Kidney Week

Abstract: SA-PO743

Identification and Characterization of a Novel CASR Mutation Causing Familial Hypocalciuric Hypercalcemia

Session Information

• Fluid, Electrolyte, Acid-Base Disorders: Clinical - II
  November 04, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid, Electrolytes, and Acid-Base Disorders

• 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

• Lin, Shih-Hua P., Tri-Service General Hospital Department of Internal Medicine, Taipei, Taiwan

Shih-Hua P. Lin,

• Lin, Chien-Ming, Tri-Service General Hospital Department of Internal Medicine, Taipei, Taiwan

Chien-Ming Lin,

• Sung, Chih-Chien, Tri-Service General Hospital Department of Internal Medicine, Taipei, Taiwan

Chih-Chien Sung,

Background

Although familial hypocalciuric hypercalcemia type 1 (FHH1) is primarily caused by monoallelic mutation in calcium-sensing receptor (CASR) gene, the characterization of the newly-identified CaSR mutation linked to clinical response to calcimimetics remains limited.

Methods

A 45-year-old male presenting with hypercalcemia, hypocalciuria, and inappropriately high parathyroid hormone (PTH) had a good response to cinacalcet (total serum calcium from 12.5 to 10.1 mg/dl). Sanger sequencing of CASR, GNA11, and AP2S1 genes was performed in this family. The simulation model was used to predict the function of the identified mutant. The in vitro studies including immunoblotting, immunofluorescence, cycloheximide chase study, Calbryte™ 520 calcium (Ca²⁺) detection, and half-maximal effective concentration (EC50) were examined.

Results

The patient was identified to carry a de novo heterozygous CASR I554N mutation, located in the cysteine-rich domain (residues 542–612) crucial to affect the ligands (Ca²⁺) binding. This missense mutation was pathogenic based on the different software prediction models and ACGME criteria. The simulation model showed CASR I554N mutation decreased its binding energy with Ca²⁺. Human CASR I554N mutation attenuated the stability of CASR protein, reduced the expression of p-ERK 1/2, and blunted the intracellular Ca²⁺ response to gradient extracellular Ca²⁺ (eCa²⁺) concentration. EC50 study also showed calcimimetics rescued the function of CASR I554N mutation.

Conclusion

This novel CASR I554N mutation decreases CASR stability and its binding affinity with Ca²⁺. Its correction of blunt response to eCa²⁺ by calcimimetics may support the therapeutic effect of cinacalcet for this patient.

Funding

• Government Support – Non-U.S.