Piret Sian E, Gorvin Caroline M, Pagnamenta Alistair T, Howles Sarah A, Cranston Treena, Rust Nigel, Nesbit M Andrew, Glaser Ben, Taylor Jenny C, Buchs Andreas E, Hannan Fadil M, Thakker Rajesh V
Academic Endocrine Unit, University of Oxford, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, UK.
Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford, UK.
J Bone Miner Res. 2016 Jun;31(6):1207-14. doi: 10.1002/jbmr.2797.
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 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 Gα11 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 α5 helix, which may affect G-protein coupled receptor binding and G-protein activation. In vitro functional expression of wild-type (Val340) and mutant (Met340) Gα11 proteins in HEK293 cells stably expressing the CaSR, demonstrated that the intracellular calcium responses following stimulation with extracellular calcium, of the mutant Met340 Gα11 led to a leftward shift of the concentration-response curve with a significantly (p < 0.0001) reduced mean half-maximal concentration (EC50 ) value of 2.44 mM (95% CI, 2.31 to 2.77 mM) when compared to the wild-type EC50 of 3.14 mM (95% CI, 3.03 to 3.26 mM), consistent with a gain-of-function mutation. A novel His403Gln variant in transforming growth factor, beta-induced (TGFBI), that may be causing keratoconus was also identified, indicating likely digenic inheritance of keratoconus and ADH2 in this family. In conclusion, our identification of a novel germline gain-of-function Gα11 mutation, Val340Met, causing ADH2 demonstrates the importance of the Gα11 C-terminal region for G-protein function and CaSR signal transduction. © 2016 American Society for Bone and Mineral Research.
常染色体显性低钙血症（ADH）的特征为低钙血症、血清甲状旁腺激素浓度异常降低以及高钙尿症。ADH在遗传上具有异质性，其中主要类型的1型ADH（ADH1）由G蛋白偶联钙敏感受体（CaSR）的种系功能获得性突变引起，而ADH2由G蛋白亚基α-11（Gα11）的种系功能获得性突变引起。迄今为止，仅在5名先证者中报道了导致ADH2的Gα11突变。我们调查了一个来自伊朗的非近亲多代家族，该家族患有ADH和圆锥角膜，目前尚不知二者存在关联，我们对两名甲状旁腺功能减退患者进行了全外显子组测序以寻找致病突变，其中一人还患有圆锥角膜，随后对变异进行了共分离分析。这在两名患者中均鉴定出一种新的杂合种系Val340Met Gα11突变，在另外两名接受检测的低钙血症亲属中也存在该突变。三维建模显示Val340Met突变可能改变C末端α5螺旋的构象，这可能影响G蛋白偶联受体结合和G蛋白激活。在稳定表达CaSR的HEK293细胞中对野生型（Val340）和突变型（Met340）Gα11蛋白进行体外功能表达，结果表明，用细胞外钙刺激后，突变型Met340 Gα11的细胞内钙反应导致浓度-反应曲线向左移动，与野生型3.14 mM（95%可信区间，3.03至3.26 mM）的半数最大效应浓度（EC50）相比，平均EC50值显著降低（p < 0.），为2.44 mM（95%可信区间，2.31至2.77 mM），这与功能获得性突变一致。还鉴定出一种可能导致圆锥角膜的转化生长因子β诱导（TGFBI）中的新型His403Gln变异，表明该家族中圆锥角膜和ADH2可能存在双基因遗传。总之，我们鉴定出一种导致ADH2的新的种系功能获得性Gα11突变Val340Met，证明了Gα11 C末端区域对G蛋白功能和CaSR信号转导的重要性。© 2016美国骨与矿物质研究学会。
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