SLC6A19 encodes B0AT1, a sodium-dependent transporter that mediates resorption of neutral amino acids across the apical membrane of renal and intestinal epithelial cells, requiring CLTRN in kidney or ACE2 in intestine for cell surface expression. The gene plays a critical role in amino acid homeostasis, including tryptophan uptake, which supports NAD synthesis and multiple metabolic pathways. Biallelic SLC6A19 mutations cause Hartnup disorder, characterized by elevated urinary neutral amino acids and neurological manifestations including ataxia, seizures, and psychiatric symptoms 1. Heterozygous maternal carriers of loss-of-function alleles may experience adverse pregnancy outcomes if dietary NAD precursors are insufficient, as reduced tryptophan transport impairs NAD synthesis during gestation 2. In inflammatory bowel disease, decreased SLC6A19 expression in colonic tissue correlates with reduced serum tryptophan and increased disease activity 3. Pharmacological inhibition of SLC6A19 represents an emerging therapeutic strategy: the investigational inhibitor JNT-517 increases urinary phenylalanine excretion and lowers plasma phenylalanine in phenylketonuria models and healthy volunteers, offering a novel approach to manage amino acid metabolism disorders 4. Conversely, SLC6A19-mediated tryptophan uptake suppresses renal cell carcinoma metastasis by activating NAD-dependent signaling pathways 5. These divergent clinical applications highlight the therapeutic potential of modulating SLC6A19 activity across distinct disease contexts.