Molecular cloning of translocation breakpoints in a case of constitutional translocation t(11;22)(q23;q11) and preparation of probes for preimplantation genetic diagnosis

In vitro fertilization (IVF) centres with preimplantation genetic diagnosis (PGD) programmes are often confronted with the problem of identifying chromosomal abnormalities in interphase cells biopsied from preimplantation embryos of carriers of a reciprocal translocation. The present authors have developed a DNA testing based approach to analyse embryos from translocation carriers, and this report describes breakpoint-spanning probes to detect abnormalities in cases of the most common human translocation (i.e. the t(11;22)(q23;q11)). Screening a yeast artificial chromosome (YAC) library for probes covering the respective breakpoint regions in the patient lead to probes for the breakpoint on chromosome 11q23. The physically mapped YAC and bacterial artificial chromosome (BAC) clones from chromosome 22 were then integrated with the cytogenetic map, which allowed localization of the breakpoint on chromosome 22q11 to an interval of less than 84 kb between markers D22S184 and KI457 and to prepare probes suitable for interphase cell analysis, in summary, breakpoint localization could be accomplished in about 4 weeks with additional time needed to optimize probes for use in PGD.