Nephrocalcinosis in a Child with Sotos Syndrome: A Case Report of Contiguous Gene Syndrome Encompassing NSD1 and SLC34A1 Genes.

Background: Nephrocalcinosis, characterized by the deposition of calcium salts within the renal parenchyma, is frequently identified incidentally in pediatric patients and may be associated with underlying genetic disorders. Sotos syndrome, a rare congenital overgrowth condition associated with neurodevelopment delay and congenital defects caused by mutations or deletions in the NSD1 gene, has been sporadically linked to renal abnormalities, including nephrocalcinosis. Clinical presentation: We report a case of a male patient with Sotos syndrome and concurrent nephrocalcinosis, in whom genetic analysis revealed a microdeletion of chromosome 5q35 with a 2.2 Mb deletion encompassing both NSD1 and SLC34A1 genes. The SLC34A1 gene encodes the NaPi-IIa sodium-phosphate cotransporter, essential for phosphate reabsorption in the renal proximal tubule. Haploinsufficiency of SLC34A1 is implicated in dysregulated phosphate and calcium homeostasis, predisposing to hypercalciuria and nephrocalcinosis. Longitudinal follow-up demonstrated biochemical stability, resolution of nephrocalcinosis, and preserved renal function, supporting the hypothesis of an age-dependent attenuation in NaPi-IIa function. Conclusions: This case underscores the relevance of contiguous gene deletions in shaping complex clinical phenotypes and highlights the importance of early wide clinical screening in patients with Sotos syndrome to mitigate long-term renal complications.