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Citrate infusion test in the diagnosis of hypocalcemia due to a mutation in the calcium-sensing receptor gene.

par Poppe, Katia ;Karmali, Rafik ;Lissens, Willy;Vanhaelst, Luc ;Liebaers, Ingeborg ;Fuss, Michel ;Velkeniers, Brigitte
Référence European journal of internal medicine, 13, 4, page (276-279)
Publication Publié, 2002-06

Article révisé par les pairs

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Résumé :

The calcium-sensing receptor (Ca-R) is a G-protein-coupled surface receptor that plays a crucial role in calcium homeostasis via parathyroid hormone secretion. Mutations of this receptor can cause a gain in, or loss of, function, leading to hypo- or hypercalcemia, respectively. We report here a family with hypocalcemia in whom a heterozygous missense mutation in exon 4 was demonstrated, predicting a proline to leucine substitution (P221L) in the extracellular part of the Ca-R. Clinical symptoms were limited to fatigue. When serum calcium was further lowered via a citrate infusion, a significant increase in circulating iPTH was observed, although with lower peak values than in normal controls, suggesting a gain in function of the Ca-R. Treatment with calcium supplements and calcitriol led to prohibitive hypercalciuria without normalizing serum calcium. The aims of this case report are: (1) to present a mutation in the Ca-R with a gain in function at a codon where previously loss of function was described, and (2) to suggest that measuring circulating iPTH during a citrate infusion in the presence of familial hypocalcemia is an additional test to diagnose this particular form of hypoparathyroidism.