Identification and characterization of a novel CASR mutation causing familial hypocalciuric hypercalcemia.

Context: Although a monoallelic mutation in the calcium-sensing receptor () gene causes familial hypocalciuric hypercalcemia (FHH), the functional characterization of the identified mutation linked to the clinical response to calcimimetics therapy is still limited.

Objective: A 45-year-old male presenting with moderate hypercalcemia, hypocalciuria, and inappropriately high parathyroid hormone (PTH) had a good response to cinacalcet (total serum calcium (Ca) from 12.5 to 10.1 mg/dl). We identified the genetic mutation and characterized the functional and pathophysiological mechanisms, and then linked the mutation to calcimimetics treatment .

Design: Sanger sequencing of the , , and genes was performed in his family. The simulation model was used to predict the function of the identified mutant. studies, including immunoblotting, immunofluorescence, a cycloheximide chase study, Calbryte™ 520 Ca detection, and half-maximal effective concentration (EC), were examined.

Results: This proband was found to carry a heterozygous missense in the cysteine-rich domain of , which was pathogenic based on the different software prediction models and ACGME criteria. The simulation model showed that mutation decreased its binding energy with Ca. Human mutation attenuated the stability of CASR protein, reduced the expression of p-ERK 1/2, and blunted the intracellular Ca response to gradient extracellular Ca (eCa) concentration. The EC study also demonstrated the correctable effect of calcimimetics on the function of the mutation.

Conclusion: This novel mutation causing FHH attenuates CASR stability, its binding affinity with Ca, and the response to eCa corrected by therapeutic calcimimetics.