Self-limited neonatal hyperparathyroidism in familial hypocalciuric hypercalcemia

Cinacalcet as a First-Line Treatment in Neonatal Severe Hyperparathyroidism Secondary to Calcium Sensing Receptor (CaSR) Mutation

INTRODUCTION

Neonatal severe hyperparathyroidism (NSHPT) is a rare cause of neonatal hypercalcemia caused by a loss of function mutation in the calcium-sensing receptor (CaSR). Hypercalcemia in NSHPT can be life-threatening. Maintenance of serum calcium within a safe range is the primary goal of treatment through hydration, forced diuresis, and bisphosphonate treatment, nevertheless most cases require parathyroidectomy. We report a case with NSHPT diagnosed on the first day of life (DoL) and successfully treated with cinacalcet as the first-line treatment from the 2nd DoL up to the age of 18 months.

CASE REPORT

A full-term baby evaluated for weight loss at postnatal 14th hour and found to have hypercalcemia (14.4 mg/dL, reference range [RR]: 8.0-11.3). Despite hydration and diuresis, hypercalcemia persisted. Further evaluation revealed a parathyroid hormone (PTH) level of 1,493 pg/mL (RR: 15-65) and urine Ca/Cr of 0.09 mg/mg (RR: 0.03-0.81). Cinacalcet treatment was initiated on the 2nd DoL with the diagnosis of NSHPT due to hypocalciuric hypercalcemia and elevated PTH level. Ca levels decreased to normal levels on the 7th DoL. She was discharged from hospital at postnatal day 15 on cinacalcet treatment and still continued at 18 months of age. Sequencing of CaSR revealed a novel homozygous c.1836G>A (p.G613E) mutation in the patient, for which the parents and sister were heterozygous.

CONCLUSION

This case represents the youngest age at cinacalcet initiation and the longest duration without parathyroidectomy in a homozygous NSHPT and demonstrates that cinacalcet is an effective first-line treatment in patients who are responsive to this treatment modality and allows avoiding/delay in surgical intervention in NSHPT.

Neonatal Severe Hyperparathyroidism: Novel Insights From Calcium, PTH, and the CASR Gene

CONTEXT

Neonatal severe hyperparathyroidism (NSHPT) is rare and potentially lethal. It is usually from homozygous or heterozygous germline-inactivating CASR variant(s). NSHPT shows a puzzling range of serum calcium and parathyroid hormone (PTH) levels. Optimal therapy is unclear.

EVIDENCE ACQUISITION

We categorized genotype/phenotype pairings related to CASRs. For the 2 pairings in NSHPT, each of 57 cases of neonatal severe hyperparathyroidism required calcium, PTH, upper normal PTH, and dosage of a germline pathogenic CASR variant.

EVIDENCE SYNTHESIS

Homozygous and heterozygous NSHPT are 2 among a spectrum of 9 genotype/phenotype pairings relating to CASRs and NSHPT. For the 2 NSHPT pairings, expressions differ in CASR allelic dosage, CASR variant severity, and sufficiency of maternofetal calcium fluxes. Homozygous dosage of CASR variants was generally more aggressive than heterozygous. Among heterozygotes, high-grade CASR variants in vitro were more pathogenic in vivo than low-grade variants. Fetal calcium insufficiency as from maternal hypoparathyroidism caused fetal secondary hyperparathyroidism, which persisted and was reversible in neonates. Among NSHPT pairings, calcium and PTH were higher in CASR homozygotes than in heterozygotes. Extreme hypercalcemia (above 4.5 mM; normal 2.2-2.6 mM) is a robust biomarker, occurring only in homozygotes (83% of that pairing). It could occur during the first week.

CONCLUSIONS

In NSHPT pairings, the homozygotes for pathogenic CASR variants show higher calcium and PTH levels than heterozygotes. Calcium levels above 4.5 mM among NSHPT are frequent and unique only to most homozygotes. This cutoff supports early and robust diagnosis of CASR dosage. Thereby, it promotes definitive total parathyroidectomy in most homozygotes.

Management of familial hyperparathyroidism syndromes: MEN1, MEN2, MEN4, HPT-Jaw tumour, Familial isolated hyperparathyroidism, FHH, and neonatal severe hyperparathyroidism

While primary hyperparathyroidism (PHPT) generally represents a common endocrine disorder, being the more frequent cause of hypercalcemia in outpatients, familial forms of PHPT (FPHPT) account for no more than 2-5% of the overall PHPT. In the last decades, many technical progresses in both molecular and biochemical-radiological evaluation have been made, and substantial advancements in understanding these disorders have been reached. Differences both in the pathogenesis and clinical presentation exist among the various hyperparathyroid syndromic forms, and, since FPHPT is frequently associated to other endocrine, proliferative and/or functional disorders, as also non-endocrine tumours, with varying clinical spectrum of occurrence in each syndrome, its early clinically detection for appropriately preventing complications (i.e. kidney and bone disorders) is strictly advised. In this review, the clinical-biochemical features and diagnostic procedures of each FPHPT form will be summarized and a general overview on surgical and pharmacological approaches to FPHPT has been also considered.

Familial Hypocalciuric Hypercalcemia as an Atypical Form of Primary Hyperparathyroidism

Familial hypocalciuric hypercalcemia (FHH) causes lifelong hypercalcemia with features that overlap with typical primary hyperparathyroidism (PHPT). The incompleteness of this overlap has led to divergent nomenclatures for FHH. I compare two nomenclatures. One sets FHH as an entity distinct from PHPT. The other groups FHH with PHPT but conditions FHH as atypical PHPT. I analyzed selected articles about calcium-sensing receptors, FHH, PHPT, CASR, GNA11, and AP2S1. FHH usually results from a heterozygous germline inactivating mutation of the CASR, and less frequently from mutation of GNA11 or AP2S1. The CASR encodes the calcium-sensing receptors. These are highly expressed on parathyroid cells, where they sense serum calcium concentration and regulate suppression of PTH secretion by serum calcium. Their mutated expression in the kidney in FHH causes increased renal tubular reabsorption of calcium (hypocalciuria). Many FHH features are shared with PHPT and thus support FHH as a form of PHPT. These include a driver mutation expressed mainly in the parathyroid cells. The mutation causes a parathyroid cell insensitivity to extracellular calcium in vivo and in vitro, a right-shift of the set point for suppression of PTH secretion by calcium. Serum PTH is normal or mildly elevated; ie, it is not appropriately suppressed by hypercalcemia. Total parathyroidectomy causes hypoparathyroidism and durable remission of hypercalcemia. Some other features are not shared with PHPT and could support FHH as a distinct entity. These include onset of hypercalcemia in the first week of life, frequent persistence of hypercalcemia after subtotal parathyroidectomy, and hypocalciuria. The features supporting FHH as a form of PHPT are stronger than those favoring FHH as a distinct entity. Classifying FHH as an atypical form of PHPT represents compact nomenclature and supports current concepts of pathophysiology of FHH and PHPT. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Heterozygous inactivating CaSR mutations causing neonatal hyperparathyroidism: function, inheritance and phenotype

BACKGROUND

Homozygous inactivating mutations of the calcium-sensing receptor (CaSR) lead to neonatal severe hyperparathyroidism (NSHPT), whereas heterozygous inactivating mutations result in familial hypocalciuric hypercalcemia (FHH). It is unknown why in some cases heterozygous CaSR mutations cause neonatal hyperparathyroidism (NHPT) clinically similar to NSHPT but with only moderately elevated serum calcium.

METHODS

A literature survey was conducted to identify patients with heterozygous CaSR mutations and NHPT. The common NHPT CaSR mutants R185Q and R227L were compared with 15 mutants causing only FHH in the heterozygous state. We studied in vitro calcium signaling including the functional consequences of co-expression of mutant and wild-type (wt) CaSR, patients' phenotype, age of disease manifestation and mode of inheritance.

RESULTS

All inactivating CaSR mutants impaired calcium signaling of wt-CaSR regardless of the patients' clinical phenotype. The absolute intracellular calcium signaling response to physiologic extracellular calcium concentrations in vitro showed a high correlation with patients' serum calcium concentrations in vivo, which is similar in NHPT and FHH patients with the same genotype. Pedigrees of FHH families revealed that paternal inheritance per se does not necessarily lead to NHPT but may only cause FHH.

CONCLUSIONS

There is a significant correlation between in vitro functional impairment of the CaSR at physiologic calcium concentrations and the severity of alterations in calcium homeostasis in patients. Whether a particular genotype leads to NHPT or FHH appears to depend on additional predisposing genetic or environmental factors. An individual therapeutic approach appears to be warranted for NHPT patients.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Uncoupling of secretion from growth in some hormone secretory tissues

CONTEXT

Most syndromes with benign primary excess of a hormone show positive coupling of hormone secretion to size or proliferation in the affected hormone secretory tissue. Syndromes that lack this coupling seem rare and have not been examined for unifying features among each other.

EVIDENCE ACQUISITION

Selected clinical and basic features were analyzed from original reports and reviews. We examined indices of excess secretion of a hormone and indices of size of secretory tissue within the following three syndromes, each suggestive of uncoupling between these two indices: familial hypocalciuric hypercalcemia, congenital diazoxide-resistant hyperinsulinism, and congenital primary hyperaldosteronism type III (with G151E mutation of the KCNJ5 gene).

EVIDENCE SYNTHESIS

Some unifying features among the three syndromes were different from features present among common tumors secreting the same hormone. The unifying and distinguishing features included: 1) expression of hormone excess as early as the first days of life; 2) normal size of tissue that oversecretes a hormone; 3) diffuse histologic expression in the hormonal tissue; 4) resistance to treatment by subtotal ablation of the hormone-secreting tissue; 5) causation by a germline mutation; 6) low potential of the same mutation to cause a tumor by somatic mutation; and 7) expression of the mutated molecule in a pathway between sensing of a serum metabolite and secretion of hormone regulating that metabolite.

CONCLUSION

Some shared clinical and basic features of uncoupling of secretion from size in a hormonal tissue characterize three uncommon states of hormone excess. These features differ importantly from features of common hormonal neoplasm of that tissue.

A novel CaSR mutation presenting as a severe case of neonatal familial hypocalciuric hypercalcemia

BACKGROUND

Familial Hypocalciuric Hypercalcemia (FHH) is a generally benign disorder caused by heterozygous inactivating mutations in the Calcium-Sensing Receptor (CaSR) gene resulting in altered calcium metabolism.

OBJECTIVE

We report a case of unusually severe neonatal FHH due to a novel CaSR gene mutation that presented with perinatal fractures and moderate hypercalcemia. CASE OVERVIEW: A female infant was admitted at 2 weeks of age for suspected non-accidental trauma (NAT). Laboratory testing revealed hypercalcemia (3.08 mmol/L), elevated iPTH (20.4 pmol/L) and low urinary calcium clearance (0.0004). Radiographs demonstrated multiple healing metaphyseal and rib fractures and bilateral femoral bowing. The femoral deformity and stage of healing were consistent with prenatal injuries rather than non-accidental trauma (NAT). Treatment was initiated with cholecalciferol, 400 IU/day, and by 6 weeks of age, iPTH levels had decreased into the high-normal range. Follow up radiographs demonstrated marked improvement of bone lesions by 3 months. A CaSR gene mutation study showed heterozygosity for a T>C nucleotide substitution at c.1664 in exon 6, resulting in amino acid change I555T in the extracellular domain consistent with a missense mutation. Her mother does not carry the mutation and the father is unknown. At 18 months of age, the child continues to have relative hyperparathyroidism and moderate hypercalcemia but is otherwise normal.

CONCLUSION

This neonate with intrauterine fractures and demineralization, moderate hypercalcemia and hyperparathyroidism was found to have a novel inactivating missense mutation of the CaSR not detected in her mother. Resolution of bone lesions and reduction of hyperparathyroidism was likely attributable to the natural evolution of the disorder in infancy as well as the mitigating effect of cholecalciferol treatment.

Benign familial hypocalciuric hypercalcemia

OBJECTIVE

To review the pathophysiology, clinical features, diagnosis, and management options for benign familial hypocalciuric hypercalcemia.

METHODS

We present a systematic summary of benign familial hypocalciuric hypercalcemia after review of the current available literature.

RESULTS

Benign familial hypocalciuric hypercalcemia is an autosomal dominant condition characterized by lifelong hypercalcemia, relative hypocalciuria, and inappropriately elevated parathyroid hormone. It is caused by a loss-of-function mutation in the calcium-sensing receptor gene (CASR). Benign familial hypocalciuric hypercalcemia is important clinically because it can be difficult to distinguish from primary hyperparathyroidism. It is a benign condition, and affected patients should be advised against parathyroidectomy. The incidence of complications associated with primary hyperparathyroidism, like osteopenia and nephrolithiasis, is not increased in persons with benign familial hypocalciuric hypercalcemia, and the rates are similar to those in the general population. Rarely, a severe form of this disease, namely neonatal severe primary hyperparathyroidism is seen in infants with homozygous CASR mutations.

CONCLUSIONS

Benign familial hypocalciuric hypercalcemia is a small but important cause of hypercalcemia, especially in the younger population. Hypercalcemia persists after subtotal parathyroidectomy. It is important to diagnose this condition, not only in the index case but also in family members, because these patients should be advised against surgical intervention.

Neonatal severe hyperparathyroidism associated with a novel de novo heterozygous R551K inactivating mutation and a heterozygous A986S polymorphism of the calcium-sensing receptor gene

INTRODUCTION

Neonatal severe hyperparathyroidism (NSHPT) is induced by inactivating mutations of human calcium-sensing receptor (CaSR). Only three heterozygous de novo inactivating mutations of CaSR causing NSHPT have been described. We report the case of a now 11-year-old boy with NSHPT and we characterize a novel inactivating mutation along with the results of some functional analyses.

PATIENT AND METHODS

As a neonate the patient presented the clinical syndrome of NSHPT. At 6 years of age persisting hypercalcaemia without clinical symptoms was documented, and the patient remained completely symptom free without parathyroid surgery until his present age of 11 years. The entire coding region of the CaSR gene of the patient and his family members was sequenced. Functional investigation was performed in HEK-293 cells, transiently transfected with wild type and mutant CaSR plasmid constructs.

RESULTS

Sequence analysis revealed a novel de novo heterozygous mutation at codon 551 (AGG-->AAG), predicting a change of arginine to lysine (R551K) and a known heterozygous polymorphism (A986S) on the same allele, which was inherited from the father. We demonstrated that the novel R551K mutation significantly reduced the calcium sensitivity of CaSR (EC50: from 3.38 +/- 0.62-6.10 +/- 0.83 mmol/l), which was not alleviated by the simultaneous presence of A986S polymorphism.

CONCLUSIONS

We present the fourth NSHPT case induced by a novel de novo heterozygous inactivating mutation (R551K) of the CaSR gene. The disease gradually reverted to a symptomless, benign condition resembling familial hypocalciuric hypercalcaemia without any surgical intervention.

Identification and functional characterization of a novel mutation in the calcium-sensing receptor gene in familial hypocalciuric hypercalcemia: modulation of clinical severity by vitamin D status

CONTEXT

Familial hypocalciuric hypercalcemia (FHH) is a benign condition associated with heterogeneous inactivating mutations in the calcium-sensing receptor (CASR) gene.

OBJECTIVE

The objective of the study was to identify and characterize a CASR mutation in a moderately hypercalcemic, hyperparathyroid individual and his family and assess the influence of vitamin D status on the clinical expression of the defect.

SUBJECTS

We studied a kindred with FHH, in which the proband (a 34-yr-old male) was initially diagnosed with primary hyperparathyroidism due to frankly elevated serum PTH levels.

METHODS

CASR gene mutation analysis was performed on genomic DNA of the proband and family members. The mutant CASR was functionally characterized by transient transfection studies in kidney cells in vitro.

RESULTS

A novel heterozygous mutation (F180C, TTC>TGC) in exon 4 of the CASR gene was identified. Although the mutant receptor was expressed normally at the cell surface, it was unresponsive with respect to intracellular signaling (MAPK activation) to increases in extracellular calcium concentrations. The baby daughter of the proband presented with neonatal hyperparathyroidism with markedly elevated PTH. Vitamin D supplementation of both the proband and the baby resulted in reduction of serum PTH levels to the normal range. The serum calcium level remained at a constant and moderately elevated level.

CONCLUSION

The identification of a novel CASR gene mutation established the basis of the hypercalcemia in the kindred. Concomitant vitamin D deficiency modulates the severity of the presentation of FHH.

Familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism associated with mutations in the human Ca2+-sensing receptor gene in three Danish families

We screened three unrelated Danish families with familial hypocalciuric hypercalcemia (FHH) for mutations in the Ca2+-sensing receptor (CASR) gene by polymerase chain reaction amplification and DNA sequencing of exons 2-7, which include the entire coding region of the gene. In one family the affected individuals have a T-->C mutation that changes the normal arginine at codon 220 to a tryptophan. In the other two FHH families, affected individuals have the same A-->G mutation, leading to conversion of the normal glycine at codon 552 to an arginine. These results confirm that FHH can be caused by non-conservative missense mutations in the CASR gene leading to abnormal calcium homeostasis. Both mutations are located in the amino-terminal extracellular domain of the receptor, which contains the binding site for extracellular Ca2+, the CASR's principal physiological agonist.

Neonatal severe hyperparathyroidism, secondary hyperparathyroidism, and familial hypocalciuric hypercalcemia: multiple different phenotypes associated with an inactivating Alu insertion mutation of the calcium-sensing receptor gene

Neonatal severe hyperparathyroidism (NSHPT) is considered an autosomal-recessive disorder, attributable in many cases to homozygous inactivating mutations of the Ca++-sensing receptor (CASR) gene at 3q13.3-21. Most heterozygotes are clinically asymptomatic but manifest as familial (benign) hypocalciuric hypercalcemia (FHH) with a laboratory profile that is variably and sometimes only marginally different from normal. In 5 NSHPT cases from 3 Nova Scotian families, we found homoallelic homozygosity for an insertion mutation in exon 7 of CASR that includes an Alu repeat element with an exceptionally long polyA tract. Four of the 5 NSHPT infants were treated by parathyroidectomy more than a decade ago and are well now. A fifth went undiagnosed until adulthood and has profound musculoskeletal and neurobehavioral deficits. Among 36 identified FHH heterozygotes are 3 individuals with an unexpected degree of hypercalcemia and elevated circulating parathyroid hormone levels consistent with secondary hyperparathyroidism. Two are obligately heterozygous offspring of NSHPT mothers with surgical hypoparathyroidism and variable compliance with vitamin D therapy. The other is an adult with coexistent celiac disease in whom hyperparathyroidism, probably secondary to vitamin D deficiency, led to surgery. In counseling affected families, the heterozygous state should not be considered entirely benign, since FHH heterozygotes, particularly infants, may be prone to secondary hyperparathyroidism and symptomatic hypercalcemia. In such families, molecular diagnosis will allow for unambiguous identification of at-risk individuals.

Hypercalcemia in children: an overview

Hypercalcemia occurs in children of all ages. A serum calcium level over 15 mg/dL can be life-threatening. The association between familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NHPT) has been discussed. FHH is characterized by a high serum calcium concentration, relatively low urine calcium excretion, and an inappropriately normal parathyroid hormone (PTH) concentration. On the other hand, NHPT is a rare disease characterized by markedly increased serum calcium (15 mg/dL) and PTH concentrations, and is fatal without parathyroidectomy early in life. Recently, a complementary DNA encoding an extracellular calcium-sensing receptor has been isolated. Furthermore, three mutations in the receptor gene in FHH and NHPT individuals have been described. Thus, heterozygotes and homozygotes of FHH may have an intermittent hypercalcemia and NHPT, respectively. Vitamin D-related hypercalcemia, and vitamin D intoxication and immobilization are also discussed.

In vivo and in vitro characterization of neonatal hyperparathyroidism resulting from a de novo, heterozygous mutation in the Ca2+-sensing receptor gene: normal maternal calcium homeostasis as a cause of secondary hyperparathyroidism in familial benign hypocalciuric hypercalcemia

We characterized the in vivo, cellular and molecular pathophysiology of a case of neonatal hyperparathyroidism (NHPT) resulting from a de novo, heterozygous missense mutation in the gene for the extracellular Ca2+ (Ca2+(o))-sensing receptor (CaR). The female neonate presented with moderately severe hypercalcemia, markedly undermineralized bones, and multiple metaphyseal fractures. Subtotal parathyroidectomy was performed at 6 wk; hypercalcemia recurred rapidly but the bone disease improved gradually with reversion to an asymptomatic state resembling familial benign hypocalciuric hypercalcemia (FBHH). Dispersed parathyroid cells from the resected tissue showed a set-point (the level of Ca2+(o) half maximally inhibiting PTH secretion) substantially higher than for normal human parathyroid cells (approximately 1.8 vs. approximately 1.0 mM, respectively); a similar increase in set-point was observed in vivo. The proband's CaR gene showed a missense mutation (R185Q) at codon 185, while her normocalcemic parents were homozygous for wild type (WT) CaR sequence. Transient expression of the mutant R185Q CaR in human embryonic kidney (HEK293) cells revealed a substantially attenuated Ca2+(o)-evoked accumulation of total inositol phosphates (IP), while cotransfection of normal and mutant receptors showed an EC50 (the level of Ca2+(o) eliciting a half-maximal increase in IPs) 37% higher than for WT CaR alone (6.3+/-0.4 vs. 4.6+/-0.3 mM Ca2+(o), respectively). Thus this de novo, heterozygous CaR mutation may exert a dominant negative action on the normal CaR, producing NHPT and more severe hypercalcemia than typically seen with FBHH. Moreover, normal maternal calcium homeostasis promoted additional secondary hyperparathyroidism in the fetus, contributing to the severity of the NHPT in this case with FBHH.

Three inherited disorders of calcium sensing

Three distinct disorders of calcium homeostasis can result from mutations in the gene encoding the human calcium-sensing receptors (CASR; MIM 145980). One form of autosomal dominant familial hypocalciuric hypercalcemia results from the heterozygous state of inactivating mutations in the CASR gene. Neonatal severe hyperparathyroidism results from homozygosity for inactivating mutations in the CASR gene. The severe phenotype demonstrates the fundamental role the calcium-sensing receptor plays in parathyroid function. Activating mutations can lead to autosomal dominant hypocalcemia. The role of the calcium-sensing receptor in the kidney, brain, and other organs in health and disease awaits clarification.

Calcium-sensing receptor mutations in familial benign hypercalcemia and neonatal hyperparathyroidism

Familial benign hypercalcemia (FBH) and neonatal hyperparathyroidism (NHPT) are disorders of calcium homeostasis that are associated with missense mutations of the calcium-sensing receptor (CaR). We have undertaken studies to characterize such CaR mutations in FBH and NHPT and to explore methods for their more rapid detection. Nine unrelated kindreds (39 affected, 32 unaffected members) with FBH and three unrelated children with sporadic NHPT were investigated for mutations in the 3,234-bp coding region of the CaR gene by DNA sequencing. Six novel heterozygous (one nonsense and five missense) mutations were identified in six of the nine FBH kindreds, and two de novo heterozygous missense mutations and one homozygous frame-shift mutation were identified in the three children with NHPT. Our results expand the phenotypes associated with CaR mutations to include sporadic NHPT. Single-stranded conformational polymorphism analysis was found to be a sensitive and specific mutational screening method that detected > 85% of these CaR gene mutations. The single-stranded conformational polymorphism identification of CaR mutations may help in the distinction of FBH from mild primary hyperparathyroidism which can be clinically difficult. Thus, the results of our study will help to supplement the clinical evaluation of some hypercalcemic patients and to elucidate further the structure-function relationships of the CaR.

Familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism. Effects of mutant gene dosage on phenotype

Neonatal severe hyperparathyroidism is a rare life-threatening disorder characterized by very high serum calcium concentrations (> 15 mg/dl). Many cases have occurred in families with familial hypocalciuric hypercalcemia, a benign condition transmitted as a dominant trait. Among several hypothesized relationships between the two syndromes is the suggestion that neonatal severe hyperparathyroidism is the homozygous form of familial hypocalciuric hypercalcemia. To test this hypothesis, we refined the map location of the gene responsible for familial hypocalciuric hypercalcemia on chromosome 3q. Analyses in 11 families defined marker loci closely linked to the gene responsible for familial hypocalciuric hypercalcemia. These loci were then analyzed in four families with parental consanguinity and offspring with neonatal severe hyperparathyroidism. Each individual who was homozygous for loci that are closely linked to the gene responsible for familial hypocalciuric hypercalcemia had neonatal severe hyperparathyroidism. The calculated odds of linkage between these disorders of > 350,000:1 (lod score = 5.56). We conclude that dosage of the gene defect accounts for these widely disparate clinical phenotypes; a single defective allele causes familial hypocalciuric hypercalcemia, while two defective alleles causes neonatal severe hyperparathyroidism.

Self limiting neonatal primary hyperparathyroidism associated with familial hypocalciuric hypercalcaemia

A boy is described who presented aged 7 weeks with severe biochemical and radiological neonatal hyperparathyroidism that had completely resolved by the age of 6 months. His mother had a normal serum calcium concentration but his father, paternal aunt, and paternal cousin all had a raised serum calcium due to familial hypocalciuric hypercalcaemia.

Parathyroid surgery in children

Parathyroid surgery in children is uncommon. Spontaneously occurring cases of hyperparathyroidism are almost always due to single-gland disease: however, on exploration all four parathyroid glands should be identified. Most of the other instances in which the surgeon needs to perform a parathyroidectomy on an infant or a child will be situations were multiple-gland disease is the rule rather than the exception. Therefore, the surgeon must have in his mind a well developed logical approach to the management of children with parathyroid disorders on the basis of multiple glandular disease. We believe that the technique of parathyroid autotransplantation very satisfactorily addresses the surgical needs of children with familial hyperparathyroid states, including the multiple endocrine neoplasias. We believe that it is mandatory treatment in patients presenting with neonatal primary hyperparathyroidism and is also the procedure of choice in children with secondary and tertiary hyperparathyroidism. The workup and diagnosis of parathyroid disorders should be familiar to the surgeon who undertakes neck exploration on children, and the entity of familial hypocalciuric hypercalcemia should be looked for, as these patients have a strong likelihood of not benefiting from parathyroidectomy.

Ionized calcium: pediatric perspective

Ionized calcium is a physiologically critical calcium pool. It is easily determined, although accuracy depends on sample handling. As a clinical parameter, directly measured ionized calcium has particular import in the care of neonates, patients with sepsis or other cardiovascular instability, massively transfused patients, and those undergoing cardiopulmonary bypass or liver transplantation. Disturbances of calcium occur in many other settings, however, and accurate diagnosis and research conclusions may depend on using the best measurement available. Clinical and investigational use of ionized calcium determinations represent appropriate applications of current proven technology. In the future, clinical calcium manipulation may include modifying specific transmembrane transport processes and intracellular calcium pools and movements. At the current time we are largely restricted to studies of extracellular calcium concentration and its interactions. Much is known, but Mother Nature still has too many secrets. The interested reader is referred to discussions of ionized calcium and hemodynamics, reviews of the endocrine disturbances of calcium and phosphorus, textbook discussions pertinent to general calcium disturbances, and critical care issues.

Late presenting, prolonged hypocalcemia in an infant of a woman with hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) is a benign autosomal dominant disorder. Infants affected with FHH however, born to unaffected mothers may develop life-threatening autonomous hyperparathyroidism, the mechanism of which is not clearly understood. There is little information recorded in the literature regarding the opposite scenario, i.e., unaffected infants born to affected mothers. Because fetal parathyroid suppression presumably occurs secondary to high maternal calciums, neonatal hypocalcemia would be expected. The authors present a case of an infant with the latter circumstances who presents with late onset, life-threatening hypocalcemia secondary to relative hypoparathyroidism. The authors explored the possibility that vitamin D deficiency and/or acute environmental stress facilitated the decompensation. The patient required therapy for 2 months.