Abstract
Background: Neonatal severe primary hyperparathyroidism (NSHPT, MIM 239200) is most often an isolated disorder that is due to biallelic inactivating mutations in the CASR, the gene encoding the calcium sensing receptor; NSHPT is inherited from parents with familial hypocalciuric hypercalcemia, each of whom has one mutated CASR allele.
Objectives: To report clinical and genetic findings in a brother and sister with NSHPT due to a novel mutation in the CASR transmitted as an autosomal recessive trait and to examine the functional effect of the mutation.
Subjects and methods: A brother and sister with marked hypercalcemia due to NSHPT were identified; the boy also had craniosynostosis requiring surgical repair. The genotyping of the CASR in both children and their parents who were eucalcemic and normophosphatemic was undertaken. In order to examine the significance of the variant CASR identified, the CASR variant was expressed in vitro and examined by three computer computational programs [PolyPhen2, MutationTaster, Sorting Intolerant From Tolerant (SIFT)] designed to evaluate the effect of a nucleotide variant on the structure and likely functional consequence upon the protein product.
Results: A sequence variant in the CASR was identified [G>T point mutation at nucleotide c.2303 in exon 7 (c.2303G>T) resulting in the replacement of glycine by valine at codon 768 (p.Gly768Val)]. Two copies of this CASR variant were present in the genome of the siblings while a single copy of the CASR variant was present in both of the clinically and biochemically normal parents, a pattern of transmission consistent with autosomal recessive inheritance of NSHPT in this family. When expressed in HEK293 cells in vitro, the novel Gly768Val variant did not interfere with protein generation or migration to the cell membrane in vitro. The analysis of the functional effect of the Gly768Val CASR variant by the PolyPhen2, MutationTaster, and Sorting Intolerant From Tolerant computer programs revealed that this mutation was very likely to be deleterious.
Conclusion: The NSHPT associated with biallelic Gly768Val mutations of the CASR in two siblings with severe hypercalcemia and hyperparathyroidism and their clinically and biochemically normal heterozygous parents was transmitted as an autosomal recessive disorder in this family.
Acknowledgments
The authors thank Gary Litman, PhD, for enabling these studies to be conducted in his laboratory; Marci O’Driscoll and Larry Dishaw, PhD, for invaluable technical assistance; Dorothy Shulman, MD, E. Verena Jorgensen, MD, and Dewey Eichler, PhD, for helpful discussion.
Conflict of interest statement
Authors’conflict of interest disclosure: The authors have no financial or competing interests to disclose.
Research funding: The present work was conducted without any extramural funding.
References
1. Hannan FM, Nesbit MA, Zhang C, Cranston T, Curley AJ, et al. Identification of 70 calcium-sensing receptor mutations in hyper- and hypo-calcaemic patients: evidence for clustering of extracellular domain mutations at calcium-biding sites. Hum Molec Genet 2012;21:2768–78.10.1093/hmg/dds105Search in Google Scholar PubMed
2. Nesbit MA, Hannan FM, Howles SA, Babinsky VN, Head RA, et al. Mutations affecting G-protein subunit α11 in hypercalcemia and hypocalcemia. N Engl J Med 2013;368:2476–86.10.1056/NEJMoa1300253Search in Google Scholar PubMed PubMed Central
3. Mannstadt M, Harris M, Bravenboer B, Chitturi S, Dreijerink KM, et al. Germline mutations affecting Gα11 in hypoparathyroidism. N Engl J Med 2013;368:2532–4.10.1056/NEJMc1300278Search in Google Scholar PubMed PubMed Central
4. Nesbit MA, Hannan FM, Howles SA, Reed AA, Cranston T, et al. Mutations in AP2S1 cause familial hypocalciuric hypercalcemia type 3. Nature Genet 2013;45:93–7.10.1038/ng.2492Search in Google Scholar PubMed PubMed Central
5. Hu J, Spiegel AM. Structure and function of the human calcium sensing receptor: insights from natural and engineered mutations and allosteric modulators. J Cell Mol Med 2007;11:908–22.10.1111/j.1582-4934.2007.00096.xSearch in Google Scholar PubMed PubMed Central
6. Letz S, Rus R, Haag C, Dörr HG, Dörr H-G, et al. Novel activating mutations of the calcium-sensing receptor: the calcilytic NPS-2143 mitigates excessive signal transduction of mutant receptors. J Clin Endocrinol Metab 2010;95:E229–33.10.1210/jc.2010-0651Search in Google Scholar PubMed
7. Gnad F, Baucom A, Mukhyaia K, Manning G, Zhang Z. Assessment of computational methods for predicting the effects of missense mutations in human cancers. BMC Genomics. 14(suppl 3):S7. DOI:10.1186/1471-2164-14-S3-S7.10.1186/1471-2164-14-S3-S7Search in Google Scholar PubMed PubMed Central
8. Reva B, Antipin Y, Sander C. Predicting the functional impact of protein mutations: application to cancer genomics. Nucleic Acids Res 2011 July 3.10.1093/nar/gkr407Search in Google Scholar PubMed PubMed Central
9. Kumar P, Henikoff S, Ng PC. Predicting the effects of coding non-synonymous variants on protein function using the SIFT program. Nat Prot 2009;4:1073–81.10.1038/nprot.2009.86Search in Google Scholar PubMed
10. Kapur K, Johnson T, Beckmann ND, Sehmi J, Tanaka T, et al. Genome-wide meta-analysis for serum calcium identifies significantly associated SNPs near the calcium-sensing receptor (CASR) gene. PLOS Genetics 2010;6:e1001035. DOI: 10.1371/journal.pgen.1001035.10.1371/journal.pgen.1001035Search in Google Scholar PubMed PubMed Central
11. Jack MM, Sone ML, Clifton-Bligh R. Neonatal hypercalcemia due to polymorphisms of the calcium sensing receptor. J Pediatr Endocrinol Metab 2009;22:561–3.10.1515/JPEM.2009.22.6.561Search in Google Scholar PubMed
12. Hu J, McLarnon SJ, Mora S, Jiang J, Thomas C, et al. A region in the seven-transmembrane domain of the human Ca2+ receptor critical for response to Ca2+. J Biol Chem 2005;280:5113–20.10.1074/jbc.M413403200Search in Google Scholar PubMed
13. Magno AL, Ward BK, Ratajczak T. The calcium-sensing receptor: a molecular perspective. Endocrine Reviews 2011;32:3–30.10.1210/er.2009-0043Search in Google Scholar PubMed
14. White E, McKenna J, Cavanaugh A, Breitwieser GE. Pharmacochaperone-mediated rescue of calcium-sensing receptor loss-of-function mutants. Mol Endocrinol 2009; 23:1115–23.10.1210/me.2009-0041Search in Google Scholar PubMed PubMed Central
15. Lietman S, Tenenbaum-Rakover Y, Jap TS, Yi-Chi W, De-Ming Y, et al. A novel loss-of-function mutation, Gln459Arg, of the calcium-sensing receptor gene associated with apparent autosomal recessive inheritance of familial hypocalciuric hypercalcemia. J Clin Endocrinol Metab 2009;94:4372–9. DOI: 10.1210/jc.2008-2484.10.1210/jc.2008-2484Search in Google Scholar PubMed PubMed Central
16. Reh CM, Hendy GN, Cole DE, Jeandron DD. Neonatal hyperparathyroidism with a heterozygous calcium-sensing receptor (CASR) R185Q mutation: clinical benefit from cinacalcet. J Clin Endocrinol Metab 2011;96:E707–12.10.1210/jc.2010-1306Search in Google Scholar PubMed
17. Egbuna OI, Brown EM. Hypercalcaemic and hypocalcaemic conditions due to calcium-sensing receptor mutations. Best Pract Res Clin Rheumatol 2008;22:129–48.10.1016/j.berh.2007.11.006Search in Google Scholar PubMed PubMed Central
18. Brown EM, Lian JB. New insights in bone biology: unmasking skeletal effects of the extracellular calcium-sensing receptor. Science Signaling 2008;35:pe40. DOI: 10.1126/scisignal.135pe40.10.1126/scisignal.135pe40Search in Google Scholar PubMed
19. Chattopadhyay N, Yano S, Tfelt-Hansen J, Rooney P, Kanuparthi D, et al. Mitogenic action of calcium sensing receptor on rat calvarial osteoblasts. Endocrinology 2004;145:3451–62.10.1210/en.2003-1127Search in Google Scholar PubMed
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The online version of this article (DOI: 10.1515/jpem-2013-0343) offers supplementary material, available to authorized users.
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