ESPN 51th Annual Meeting

ESPN 2018


 
Npt2c/SLC34A3 mutations can be found in patients with normal phosphate levels
NATHALIE TRAM 1 AURéLIA BERTHOLET-THOMAS 1 SANDRINE LEMOINE 1 LAURENCE DUBOURG 1 ARNAUD MOLIN 2 JUSTINE BACCHETTA 1

1- HOSPICES CIVILS DE LYON ET UNIVERSITé LYON 1, LYON, FRANCE
2- CHU DE CAEN, CAEN, FRANCE
 
Introduction:

 Hypercalciuria is the most frequent metabolic disorder associated with nephrolithiasis and/or nephrocalcinosis. Npt2c is a sodium-phosphate cotransporter located in the apical membrane of renal proximal tubular cells; mutations induce decreased renal phosphate reabsorption, subsequent hypophosphatemia, down-regulation of FGF23 and PTH, and further increased 1,25(OH)2D3 levels. This in turn induces increased phosphate and calcium intestinal absorption as well as increased renal calcium excretion. Adult patients usually present with hypophosphatemia, nephrolithiasis and/or nephrocalcinosis, and osteoporosis.

 

Material and methods:

 We report on a pediatric patients with a diagnosis of Npt2c mutation with normal phosphatemia and phosphate tubular reabsorption.

 

Results:

A 15-year old boy presented with nephrocalcinosis. Biological investigations found hypercalcemia (2.72 mmol/L), hypercalciuria (0.19 mmol/kg/d), normal phosphate levels (1.16 mmol/L, normal range for age 0.8-1.5), normal tubular phosphate reabsorption (TmP/GFR 1.01 mmol/L, normal range for age 0.75-1.66), increased 1-25-D (279 pmol/L) with low PTH (8 ng/L, local normal range 15-65) levels; eGFR was 68 mL/min/1.73 m². ALP were normal. Genetic analyses found heterozygous mutations in SLC34A3 (Ex9: C925+20_926-48del; Ex 10 : c.1055_1058dup).  

Conclusions:

 Children with Npt2c mutations can present with a less typical phenotype, notably with subnormal phosphatemia and TmP/GFR. In case of increased 1-25-D without CYP24A1 mutation, Npt2 mutations should also be discussed.