85. Von Willebrand Factor (VWF) Gene Targeting by Double-Strand Break Enhanced Homologous Recombination

Gene targeting by replacing the aberrant nucleotide sequence in the defective gene with the corresponding functional or |[ldquo]|normal|[rdquo]| sequence offers an idealized solution for treating genetic disorders. However therapeutic gene targeting has yet to be realized. Major advances have been made in gene targeting by utilizing site-directed DNA double strand break enhanced homologous recombination (DSB-GT). Most recently Urnov et al (2005) demonstrated DSBGT efficiencies approaching 20% in a gene, IL2R|[gamma]|, whose dysfunction can lead to human X-linked severe combined immune deficiency (X-SCID). This remarkable validation of DSB-GT technology utilized four fingered zinc-finger nucleases (ZFN) that recognized a unique endogenous sequence at a very high affinity.