Ca&Bone

[The pathophysiological role of the cell surface calcium-sensing receptor New clinical entities and drugs, potential therapeutic targets]

TÓTH Miklós

NOVEMBER 20, 2004

Ca&Bone - 2004;7(04)

[The extracellular calcium-sensing receptor (CaSR) was recognized and cloned a decade ago. It is a G-proteincoupled receptor that plays an essential role in the regulation of extracellular calcium homeostasis. Diseases known as familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism and autosomal dominant hypocalcemia are the consequences of naturally occurring mutations of the CaSR. However, the spectrum of the CaSR diseases became more complex with the recognition of both hypo- and hypercalcemic states caused by anti-CaSR autoantibodies. Activating anti-CaSR autoantibodies have been implicated in the pathogenesis of isolated idiopathic hypoparathyroidism and of hypoparathyroidism associated with autoimmune polyglandular syndromes. Inactivating CaSR autoantibodies may cause fluctuating hypercalcemic disorder that resembles primary hyperparathyroidism. The CaSR recently became one of the most intensively investigated target of potential new drugs. Cinacalcet has been approved for the treatment of secondary hyperparathyroidism associated with chronic renal insufficiency and for the management of inoperable or metastatic parathyroid carcinoma.The CaSR may be one of the main molecular target of strontium ranelate, wich is a new antiosteoporotic compound.]

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Further articles in this publication

Ca&Bone

[Comparison of osteodensitometric and quantitative bone ultrasound parameters among patients with pseudopseudohypoparathyroidism, pseudohypoparathyroidism type Ia and primary hyperparathyroidism]

CSUPOR EMŐKE, SZABOLCS István, FERENCZ VIKTÓRIA, GÓTH Miklós, IVÁN Gabriella, GYŐRI Gabriella, KOVÁCS LÁSZLÓ, TÓTH EDIT, MÉSZÁROS SZILVIA, HORVÁTH CSABA

[INTRODUCTION - Parathyroid hormone (PTH) excretion is increased both in primary hyperparathyroidism (pHPT) and in pseudohypoparathyroidism type Ia (PHP Ia). Pseudo-pseudohypoparathyroidism (P-PHP) is considered to be the normocalcemic form of pseudohypoparathyroidism type Ia. Our aim was to assess bone mineral content and bone quality as well as to determine whether these parameters are related to PTH levels in the above mentioned disorders. PATIENTS AND METHOD - 10 patients with pseudopseudohypoparathyroidism (P-PHP, age: 41.6 ±5.4 ys) were compared to 10 patients with primary hyperparathyroidism (pHPT) and to 10 healthy subjects, matched for age and gender. Moreover, nine patients with pseudohypoparathyroidism type Ia (PHP, age: 34.2 ±5.43 ys) were compared to nine age- and gender-matched patients with primary hyperparathyroidism and to nine healthy controls, respectively.The occurrence of previous bone fractures was recorded and bone mass was measured (by dual photon absorptiometry on the axial bones and by single photon absorptiometry on the forearm). Quantitative ultrasound (QUS) examination was performed both on the calcaneus by broadband ultrasound attenuation (BUA, dB/MHz) and speed of sound (SOS, m/s) measurements and on the proximal phalanges by amplitude-dependent speed of sound (AdSOS, m/s) measurements. In addition, some laboratory parameters of calcium metabolism were tested. RESULTS - No difference was found between PHP Ia and pHPT in bone mass.The lowest value was observed at the radius. Among the QUS parameters, pathologically low AdSOS was found at the phalanges in PHP Ia and it was lower than in pHPT patients, whereas at the calcaneus BUA showed a similar tendency. Bone mass did not significantly differ between P-PHP and healthy controls, it was decreased, however, at the forearm in the patients. Pathological AdSOS was found in P-PHP, which was lower than in pHPT. SOS at the calcaneus was lower in P-PHP than in pHPT, though it was not considered pathological. Laboratory results were typical for the diseases and the radiological examinations confirmed the diagnosis. Bone fractures occurred in three and two patients with PHP Ia and P-PHP, respectively, while no fractures were recorded in the pHPT and healthy groups. CONCLUSION - Bone loss among patients with PHP Ia is considered to be the impact of PTH excess on bone tissue.The deterioration of bone quality and architecture may play a role in the development of bone fractures.]

Ca&Bone

[A de novo heterozygous R551K point mutation and an A986S polymorphism in a patient with neonatal severe primary hyperparathyroidism]

CSÁKVÁRY Violetta, TÓTH Miklós, PATÓCS Attila, VARGA Ibolya, OROSZLÁN György, RÁCZ Károly

[INTRODUCTION - Familial hypocalciuric hypercalcemia and neonatal severe primary hyperparathyroidism are caused by inactivating mutations of the calcium-sensing receptor (CaSR) gene. We report the case of a now 9.5 years old boy who presented with the clinical syndrome of neonatal severe hyperparathyroidism. PATIENT AND METHODS - At the age of 2 days the patient developed respiratory distress. Clinical studies revealed increased serum calcium (3.1 mmol/l), non-suppressed serum parathyroid hormone level (48.3 pg/ml) and severe undermineralization of bones, as well as periosteal calcification in the distal part of both femurs suggesting fractures during the intrauterine life. Parathyreoidectomy was not performed.At the age of 6 years normal mental and physical development, persisting hypercalcemia without clinical symptoms, normal skeletal morphology, absence of new bone fractures, and absence of renal stones or nephrocalcinosis were documented, and the patient has remained completely symptom-free until his present age of 9.5 years. Sequence analysis of the entire coding region (exons 2-7) of the CaSR gene in peripheral leukocyte DNA revealed a heterozygous mutation at codon 551 (AGG→AAG) predicting a change of arginine to lysine (R551K). In addition, a known heterozygous polymorphism at codon 986 (GCC→TCC) was found in the proband and in his father. CONCLUSION - Our patient seems to represent the fourth reported case of neonatal severe primary hyperparathyroidism with a heterozygous de novo mutation of the CaSR gene. In addition, this case provides new evidence that with time the disease of neonatal severe hyperparathyroidism may spontaneously turn into a symptomless, benign condition resembling familial hypocalciuric hypercalcemia.]

Ca&Bone

[Biochemical processes of the bone in patients treated with clodronate for metastatic prostate cancer]

GERVAIN Mihály, BEZZEGH Attila, PREKOPP Gábor, VANIK Miklós, FÉL Pál, VARGA Béla, BORSI László, PÁSZTOR Imre, KORÁNYI LÁSZLÓ, PINTÉR Erzsébet

[INTRODUCTION - The bone remodelling process of 81 patients with metastatic prostate cancer was analyzed and correlated to PSA levels. PATIENTS AND METHODS - The patients were recruited from 9 collaborating urology departments. Levels of β-CrossLaps, BALP, urine calcium and urine phosphate were measured. All patients were treated identically (TUR plus an LH-RH analogue or MAB), according to GCP guidelines. After the appearance of metastasis, the patients also received a bisphosphonate compound (clodronate). RESULTS - Bone degradation and formation showed a correlation both in living and deceased patients, indicating that the two processes are not independent. A progressive decrease in the PSA level was associated with a decrease in the β-CrossLaps level. CONCLUSION - In addition to PSA, β-CrossLaps and BALP, two markers of bone metabolism, might prove good predictors of metastasis formation and of response to therapy. Evaluation of the markers relative to agedependent osteoporosis can further improve their predictive value.]

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Hypertension and nephrology

[Role of calcimimetics in the treatment of secondary hyperparathyroidism in dialysed patients ]

[The authors summarize the pathophysiology and main clinical features of the condition which was previously called secondary hyperparathyroidism (sHTP) and renal osteodystrophy (ROD) in chronic kidney disease patients. Recently this entity has been renamed as chronic kidney disease - mineral and bone disorders (CKD-MBD), which more accurately describes the complexity of the condition including changes in laboratory parameters, bone turnover and vascular calcification. The calcium sensing receptor (CaR) plays a central role in the pathophysiology of CKD-MBD. Calcimimetics, which increase the sensitivity of the CaR to calcium, represent a novel and potentially advantageous class of medications for the management of the condition. Currently cinacalcet is the only available calcimimetic for clinical practice. Robust preclinical and human clinical trials have demonstrated that calcimimetics increase the expression of calcium sensing and the vitamin D receptors, attenuate parathyroid hyperplasia, decrease all four laboratory parameters (iPTH, Ca, P and Ca × P), optimize bone turnover and may slow down vascular calcification. As a results, cinacalcet based therapy is preferable and beneficial strategy in the treatment of CKD-MBD in patients on maintenance dialysis.]

Ca&Bone

[A de novo heterozygous R551K point mutation and an A986S polymorphism in a patient with neonatal severe primary hyperparathyroidism]

CSÁKVÁRY Violetta, TÓTH Miklós, PATÓCS Attila, VARGA Ibolya, OROSZLÁN György, RÁCZ Károly

[INTRODUCTION - Familial hypocalciuric hypercalcemia and neonatal severe primary hyperparathyroidism are caused by inactivating mutations of the calcium-sensing receptor (CaSR) gene. We report the case of a now 9.5 years old boy who presented with the clinical syndrome of neonatal severe hyperparathyroidism. PATIENT AND METHODS - At the age of 2 days the patient developed respiratory distress. Clinical studies revealed increased serum calcium (3.1 mmol/l), non-suppressed serum parathyroid hormone level (48.3 pg/ml) and severe undermineralization of bones, as well as periosteal calcification in the distal part of both femurs suggesting fractures during the intrauterine life. Parathyreoidectomy was not performed.At the age of 6 years normal mental and physical development, persisting hypercalcemia without clinical symptoms, normal skeletal morphology, absence of new bone fractures, and absence of renal stones or nephrocalcinosis were documented, and the patient has remained completely symptom-free until his present age of 9.5 years. Sequence analysis of the entire coding region (exons 2-7) of the CaSR gene in peripheral leukocyte DNA revealed a heterozygous mutation at codon 551 (AGG→AAG) predicting a change of arginine to lysine (R551K). In addition, a known heterozygous polymorphism at codon 986 (GCC→TCC) was found in the proband and in his father. CONCLUSION - Our patient seems to represent the fourth reported case of neonatal severe primary hyperparathyroidism with a heterozygous de novo mutation of the CaSR gene. In addition, this case provides new evidence that with time the disease of neonatal severe hyperparathyroidism may spontaneously turn into a symptomless, benign condition resembling familial hypocalciuric hypercalcemia.]

Hypertension and nephrology

[Terciary hyperparathyreosis or not? ? You cannot solve it alone: combined treatment in severe osteitis fibrosa cystica]

HERSZÉNYI Eszter, PATÓ Éva, SZALAY László, BÍRÓ Zsolt, György Andrea, DEÁK György

[Phosphate retention, consequential rise of the phosphaturic fibroblast growth factor-23 that decreases the level of calcitriol resulting in hypocalcemia facilitates the development of secondary hyperparathyroidism (sHPT) in chronic kidney disease (CKD). Hyperphosphatemia, hypocalcemia and low calcitriol level result in increasing secretion of parathormone (PTH). While sHPT occures frequently in CKD, the development of therapy-resistant and hypercalcemic tertiary hyperparathyroidism is rare due to current therapeutic approaches. We present the case of a 41 year old, treated schizophrenic, hemodialized male patient with severe osteitis fibrosa cystica, severe hyperparathyroidism (PTH 2500 pg/ml) - considered to be tertiary - and with repeated pathologic fractures. While hospitalized, the patient was under supervised, combined therapy with the vitamin D receptor activator paricalcitol and the calcimimetic cinacalcet that resulted in marked decrease of PTH level to 1589 pg/ml. However, after discharge from the hospital due to the lack of compliance he failed to take his medications and PTH had risen to the initial level. This case demonstrates that severe hyperparathyroidism thought to be therapy resistant responds well to a combination of paricalcitol and cinacalcet however, patient compliance is essential to therapeutic success.]