Absence of pathogenic calcium sensing receptor mutations in sporadic idiopathic hypoparathyroidism.
BACKGROUND
Sporadic idiopathic hypoparathyroidism (SIH) is the most common cause of hypoparathyroidism. While calcium sensing receptor (CaSR) autoantibodies are observed in 49% of cases, aetiopathogenetic mechanisms in others are under investigation. Mutations in the PTH gene including its 3' untranslated region, autoimmune regulator gene and lead CTLA-4 gene single nucleotide polymorphism (SNPs) are not associated with the disease. There are reports of de novo activating mutations of the CaSR gene in a few patients with SIH.


OBJECTIVE
To assess the frequency of CaSR mutations in patients with SIH.


METHODS
DNA sequencing of all six translating exons and nine of 12 intron/exon boundaries of the CaSR gene was performed by Sangers dideoxy chain termination method using an automated sequencer in 39 patients with SIH. Spot urinary calcium/creatinine ratio in the fasting state and ultrasonography of the abdomen was performed to assess hypercalciuria and nephrolithiasis. The PCR-RFLP analysis was performed using Hin1II restriction endonuclease in 32 additional patients with SIH and 90 healthy controls to further assess the prevalence of a novel missense SNP observed in the DNA sequencing.


RESULTS
Nucleotide sequence analysis revealed the presence of a wild type CaSR gene in all subjects, except in one patient who showed a missense mutation (Val621Met) due to substitution of base G-->A in the heterozygous state at position 79877 in exon 7 (codon 621) coding for the first transmembrane loop of the CaSR. The V621M polymorphism was confirmed by PCR-RFLP and was due to a maternal allele. However, the mother and brother of this patient with the same SNP were asymptomatic and had normal serum chemistry indicating the functionally inert nature of the polymorphism. None of the additional 32 patients with SIH and 90 controls showed V621M SNP. The urinary calcium/creatinine ratio and ultrasonography were normal in all patients with SIH.


CONCLUSIONS
De novo activating mutation of the CaSR gene typical of familial hypoparathyroidism is not common among patients with SIH in India.
Sarin
Ritu
R
Department of Endocrinologya nd Metabolism, All India Institute of Medical Sciences, New Delhi, India.
Tomar
Neeraj
N
Ray
Debarti
D
Gupta
Nandita
N
Sharma
Yagya Dutta
YD
Goswami
Ravinder
R
D000328:Adult; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005091:Exons; D005260:Female; D005787:Gene Frequency; D006801:Humans; D007011:Hypoparathyroidism / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D044169:Receptors, Calcium-Sensing / Q000235:genetics*; D017422:Sequence Analysis, DNA
D017931:DNA Primers; D044169:Receptors, Calcium-Sensing