Identification and functional analysis of novel calcium-sensing receptor gene mutation in familial hypocalciuric hypercalcemia.

[familial hypocalciuric hypercalcemia]

Familial hypocalciuric hypercalcemia (FHH ) is a benign disorder with heterozygous inactivating mutations in the calcium-sensing receptor (CASR ) gene . The present study describes the identification and functional analysis of a novel CASR gene mutation leading to FHH . The proband is a 33 -yr -old woman (Ca 11 .0 mg /dL , intact-PTH 68 pg /mL , FECa 0 .17 %). Leukocyte DNA was isolated in four family members and a novel heterozygous mutation (D 190 G , GAT >GGT ) in exon 4 of CASR gene was identified by direct sequence analysis . The mutant CASR expression vector was constructed by mutagenesis procedure and its response to Ca (2 +) was characterized by transient transfection into human embryonic kidney (HEK ) 293 cells and treatment with increasing extracellular Ca (2 +) concentrations . HEK cells did n't activate intracellular signaling (MAPK activation ) in response to increases of extracellular Ca (2 +) concentrations when the mutant receptor was expressed normally at the cell surface . The novel heterozygous mutation (D 190 G ) identified in the present study showed that the reduction of activity of CASR to extracellular Ca (2 +) caused FHH in patients and our study demonstrated the importance of Asp-190 participated in response to Ca (2 +) in CASR .