Does CASR rs1801725 shift the calcium-sensing receptor set point upward?

The calcium-sensing receptor (CaSR) is a G-protein-coupled receptor crucial for maintaining systemic calcium homeostasis, primarily through its action in parathyroid and renal cells.

Receptor sensitivity and calcium homeostasis

• Mechanistic pathway: The CASR rs1801725 (A986S) polymorphism is a missense, hypomorphic variant located in the receptor's cytoplasmic tail. This genetic alteration reduces the receptor's sensitivity to extracellular calcium, shifting the homeostatic calcium-sensing set point rightward and upward.
• Serum calcium elevations: Because parathyroid and renal cells perceive circulating calcium as lower than it actually is, regulatory negative feedback loops are altered. Genome-wide association studies show that each copy of the minor T (986S) allele modestly increases baseline total and ionized serum calcium by approximately 0.018 to 0.019 mmol/L. These elevated levels typically remain within the normal physiological reference range.

Clinical implications and risk factors

• Urolithiasis susceptibility: Beyond a benign elevation in serum calcium, this altered homeostatic set point carries practical clinical significance. Meta-analyses and population studies consistently link the rs1801725 minor allele to an increased risk of idiopathic hypercalciuria and urolithiasis (calcium kidney stones), driven by altered renal handling and excretion of calcium.

Bottom line

• The CASR rs1801725 variant modestly shifts the calcium-sensing receptor set point upward, leading to a genetically driven, normal-range elevation in serum calcium (~0.018–0.019 mmol/L per allele) while increasing the risk of calcium-based kidney stones.