Preimplantation genetic diagnosis of X-linked retinoschisis.

The aim of this study was to perform preimplantation genetic diagnosis (PGD) for X-linked retinoschisis using multiple displacement amplification (MDA) for whole genome amplification and linked markers to the RS1 gene. The study evaluates the ability of MDA to amplify the whole genome directly from a single blastomere. MDA products were used for polymerase chain reaction analysis of two polymorphic markers flanking the RS1 gene and a new X/Y marker, X22, to sex embryos in an X-linked retinoschisis PGD programme. Two couples in whom the wives were carriers of the RS1 gene mutation (599G-->A), previously identified in their families, were subjected to two PGD cycles each. The main outcome measure was the ability to analyse single blastomeres for X-linked retinoschisis using MDA. As a result, the development of an MDA-PGD protocol for X-linked retinoschisis allowed for the diagnosis of 20 embryos in the four PGD cycles performed. These were biopsied on day 3 of culture and analysed. Eight embryos were affected males and two embryos were female carriers. In summary, three healthy female and four healthy male embryos, and a female carrier embryo, were transferred 48 h after biopsy. One single pregnancy was achieved. This report shows that the MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD. It also allows the simultaneous amplification of different targets to perform diagnosis of any known gene defect and sexing test by standard methods and conditions.