This mutation was homozygous in three siblings with Cystinuria, while the heterozygous parents and fourth sibling were unaffected (LOD = 1.9). Five other patients were heterozygous at this position, two of whom were siblings — presumably these were compound heterozygous. The variant was not seen on any of 126 control chromosomes. It also represents 40% of chromosomes from Cystinuria patients from Spain. Injection of mutated rBAT RNA into Xenopus oocytes had nearly abolished amino acid transport activity compared to wild type. Counting probands, case+: 5, case-: 16, control+: 0, control-: 63. This has significance = 0.00066 and an OR estimated at 29.