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

Autosomal dominant hypocalcemia (ADH) is characterized by hypocalcemia, inappropriately low serum parathyroid hormoneconcentrations and hypercalciuria. ADH is genetically heterogeneous with ADH type 1 (ADH1), the predominant form, being causedby germline gain-of-function mutations of the G-protein coupled calcium-sensing receptor (CaSR), and ADH2 caused by germlinegain-of-function mutations of G-protein subunit a-11 (Ga11). To date Ga11 mutations causing ADH2 have been reported in only fiveprobands. We investigated a multigenerational nonconsanguineous family, from Iran, with ADH and keratoconus which are notknown to be associated, for causative mutations by whole-exome sequencing in two individuals with hypoparathyroidism, of whomone also had keratoconus, followed by cosegregation analysis of variants. This identified a novel heterozygous germline Val340MetGa11 mutation in both individuals, and this was also present in the other two relatives with hypocalcemia that were tested. Threedimensionalmodeling revealed the Val340Met mutation to likely alter the conformation of the C-terminal a5 helix, which may affectG-protein coupled receptor binding and G-protein activation. In vitro functional expression of wild-type (Val340) and mutant(Met340) Ga11 proteins in HEK293 cells stably expressing the CaSR, demonstrated that the intracellular calcium responses followingstimulation with extracellular calcium, of the mutant Met340 Ga11 led to a leftward shift of the concentration-response curve with asignificantly (p