Limits...
A novel mutation in calcium-sensing receptor gene associated to hypercalcemia and hypercalciuria.

Mastromatteo E, Lamacchia O, Campo MR, Conserva A, Baorda F, Cinque L, Guarnieri V, Scillitani A, Cignarelli M - BMC Endocr Disord (2014)

Bottom Line: The father was treated with Cinacalcet 90 mg/day, with a decrease of total serum calcemia from an average value of 12.2 mg/dl to 10.9 mg/dl.Functional assay demonstrated that the 972 M variant influenced the maturation of the protein, in terms of the post-translational glycosylation.The impairment of the receptor activity is in keeping with the specific localization of the 972 residue in the C-terminal tail, assigned to the intracellular signalling, that on the basis of the our findings appears to be differently modulated in parathyroid gland and in kidney.

View Article: PubMed Central - PubMed

Affiliation: Unit of Endocrinology and Metabolic Diseases, Department of Medical and Surgical Sciences, University of Foggia, Italy, Viale Pinto, 1, 71122 Foggia, Italy. mauro.cignarelli@unifg.it.

ABSTRACT

Background: Familial Hyperparathyroidism (HPT) and Familial benign Hypocalciuric Hypercalcemia (FHH) are the most common causes of hereditary hypercalcemia. FHH has been demonstrated to be caused by inactivating mutations of calcium-sensing receptor (CaSR) gene, involved in PTH regulation as well as in renal calcium excretion.

Case presentation: In two individuals, father and son, we found a novel heterozygous mutation in CaSR gene. The hypercalcemia was present only in father, which, by contrast to the classic form of FHH showed hypercalciuria (from 300 to 600 mg/24 h in different evaluations) and a Calcium/Creatinine ratio of 0.031, instead of low or normal calciuria (<0.01 typical finding in FHH). His son showed the same mutation in CaSR gene, but no clinical signs or hypercalcemia although serum ionized calcium levels were close to the upper limit of normal values (1.30 mmol/L: normal range: 1.12-1.31 mmol/L). Sequence analysis revealed a point mutation at codon 972 of CaSR gene (chromosome 3q), located within cytoplasmic domain of the CaSR, that changes Threonine with Methionine. The father was treated with Cinacalcet 90 mg/day, with a decrease of total serum calcemia from an average value of 12.2 mg/dl to 10.9 mg/dl.

Conclusion: This is a case of a novel inactivating point mutation of CaSR gene that determines an atypical clinical presentation of FHH, characterized by hypercalcemia, hypercalciuria and inadequate normal PTH levels. Functional assay demonstrated that the 972 M variant influenced the maturation of the protein, in terms of the post-translational glycosylation. The impairment of the receptor activity is in keeping with the specific localization of the 972 residue in the C-terminal tail, assigned to the intracellular signalling, that on the basis of the our findings appears to be differently modulated in parathyroid gland and in kidney.

Show MeSH

Related in: MedlinePlus

CaSR signaling activity measured as the ratio between the level of phosphorylated and total p42/44 proteins. a: compared with the WT for both the Ca2+ concentrations, the 972 M variant induced a lower level of phosphorylation, similarly to the activity mediated by the inactivating control (F351V). Values were normalized with respect to the WT at 10 mM. Data are reported as mean ± SEM of three replicate experiments. * = p <0.05 compared with the WT; b: a representative western blot was shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4197257&req=5

Fig4: CaSR signaling activity measured as the ratio between the level of phosphorylated and total p42/44 proteins. a: compared with the WT for both the Ca2+ concentrations, the 972 M variant induced a lower level of phosphorylation, similarly to the activity mediated by the inactivating control (F351V). Values were normalized with respect to the WT at 10 mM. Data are reported as mean ± SEM of three replicate experiments. * = p <0.05 compared with the WT; b: a representative western blot was shown.

Mentions: We also tested the mutation by either qualitative assay in order to investigate the protein conformation effect or by quantitative assay to verify in addition the alteration of protein function. In our functional assays on WT and mutant CaSR proteins, we showed that, with respect the WT, the 972 M variant is slightly underexpressed as far as the 160 kDa glycosylated form (Figure 3). The signaling activity of the 972 M mutant receptor, compared to the WT, resulted strongly impaired even at higher Ca++ concentration (10 mM), showing a pattern similar to the inactivating mutant control (Figure 4).Figure 3


A novel mutation in calcium-sensing receptor gene associated to hypercalcemia and hypercalciuria.

Mastromatteo E, Lamacchia O, Campo MR, Conserva A, Baorda F, Cinque L, Guarnieri V, Scillitani A, Cignarelli M - BMC Endocr Disord (2014)

CaSR signaling activity measured as the ratio between the level of phosphorylated and total p42/44 proteins. a: compared with the WT for both the Ca2+ concentrations, the 972 M variant induced a lower level of phosphorylation, similarly to the activity mediated by the inactivating control (F351V). Values were normalized with respect to the WT at 10 mM. Data are reported as mean ± SEM of three replicate experiments. * = p <0.05 compared with the WT; b: a representative western blot was shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4197257&req=5

Fig4: CaSR signaling activity measured as the ratio between the level of phosphorylated and total p42/44 proteins. a: compared with the WT for both the Ca2+ concentrations, the 972 M variant induced a lower level of phosphorylation, similarly to the activity mediated by the inactivating control (F351V). Values were normalized with respect to the WT at 10 mM. Data are reported as mean ± SEM of three replicate experiments. * = p <0.05 compared with the WT; b: a representative western blot was shown.
Mentions: We also tested the mutation by either qualitative assay in order to investigate the protein conformation effect or by quantitative assay to verify in addition the alteration of protein function. In our functional assays on WT and mutant CaSR proteins, we showed that, with respect the WT, the 972 M variant is slightly underexpressed as far as the 160 kDa glycosylated form (Figure 3). The signaling activity of the 972 M mutant receptor, compared to the WT, resulted strongly impaired even at higher Ca++ concentration (10 mM), showing a pattern similar to the inactivating mutant control (Figure 4).Figure 3

Bottom Line: The father was treated with Cinacalcet 90 mg/day, with a decrease of total serum calcemia from an average value of 12.2 mg/dl to 10.9 mg/dl.Functional assay demonstrated that the 972 M variant influenced the maturation of the protein, in terms of the post-translational glycosylation.The impairment of the receptor activity is in keeping with the specific localization of the 972 residue in the C-terminal tail, assigned to the intracellular signalling, that on the basis of the our findings appears to be differently modulated in parathyroid gland and in kidney.

View Article: PubMed Central - PubMed

Affiliation: Unit of Endocrinology and Metabolic Diseases, Department of Medical and Surgical Sciences, University of Foggia, Italy, Viale Pinto, 1, 71122 Foggia, Italy. mauro.cignarelli@unifg.it.

ABSTRACT

Background: Familial Hyperparathyroidism (HPT) and Familial benign Hypocalciuric Hypercalcemia (FHH) are the most common causes of hereditary hypercalcemia. FHH has been demonstrated to be caused by inactivating mutations of calcium-sensing receptor (CaSR) gene, involved in PTH regulation as well as in renal calcium excretion.

Case presentation: In two individuals, father and son, we found a novel heterozygous mutation in CaSR gene. The hypercalcemia was present only in father, which, by contrast to the classic form of FHH showed hypercalciuria (from 300 to 600 mg/24 h in different evaluations) and a Calcium/Creatinine ratio of 0.031, instead of low or normal calciuria (<0.01 typical finding in FHH). His son showed the same mutation in CaSR gene, but no clinical signs or hypercalcemia although serum ionized calcium levels were close to the upper limit of normal values (1.30 mmol/L: normal range: 1.12-1.31 mmol/L). Sequence analysis revealed a point mutation at codon 972 of CaSR gene (chromosome 3q), located within cytoplasmic domain of the CaSR, that changes Threonine with Methionine. The father was treated with Cinacalcet 90 mg/day, with a decrease of total serum calcemia from an average value of 12.2 mg/dl to 10.9 mg/dl.

Conclusion: This is a case of a novel inactivating point mutation of CaSR gene that determines an atypical clinical presentation of FHH, characterized by hypercalcemia, hypercalciuria and inadequate normal PTH levels. Functional assay demonstrated that the 972 M variant influenced the maturation of the protein, in terms of the post-translational glycosylation. The impairment of the receptor activity is in keeping with the specific localization of the 972 residue in the C-terminal tail, assigned to the intracellular signalling, that on the basis of the our findings appears to be differently modulated in parathyroid gland and in kidney.

Show MeSH
Related in: MedlinePlus