Preimplantation diagnosis for single gene disorders.

Preimplantation genetic diagnosis (PGD) allows patients who are carriers or who are affected by genetic diseases to select unaffected embryos for transfer before becoming pregnant. The practice of PGD is evolving with rapid advances in technology and biopsy methods. Testing for a specific gene mutation can be performed in combination with 24-chromosome aneuploidy screening. Several unique applications of PGD are reviewed, including exclusion diagnosis for couples from Huntington disease families, testing for fragile X premutations, and human leukocyte antigen matching for stem cell donor siblings. Although PGD for single gene mutations allows patients to gain information about their embryos and perhaps avoid a difficult decision about whether or not to terminate an ongoing pregnancy, this technique also provides for much ethical debate encompassing the well-being of the prospective couple, embryo, child, and people in the community affected by the diseases being screened. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.