title: Identification and characterization of D410E, a novel mutation in the loop 3 domain of CASR, in autosomal dominant hypocalcemia and a therapeutic approach using a novel calcilytic, AXT914.
abstract: OBJECTIVE
  Activating mutations of the calcium-sensing receptor (CASR) gene are associated with autosomal dominant hypocalcemia (ADH) characterized by benign hypocalcemia, inappropriately low (PTH) levels and mostly hypercalciuria. Herein, we report a novel activating mutation in the CASR gene in a Korean family with ADH.
  
  
  METHODS
  The CASR gene was sequenced in the patient with ADH. The identified mutations were also evaluated in the patient's family members by PCR-based sequencing. For functional studies, we examined phosphorylation of ERK1/2. In addition, intracellular Ca(2+) mobilization and the effects of the calcilytic, AXT914 were measured using fluorophore Fura-2 dye.
  
  
  RESULTS
  Direct sequencing analysis of the CASR gene showed that the proband and her daughter possess a novel mutation c.1230T>A, resulting in a D410E missense mutation on exon 4 of the CASR gene. Escalation of the extracellular Ca(2+) concentration resulted in stronger phosphorylation of ERK1/2 and higher levels of intracellular Ca(2+) in HEK293 cells expressing mutant CASR, compared with wild-type CASR. The increase in intracellular Ca(2+) signalling via CASR was successively blunted by treatment with AXT914.
  
  
  CONCLUSIONS
  Over 60 activating mutations in the CASR gene have been identified to cause ADH so far. Here, we add one more activating mutation that causes ADH. The novel activating mutation (D410E) occurred in the loop 3 region of CASR, where its function was believed to be of little importance; therefore, this mutation may be of interest. Further clinical study will be needed to validate the effectiveness of calcilytics in treatment of ADH in vivo.
authors.affiliation: Department of Internal Medicine, Cheil General Hospital, Kwandong University College of Medicine, Seoul, Korea.
authors.forename: So Young
authors.initials: SY
authors.lastname: Park
authors.forename: Hee-Chang
authors.initials: HC
authors.lastname: Mun
authors.forename: Young Sil
authors.initials: YS
authors.lastname: Eom
authors.forename: Hae Lim
authors.initials: HL
authors.lastname: Baek
authors.forename: Tae Sik
authors.initials: TS
authors.lastname: Jung
authors.forename: Chul Hoon
authors.initials: CH
authors.lastname: Kim
authors.forename: Suntaek
authors.initials: S
authors.lastname: Hong
authors.forename: Sihoon
authors.initials: S
authors.lastname: Lee
mesh_terms: D000328:Adult; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D006996:Hypocalcemia / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D044169:Receptors, Calcium-Sensing / Q000235:genetics* / Q000378:metabolism
chemical_list: D044169:Receptors, Calcium-Sensing; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3