Identification and functional analysis of novel calcium-sensing receptor gene mutation in familial hypocalciuric hypercalcemia

Role of LncRNA score and PVT1 in primary hyperparathyroidism-- a preliminary study

BACKGROUND

Dysregulated lncRNA score and PVT1 expression may be involved in cancer. However, relationships of lncRNAs with hyperparathyroidism and parathyroid cancer (PC) diagnosis remain mysterious.

METHODS

Using quantitative real-time polymerase chain reaction (RT-qPCR), expression profile of PVT1 was evaluated in 57 patients with primary hyperparathyroidism, including 11 with parathyroid cancer (PC) and 46 with parathyroid adenoma (PA).

RESULTS

Higher levels of lncRNA score and PVT1 expression were associated with increased serum calcium level after water ingestion and PC risk (P < 0.05). Accordingly, lncRNA score and PVT1 expression were increased with varying degrees of hypercalcemia in PC. A higher level of lncRNA score (but not PVT1) was an independent risk factor of PC, with an AUC up to 0.872 (95% CI: 0.756-0.945, P < 0.001). Moreover, lncRNA score was more valuable (with AUC 0.974, sensitivity of 85.71% and specificity of 100%, respectively) than intact parathyroid hormone (iPTH) in predicting risk of PC among patients with hypercalcemia (especially based on greater AUC, P = 0.010).

CONCLUSION

Increased lncRNA score is correlated with an elevated level of serum calcium, which may serve as a potential biomarker for PC diagnosis, especially with hypercalcemia.

Loss-of-function and gain-of-function mutations of calcium-sensing receptor: functional analysis and the effect of allosteric modulators NPS R-568 and NPS 2143

OBJECTIVE

Activating mutations in the calcium-sensing receptor (CASR) gene cause autosomal dominant hypoparathyroidism, and heterozygous inactivating CASR mutations cause familial hypocalciuric hypercalcemia. Recently, there has been a focus on the use of allosteric modulators to restore the functional activity of mutant CASRs. In this study, the effect of allosteric modulators NPS R-568 and NPS 2143 on CASR mutants was studied in vitro.

METHODS

DNA sequence analysis of the CASR gene was undertaken in autosomal dominant hypoparathyroidism and familial hypocalciuric hypercalcemia Japanese patients, and the functional consequences for the Gi-MAPK pathway and cell surface expression of CASR were determined. Furthermore, we studied the effect of NPS R-568 and NPS 2143 on the signal transduction activity and cell surface expression of each mutant CASR.

RESULTS

We identified 3 activating mutations (S122C, P569H, and I839T) and 2 inactivating mutations (A110T and R172G) in patients. The activating and inactivating mutations caused leftward and rightward shifts, respectively, in the dose-response curves of the signaling pathway. NPS R-568 rescued the signal transduction capacity of 2 inactivating mutants without increasing cell surface expression levels. NPS 2143 suppressed the enhanced activity of the activating mutants without altering cell surface expression levels, although A843E, which is a constitutively active mutant, was suppressed to a lesser degree.

CONCLUSIONS

We have identified 4 novel mutations of CASR. Moreover, our results indicate that allosteric modulators can restore the activity of the loss- and gain-of-function mutant CASRs, identified in this study.

Familial hypocalciuric hypercalcemia: new mutation in the CASR gene converting valine 697 to methionine

Familial hypocalciuric hypercalcemia is an uncommon cause of hypercalcemia that arises from mutations in the calcium-sensing receptor gene. Inactivation of this receptor leads to a decreased receptor sensitivity to calcium, determining that higher concentrations of calcium are needed to inhibit the release of parathormone in the parathyroid glands. Patients usually are asymptomatic. Diagnosis is usually made casually after a routine blood analysis. The syndrome is characterized by mild or moderate hypercalcemia, hypocalciuria, and normal or slightly increased levels of parathormone. The degree of hypercalcemia depends on the type of mutation. The accurate diagnosis is important since it is a benign disorder that does not require medical or surgical treatment. We report a 9-year-old female with persistent hypercalcemia in several routine blood analyses, who was diagnosed with familial hypocalciuric hypercalcemia after genetic studies were performed. A new mutation determining a nucleotide change c.2089G>A in the calcium-sensing receptor gene (exon 7) was detected. This mutation was also found in the patient's mother and brother.

Clinical utilization of cinacalcet in hypercalcemic conditions

INTRODUCTION

Cinacalcet has recently been introduced as a treatment for secondary hyperparathyroidism in dialysis patients and for parathyroid carcinoma. However, there has been an increasing interest in finding out whether cinacalcet can be used as a treatment for other parathyroid hormone (PTH)-dependent hypercalcemic conditions also.

AREAS COVERED

The article reports the most relevant recent contributions dealing with calcium sensing receptor (CaSR) physiology as well as cinacalcet pharmacokinetics and pharmacodynamics. It also looks at the different hypercalcemic conditions where the use of cinacalcet has been proposed. This article was researched using clinical trials, case reports and outstanding basic research published in the last 3 years (MEDLINE database up to 31 November 2010). It provides the reader with an insight into the many unaddressed issues regarding cinacalcet that need to be resolved before it can be used in newly proposed fields.

EXPERT OPINION

Since cinacalcet may not only have an effect on parathyroid CaSR but also on CaSR expressed at bone and renal levels, it can currently only be considered a good alternative to parathyroidectomy in PTH-dependent hypercalcemic conditions when surgical intervention is burdened by a high failure rate or when it can be considered a risky procedure. At present, cinacalcet cannot be considered the first choice treatment in asymptomatic primary hyperparathyroidism or in mild-to-moderate forms of familial hypocalciuric hypocalcemia.