Familial hypocalciuric hypercalcemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
Historical Perspective
Until 1966 many asymptomatic hypercalcemic patients were identified to have familial hypocalciuric hypercalcemia, then Jackson and Boonstra described their first patient with hypercalcemia presumed to have hyperparathyroidism. He wasn't cured despite the removal of three and a half hyperplastic parathyroid glands. Subsequently, seventeen family members with hypercalcemia were identified in three generation.
Classification
Three genetically heterogeneous variants are reported so far for familial hypocalciuric hypercalcemia. Type 1 - due to loss-of-functional mutations of the calcium-sensing receptor (encoded by CASR). Type 2 - unknown cause. Type 3 - associated with adaptor-related protein complex 2, sigma 1 subunit (AP2S1) mutations, which alter calcium-sensing receptor endocytosis
Pathophysiology
The pathophysiology of Familial hypocalciuric hypercalcemia is due to an inactivating missense mutation in the calcium-sensing receptor (CaSR) located on the short arm of the chromosome 3 (FBHH3q). The mutation of CaSR is associated with two inherited conditions FBHH and neonatal hyperparathyroidism. CaSR is a plasma membrane G protein-coupled receptor which is expressed on the chief cells of the parathyroid glands and the cells lining the renal tubules. CasR has the ability to sense any changes in the circulating calcium concentrated and send this information through the signaling pathway to the Parathyroid gland that modifies the PTH secretion.
Causes
Differentiating ((Page name)) from Other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Prenatal testing for FHH is not recommended routinely. If both parents have type-1 FHH, their children should be screened for CASR mutation. Genetic screening for the CASR familial mutation is also offered to family members of affected individuals. CaSR and AP2S1 sequencing are done in patients with familial hyperparathyroidism and phenotype suggesting FHH. Learning disabilities in patients, associated with higher serum calcium and magnesium levels may suggest the presence of AP2S1 mutation and may require further genetic evaluation..