Three novel activating mutations in the calcium-sensing receptor responsible for autosomal dominant hypocalcemia
Y P Conley1, D N Finegold, D G Peters
1Department of Human Genetics, Graduate School of Public Health, Pittsburgh, Pennsylvania 15261, USA. yconley@pitt.edu
Abstract:
We report three novel activating mutations in the calcium-sensing receptor (CASR) that are responsible for autosomal dominant hypocalcemia (ADH) in three unrelated families. Each mutation involves a missense substitution resulting in a nonconservative amino acid alteration, P221L, E228Q, and Q245R. These mutations were observed in affected family members, but not in unaffected family members or in unrelated control samples. All three mutations are clustered in the extracellular domain of the CASR in a region dominated by negatively charged amino acids. Each mutant and wild-type receptor was expressed in Cos-1 cells. A luciferase reporter gene assay was utilized to detect the level of receptor activity by utilizing a protein kinase C-activated promoter to drive the production of luciferin, the reporter gene product. All three mutant receptors exhibited an increased sensitivity to calcium at all concentrations tested when compared to the wild-type receptor, supporting the hypothesis that these are activating mutations and are responsible for the ADH phenotype in these families. The data presented in this study suggest the importance of this highly negatively charged region of the extracellular domain in normal CASR function.
Insights
Three novel activating mutations in the calcium-sensing receptor (CASR) cause autosomal dominant hypocalcemia (ADH). These CASR mutations increase receptor sensitivity to calcium, leading to the ADH phenotype.
Area of Science:
- Genetics
- Molecular Biology
- Endocrinology
Background:
- Autosomal dominant hypocalcemia (ADH) is a rare genetic disorder characterized by low calcium levels in the blood.
- The calcium-sensing receptor (CASR) plays a crucial role in regulating calcium homeostasis.
- Mutations in CASR are a known cause of ADH, but novel mutations continue to be identified.
Purpose of the Study:
- To identify and characterize novel mutations in the CASR gene associated with autosomal dominant hypocalcemia.
- To investigate the functional consequences of these novel mutations on CASR activity.
Main Methods:
- Genetic analysis of three unrelated families with ADH to identify mutations in the CASR gene.
- Expression of wild-type and mutant CASR in Cos-1 cells.
- Luciferase reporter gene assay to measure CASR activity in response to varying calcium concentrations.
Main Results:
- Three novel missense mutations (P221L, E228Q, Q245R) in the extracellular domain of CASR were identified in affected individuals.
- All three mutant CASR receptors showed increased sensitivity to calcium compared to the wild-type receptor.
- The identified mutations are clustered in a negatively charged region of the CASR extracellular domain.
Conclusions:
- The identified novel mutations (P221L, E228Q, Q245R) are activating mutations of the CASR.
- These activating CASR mutations are responsible for the autosomal dominant hypocalcemia phenotype in the studied families.
- The findings highlight the importance of the negatively charged extracellular region in normal CASR function and calcium regulation.
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