Mutations in the calcium-sensing receptor and their clinical implications

Area of Science:

• Endocrinology
• Nephrology
• Molecular Biology

Background:

• Specialized parathyroid chief cells utilize the calcium-sensing receptor (CaR) to monitor extracellular calcium (Ca2+o) levels, crucial for mineral ion homeostasis.
• The CaR is expressed in kidney nephron segments involved in calcium regulation and other tissues, including the brain and intestines.
• CaR mutations lead to genetic disorders such as familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (inactivating mutations) or autosomal dominant hypocalcemia (activating mutations).

Purpose of the Study:

• To elucidate the physiological role of the CaR in mineral ion and water metabolism.
• To understand the implications of CaR mutations in human diseases.
• To explore the therapeutic potential of CaR-activating drugs (calcimimetics).

Main Methods:

• Cloning of the CaR from bovine parathyroid.
• Identification and characterization of CaR mutations in patients with hypercalcemic and hypocalcemic disorders.
• Analysis of Ca2+o and Mg2+o sensing by the CaR.
• Investigation of water handling abnormalities in FHH patients.

Main Results:

• CaR mutations directly correlate with specific mineral ion imbalances and associated clinical phenotypes.
• The CaR functions as a sensor for both Ca2+o and Mg2+o.
• Patients with FHH exhibit altered water handling, suggesting CaR's role in integrated mineral and water metabolism.
• Calcimimetics show promise for pharmacological manipulation of CaR function.

Conclusions:

• The CaR is a pivotal regulator of extracellular calcium and magnesium homeostasis.
• Dysfunctional CaR underlies significant human endocrine and metabolic disorders.
• Targeting the CaR with calcimimetics offers a potential therapeutic strategy for conditions like primary hyperparathyroidism.