New Technique Helps Couples With Known Genetic Problems Two sophisticated technologies can now be combined to help parents who carry a genetic defect prevent the passage of that defect to their offspring. For over twenty-five years, infertile couples have taken advantage of in vitro fertilization (IVF) to help create their families. The latest advance in this reproductive technology is pre-implantation genetic diagnosis (PGD). This technology allows doctors to select embryos free of a specific genetic problem in order to create healthy babies. This has evolved after complete mapping of the human genome identified the location of over 1000 genetic diseases. Now scientists have the ability to create probes to find a specific genetic problem in as little as a single cell. Until recently, if a couple was aware of a disease caused by a single gene defect in their family, all they could do to prevent the birth of an affected baby was prenatal diagnosis in the already pregnant woman with amniocentesis or chorionic villus sampling (CVS). These procedures can detect the presence of the abnormal gene in the fetus, but if present, the only alternative to having an abnormal child is to abort the pregnancy. Now with IVF and PGD, embryos can be screened in the laboratory for a specific genetic disease and only embryos not affected with the condition in question are transferred into the mother. This prevents the disease caused by the genetic defect from being transmitted to their child When either the mother or father is a known carrier of a genetic defect, they can undergo PGD to find embryos harboring the defective gene. While there is a growing list of single genetic defects for which molecular diagnosis is possible, common indications today include cystic fibrosis, Tay-Sachs, B- thalassemia, muscular dystrophy, and Huntington’s disease. Gender selection of a female embryo is another strategy when the mother is a known carrier of an X-linked disorder for which there is not yet a specific molecular diagnosis. In this scenario, PGD is used to identify the male embryos, half of which would be affected, so that only female embryos will be utilized for the hoped for pregnancy.