Preimplantation Genetic Diagnosis
What Is PGD?
Preimplantation Genetic Diagnosis (PGD) is a procedure combining recent significant advances in molecular genetics and assisted reproductive technology. PGD allows physicians to identify various genetic diseases in the embryo (fertilized egg with several divisions) prior to implantation, that is, before the pregnancy is established. It is of special value for those who are at risk of having children with serious genetic problems.
Who Should Consider PGD?
The primary candidates for PGD are couples who might have been previously discouraged from having children of their own because of the danger of transferring genetic problems to the next generation. When the possibility of a genetic abnormality is identified, they are faced with the difficult decision to terminate the pregnancy. This decision is especially difficult for women who have had trouble conceiving and finally were able to get pregnant only through one of the assisted reproductive technologies.
How Available Is PGD?
Therefore, PGD is of enormous value to patients who wish both to conceive a normal child and avoid the dilemma of termination. PGD is a technically demanding and very complex procedure, which requires specials skills. For this reason, it is available in only a handful of centers in this country.
Categories of Diseases
Preimplantation Genetic Diagnosis can be offered for three major categories of diseases: sex linked diseases, molecular disorders, and chromosomal disorders.
In the first category, it can be used to determine the sex of the embryo for sex-linked disorders where the specific genetic defect is unknown, variable, or unsuitable for testing on single cells. An example of this group is Duchenne muscular dystrophy.
In the second category, PGD can be used to identify single-gene defects such as cystic fibrosis, where the molecular abnormality is testable using molecular techniques.
The last category includes chromosomal disorders, where a variety of chromosomal rearrangements, including translocations, inversions, and chromosome deletions, can be detected using Fluorescence In Situ Hybridization (FISH). Some potential parents who carry a chromosomal rearrangement may have never achieved a viable pregnancy if each previous conception resulted in a chromosomally un- balanced embryo that miscarried spontaneously.
Click Here For A List Of Genetic Diseases We Can Presently Diagnose
The number of diseases we can diagnose and control the transmission of continues to grow. Some diseases we are already able to test. Others are being studied. If you are concerned about any disease, please contact us to make sure that PGD is available for your case.
Genetic Evaluation
The genetic laboratory is faced with the difficult task of evaluating a single cell for a specific genetic disorder or for sex determination. With the current available technology, the PGD laboratory cannot truly screen for multiple possible abnormalities. It can only identify the presence or absence of a specific disorder.
Various methodologies are used for this purpose, depending on the genetic problem known to exist in one or both parents. Only embryos proven not to carry the genetic abnormality in question are used for transfer or freezing.
Risks Of The Procedure
There may be a number of risks and/or possibilities of complications. From the patient's point of view, even after going through their treatment cycle (In Vitro Fertilization and Preimplantation Genetic Diagnosis), there is no certainty that pregnancy will occur. In most patients the IVF technology can produce embryos in vitro, but after they are transferred back into the uterus no one can guarantee that each embryo will implant. Statistics indicate that younger patients have better chances for successful implantation and ongoing pregnancy than older patients. In general, the chances decline in the mid-thirties and after. There are also individual exceptions, when patients below the age of thirty-five might be "poor responders" to stimulation of ovaries and produce only a limited number of eggs. On the other hand, patients who are in their high thirties, or even forties, might respond very well and produce a significant number of eggs ready for fertilization.
The general experience and statistics are for informational purposes only. Patients should be evaluated individually. When the In Vitro Fertilization procedure is combined with Preimplantation Genetic Diagnosis, there are some handicaps and some advantages. Obviously, biopsy of the developing embryo does not make anything better. However, embryos that are found to be genetically normal have an overall better chance to implant and develop into an ongoing pregnancy. It is also believed that pregnancy rates with Preimplantation Genetic Diagnosis might be better than in patients having simple In Vitro Fertilization.
The number of diseases we can diagnose and control the transmission of continues to grow. Some diseases we are already able to test. Others are being studied. If you are concerned about any disease, please contact us to make sure that PGD is available for your case.
According to the March of Dimes
1. 1 out of every 100 Americans is born with a serious genetic defect.
2. Approximately 20,994 California babies are born with a birth defect annually.
3. There are more than 4,000 known birth defects.
4. Birth defects are the leading cause of death in the first year of life and account for more than 1 in 5 infant deaths.
5. For babies born with birth defects, estimated lifetime costs total 48 billion.
6. According to the National Center for Health Statistics, in 1995, 11.6% or 453,722 babies were born to women over 35.
From the book "Planning Your Pregnancy and Birth" by the American College of Obstetrics and Gynecologists:
1. All human cells have 46 chromosomes each possessing between 50 million and 250 million base pairs of DNA molecules in each chromosome.
2. A gene is a segment of DNA that is coded to pass along a certain trait.
3. The body has about 50,000 to 100,000 genes.
4. There is a 1 in 4 chance of passing a genetic disorder on to the child if both partners carry the disease.
5. In the United States:
a. About 1 in 625 African Americans has sickle cell disease and 1 in 10 are carriers.
b. 1 in 2,500 Caucasians have cystic fibrosis and 1 in 25 are carriers.
c. About 1 in 800 babies is born with Down Syndrome.
Facts from the American Society of Reproductive Medicine:
1. About 7% of stillbirths and neonatal deaths have chromosomal abnormalities.
2. Recurrent miscarriages may be due to genetic abnormalities.
3. Preimplantation Genetic Diagnosis - PGD was first performed in 1989.
4. Nearly 200 babies that have been tested have been born following the first PGD.
5. Over 200 disorders could potentially be prevented by using PGD to screen gender-based disorders.
PGD and Cancer Prevention
Preimplantation Genetic Diagnosis can also be offered for the prevention of cancer in families with a history of a determined cancer. The exact cause of Cancer is unknown. Men or women with familial history of a determined Cancer are at an increased risk, lending support to the belief that Cancer may be hereditary in some cases. Some cases of Cancer have been traced to genetic abnor- malities. For example, looking at breast cancer, those without the genetic background and genetic line have a risk of 2% to 10% of developing breast cancer, depending on age. However, those with a definite genetic line face a higher danger, up to 70%, of developing cancer of the breast. In cancers that are more prevalent in one gender than the other, as in the case of Prostate Cancer, which exclusively occurs among males, PGD will reduce the chances of having an affected child. The Preimplantation Genetic Diagnosis can find the gender of the embryo prior to implantation inside the uterus. Using PGD to implant only female embryos will ensure the couple with a strong family history of this disease that their child will not be affected with Prostate Cancer. Couples should consult with a genetic counselor about their actions. PGD can currently test for a variety of diseases, inclusive of X-linked diseases, and those that primarily affect a specific gender. PGD is continuously being improved so we may be able to test for more and more genetic disorders in the near future.
