Cinacalcet Rectifies Hypercalcemia in a Patient With Familial Hypocalciuric Hypercalcemia Type 2 (FHH2) Caused by a Germline Loss‐of‐Function Gα11 Mutation.

ABSTRACT: G‐protein subunit α‐11 (Gα₁₁) couples the calcium‐sensing receptor (CaSR) to phospholipase C (PLC)‐mediated intracellular calcium (Ca²⁺_i) and mitogen‐activated protein kinase (MAPK) signaling, which in the parathyroid glands and kidneys regulates parathyroid hormone release and urinary calcium excretion, respectively. Heterozygous germline loss‐of‐function Gα₁₁ mutations cause familial hypocalciuric hypercalcemia type 2 (FHH2), for which effective therapies are currently not available. Here, we report a novel heterozygous Gα₁₁ germline mutation, Phe220Ser, which was associated with hypercalcemia in a family with FHH2. Homology modeling showed the wild‐type (WT) Phe220 nonpolar residue to form part of a cluster of hydrophobic residues within a highly conserved cleft region of Gα₁₁, which binds to and activates PLC; and predicted that substitution of Phe220 with the mutant Ser220 polar hydrophilic residue would disrupt PLC‐mediated signaling. In vitro studies involving transient transfection of WT and mutant Gα₁₁ proteins into HEK293 cells, which express the CaSR, showed the mutant Ser220 Gα₁₁ protein to impair CaSR‐mediated Ca²⁺_i and extracellular signal‐regulated kinase 1/2 (ERK) MAPK signaling, consistent with diminished activation of PLC. Furthermore, engineered mutagenesis studies demonstrated that loss of hydrophobicity within the Gα₁₁ cleft region also impaired signaling by PLC. The loss‐of‐function associated with the Ser220 Gα₁₁ mutant was rectified by treatment of cells with cinacalcet, which is a CaSR‐positive allosteric modulator. Furthermore, in vivo administration of cinacalcet to the proband harboring the Phe220Ser Gα₁₁ mutation, normalized serum ionized calcium concentrations. Thus, our studies, which report a novel Gα₁₁ germline mutation (Phe220Ser) in a family with FHH2, reveal the importance of the Gα₁₁ hydrophobic cleft region for CaSR‐mediated activation of PLC, and show that allosteric CaSR modulation can rectify the loss‐of‐function Phe220Ser mutation and ameliorate the hypercalcemia associated with FHH2. © 2017 The Authors. <italic>Journal of Bone and Mineral Research</italic> Published by Wiley Periodicals Inc. [ABSTRACT FROM AUTHOR]