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Tencza AL, Ichikawa S, Dang A, Kenagy D, McCarthy E, Econs MJ, Levine MA: Hypophosphatemic rickets with hypercalciuria due to mutation in SLC34A3/type IIc sodium-phosphate cotransporter: presentation as hypercalciuria and nephrolithiasis. J Clin Endocrinol Metab. 2009 Nov;94(11):4433-8. Epub 2009 Oct 9.
CONTEXT: Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a metabolic disorder due to homozygous loss-of-function mutations in the SLC34A3 gene encoding the renal type IIc sodium-phosphate cotransporter (NaPi-IIc). The typical presentation is severe rickets and hypophosphatemia, and hypercalciuria is often discovered later or overlooked. OBJECTIVE: We sought to determine the genetic basis for severe hypercalciuria and nephrolithiasis/nephrocalcinosis in an adolescent male with elevated serum levels of calcitriol but normal serum levels of calcium and phosphorus. DESIGN AND SETTING: We used PCR to analyze the SLC34A3 gene in the proband and members of his family. RESULTS: The proband was a compound heterozygote for two SLC34A3 missense mutations, a novel c.544C--> T in exon 6 that results in replacement of arginine at position 182 by tryptophan (R182W) and c.575C--> T in exon 7 that results in replacement of serine at position 192 by leucine (S192L). The R182W and S192L alleles were inherited from the mother and father, respectively, both of whom had hypercalciuria. A clinically unaffected brother was heterozygous for S192L. CONCLUSION: We report a novel mutation in the SLC34A3 gene in a patient with an unusual presentation of HHRH. This report emphasizes that moderate and severe hypercalciuria can be manifestations of heterozygous or homozygous loss-of-function mutations in the SLC34A3 gene, respectively, providing further evidence for a gene dosage effect in determining the phenotype. HHRH may be an underdiagnosed condition that can masquerade as idiopathic hypercalciuria or osteopenia. |
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