Thus far, cystinuria is thought to be caused by defects in two genes, SLC3A1 and SLC7A9. SLC3A1 (MIM #104614) is located on chromosome 2 (2P16.3) and encodes the heavy subunit of the renal amino acid transporter (rBAT) needed to localize the transporter to the plasma membrane. The gene discussed is SLC7A9; the disease is cystinuria.