Definition:

The mutations in the CASR gene which expresses in the parathyroid hormone producing chief cells of the parathyroid gland and the cells lining the kidney tubule affect calcium homeostasis. Loss-of-function mutations in the CASR gene are responsible for familial hypocalciuric hypercalcemia (FHH1) and for neonatal severe hyperparathyroidism (NSHPT). FHH1 is caused by homozygous mutations and characterized by benign symptoms with mild hypercalcaemia, whereas NSHPT is caused by homozygous mutations and characterized by more severe ones with severe hypercalcaemia and hyperparathyroid bone disease. Gain-of-function mutations are responsible for autosomal dominant hypocalcemia (ADH) that characterized by seizures in infancy, moderate hypocalcaemia and, absolute hypercalciuria.