ESPE Abstracts

Introduction: The SLC34A1 gene encodes the NaPi-IIa cotransporter, which plays an important role in phosphate reabsorption in the kidney proximal tubule. Inactivating mutations of this gene cause nephrolithiasis and osteoporosis, together with clinical pictures such as hypophosphatemic rickets type 1, Fanconi renotubular syndrome type 2, and infantile hypercalcemia type 2.

Case: A 40-day-old male patient presented with medullary nephrocalcinosis and hypercalcemia. He was born at 35 weeks, 2660 g. It was learned that the patient had hyperechogenic kidneys and oligohydramnios on antenatal ultrasonography (USG), and a combined heterozygous mutation in the SLC34A1 gene was detected in the amniotic fluid sample at the 21st gestational week. There were no signs of developmental delay and dehydration in his physical examination. At the time of admission, he had hypercalcemia, lower limit phosphorus level, increased alkaline phosphatase, low parathormone, and hypercalciuria. 25OHD level was normal. In urinary USG, renal parenchyma echogenicity increase and millimetric stones in the renal medulla were detected. 24-hour urine protein level was normal, urine protein electrophoresis and urine glucose were negative, and proximal tubulopathy was excluded. Oral phosphorus solution at a dose of 30 meq/kg/day was started. In the follow-up of the patient, hypercalcemia and hypercalciuria regressed and returned to the normal range. In the family screening of the patient, a novel variant in the SLC34A1 gene was detected in the father {c.1256G>A (P.S419N)(p.Ser419Asn)(heterozygous)} and mother {IVS6+1G>A (c.644+1G>A)(heterozygous)}. The patient's genetic result, clinical and laboratory findings were found to be compatible with infantile hypercalcemia type 2. In his brother, crystalloid was detected in his urinary USG, his laboratory values were normal and he had no complaints. In the genetic analysis, the same variant changes were detected in the same gene as the patient.

Conclusion: SLC34A1 mutation may present with different clinical manifestations. Despite the absence of significant low phosphate and phosphaturia in our case, success was achieved with the phosphorus treatment that was initiated. Therefore, this mutation should be considered in children with hypercalcemia close to the lower limit of normal or with slightly low phosphorus levels, as in our case. Although the patient's sibling has the same variant changes, the fact that there is no hypercalcemia and only kidney crystalloid can be considered that mutations in this gene may cause a wide spectrum of disease.