Thirteen years' experience of preimplantation diagnosis: report of the Fifth International Symposium on Preimplantation Genetics.

Preimplantation genetic diagnosis (PGD) has been further developed into a practical option for avoiding the birth of affected children, representing an important complement to traditional prenatal diagnosis. More than 1000 unaffected children have been born after PGD, suggesting the accuracy and safety of the procedure, which is currently also used with the establishment of potential donor progeny for stem cell treatment of siblings. Together with progress in the establishment of embryonic stem (ES) cells, this may contribute to the development and application of stem cell therapy. The accumulated experience of thousands of PGD cycles for poor prognosis IVF patients provides further evidence of the improvement of clinical outcome, particularly obvious from the reproductive history of PGD patients. A high prevalence of aneuploidies in oocytes and embryos may affect the accuracy of PGD for single gene disorders, making aneuploidy testing an important part of PGD for causative genes and preimplantation human leukocyte antigen (HLA) typing. A sequential sampling of both oocytes and the resulting embryos may improve accuracy of aneuploidy testing and may also allow the detection and avoidance of transfer of embryos with uniparental disomies. Current developments and application of nuclear transfer and sperm duplication techniques, and microarray technology, may also contribute to the improvement of PGD and help in the development of PGD for genetic expression disorders.