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Abstract titles should be brief and reflect the content of the abstract.
Renal medullary nephrocalcinosis is characterized by calcium deposition in the renal medulla and is often secondary to metabolic or tubular disorders. However, in some cases, no clear etiology is identified despite extensive evaluation. Advances in next-generation sequencing have expanded understanding of hereditary forms of nephrocalcinosis, implicating mutations in genes involved in renal phosphate and calcium handling.
A 32-year-old female presented with bilateral mild flank discomfort and on evaluation was detected to have bilateral renal medullary nephrocalcinosis on ultrasound and the same was confirmed with non-contrast CT-KUB. She had normal renal function, electrolytes, calcium, phosphate, parathyroid hormone,25 hydroxy vitamin-D levels, Thyroid hormone levels and acid–base status, with no evidence of proximal or distal renal tubular acidosis. Urine analysis showed no glycosuria, aminoaciduria, oxaluria, hyperphosphaturia or hypercalciuria. Her ANA profile done was negative. There was no family history of renal disease. In view of normal lab parameters, she underwent whole exome sequencing.
Genetic Findings: Whole exome sequencing revealed a heterozygous frameshift variant in the SLC34A1 gene — c.981_982insG (p.Lys328GlufsTer37) — and a heterozygous missense variant in the KCNJ1 gene — c.665C>A (p.Thr222Asn). Both variants were classified as variants of uncertain significance (VUS). The SLC34A1 mutation, located in exon 9, is predicted to cause a premature truncation of the NaPi-IIa protein; however, it is seen to occur in a non-canonical transcript and in a heterozygous state. The KCNJ1 variant affects the ROMK potassium channel but is also heterozygous for an autosomal recessive condition (Bartter syndrome type 2). No additional pathogenic variants or copy number changes were detected
The SLC34A1 gene encodes a sodium–phosphate cotransporter (NaPi-IIa). critical for phosphate reabsorption in the proximal tubule. Pathogenic variants are associated with phosphate wasting, nephrolithiasis, and nephrocalcinosis. Although most reported cases involve biallelic mutations, emerging evidence suggests that heterozygous carriers may manifest milder phenotypes or isolated renal calcification. The coexistence of a KCNJ1 variant may further modify tubular ion transport, contributing to the observed nephrocalcinosis. Given the absence of biochemical derangements, this finding likely represents a subclinical genetic predisposition rather than a fully penetrant tubular disorder.
This case highlights the diagnostic value of genomic testing in patients with idiopathic nephrocalcinosis, especially when conventional workup is unrevealing. The identification of a novel heterozygous SLC34A1 frameshift variant raises the possibility of incomplete penetrance or dominant susceptibility to nephrocalcinosis. Long-term follow-up, segregation analysis, and functional studies are warranted to determine the pathogenic relevance of this variant and its role in renal calcium–phosphate homeostasis.
