A novel loss-of-function mutation, Gln459Arg, of the calcium-sensing receptor gene associated with apparent autosomal recessive inheritance of familial hypocalciuric hypercalcemia.
BACKGROUND
Mutations that inactivate one allele of the gene encoding the calcium sensing receptor (CaSR) cause autosomal dominant familial hypocalciuric hypercalcemia (FHH), whereas homozygous mutations cause neonatal severe hyperparathyroidism.


OBJECTIVE
We describe the identification and biochemical characterization of a novel CASR gene mutation that caused apparent autosomal recessive FHH in an extended consanguineous kindred.


METHODS
The study design involved direct sequence analysis of the CaSR gene, clinical and biochemical analyses of patients, and in vitro immunobiochemical studies of the mutant CaSR.


RESULTS
A novel inactivating mutation (Q459R) was identified in exon 4 of both alleles of the CASR in the proband, who presented with asymptomatic hypercalcemia and hypocalciuria at age 2 yr. The proband's parents were heterozygous for the Q459R mutation consistent with autosomal recessive inheritance of FHH. Among 13 family members that were studied, eight subjects were heterozygous for the Q459R mutation and five had normal genotypes. All heterozygous subjects were asymptomatic and normocalcemic apart from one subject who was mildly hypercalcemic. The Q459R mutant CaSR was normally expressed at the cell membrane but retained only 30-50% of the calcium-dependent activity of the wild-type CaSR.


CONCLUSIONS
We identified a novel loss-of-function Q459R mutation in the CASR gene that exhibits mildly reduced sensitivity to calcium and that is associated with apparent autosomal recessive transmission of FHH. This study demonstrates the importance of genetic testing in FHH to distinguish between de novo and inherited mutations of the CASR gene and assist in management decisions.
Lietman
Steven A
SA
Departments of Orthopaedic Surgery, Cleveland Clinic Lerner Research Institute and Foundation, Cleveland, Ohio 44195, USA. lietmas@ccf.org
Tenenbaum-Rakover
Yardena
Y
Jap
Tjin Shing
TS
Yi-Chi
Wu
W
De-Ming
Yang
Y
Ding
Changlin
C
Kussiny
Najat
N
Levine
Michael A
MA
D019943:Amino Acid Substitution; D001120:Arginine / Q000235:genetics; D002118:Calcium / Q000097:blood; D002460:Cell Line; D002675:Child, Preschool; D025063:Chromosome Disorders / Q000235:genetics; D005091:Exons / Q000235:genetics; D005260:Female; D020868:Gene Silencing; D005808:Genes, Recessive / Q000235:genetics*; D005973:Glutamine / Q000235:genetics; D006579:Heterozygote; D006801:Humans; D006934:Hypercalcemia / Q000150:complications / Q000235:genetics*; D053565:Hypercalciuria / Q000150:complications / Q000235:genetics*; D008297:Male; D009154:Mutation; D010281:Parathyroid Hormone / Q000097:blood; D010375:Pedigree; D044169:Receptors, Calcium-Sensing / Q000235:genetics*; D014162:Transfection
D010281:Parathyroid Hormone; D044169:Receptors, Calcium-Sensing; D005973:Glutamine; D001120:Arginine; D002118:Calcium