Preimplantation Genetic Diagnosis

Approximately 1 in 500 babies born in the united states are afflicted by a sex-linked disorder (when a genetically defective Y (male) chromosome is transmitted to offspring). Another 1 in 300 newborns has an autosomal genetic disorder, an abnormality of 1 or more genes involving the 44 remaining autosomes (non-sex chromosomes). This means that approximately 1 in 20,000 babies born annually in the U.S. will have one or other genetic or chromosomal disorder. In addition, about 1: 50 babies are born with an identifiable major genetic abnormality.

Many couples who parent a child with a severe birth defect will subsequently elect not to have another child or to adopt.  These facts and figures offer a glimpse at the magnitude of the challenge confronting the medical profession, government, and society in general. The advent of IVF/ET provides a unique opportunity to diagnose and/or exclude genetic chromosomal (structural or numerical) disorders that have the potential to impact adversely on pregnancy outcome and the very quality of life after birth, using preimplantation genetic diagnosis (PGD or preimplantation genetic testing/sampling  (PGT/PGS) for numerical chromosomal defects (aneuploidy).

The procedures both start with biopsying an IVF-generated embryo, 3-6 days post-fertilization. The biopsied material is then subjected to genetic testing whereupon 1 or more, advanced embryos, presumably free of the chromosomal/genetic defect are selectively transferred to the uterus (almost always) during a subsequent frozen embryo transfer (FET) cycle. As such PGD/PGT, has provided the ability to prevent some diagnosable chromosome/genetic disorders prior to the initiation of pregnancy and thereby, provide many desperate couples who might transmit a potential genetic catastrophe to their offspring, with real hope.

PGD allows studying the DNA of eggs or embryos to select those that carry certain mutations for genetic diseases. It is used to identify:

Monogenic conditions: Disorders due to a single gene (Monogenic disorders), (autosomal or X-linked)—or structural of chromosomal defects (e.g. balanced translocation). Relatively common autosomal recessive  disorders that are so detectable include: sickle-cell anemia, Tay Sachs disease. Relatively common autosomal Dominant disorders include:  Huntington’s disease and Charcot–Marie–Tooth disease; myotonic dystrophy etc. X-linked diseases include: Hemophilia A; fragile X syndrome, and Duchenne muscular dystrophy.

Cancer predisposition: Examples include  BRCA1 & II mutations and multiple polyposis of the colon

Minor disabilities such as deafness, in order that the child would share that characteristic with the parents.