Disorders of the calcium-sensing receptor.

The human calcium-sensing receptor (CaSR) is a 1078-amino-acid cell surface protein which is expressed in the parathyroids, thyroid cells and the kidney, and is a member of the family of G protein-coupled receptors. The CaSR allows regulation of parathyroid hormone (PTH) secretion and renal tubular calcium reabsorption in response to alterations in extracellular calcium concentrations. The human CaSR gene is located on chromosome 3q13.3-q21, and loss of function CaSR mutations have been reported in the hypercalcaemic disorders of familial benign (hypocalciuric) hypercalcaemia (FBH or FHH) and neonatal severe primary hyperparathyroidism (NSHPT). In addition, gain of function CaSR mutations have been observed in a novel familial syndrome of hypocalcaemia with hypercalciuria. The human CaSR gene on chromosome 3q13.3-q21 is likely to be one of several, as two other loci for FBH have been located on chromosome 19p and 19q13. Cloning and characterisation of these genes will help to further elucidate the mechanisms regulating extracellular calcium.