 ≤ Ccr ˂80), moderate (30 ≤ Ccr ˂50), and severe (Ccr ˂30). Hypocalcemia was evaluated using the Common Terminology Criteria for Adverse Events (v5.0) based on the albumin-adjusted serum calcium levels; its incidence (stratified by renal function) and risk factors were investigated using a Chi-square test and logistic regression analysis. RESULTS: Of 524 patients (age: 69 ± 11 years; 303 men), 153 had a normal renal function and 222, 117, and 32 had mild, moderate, and severe renal dysfunction. The albumin-adjusted serum calcium level was higher than the measured (total) calcium level in most patients. The incidence of grade ≥ 1 hypocalcemia was 32.0% in the normal group and 37.4%, 29.9%, and 62.5% in the mild, moderate, and severe renal dysfunction groups, respectively. It was, therefore, higher in the severe renal dysfunction groups than in the normal group (P = 0.002). The incidence of grade ≥ 3 hypocalcemia did not differ significantly among the groups. Pre-treatment low serum calcium levels and severe renal dysfunction were risk factors for hypocalcemia. CONCLUSIONS: Evaluating denosumab-induced hypocalcemia required albumin adjustment, and its incidence was high among patients with severe renal dysfunction. Reduced serum calcium levels and severely impaired renal function were associated with an elevated hypocalcemia risk.

Identification of a Novel Homozygous Missense Mutation in the CLDN16 Gene to Decipher the Ambiguous Clinical Presentation Associated with Autosomal Dominant Hypocalcaemia and Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis in an Indian Family.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHNNC) is a rare autosomal recessive renal tubulopathy disorder characterized by excessive urinary loss of calcium and magnesium, polyuria, polydipsia, bilateral nephrocalcinosis, progressive chronic kidney disease, and renal failure. Also, sometimes amelogenesis imperfecta and severe ocular abnormalities are involved. The CLDN-16 and CLDN-19 genes encode the tight junction proteins claudin-16 and claudin-19, respectively, in the thick ascending loop of Henle in the kidney, epithelial cells of the retina, dental enamel, etc. Loss of function of the CLDN-16 and/or CLDN-19 genes leads to FHHNC. We present a case of FHHNC type 1, which was first confused with autosomal dominant hypocalcaemia (ADH) due to the presence of a very low serum parathyroid hormone (PTH) concentration and other similar clinical features before the genetic investigations. After the exome sequencing, FHHNC type 1 was confirmed by uncovering a novel homozygous missense mutation in the CLDN-16 gene (Exon 2, c.374 T > C) which causes, altered protein structure with F55S. Associated clinical, biochemical, and imaging findings also corroborate final diagnosis. Our findings expand the spectrum of the CLDN-16 mutation, which will further help in the genetic diagnosis and management of FHNNC.

Effective peripheral blood stem cell collection in a 4.6-kg child.

BACKGROUND: Due to unique technical challenges, effective peripheral blood stem cell collections (PBSCs) have not been consistently reported in patients weighing less than 5 kg. We describe three PBSCs performed in a 4.6-kg child undergoing myeloablative chemotherapy for high-grade glioma. STUDY DESIGN AND METHODS: A multidisciplinary group representing the clinical and apheresis teams adapted a PBSC protocol to accommodate the patient's size and collection targets. Special considerations included timing of the collection relative to chemotherapy, vascular access, strategies for monitoring adverse events during collection, and contingencies. RESULTS AND DISCUSSION: The patient underwent three PBSC procedures over 2 days due to suboptimal collection after the first two procedures. For procedure 1, a conservative inlet: anticoagulant (AC) ratio and AC infusion rate of 15 and 0.6 mL/min/L total blood volume (TBV) resulted in premature discontinuation due to clotting. A ratio of 8 and AC infusion rate of 1.5-1.7 mL/min/L TBV with subsequent titration to higher levels were adopted for the second and third procedures. These changes resulted in greater acid-citrate-dextrose exposure, that was managed by continuous calcium chloride infusion. There was no hypocalcemia, hypotension, or distress during any procedure. A total of 15 × 106 CD34+ cells/kg were collected. This retrospective review illustrates that PBSC can be safely undertaken in children weighing less than 5 kg.

Hypocalcemia and cardiovascular mortality in cinacalcet users.

BACKGROUND: Calcimimetics are widely used in hemodialysis patients and influence serum calcium levels. Although the Kidney Disease: Improving Global Outcomes guidelines argued that low calcium levels induced by calcimimetics may be harmless, large observational studies investigating the association between hypocalcemia and mortality are scarce. We investigated the association between serum calcium levels and cardiovascular mortality in calcimimetics users using the nationwide Japanese registry for dialysis patients. METHODS: In this 9-year prospective cohort study, the baseline data were collected at the end of 2009. We enrolled patients on maintenance hemodialysis or hemodiafiltration. We employed three models (baseline, time-dependent and time-averaged) to conduct Cox proportional hazard regression analyses. RESULTS: Cinacalcet was prescribed to 12.7% (N = 22 853) at baseline. The median observation period was 98 (interquartile range 40-108) months and 108 (interquartile range 59-108) months in the whole cohort (N = 180 136) and in cinacalcet users, respectively. Three-quarters of survivors at the end of 2019 had continued calcimimetic therapy for 10 years, corresponding to a mean annual dropout rate of 2.9%. Hypocalcemia was not associated with cardiovascular mortality in the baseline or time-averaged model. In the time-dependent model, however, the lowest calcium decile (corrected calcium <8.4 mg/dL) was significantly associated with higher cardiovascular mortality than the reference (corrected calcium 8.7-8.9 mg/dL) in both cinacalcet users and all patients [hazard ratio (95% confidence interval) 1.32 (1.00, 1.75) and 1.15 (1.05, 1.26), respectively]. Hypocalcemia was especially associated with sudden death and death due to hemorrhagic stroke, heart failure and ischemic heart disease. Higher rate of fatal and non-fatal cardiovascular events was observed in hypocalcemic patients regardless of cinacalcet usage. CONCLUSIONS: Our findings suggest that transient hypocalcemia was associated with an increased risk of cardiovascular death independent of cinacalcet usage. We should pay attention to hypocalcemia transiently induced by cinacalcet.

Identification of novel risk factors for postoperative severe hypocalcemia in patients with primary hyperparathyroidism undergoing parathyroidectomy: a case control study.

BACKGROUND: Patients with primary hyperparathyroidism (PHPT) are at risk for severe hypocalcemia (SH) following parathyroidectomy (PTX), but limited data exist on the predictors of SH. We aimed to identify risk factors for early postoperative SH after PTX in patients with PHPT and to evaluate the predictive value of clinical parameters. METHODS: A retrospective review of patients with PHPT who underwent PTX between January 2010 and December 2022 was performed. A total of 46 patients were included in the study, with 15 (32.6%) experiencing postoperative SH, 19 (41.3%) having calculi in the ureter or kidney, and 37 (80.4%) having osteoporosis. Patients were divided into SH and non-SH groups based on postoperative serum calcium levels. Preoperative biochemical indicators, bone turnover markers, and renal function parameters were analyzed and correlated with postoperative SH. RESULTS: Statistically significant (P < 0.05) differences were found in preoperative serum calcium (serum Ca), intact parathyroid hormone, serum phosphorus (serum P), serum Ca/P, percentage decrease of serum Ca, total procollagen type 1 intact N-terminal propeptide, osteocalcin (OC), and alkaline phosphatase levels between the two groups. Multivariate analysis showed that serum P (odds ratio [OR] = 0.989; 95% confidence interval [95% CI] = 0.981-0.996; P = 0.003), serum Ca (OR = 0.007; 95% CI = 0.001-0.415; P = 0.017), serum Ca/P (OR = 0.135; 95% CI = 0.019-0.947; P = 0.044) and OC levels (OR = 1.012; 95% CI = 1.001-1.024; P = 0.036) were predictors of early postoperative SH. The receiver operating characteristic curve analysis revealed that serum P (area under the curve [AUC] = 0.859, P < 0.001), serum Ca/P (AUC = 0.735, P = 0.010) and OC (AUC = 0.729, P = 0.013) had high sensitivity and specificity. CONCLUSION: Preoperative serum P, serum Ca/P and osteocalcin levels may identify patients with PHPT at risk for early postoperative SH after PTX.

Pamidronate-induced irreversible symptomatic hypocalcemia in a dog with hypercalcemia after glucocorticoid withdrawal: a case report.

BACKGROUND: Pamidronate is used for the treatment of hypercalcemia. However, a rare but potential adverse event of pamidronate treatment is hypocalcemia. This report describes an unusual case of severe, irreversible hypocalcemia after a single injection of pamidronate for the treatment of hypercalcemia due to glucocorticoid withdrawal in a dog. CASE PRESENTATION: An 11-year-old castrated male Maltese dog presented with anorexia, vomiting, and diarrhea (day 0). The patient had calcinosis cutis throughout the body, calcification of intraabdominal organs, mild azotemia, and severe hypercalcemia. The severe calcification was attributed to long-term glucocorticoid administration, which was discontinued 1 month before presentation. Fluid therapy, diuretics, calcitonin, and a single intravenous injection of pamidronate were used for the treatment of hypercalcemia. On day 14, normocalcemia was achieved, but renal failure occurred. On day 20, severe and irreversible hypocalcemia occurred, and on day 42, the patient was euthanized at the owner's request because of worsened hypocalcemia and renal failure. CONCLUSIONS: Although hypocalcemia is an extremely rare adverse event of bisphosphonate treatment, bisphosphonates like pamidronate can result in potentially life-threatening conditions according to the patient's underlying conditions. Therefore, the patient's condition should be closely monitored and any underlying conditions should be carefully evaluated before initiating the treatment for hypercalcemia using pamidronate.

Hypocalcemia in combination with hyperphosphatemia impairs muscle cell differentiation in vitro.

PURPOSE: Hypoparathyroidism is a rare endocrine disorder characterized by low or absent secretion of parathyroid hormone (PTH), which leads to decreased calcium and increased phosphorus levels in the serum. The diagnosis of hypoparathyroidism is based on the identification of the aforementioned biochemical abnormalities, which may be accompanied by clinical manifestations. Symptoms of hypoparathyroidism, primarily attributed to hypocalcemia, include muscle cramps or spasms, facial, leg, and foot pain, seizures, and tingling in the lips or fingers. The treatment of hypoparathyroidism depends on the severity of symptoms and the underlying pathology. Over the long term, calcium supplements, active vitamin D analogs, and thiazide diuretics may be needed. In fact, in patient cohorts in which optimal disease control still remains elusive, replacement therapy with recombinant parathyroid hormone analogs may be contemplated. Despite the predominantly neuromuscular symptoms of hypoparathyroidism, further effects of parathyroid hormone deficiency at the muscle cell level remain poorly understood. Thus, the aim of our study was to evaluate the effects of hypocalcemia in combination with hyperphosphatemia on muscle cells differentiation in vitro. METHODS: C2C12 cells, an in vitro model of muscle cells, were differentiated for 2 or 6 days in the presence of hypocalcemia (CaCl2 0.9 mmol/l) and moderate (PO4 1.4 mmol/l) or severe (PO4 2.9 mmol/l) hyperphosphatemia, or combinations of both conditions. Cell differentiation and expression of genes linked to muscle differentiation were evaluated. RESULTS: The combination of hypocalcemia with hyperphosphatemia induced a significant reduction (50%) in differentiation marker levels, such as MyoD (protein 1 for myoblast determination) and myogenin on the 1st day of differentiation, and MHC (myosin heavy chains) after 6 days of differentiation compared to control. Furthermore, this condition induced a statistically significant reduction of insulin-like growth factor-1 (IGF-1) mRNA expression and inhibition of IGF signaling and decrease in ERK phosphorylation compared to control cells. CONCLUSIONS: Our results showed that a condition of hypocalcemia with hyperphosphatemia induced an alteration of muscle cell differentiation in vitro. In particular, we observed the reduction of myogenic differentiation markers, IGF-1 signaling pathway, and ERK phosphorylation in differentiated skeletal myoblasts. These data suggest that this altered extracellular condition might contribute to the mechanisms causing persistence of symptoms in patients affected by hypoparathyroidism.

Clinical and molecular characteristics of two Italian kindreds with hypoparathyroidism, deafness and renal dysplasia (HDR) syndrome.

PURPOSE: Hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome, also known as Barakat syndrome, is a rare autosomal dominant disease characterized by the triad of hypoparathyroidism, deafness, and renal abnormalities. The disorder is caused by the haploinsufficiency of the zinc finger transcription factor GATA3 and exhibits a great clinical variability with an age-dependent penetrance of each feature. We report two unrelated kindreds whose probands were referred to our outpatient clinic for further evaluation of hypoparathyroidism. METHODS: The proband of family 1, a 17-year-old boy, was referred for severe hypocalcemia (5.9 mg/dL) incidentally detected at routine blood tests. Abdomen ultrasound showed bilateral renal cysts. The audiometric evaluation revealed the presence of bilateral moderate hearing loss although the patient could communicate without any problem. Conversely, the proband of family 2, a 19-year-old man, had severe symptomatic hypocalcemia complicated by epileptic seizure at the age of 14 years; his past medical history was remarkable for right nephrectomy at the age of 4 months due to multicystic renal disease and bilateral hearing loss diagnosed at the age of 18 years. RESULTS: Based on clinical, biochemical, and radiologic data, HDR syndrome was suspected and genetic analysis of the GATA3 gene revealed the presence of two pathogenetic variants in exon 3, c.404dupC and c.431dupG, in the proband of family 1 and 2, respectively. CONCLUSION: HDR syndrome is a rare cause of hypoparathyroidism and must be excluded in all patients with apparently idiopathic hypoparathyroidism. A correct diagnosis is of great importance for early detection of other HDR-related features and genetic counseling.

Endocrine manifestations in adults with 22q11.2 deletion syndrome: a retrospective single-center cohort study.

INTRODUCTION AND OBJECTIVE: Patients with the 22q11.2 deletion syndrome (22q11DS) frequently display cardiological and psychiatric diseases, but are also at increased risk for endocrine manifestations. The aim of this study was to evaluate the screening, prevalence, and management of hypoparathyroidism and thyroid disease in patients with 22q11DS, to evaluate the metabolic profile, and to compare these results with current literature and guidelines. DESIGN: We performed a retrospective study of patients with genetically confirmed 22q11DS, followed at the center for human genetics of the University Hospitals Leuven, resulting in a cohort of 75 patients. Medical history, medication, and laboratory results concerning hypoparathyroidism, thyroid dysfunction, and the metabolic profile were collected. RESULTS: Of the total cohort, 26 patients (35%) had at least one hypocalcaemic episode. During hypocalcaemia, parathyroid hormone (PTH) was measured in only 12 patients with 11 having normal or low PTH, confirming a diagnosis of hypoparathyroidism. Recurrent episodes of hypocalcaemia occurred in seventeen patients (23%). Adherence to the guidelines was low, with 13% of patients having a yearly serum calcium evaluation, 12% receiving daily calcium supplements, and 20% receiving non-active vitamin D. Hypothyroidism was present in 31 patients (44%) and hyperthyroidism in 6 patients (8%). Information on body mass index (BMI) was available in 52 patients (69%), of which 38% were obese (BMI ≥ 30 kg/m2). CONCLUSION: Hypoparathyroidism, hypothyroidism, and obesity are common endocrine manifestations in patients with 22q11DS but are probably underdiagnosed and undertreated, indicating the need for multidisciplinary follow-up including an endocrinologist.

Measurement of plasma total calcium before plasma free ionized calcium - a possibility with affordable pitfalls.

Free ionized calcium (fCa) is considered the gold standard for assessing calcium status in patients, but it is relatively expensive and is associated with several preanalytical and analytical error sources. We investigated the feasibility of using a reflex test that involves first measuring total calcium (tCa) and if out of reference range, then measure fCa, with expectation of reducing the number of fCa measurements. We used data from 1815 unique patients with concurrent measurement of fCa, tCa and albumin adjusted calcium (aCa). Patients were stratified by albumin level, and the association of fCa to tCa and aCa respectively was assessed with linear regression. The regression analysis showed the best linearity for tCa and aCa at albumin <35 g/L (R2: 0.80-0.90), and the poorest at albumin >40 g/L (R2: tCa 0.58; aCa 0.59). We examined the accuracy of hypo- and hypercalcemia classifications for tCa, aCa and the reflex test. aCa had more misclassifications of hypo- and hypercalcemia than tCa, with respectively 25% and 21%. Implementation of the reflex test would correct any false hypo- or hypercalcemia classified by tCa, leaving only false negative results corresponding to 9% of all tCa measurements. False negative results were on average 0.04 mmol/L above or below the reference range of fCa. Implementation of the reflex test reduces the number of fCa by 68% without major errors diagnosing hyper- or hypocalcemia.

Development of a tool to calculate the probability of hypocalcemia after total thyroidectomy: a prospective study.

PURPOSE: This study aimed to evaluate the ability of the percentage of decrease in serum PTH level in the first 8 h after total thyroidectomy (TT) to predict hypocalcemia requiring Ca supplementation and develop a tool to predict it. METHODS: 97 patients who underwent TT with measurement of preoperative parathyroid hormone (PTH) levels were prospectively evaluated 1 and 8 h after TT; postoperative magnesium (Mg2PO) and phosphorus levels were evaluated on the 2nd day after surgery. The percentage of decrease in PTH level 1 h (%dPTH1h) and 8 h (%dPTH8h) postoperatively and predictors of hypocalcemia requiring Ca supplementation were evaluated and an equation was developed to predict this outcome. RESULTS: %dPTH1h (p = 0.002), %dPTH8h (p = 0.001) and (Mg2PO) (p < 0.01) were isolated predictors of postoperative hypocalcemia requiring Ca supplementation. The data obtained led to the development of two tools to predict this complication. CONCLUSIONS: The percentage of decrease in PTH level 1 h and 8 h postoperatively and the magnesium level on the 2nd day after surgery were predictors of more severe hypocalcemia, and an auxiliary tool for predicting this complication was developed.

The application of autofluorescence system contributes to the preservation of parathyroid function during thyroid surgery.

PURPOSE: The purpose of this study was to investigate the impact of autofluorescence technology on postoperative parathyroid function and short-term outcomes in patients undergoing thyroid surgery. METHODS: A total of 546 patients were included in the study, with 287 in the conventional treatment group and 259 in the autofluorescence group. Both groups underwent central lymph node dissection, which is known to affect parathyroid function. Short-term outcomes, including rates of postoperative hypocalcemia and parathyroid dysfunction, serum calcium and PTH levels on the first postoperative day, as well as the need for calcium supplementation, were analyzed. A multivariable analysis was also conducted to assess the impact of autofluorescence on postoperative parathyroid dysfunction, considering factors such as age, BMI, and preoperative calcium levels. RESULTS: The autofluorescence group demonstrated significantly lower rates of postoperative hypocalcemia and parathyroid dysfunction compared to the conventional treatment group. The autofluorescence group also had better serum calcium and PTH levels on the first postoperative day, and a reduced need for calcium supplementation. Surprisingly, the use of autofluorescence technology did not prolong surgical time; instead, it led to a shorter hospitalization duration. The multivariable analysis showed that autofluorescence significantly reduced the risk of postoperative parathyroid dysfunction, while factors such as age, BMI, and preoperative calcium levels did not show a significant correlation. CONCLUSION: This study provides evidence that autofluorescence technology can improve the preservation of parathyroid function during thyroid surgery, leading to better short-term outcomes and reduced postoperative complications. The findings highlight the potential of autofluorescence as a valuable tool in the management of parathyroid hypofunction. Further research and validation are needed to establish the routine use of autofluorescence technology in the thyroid.

Autosomal dominant hypercalciuric hypocalcaemia: the calcium-sensing receptor in renal calcium homeostasis and the impact of renal transplantation.

Calcium-sensing receptors (CaSRs) are G protein-coupled receptors that help maintain Ca2+ concentrations, modulating calciotropic hormone release (parathyroid hormone (PTH), calcitonin and 1,25-dihydroxyvitamin D) by direct actions in the kidneys, gastrointestinal tract and bone. Variability in population calcium levels has been attributed to single nucleotide polymorphisms in CaSR genes, and several conditions affecting calcium and phosphate homeostasis have been attributed to gain- or loss-of-function mutations. An example is autosomal dominant hypercalciuric hypocalcaemia, because of a missense mutation at codon 128 of chromosome 3, as reported in our specific case and her family. As a consequence of treating symptomatic hypocalcaemia as a child, this female subject slowly developed progressive end-stage kidney failure because of nephrocalcinosis and nephrolithiasis. After kidney transplantation, she remains asymptomatic, with decreased vitamin D and elemental calcium requirements, stable fluid and electrolyte homeostasis during intercurrent illnesses and has normalised urinary calcium and phosphate excretion, reducing the likelihood of hypercalciuria-induced graft impairment. We review the actions of the CaSR, its role in regulating renal Ca2+ homeostasis along with the impact of a proven gain-of-function mutation in the CaSR gene resulting in autosomal dominant hypercalciuric hypocalcaemia before and after kidney transplantation.