J Clin Res Pediatr Endocrinol. 2016; 8(3): 341-346 | DOI: 10.4274/jcrpe.2800

Identification and Functional Characterization of a Calcium-Sensing Receptor Mutation in an Infant with Familial Hypocalciuric Hypercalcemia

Anna Papadopoulou¹, Evangelia Gole¹, Katerina Melachroinou², Christos Meristoudis³, Tania Siahanidou⁴, Anastasios Papadimitriou^1
1Athens University Medical School, University General Hospital “Attikon”, Third Department Of Pediatrics, Athens, Greece
²Biomedical Research Foundation Of The Academy Of Athens, Division Of Basic Neurosciences, Athens, Greece
³University Of Ioannina, Department Of Biological Applications And Technology, Ioannina, Greece
⁴Athens University Medical School, “Aghia Sophia” Children’S Hospital, First Department Of Pediatrics, Athens, Greece

Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant disorder, associated with inactivating mutations of the calcium-sensing receptor (CaSR). To evaluate the functional significance of a CaSR mutation, identified in a young infant who presented with hypercalcemia and hypocalciuria. The CaSR gene coding sequences were analyzed by polymerase chain reaction amplification and direct sequencing analysis. The mutation identified was introduced by site-directed mutagenesis into a wild-type (WT) CaSR plasmid, and human embryonic kidney 293 T cells were transfected with either the WT or mutant CaSR. The function of the mutated CaSR protein was analyzed by evaluating the free intracellular calcium [(Ca2+)i] response after challenge with extracellular calcium (Ca2+). We identified a heterozygous mutation c.772_773delGTinsA in exon 4 resulting in the substitution of amino acid valine (Val) with amino acid arginine (Arg) and the premature pause of the translation 46 amino acids later (Val258ArgfsTer47). Functional assay showed that cells transfected with the mutant CaSR had a significantly poorer response to extracellular Ca2+ stimulation compared with the WT. We have shown that the c.772_773delGTinsA mutation causes a significant alteration of CaSR function leading to features of FHH in an affected young infant since the first months of life.

Keywords: Familial hypocalciuric hypercalcemia,calcium-sensing receptor,calcium,hyperparathyroidism

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