Calcium-sensing receptor (CASR) mutations in hypercalcemic states: studies from a single endocrine clinic over three years.
BACKGROUND
Inactivating mutations of the calcium-sensing receptor (CASR) are implicated in different hypercalcemic syndromes, including familial hypocalciuric hypercalcemia (FHH), primary hyperparathyroidism (PHPT), and familial isolated hyperparathyroidism (FIHP). However, molecular diagnostics applied to large nonselected hypercalcemic cohorts from a single center have not been reported.


OBJECTIVE
Our objective was to describe the prevalence, type, and potential pathogenicity of CASR mutations in a series of cases with FHH (n = 17), PHPT (n = 165), and FIHP (n = 3) and controls (n = 198) presenting at a single endocrine clinic.


METHODS
All were prospectively evaluated at the "Casa Sollievo della Sofferenza" Hospital in southern Italy over a 3-yr period.


METHODS
CASR screening was conducted by denaturing HPLC. The variant CASRs were functionally characterized by transient transfection studies in kidney cells in vitro.


RESULTS
A single novel missense variant was identified in one PHPT case. However, in FHH probands, mutations were found in eight of 17 (47%). With a hypercalcemic family member, mutation detection rate in FHH rose to seven of eight (87%), whereas only one of nine sporadic cases was positive, and none of the three FIHP cases had detectable CASR mutations. Five missense variant CASRs, identified in control subjects, performed as wild type in functional assays, whereas the missense mutant CASRs identified in the FHH patients, and in the one PHPT case, exhibited significant impairment. A novel intronic mutation (IVS4-19a-->c) found in one FHH family, created an abnormally spliced product in an in vitro minigene assay.


CONCLUSIONS
CASR testing, with functional analysis, provides critical confirmatory evidence in the differential diagnosis of hypercalcemic states.
Guarnieri
Vito
V
Departments of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada M5G 1L5.
Canaff
Lucie
L
Yun
Francisco H J
FH
Scillitani
Alfredo
A
Battista
Claudia
C
Muscarella
Lucia A
LA
Wong
Betty Y L
BY
Notarangelo
Angelantonio
A
D'Agruma
Leonardo
L
Sacco
Michele
M
Cole
David E C
DE
Hendy
Geoffrey N
GN
D000368:Aged; D002118:Calcium / Q000097:blood / Q000652:urine; D015331:Cohort Studies; D019295:Computational Biology; D003404:Creatinine / Q000097:blood; D004247:DNA / Q000235:genetics; D030541:Databases, Genetic; D005260:Female; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D006934:Hypercalcemia / Q000188:drug therapy / Q000235:genetics*; D049950:Hyperparathyroidism, Primary / Q000097:blood / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000502:physiology; D020125:Mutation, Missense / Q000235:genetics / Q000502:physiology; D010280:Parathyroid Glands / Q000473:pathology; D010281:Parathyroid Hormone / Q000097:blood; D010375:Pedigree; D010710:Phosphates / Q000097:blood; D044169:Receptors, Calcium-Sensing / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D010281:Parathyroid Hormone; D010710:Phosphates; D044169:Receptors, Calcium-Sensing; D004247:DNA; D003404:Creatinine; D002118:Calcium