SLC6A19 encodes B0AT1, a sodium-dependent, chloride-independent transporter mediating resorption of neutral amino acids across apical membranes of renal and intestinal epithelial cells 123. The transporter requires tissue-specific ancillary proteins—CLTRN in kidney or ACE2 in intestine—for proper cell surface expression and function 43. SLC6A19 is particularly critical for tryptophan absorption, which serves as a precursor for NAD synthesis; maternal heterozygosity impairs tryptophan availability during pregnancy, causing metabolic perturbation and congenital NAD deficiency disorder in mice 5. Loss-of-function SLC6A19 mutations cause Hartnup disorder, characterized by elevated urinary neutral amino acids, pellagra-like rashes, ataxia, and neurological symptoms including seizures 6. Additionally, SLC6A19 mutations lead to hyperglycinuria and increased nephrolithiasis risk due to elevated urinary glycine and oxalate 7. Pharmacological SLC6A19 inhibition represents a novel therapeutic approach for phenylketonuria, increasing urinary phenylalanine excretion and reducing toxic plasma levels 8. Reduced SLC6A19 expression in inflammatory bowel disease patients correlates with disease activity and tryptophan deficiency, suggesting a potential role in intestinal homeostasis 9.