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Query: UMLS:C0221002 (primary hyperparathyroidism)
 4,921 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In vivo dynamic tests of parathyroid gland function have provided useful information about the secretory behavior of parathyroids in various clinical disorders, but the limitations of this approach must be recognized when applied to studies of parathyroid gland physiology. Set point abnormalities have been documented in vivo both in primary hyperparathyroidism and in familial hypocalciuric hypercalcemia. Such findings are consistent with in vitro results obtained in studies of dispersed parathyroid cells from patients with primary hyperparathyroidism and with recently described alteration in calcium receptor expression in patients with FHH. The assessment of parathyroid gland function in patients with end-stage renal disease presents distinct methodological problems, however, because of marked variation in the degree of parathyroid gland enlargement. Neither the four parameter model originally used to describe set point abnormalities both in vitro and in vivo or alternative approaches to the assessment of PTH secretion in vivo adequately address this important issue. Results from recent in vivo studies of patients with chronic renal failure do not support the view that the set point for calcium-regulated PTH release is abnormal in secondary hyperparathyroidism or that treatment with calcitriol lowers the set point for calcium-regulated PTH release in patients with uremic secondary hyperparathyroidism. The concept of set point disturbances has strongly influenced discussions about the pathogenesis of secondary hyperparathyroidism, and it has served as a focal point for examining the therapeutic response to calcitriol in patients with this disorder. This matter requires careful reconsideration, however, in light of recent clinical findings and the development of techniques to directly assess the molecular mechanisms responsible for regulating calcium-mediated PTH release in renal failure and other disorders of mineral metabolism. Although knowledge in this area remains limited, the extent of parathyroid hyperplasia and the role of factors that influence the development of parathyroid gland enlargement may ultimately prove to be particularly important modifiers of parathyroid gland function in chronic renal failure.
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PMID:In vivo assessments of calcium-regulated parathyroid hormone release in secondary hyperparathyroidism. 894 64

These results in difficult patients with previously missed parathyroid adenomas demonstrate that a prospective strategy to treat these patients surgically can be used with a high degree of success. This strategy required collaboration among endocrinologists, radiologists, and surgeons. Prospectively, only patients with symptomatic persistent or recurrent primary hyperparathyroidism were included. Operative reports and pathology results from the initial operation and all previous operations were reviewed in detail. Patients with FHH or hypercalcemia from other causes were excluded. State-of-the-art radiologic localization procedures were used to localize the abnormal parathyroid gland. Most patients had only noninvasive procedures, such as the sestamibi scan, but some whose results were equivocal underwent invasive localization, including selective angiography and venous sampling. All patients underwent surgery even if the localization procedures were negative. The operative approach and strategy were dependent on the previous operative result and results of the imaging studies. Operative techniques like IOUS and urinary cAMP determination helped facilitate a more rapid successful outcome. However, in some patients, operative success was only achieved by complete dissection and removal of all tissue that might harbor the adenoma such as a lobe of the thyroid or the thymus. Abnormal parathyroid tissue was cryopreserved for possible subsequent autotransplantation in the event of hypoparathyroidism. The reoperative success rate for missed adenoma was 97%, the highest ever reported with a very acceptable complication rate and no deaths. Postoperative hypoparathyroidism, which was really a complication of the initial previous operations during which normal parathyroid tissue was removed, was treated by autotransplantation of cryopreserved tissue in 12 patients, and 8 functioned perfectly. With attention to details and possible pitfalls, reoperations for missed parathyroid adenomas can be performed safely and effectively.
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PMID:Reoperation for missed parathyroid adenoma. 940 98

The human calcium-sensing receptor (CaSR) is a 1078-amino-acid cell surface protein which is expressed in the parathyroids, thyroid cells and the kidney, and is a member of the family of G protein-coupled receptors. The CaSR allows regulation of parathyroid hormone (PTH) secretion and renal tubular calcium reabsorption in response to alterations in extracellular calcium concentrations. The human CaSR gene is located on chromosome 3q13.3-q21, and loss of function CaSR mutations have been reported in the hypercalcaemic disorders of familial benign (hypocalciuric) hypercalcaemia (FBH or FHH) and neonatal severe primary hyperparathyroidism (NSHPT). In addition, gain of function CaSR mutations have been observed in a novel familial syndrome of hypocalcaemia with hypercalciuria. The human CaSR gene on chromosome 3q13.3-q21 is likely to be one of several, as two other loci for FBH have been located on chromosome 19p and 19q13. Cloning and characterisation of these genes will help to further elucidate the mechanisms regulating extracellular calcium.
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PMID:Disorders of the calcium-sensing receptor. 992 Apr 7

Cloning of the CaR has increased understanding of the normal control of mineral ion homeostasis and has clarified the pathophysiology of PTH-dependent hypercalcemia. Cloning of the CaR has enabled identification of FHH and NSHPT as inherited conditions with generalized resistance to Ca2+o, which is caused in many cases by inactivating mutations in the CaR gene. In most kindreds with FHH, there is resetting of Ca2+o to a mildly elevated level that does not require an increase in the circulating level of PTH above the normal range to maintain it. FHH is not accompanied by the usual symptoms, signs, and complications of hypercalcemia. The kidney participates in the genesis of the hypercalcemia in FHH by avidly reabsorbing Ca2+; consequently, there is no increased risk of forming urinary calculi in most cases. Generally, there is no compelling rationale for attempting to lower the level of Ca2+o in these patients to a nominal normal level. In contrast, in primary hyperparathyroidism, the Ca2+o resistance is limited to the pathologic parathyroid glands, and the rest of the body suffers the consequences of high circulating levels of calcium, PTH, or both. In this condition, removal of the offending parathyroid glands is often the treatment of choice. Parathyroidectomy may also be appropriate in disorders with generalized resistance to Ca2+o owing to inactivating CaR mutations in the following special circumstances: in selected families with FHH in which there is unusually severe hypercalcemia, frankly elevated PTH levels, or atypical features such as hypercalciuria; in cases of NSHPT with severe hypercalcemia and hyperparathyroidism; and in the occasional mild case of homozygous FHH owing to CaR mutations that confer mild-to-moderate resistance to Ca2+o that escapes clinical detection in the neonatal period. As discussed elsewhere in this issue, selective calcimimetic CaR activators are being tested in clinical trials, which potentiate the activation of the CaR by Ca2+o, thereby resetting the elevated set point for Ca2+o-regulated PTH release in primary and secondary hyperparathyroidism toward normal. It is hoped that these agents may become an effective medical therapy for the acquired Ca2+o resistance in primary and secondary hyperparathyroidism and perhaps for that present in the unusual cases of FHH and NSHPT, resetting the "calciostat" downward and thereby reducing Ca2+o and PTH toward normal.
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PMID:Familial hypocalciuric hypercalcemia and other disorders with resistance to extracellular calcium. 1103 58

Hyperparathyroidism (HPT) in its hereditary variants assumes special forms, has special associations, and requires special managements. Familial hypocalciuric hypercalcemia (FHH or FBHH) and neonatal severe primary hyperparathyroidism (NSHPT) reflect heterozygous or homozygous mutations, respectively, in the calcium-sensing receptor. FHH and NSHPT represent the mildest and severest variants of HPT. Both cause hypercalcemia from birth and atypical HPT that always and uniquely persists after subtotal parathyroidectomy. Their HPT is likely polyclonal and nonneoplastic. In contrast, mono- or oligo-clonal parathyroid neoplasia underlays most other HPT variants: multiple endocrine neoplasia type 1 (MEN1), multiple endocrine neoplasia type 2A (MEN2A), and hyperparathyroidism-jaw tumor syndrome (HPT-JT). Familial-isolated HPT combines several diagnoses, including occult forms of the above syndromes. Each neoplastic variant has tumors in multiple parathyroids and a delayed, but still early age of onset for HPT (average age, 25-35 years). Each justifies special and similar approaches to parathyroidectomy: typically, identification of four glands, subtotal parathyroidectomy, rapid intraoperative parathyroid hormone (PTH) assays, and parathyroid cryopreservation. Outcomes of parathyroidectomy remain suboptimal in each. Each syndrome of parathyroid neoplasia associates with characteristic cancer(s): enteropancreatic neuroendocrine or foregut carcinoid tissues (MEN1), thyroidal C cells (MEN2A), or parathyroid (HPT-JT). HPT has promoted gene discovery more through its rare hereditary variants than through common adenoma; the main genes causing four of six hereditary variants are known. The RET mutation test became essential in management of MEN2A. The MEN1 test is less urgent, because it rarely guides a major patient benefit. The CASR test, perhaps least urgent, has largely been unavailable. Further progress in molecular genetics will enhance understandings, diagnosis, and therapy of HPT.
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PMID:Hyperparathyroidism in hereditary syndromes: special expressions and special managements. 1241 76

There has been a shift in the referral patterns in recent years that has resulted in increasing numbers of patients being referred to surgeons with a diagnosis of hypercalcemia rather than primary hyperparathyroidism. The surgeon must perform a thorough history, including medications, and laboratory assessment, including serum calcium and parathyroid hormone measurements. A 24-hour urinary calcium excretion should be routinely ordered to exclude FHH. After the diagnosis of primary hyperparathyroidism is made, preoperative localization studies will benefit 78% to 90% of patients, with sestamibi scan being the most commonly used.
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PMID:Current issues in hyperparathyroidism. 1280 17

The human calcium-sensing receptor (CaSR) is a 1078 amino acid cell surface protein, which is predominantly expressed in the parathyroids and kidney, and is a member of the family of G protein-coupled receptors. The CaSR allows regulation of parathyroid hormone (PTH) secretion and renal tubular calcium reabsorption in response to alterations in extracellular calcium concentrations. The human CaSR gene is located on chromosome 3q21.1 and loss-of-function CaSR mutations have been reported in the hypercalcaemic disorders of familial benign (hypocalciuric) hypercalcaemia (FHH, FBH or FBHH) and neonatal severe primary hyperparathyroidism (NSHPT). However, some individuals with loss-of-function CaSR mutations remain normocalcaemic. In addition, there is genetic heterogeneity amongst the forms of FHH. Thus, the majority of FHH patients have loss-of-function CaSR mutations, and this is referred to as FHH type 1. However, in one family, the causative gene for FHH is located on 19p13, referred to as FHH type 2, and in another family it is located on 19q13, referred to as FHH type 3. Gain-of-function CaSR mutations have been shown to result in autosomal dominant hypocalcaemia with hypercalciuria (ADHH) and Bartter's syndrome type V. CaSR auto-antibodies have been found in FHH patients who did not have loss-of-function CaSR mutations, and in patients with an acquired form (i.e. autoimmune) of hypoparathyroidism. Thus, abnormalities of the CaSR are associated with three hypercalcaemic and three hypocalcaemic disorders.
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PMID:Diseases associated with the extracellular calcium-sensing receptor. 1520 Jan 51

Familial benign hypocalciuric hypercalcemia (FBHH), in which calcium homeostasis is disordered, can be distinguished from mild primary hyperparathyroidism by the finding of a heterozygous loss-of-function mutation in the calcium-sensing receptor (CaSR). Here, we report a Polish kindred with FBHH, the proband of which had undergone an unsuccessful parathyroidectomy. Direct sequence analysis of exon 4 of her CASR gene identified a heterozygous R227Q mutation in the extracellular domain of the receptor. This mutation segregated with other affected family members. A de novo heterozygous R227L mutation had previously been identified in a case of neonatal hyperparathyroidism. We performed a functional analysis by transiently transfecting wild-type and mutant (R227Q, R227L) CaSRs in human embryonic kidney (HEK293) cells. Both mutant receptors were expressed at a similar level to that of the wild-type, demonstrated a 160-kDa molecular species consistent with having undergone full maturation, and were visualized on the cell surface. Although both mutants were impaired in their MAPK responses to increasing extracellular calcium concentrations relative to wild type, this was more marked for R227L (EC(50) = 9.7 mM) than R227Q (EC(50) = 7.9 mM) relative to wild type (EC(50) = 3.7 mM). When cotransfected with wild-type CaSR to mimic the heterozygous state, the curves for both R227Q and R227L were right shifted intermediate to the curves for wild type and the respective mutant. This differential responsiveness may account, in part, for the markedly different clinical presentation of the R227Q mutation, classic FBHH, vs. the neonatal hyperparathyroidism of the R227L mutation.
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PMID:Functional characterization of calcium-sensing receptor codon 227 mutations presenting as either familial (benign) hypocalciuric hypercalcemia or neonatal hyperparathyroidism. 1557 18

Current views on the molecular aspects of familial parathyroid gland diseases have been presented (familial primary hyperparathyroidism, hypoparathyroidism and psuedohypoparathyroidism). Their inherited mode and genetic abnormalities have been described. Particularly, the following genes: HRPT2, MEN1, RET, CASR, GNAS have been shown. Localization, structure, expression and structural changes (mutations) found in patients with familial parathyroid gland diseases have been presented. Attention has been paid to clinical and histopathologic symptoms, which should indicate the need to undertake genetic studies.
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PMID:[Molecular aspects of the etiopathogenesis of the parathyroid gland diseases]. 1635 Jul 27

We present a male patient with neonatal severe primary hyperparathyroidism, whose manifestation was exceptionally serious for the heterozygous inactivating mutation he carried in the CASR gene. The patient presented soon after birth with respiratory distress requiring long-term mechanical ventilation, bone and chest deformities, feeding problems, and hypotonia. He had hypercalcaemia, hypophosphataemia, and hyperparathyroidism. There was no known history of calcium metabolism disorders in the family. As the impact on calcaemia of a rescue therapy with bisphosphonates was only transient, a subtotal and subsequently total parathyroidectomy were performed in the fourth month of life. Afterwards his clinical status improved and the fractures healed, but his neuropsychological development is delayed due to cerebral atrophy. Genetic analysis revealed a heterozygous missense CASR mutation R185Q, and an approximately equal expression of the mutated and wild-type RNA in the parathyroid tissue. The mother of the child was homozygous for the wild-type allele; the father is unknown. In conclusion, this patient demonstrates how serious neonatal hyperparathyroidism can be when caused by a heterozygous mutation. This may be attributable to a combination of dominant-negative action of the mutant allele with an intrauterine foetal hyperparathyroidism developed in the mother's normocalcaemic environment, further aggravated by a putative maternal vitamin D deficiency during pregnancy.
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PMID:Unusually severe phenotype of neonatal primary hyperparathyroidism due to a heterozygous inactivating mutation in the CASR gene. 1875 24


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