Fluconazole as a New Therapeutic Tool to Manage Patients With NPTIIc (SLC34A3) Mutation: A Case Report

Abstract

Mutations in the SLC34A3 gene, encoding the sodium/phosphate cotransporter 2C (NPTIIc), induce decreased renal phosphate reabsorption, hypophosphatemia, decreased fibroblast growth factor 23 and parathyroid hormone, and increased 1,25-dihydroxyvitamin D (1,25[OH]₂D) levels. The complete phenotype is characterized by hypophosphatemia, hypercalciuria, and nephrolithiasis/nephrocalcinosis, leading to chronic kidney disease and osteoporosis in adults. We report a 15-year-old boy referred for nephrocalcinosis. The patient demonstrated hypercalcemia, hypercalciuria, normal serum phosphate level, normal tubular phosphate reabsorption, and increased serum 1,25(OH)₂D level with suppressed serum parathyroid hormone. Compound heterozygous mutations in SLC34A3 were found. Hydrochlorothiazide failed to decrease calciuria. Fluconazole, an inhibitor of 1α-hydroxylase, was effective in normalizing calciuria without decreasing glomerular filtration rate. We conclude that children with SLC334A3 mutations can present with a less-typical phenotype, having normal serum phosphate levels and normal renal phosphate reabsorption. Genetic abnormalities of NPTIIc should be considered in cases of increased 1,25(OH)₂D levels without mutations in CYP24A1. The utility of fluconazole to decrease 1,25(OH)₂D levels requires confirmation in larger studies.

Keywords: 1,25-dihydroxyvitamin D (1,25(OH)(2)D); 1α-hydroxylase; NPT2c; SLC34A3; case report; chronic kidney disease (CKD); fluconazole; hypercalciuria; mutation; off-label drug; phosphate.