SLC34A1 encodes the renal sodium-phosphate cotransporter 2A (NaPi-IIa), which plays a critical role in maintaining phosphate homeostasis through active phosphate transport in proximal tubule cells 1. The transporter is located in the brush border membrane and mediates sodium-dependent phosphate reabsorption with a Na+:Pi stoichiometry of 3:1 2. Loss-of-function mutations in SLC34A1 cause primary renal phosphate wasting, leading to inappropriate production of 1,25-(OH)2D3 and subsequent symptomatic hypercalcemia characteristic of idiopathic infantile hypercalcemia (IIH) 1. Both biallelic and monoallelic pathogenic variants can cause disease, with patients presenting hypercalcemia, hypercalciuria, nephrocalcinosis, and hypophosphatemia 3. Clinical manifestations vary with onset age, and hypercalcemia may not necessarily present after infancy 3. SLC34A1 variants are significantly enriched in adult kidney stone formers, with monoallelic carriers comprising 8.1% of unselected patients 4. Common genetic variants near SLC34A1 are associated with increased kidney stone disease risk through decreased serum phosphate concentrations 5. Early genetic testing and differentiation from other causes of IIH is critical for targeted phosphate supplementation therapy 1.