Mutations in SLC12A1 (encoding NKCC2) (Simon et al. 1996a,b), KCNJ1 (encoding ROMK) (Simon et al. 1996a,b), CLCNKB (encoding CLC-Kb) (Simon et al. 1997), CLCNKA (encoding CLC-Ka) (Schlingmann et al. 2004), BSND (encoding Barttin) (Birkenhager et al. 2001), and CASR (encoding CaSR) (Watanabe et al. 2002) may all cause a BS phenotype. The gene discussed is SLC12A1; the disease is Bloom syndrome.