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Identification of a G-Protein Subunit-?11 Gain-of-Function Mutation, Val340Met, in a Family With Autosomal Dominant Hypocalcemia Type 2 (ADH2).

ABSTRACT: Autosomal dominant hypocalcemia (ADH) is characterized by hypocalcemia, inappropriately low serum parathyroid hormone concentrations and hypercalciuria. ADH is genetically heterogeneous with ADH type 1 (ADH1), the predominant form, being caused by germline gain-of-function mutations of the G-protein coupled calcium-sensing receptor (CaSR), and ADH2 caused by germline gain-of-function mutations of G-protein subunit ?-11 (G?11 ). To date G?11 mutations causing ADH2 have been reported in only five probands. We investigated a multigenerational nonconsanguineous family, from Iran, with ADH and keratoconus which are not known to be associated, for causative mutations by whole-exome sequencing in two individuals with hypoparathyroidism, of whom one also had keratoconus, followed by cosegregation analysis of variants. This identified a novel heterozygous germline Val340Met G?11 mutation in both individuals, and this was also present in the other two relatives with hypocalcemia that were tested. Three-dimensional modeling revealed the Val340Met mutation to likely alter the conformation of the C-terminal ?5 helix, which may affect G-protein coupled receptor binding and G-protein activation. In vitro functional expression of wild-type (Val340) and mutant (Met340) G?11 proteins in HEK293 cells stably expressing the CaSR, demonstrated that the intracellular calcium responses following stimulation with extracellular calcium, of the mutant Met340 G?11 led to a leftward shift of the concentration-response curve with a significantly (p?

SUBMITTER: Piret SE

PROVIDER: S-EPMC4915495 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Identification of a G-Protein Subunit-α11 Gain-of-Function Mutation, Val340Met, in a Family With Autosomal Dominant Hypocalcemia Type 2 (ADH2).

Piret Sian E SE Gorvin Caroline M CM Pagnamenta Alistair T AT Howles Sarah A SA Cranston Treena T Rust Nigel N Nesbit M Andrew MA Glaser Ben B Taylor Jenny C JC Buchs Andreas E AE Hannan Fadil M FM Thakker Rajesh V RV

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 20160601 6

Autosomal dominant hypocalcemia (ADH) is characterized by hypocalcemia, inappropriately low serum parathyroid hormone concentrations and hypercalciuria. ADH is genetically heterogeneous with ADH type 1 (ADH1), the predominant form, being caused by germline gain-of-function mutations of the G-protein coupled calcium-sensing receptor (CaSR), and ADH2 caused by germline gain-of-function mutations of G-protein subunit α-11 (Gα11 ). To date Gα11 mutations causing ADH2 have been reported in only five ...[more]

PMID: 26818911

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Project description:Familial hypocalciuric hypercalcemia is a genetically heterogeneous disorder with three variants: types 1, 2, and 3. Type 1 is due to loss-of-function mutations of the calcium-sensing receptor, a guanine nucleotide-binding protein (G-protein)-coupled receptor that signals through the G-protein subunit ?11 (G?11). Type 3 is associated with adaptor-related protein complex 2, sigma 1 subunit (AP2S1) mutations, which result in altered calcium-sensing receptor endocytosis. We hypothesized that type 2 is due to mutations effecting G?11 loss of function, since G?11 is involved in calcium-sensing receptor signaling, and its gene (GNA11) and the type 2 locus are colocalized on chromosome 19p13.3. We also postulated that mutations effecting G?11 gain of function, like the mutations effecting calcium-sensing receptor gain of function that cause autosomal dominant hypocalcemia type 1, may lead to hypocalcemia.We performed GNA11 mutational analysis in a kindred with familial hypocalciuric hypercalcemia type 2 and in nine unrelated patients with familial hypocalciuric hypercalcemia who did not have mutations in the gene encoding the calcium-sensing receptor (CASR) or AP2S1. We also performed this analysis in eight unrelated patients with hypocalcemia who did not have CASR mutations. In addition, we studied the effects of GNA11 mutations on G?11 protein structure and calcium-sensing receptor signaling in human embryonic kidney 293 (HEK293) cells.The kindred with familial hypocalciuric hypercalcemia type 2 had an in-frame deletion of a conserved G?11 isoleucine (Ile200del), and one of the nine unrelated patients with familial hypocalciuric hypercalcemia had a missense GNA11 mutation (Leu135Gln). Missense GNA11 mutations (Arg181Gln and Phe341Leu) were detected in two unrelated patients with hypocalcemia; they were therefore identified as having autosomal dominant hypocalcemia type 2. All four GNA11 mutations predicted disrupted protein structures, and assessment on the basis of in vitro expression showed that familial hypocalciuric hypercalcemia type 2-associated mutations decreased the sensitivity of cells expressing calcium-sensing receptors to changes in extracellular calcium concentrations, whereas autosomal dominant hypocalcemia type 2-associated mutations increased cell sensitivity.G?11 mutants with loss of function cause familial hypocalciuric hypercalcemia type 2, and G?11 mutants with gain of function cause a clinical disorder designated as autosomal dominant hypocalcemia type 2. (Funded by the United Kingdom Medical Research Council and others.).

Project description:Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by heterozygous, gain-of-function mutations of the calcium-sensing receptor gene (CAR). Individuals are hypocalcemic with inappropriately low parathyroid hormone (PTH) secretion and relative hypercalciuria. Calcilytics are negative allosteric modulators of the extracellular calcium receptor (CaR) and therefore may have therapeutic benefits in ADH1. Five adults with ADH1 due to four distinct CAR mutations received escalating doses of the calcilytic compound NPSP795 (SHP635) on 3 consecutive days. Pharmacokinetics, pharmacodynamics, efficacy, and safety were assessed. Parallel in vitro testing with subject CaR mutations assessed the effects of NPSP795 on cytoplasmic calcium concentrations (Ca2+ i ), and ERK and p38MAPK phosphorylation. These effects were correlated with clinical responses to administration of NPSP795. NPSP795 increased plasma PTH levels in a concentration-dependent manner up to 129% above baseline (p = 0.013) at the highest exposure levels. Fractional excretion of calcium (FECa) trended down but not significantly so. Blood ionized calcium levels remained stable during NPSP795 infusion despite fasting, no calcitriol supplementation, and little calcium supplementation. NPSP795 was generally safe and well-tolerated. There was significant variability in response clinically across genotypes. In vitro, all mutant CaRs were half-maximally activated (EC50 ) at lower concentrations of extracellular calcium (Ca2+ o ) compared to wild-type (WT) CaR; NPSP795 exposure increased the EC50 for all CaR activity readouts. However, the in vitro responses to NPSP795 did not correlate with any clinical parameters. NPSP795 increased plasma PTH levels in subjects with ADH1 in a dose-dependent manner, and thus, serves as proof-of-concept that calcilytics could be an effective treatment for ADH1. Albeit all mutations appear to be activating at the CaR, in vitro observations were not predictive of the in vivo phenotype or the response to calcilytics, suggesting that other parameters impact the response to the drug. © 2019 American Society for Bone and Mineral Research.

Dataset Information

Identification of a G-Protein Subunit-?11 Gain-of-Function Mutation, Val340Met, in a Family With Autosomal Dominant Hypocalcemia Type 2 (ADH2).

Publications

Identification of a G-Protein Subunit-α11 Gain-of-Function Mutation, Val340Met, in a Family With Autosomal Dominant Hypocalcemia Type 2 (ADH2).

Similar Datasets

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