title: Calcium-sensing receptor sequencing in 21 patients with idiopathic or familial parathyroid disorder: pitfalls and characterization of a novel I32 V loss-of-function mutation.
abstract: The calcium-sensing receptor (CaSR) is a G-protein-coupled receptor with a crucial role in calcium homeostasis. Mutations in the CaSR gene may lead to specific parathyroid disorders due to either gain-of-function (autosomal dominant hypercalciuric hypocalcemia; ADHH) or loss-of-function (familial hypocalciuric hypercalcemia; FHH). Our aim was to evaluate CaSR mutations as a cause of disease in selected patients. We identified and recruited patients with phenotypes suggestive of CaSR-related parathyroid disorders. DNA was extracted, and CaSR gene was sequenced. Live-ratiometric measurements of intracellular [Ca(2+)] and Western blot assays for evaluation of MAPK phosphorylation in response to changes in extracellular [Ca(2+)] were performed in transiently transfected HEK-293T cells to functionally characterize mutants. A total of 21 patients were evaluated, seven of them with idiopathic hypoparathyroidism (suspected ADHH) and 14 with hyperparathyroidism (suspected FHH). In the latter group two patients were found to harbor missense mutations: a novel heterozygous I32 V mutation in a female index case and a sporadic known R185Q mutation in a 1-year-old girl. In-vitro functional studies showed that I32 V is an inactivating mutation. In our study, most patients had normal CaSR sequencing. This suggests that phenotypic pitfalls may occur at time of patients' selection for CaSR sequencing. In one patient with strong positive pre-test probability based on both familial history and appropriate phenotype, a novel I32 V mutation leading to FHH was identified and characterized. In cases of familial parathyroid disorders, CaSR sequencing should be performed, but if negative, one should consider involvement of alternative genes or mechanisms.
authors.affiliation: Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, POB 24035, 91240, Jerusalem, Israel, auryans@hadassah.org.il.
authors.forename: Auryan
authors.initials: A
authors.lastname: Szalat
authors.forename: Michal
authors.initials: M
authors.lastname: Shahar
authors.forename: Shoshana
authors.initials: S
authors.lastname: Shpitzen
authors.forename: Boaz
authors.initials: B
authors.lastname: Nachmias
authors.forename: Gabriel
authors.initials: G
authors.lastname: Munter
authors.forename: David
authors.initials: D
authors.lastname: Gillis
authors.forename: Ronen
authors.initials: R
authors.lastname: Durst
authors.forename: Dror
authors.initials: D
authors.lastname: Mevorach
authors.forename: Eran
authors.initials: E
authors.lastname: Leitersdorf
authors.forename: Vardiella
authors.initials: V
authors.lastname: Meiner
authors.forename: Haim
authors.initials: H
authors.lastname: Rosen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000151:congenital* / Q000235:genetics; D053565:Hypercalciuria / Q000235:genetics; D006961:Hyperparathyroidism / Q000151:congenital / Q000235:genetics*; D006996:Hypocalcemia / Q000235:genetics; D007011:Hypoparathyroidism / Q000151:congenital / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D044169:Receptors, Calcium-Sensing / Q000235:genetics*; D017422:Sequence Analysis, DNA; D055815:Young Adult
chemical_list: D044169:Receptors, Calcium-Sensing
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