Two genes responsible for cystinuria and CU have been identified: SLC3A1, which encodes the heavy subunit rBAT of the renal b0,+ transporter; and SLC7A9, which encodes b0,+AT, the interacting light subunit of the b0,+ transporter (Calonge et al., 1994; Feliubadaló et al., 1999). This evidence concerns the gene SLC3A1 and cystinuria.