Defective amino acid transport by SLC7A9 causes cystinuria (CSNU)

SLC7A9 encodes the b(0,+)-type amino acid transporter 1 BAT1. As a heterodimer with SLC3A1 in the plasma membrane, SLC7A9 mediates the high-affinity, sodium-independent transport of cystine (CySS-, the oxidised form of L-cysteine) and dibasic amino acids in exchange for neutral amino acids and is thought to be responsible for the reabsorption of CySS- and dibasic amino acids in the kidney tubule. Defects in SLC7A9 (or SLC3A1) can cause cystinuria (CSNU; MIM:220100), an autosomal disorder characterised by impaired renal reabsorption of cystine and dibasic amino acids. The low solubility of cystine causes the formation of calculi in the urinary tract resulting in obstructive uropathy, pyelonephritis, and, rarely, renal failure. Cystinuria is subcategorised as type A (mutations on SLC3A1) and type B (mutations on SLC7A9).

Summary from Reactome (R-HSA-5660883), read 2026-09-23.