SLC6A18 is a sodium-dependent amino acid transporter belonging to the solute carrier family 6, primarily expressed in the proximal straight tubule of the kidney 1. While initially characterized as a glycine transporter based on knockout mouse studies, recent evidence suggests SLC6A18 functions as a glycine/urea antiporter that secretes urea into the tubular lumen in exchange for glycine and sodium 1. This transporter requires an accessory protein for surface expression, similar to other SLC6 family members 2. The urea secretion mediated by SLC6A18 contributes to efficient nitrogen excretion and influences glomerular filtration rate regulation through the tubulo-glomerular feedback mechanism 1. Disease relevance includes mutations in SLC6A18 associated with iminoglycinuria and/or hyperglycinuria 3, though genetic testing may not always detect mutations, particularly in underrepresented populations 4. Clinical significance extends beyond renal function, as genetic variants have been associated with myocardial infarction susceptibility in some populations 5, though not with hypertension 67. The transporter's dual role in amino acid transport and urea handling makes it important for understanding kidney physiology and nitrogen metabolism disorders.