SLC12A1 encodes the sodium-potassium-chloride cotransporter 2 (NKCC2), a secondary active transporter that mediates electroneutral movement of Na+, K+, and Cl- in a 1:1:2 ratio across cell membranes 1. Expressed on the apical membrane of thick ascending limb epithelial cells, SLC12A1 is the primary molecular target of loop diuretics like furosemide and bumetanide, and plays an essential role in transepithelial NaCl reabsorption and urinary concentration/volume regulation 1. The transporter also substitutes NH4+ for K+, enabling ammonium transport crucial for maintaining ammonium homeostasis, particularly during metabolic acidosis. Loss-of-function SLC12A1 mutations cause Bartter syndrome type 1, an autosomal recessive renal tubular disorder characterized by hypokalemic, hypochloremic metabolic alkalosis, hypercalciuria, and nephrocalcinosis 2, 3. Neonatal presentations include polyuria, failure to thrive, and intrauterine growth retardation 2. Beyond kidney physiology, SLC12A1 overexpression is implicated in hepatocellular carcinoma pathogenesis through the WNK1/ERK5 pathway, with SLC12A1 antagonists showing therapeutic potential in preclinical xenograft models 4. Pathogenic variants span from common exonic mutations to rare deep intronic variants affecting splicing 5.