A molecular strategy for routine preimplantation genetic diagnosis in both reciprocal and Robertsonian translocation carriers

Preimplantation genetic diagnosis (PGD) for structural chromosome abnormalities traditionally uses fluorescence in situ hybridization (FISH) techniques. Although relatively straight forward, FISH is technically demanding with several process problems which include cell loss, cell overlap, variable cell fixation and hybridization as well as sample mosaicism. Increasingly, alternative techniques for chromosome analysis in embryos are being investigated in an attempt to improve on current test outcomes. Here, we report on the first routine application of a polymerase chain reaction (PCR)-based protocol for translocation analysis utilizing multiplexed short tandem repeat (STR) markers located on both segments of the translocated chromosomes. Resulting STR profiles permit the analysis of qualitative dosage of each chromosomal segment to identify translocation malsegregants from the balanced/normal chromosome complements. A total of 29 patients have undergone clinical PGD testing of 78 embryos using this method. The proportion of alternate segregations (i.e. balanced carrier and non-carriers) detected for reciprocal and Robertsonian translocation carriers was 33% and 77%, respectively. Fetal heart pregnancy rates per embryo transferred was 46% for reciprocal carriers and 40% for Robertsonian carriers (mean number of embryos transferred was 1.0). This novel approach can be applied easily within any existing PGD PCR laboratory and allows for a significant improvement in the identification of segregation types when compared with the standard FISH protocol using combinations of distal and proximal probes. This approach increases test robustness and reliability with improved interpretation of segregation outcomes, decreased analysis time and also enables the straight forward combining of structural chromosome analysis with monogenic testing.