Gina Paoletti-Falcone, RN, BSN – Freedom Drug Priority Healthcare
The term preimplantation genetic diagnosis, PGD, is actually somewhat self explanatory. It implies that there will be a genetic diagnosis of something before implantation. In this case, that something would be an embryo or the egg that could contribute to the formation of an embryo prior to embryo transfer in an in vitro fertilization, IVF, cycle. PGD is a laboratory technique that combines the use of IVF, often with intracytoplasmic sperm injection (ICSI), and micromanipulation of eggs or embryos by skilled embryologists to biopsy a cell which subsequently undergoes genetic analysis by one of several techniques. PGD is therefore the earliest prenatal testing available to those trying to conceive who may be at greater risk, for a variety of reasons, of not conceiving at all, conceiving and losing a pregnancy or conceiving a child who will be affected by a number of diseases that have their basis in genetic abnormalities. The results allow decisions to be made regarding which embryo(s) would be suitable for transfer to the uterus following IVF to increase the likelihood of the pregnancy and birth of a healthy child.
Edwards and Gardner performed the first successful embryo biopsy on rabbits to sex blastocysts in 1968. Advances in molecular biology and assisted reproductive technologies led to clinical research throughout the 1980s. In 1990 both Handyside and Verlinsky reported on their techniques for PGD. Handyside biopsied embryos at the cleavage stage for sexing by Y specific DNA amplification in X-linked disorders while Verlinksy tested polar bodies for autosomal recessive disease. The First International Symposium on Preimplantation Genetics was held in Chicago that same year. Today PGD is a clinical option in many countries throughout the world with an estimate of over 1000 healthy children born as a result of this technology that combines assisted reproductive technology, embryology and genetics. PGD has enhanced the specialty of prenatal diagnosis by allowing couples at risk for having a child with a genetic disease to make choices prior to pregnancy rather than being faced with the agonizing decision of terminating the pregnancy of an affected child.
PGD can be used to screen eggs, sperm and embryos for chromosome abnormalities and embryos for single gene disorders, sex and human leukocyte antigen (HLA) matching. It is helpful to review some basic information before discussing each of these applications. Human cells should each contain 46 chromosomes. These chromosomes are string like structures that are found in the nucleus, or cell center. 23 chromosomes come from the egg and the other 23 from the sperm that unite to form the embryo. Chromosomes 1 through 22, largest to smallest, are the same for males and females. The 23rd chromosome determines sex. A female has 2 X chromosomes, inheriting one from her mother and one from her father. A male has 1 X chromosome from his mother and 1 Y chromosome from his father. Chromosomes are made of genes which act as chemical messages that tell cells how to grow and function in the various processes that take place in the human body. There are more than 30,000 different genes and each cell contains a pair of each, one from the mother and one from the father. Genes are made of DNA arranged in a particular sequence that holds the “code” for that particular gene and its function.
There are four types of nucleotides that are the building blocks of nucleic acids. Each nucleotide consists of a 5 carbon sugar (which is deoxyribose in DNA), a phosphate group, and one of the following nitrogen bases:
A Adenine G Guanine T Thymine C Cytosine
DNA consists of two strands of these nucleotides, held together at their bases by hydrogen bonds. The bonds form when the two strands run in opposing directions and twist together into a double helix. Two kinds of base pairings form along the length of the molecule: A-T and G-C. This bonding pattern permits variation on the order of the bases in any given strand. Even though all DNA molecules show the same bonding pattern, each species has unique base sequences in its DNA. This molecular constancy and variation among species is the foundation for the unity and diversity of life.
(from Biology The Unity and Diversity of Life 2001).
Disruptions in “normal” structure (code) or number of genes or chromosomes can have consequences. The goal of PGD is to detect these changes prior to embryo transfer and avoid those consequences.
PGD is usually performed on one or two cells that can be obtained in two ways: polar body biopsy of the egg or blastomere biopsy of the embryo. As an egg matures and undergoes meiotic division, it extrudes two polar bodies. The first polar body is a by product of the first meiotic division (prior to fertilization) and the second polar body is a by product of the second division (after fertilization). Fertilization is confirmed by the presence of two pronuclei, about 15-18 hours after insemination with sperm, and the presence of the second polar body in the perivitelline space, the space between the zona pellucida and the cytoplasmic membrane. The most common method for polar body biopsy is to make a slit in the zona pellucida, outer covering of the egg, using a PZD microneedle and aspirate the polar bodies. The disadvantage of polar body biopsy is that it only gives genetic information about the egg and does not allow for testing of the paternal genetic contribution to the embryo. This means that it cannot be used to detect chromosomal abnormalities that occur after fertilization, including translocations that are transmitted paternally, autosomal dominant diseases or sexing of embryos.
Blastomere biopsy is the more widely used method to obtain cells for PGD. It allows testing of both the maternal and paternal genetic contribution to the resulting embryo(s). A blastomere is simply a cell from an embryo. Research established that the 8 cell stage was most suitable for blastomere biopsy which means performing the biopsy on day 3 after egg retrieval with embryo transfer pushed out to day 5. On day 3 the blastomeres are still totipotent, undifferentiated and having potential to develop into any type of cell, and have not yet compacted as in the morula stage. Removing a cell or two, therefore, will not effect fetal development but simply delays cell division for a couple of hours at which point the embryo resumes normal division. The embryo is usually incubated in a calcium and magnesium free media for about 20 minutes prior to biopsy to reduce the adherence of one blastomere to another. The biopsied blastomere must have a visible nucleus present. Before removing the blastomere with the biopsy pipette an opening is made in the outer covering, zona pellucida. This is accomplished using either the application of acidic Tyrode’s solution, a diode laser or a PZD microneedle.
Once the cell is removed, it must be prepared for one of two techniques used to analyze it. The technique used will be determined, in advance, by the reason for PGD and the test required. FISH, fluorescent in situ hybridization, can be used on both polar bodies and embryos to analyze whole chromosomes while PCR, polymerase chain reaction, is used to analyze genes on embryos. Preparation for FISH requires that the cell be spread on a slide and fixative is applied such that the cytoplasm dissolves leaving just the nuclear chromosomes. Preparation for PCR requires the cell to be placed in a special tiny PCR tube containing a buffer that allows a reaction for replication and amplification of the genetic signal. All embryos in culture dishes, slides for FISH and PCR tubes must be meticulously prepared and labeled so unequivocal matching of each embryo with it’s final PGD report is assured.
FISH uses probes, small pieces of DNA, that are a match for the chromosomes that need to be analyzed. Each probe is labeled with a different color fluorescent dye which is then applied to the biopsied cell on the slide. A coverslip is applied and sealed and then the slide is placed on a slide warmer, then in a humidification incubator. Finally, under a fluorescent microscope, each chromosome color can be counted and cells/embryos that are normal (2 of each analyzed chromosome) can be distinguished from those that are not normal.
FISH can be used for:
Aneuploidy screening in women of advanced maternal age
Aneuploidy screening for male infertility
Aneuploidy screening with repeated IVF failure
Identification of sex in X linked diseases and for non medical reasons
Recurrent miscarriages caused by parental translocations
**HINT TO REMEMBER
“BIG FISH” used to analyze whole chromosomes
Each biopsed cell contains a tiny amount of DNA, which makes up the genes on the chromosomes. It would be very difficult to accurately read this small amount of DNA. PCR allows the amplification of a specific DNA sequence(s) by using enzymes that allow it to be copied and multiplied billions of times so that it can be read. PCR consists of 3 steps that are repeated 20-40 times.
Step 1 – Denaturation of the two complimentary DNA strands at high temperature. This causes the two strands to unwind and separate into two single strands each serving as a template to build a new double strand.
Step 2 – Annealing at a lower temperature which allows primers (short complimentary pieces of DNA) to connect on either end on the DNA sequence to be amplified
Step 3 – Extension allows a heat resistant DNA polymerase to insert dinucleotide building blocks starting at each primer and working inward thus building two new identical strands.
At the end of this cycle the number of DNA molecules has doubled and the cycle starts again. The mutation or disease being tested for requires the development of a PCR test specific for it. The test development takes time and generally involves blood samples from the couple. Once the DNA has been amplified there are a variety of laboratory techniques to screen that gene for the abnormality such as gel electrophoresis, where a mismatch results in differential migration on the gel, and automated DNA sequencing.
**HINT TO REMEMBER
“Piece C R” used to analyze specific genes (pieces on chromosomes)
PCR for single gene defects requires the use of ICSI, intracytoplasmic sperm injection, to prevent contamination of the biopsied cell with DNA from surplus sperm that may still be embedded in the zona pellucida at the time of blastomere biopsy if conventional IVF drop insemination was used. The cumulus cells attached to the zona can cause similar problems and should be removed prior to blastomere biopsy. The goal is to insure that pure, high quality DNA is available for analysis that is not contaminated by another cell or piece of DNA.
Clinically PGD can benefit a variety of patients who undergo assisted reproductive technologies specifically for PGD or are undergoing assisted reproductive technologies to treat infertility with the addition of PGD to enhance their outcome. Aneuploidy, the most common chromosomal abnormality, simply means having an extra chromosome, trisomy, or a missing chromosome, monosomy. If the egg or the sperm that create the embryo has an extra or missing chromosome then that embryo will be affected in the same way. When there are extra or missing large chromosomes the likelihood of implantation decreases and the spontaneous miscarriage rate increases. When chromosomes 13, 18, 21, X or Y are involved, the pregnancy may implant and continue to develop resulting in the birth of a child with a chromosome condition that can include physical differences and intellectual retardation. Trisomy 21 or Down’s Syndrome is the most common trisomy. Others include Patau Syndrome ( trisomy 13), Edward Syndrome ( trisomy 18), Klinefelter Syndrome ( 47 XXY an extra sex chromosome) and Turner Syndrome ( 45 X a missing sex chromosome). Trisomy 16, 22, 15 and 21 are commonly found in spontaneous miscarriages. The most common aneuploidies in day 3 embryos are 22,16,21,15 and 17.
The chance of aneuploidy increases with increasing maternal age. Since women are born with their lifetime supply of eggs, the thought is that older eggs are more likely to make mistakes as their chromosomes divide resulting in a greater percentage of eggs that have either a missing or extra chromosome. This is likely the explanation for the dramatic decline in pregnancy rates and increase in miscarriage rates for women as they age, even with assisted reproductive technologies. Studies have shown that more than 20% of embryos from women 35-39 and 40-60% of embryos in women 40 and older are aneuploid. Screening for aneuploidy using FISH on polar bodies or blastomeres could therefore potentially increase implantation and pregnancy rates, while decreasing pregnancy loss and the number of pregnancies affected by trisomies or monosomy. Several studies have shown increased implantation rates with aneuploidy screening for 8 chromosomes. While PGD for aneuploidy significantly decreases the risk of having a child affected by a trisomy or monosomy, it is not possible at this time to test all of the chromosomes. The most common chromosomes in which monosomies or trisomies have been seen are tested for: 13, 15, 16, 17, 18, 21, 22 and X, Y. The accuracy of PGD for aneuploidy is about 90%. Misdiagnosis may occur because of mosaicism. This means that some of the blastomeres within the embryo are normal and some are abnormal. If a normal blastomere is biopsied, the result could be the transfer of an embryo that could carry an abnormality. Prenatal testing by either chorionic villus sampling or amniocentesis is currently recommended in any pregnancy after PGD to confirm the diagnosis and rule out any other possible aneuploidies not tested for.
PGD can also be used to detect translocations, a change in the structure of chromosomes. Individuals who have “balanced” translocations are generally unaffected as there is no extra or missing chromosomal material and the break does not generally disrupt gene function. Typically these people have no medical problems although some have reduced fertility. This is likely due to producing eggs or sperm that are “unbalanced”. An “unbalanced” translocation is one in which there is extra or missing chromosomal material. An embryo with an unbalanced translocation is less likely to implant, more likely to miscarry if it does implant or may result in the livebirth of a child who will likely have physical or mental problems. Therefore individuals with translocations are at risk for pregnancy loss or having a child with severe medical handicaps that may be incompatible with life. Reciprocal translocations affect about 1 in 625 people. This type of translocation involves a break anywhere on two different chromosomes allowing pieces to be swapped between them. About 1 in 900 people have a Robertsonian translocation involving chromosomes 13, 14, 15, 21 or 22. These chromosomes have much larger bottom halves which can fuse together. The risk for having children who are normal, balanced, unbalanced or recurrent pregnancy loss is influenced by the chromosome(s) involved and the size of the fragments exchanged.
Polar body biopsy can be used if the woman has a translocation, although blastomere biopsy is more commonly used. FISH analysis is used to identify normal/balanced and unbalanced genotypes. Analysis of embryos from translocation carriers has shown that:
PGD for translocations significantly decreases the likelihood of having a child with a translocation as it is about 90% accurate. Prenatal testing by either chorionic villus sampling or amniocentesis is recommended to account for the error rate as well as to test for other chromosomal conditions not tested for. PGD significantly reduces the chance of pregnancy loss in patients with translocations. According to Munne, patients with translocations who achieved a pregnancy after PGD had experienced miscarriage in >90% of their previous pregnancies. After PGD, fewer than 10% of pregnancies resulted in a loss. Munne also noted that female translocation patients produced an average of 9.5 mature eggs in comparison to 13 mature eggs in females without translocations. On average 65% of embryos are abnormal and in 22% of cycles there were no normal embryos available for transfer.
In the past the first indication that many couples had that one or both of them carried a genetic mutation was the birth of a child with a serious medical condition or a history of a relative with a genetic medical condition. Individuals could be tested to see if they “carried” the gene and then counseled as to the odds of having a child with the disease. Prenatal genetic testing by either chorionic villus sampling or amniocentisis then made it possible to diagnose many of these diseases in a fetus during pregnancy. A positive diagnosis placed these couples in the unenviable position of deciding whether or not to continue with the pregnancy or terminate at a point when pregnancy was well established. IVF and micromanipulation for ICSI as well as the Human Genome Project and the development of PCR for DNA amplification have all made detection of many single gene disorders using PGD possible. Single gene disorders are those diseases that are caused by the inheritance of a single defective gene.
There are two categories of single gene disorders:
Errors in hundreds of different genes are responsible for hundreds of diseases identified. Many are rare but some are common enough among certain subgroups of the population that they should routinely be screened to see if they are carriers and see a genetic counselor if they are. The following tables list single gene disorders that PGD has been used to screen for.
Alpha and Beta Thalassemia HLA genotyping
Cystic Fibrosis Sanhoff Disease
Sickle Cell Anemia Epidermolysis bullosa
Gaucher Disease Adenosine Deaminase deficiency
Tay Sachs Disease Glycogen Storage Disease type !A Fanconi Anemia types A,C and G Adrenal hyperplasia
Spinal Muscular Atrophy LCHAD
Neurofibromatosis 1 and 2 Li-Fraumini (p53 gene)
Von-Hippel Lindau Myotonis dystrophy
Huntington’s Disease Marfan syndrome
Osteogenesis Imperfecta types I and IV Charcot-Marie-Tooth type IA
APP early onset Alzheimers Polycystic Kidney Disease types 1and 2
Multiple Epiphyseal Dysplasia Retinitis pigmentosa
Familial Adenomatous Polyposis (APC gene)
Ornithine Carbamyl Transferase (OTC) deficiency
X linked hydrocephalus
Hemophilia A and B
Duchenne Muscular Dystrophy
Both ASRM and ACOG have recommended preconception screening for some of the most common single gene disorders such as CF and Tay Sachs in the at risk population. In order to do PGD blood samples from the couples may be needed to confirm the particular mutation and the ability to test for it. Reports of genetic testing are also needed to identify the specific mutation. Cystic fibrosis is the most common autosomal recessive disease in Caucasians of European descent. Approximately 1 in 25 carries a defective copy of the gene. Because it is a recessive disease two copies of the defective gene are necessary, one from each parent, to be affected. One copy of the defective gene makes a “carrier”. Two carriers have a 25% chance that their child will be affected, a 50% chance that their child will be a carrier and a 25% chance that the child will not have a copy of the defective gene. There are many possible mutations in the CF gene. The most common is deltaF508. A different mutation causes congenital bilateral absence of the vas deferens, CBAVD, a cause of male infertility. Another common autosomal recessive disease is Tay Sachs. The odds of carrying the Tay Sachs mutation are increased among eastern European Ashkenazi Jews. Approximately 1 in 27 Jews in the US is a carrier. Hemoglobin diseases are the most common single gene disorders overall with sickle cell disease common in African ancestry and beta thalassemia common in Mediterranean countries/ancestry. Each of theses diseases has devastating effects on the affected child and is eventually fatal.
Prior to PGD, families with known histories of these diseases were faced with either not having their own children to avoid transmittal of the disease or taking a chance, undergoing amniocentesis and being faced with the possible choice of terminating an affected pregnancy or having an affected child. PGD has given these couples the option of testing embryos prior to conception which could theoretically eliminate the transmission of some of these diseases to the next generation. Additionally, because of preconception screening, families “at risk” (2 carriers of the CF mutation) will be alerted of their risk before they ever have a family history of the disease.
Huntington’s disease is a late onset dominant single gene disorder. Symptoms usually present after the individual has had children and potentially passed on the single defective gene. Because it is dominant, having a parent with Huntington’s disease means a 50% chance of inheriting Huntington’s disease. Studies show that presymptomatic genetic testing is not something the majority of those at risk choose, yet given the opportunity they would choose to prevent the transmission of that dominant gene to their children. Some of these couples undergo IVF and PGD in a “nondisclosure” cycle meaning that they are given no information about the number of eggs or embryos obtained or the results of PGD in their embryos. They are given no information that would allow them to infer that they have the defective Huntington’s gene but would only have an embryo transfer of disease free embryos which could eliminate the disease from the next generation of their family. Despite the relative simplicity of this train of thought, it does raise ethical questions that are difficult to answer.
PGD can also be used to screen embryos as an HLA match for a sibling with a life threatening disorder. This may be the last resort for families with a child affected by thalassemia, Fanconi’s anemia, leukemia and other inherited or sporadic diseases requiring a hematopoietic stem cell transplant. Matched sibling donors are the best candidates but if none exist IVF with PGD can provide both screening to prevent the transmission of the disease to another child (if it is an inherited disease) and the HLA matched sibling to save the life of the existing child using chord blood obtained at birth.
It is apparent then that the following patients are most likely to benefit from PGD and the information it provides:
Once the appropriate PGD testing has been done, results are communicated so that decisions about embryo transfer can be made. Embryos will be classified as normal, abnormal or undiagnosed. Because of all the intricate steps involved in both the biopsy and the actual FISH or PCR technologies, there can be technical difficulties that result in a “non-diagnosis.” Reasons for this can include:
No nucleus in the cell biopsied therefore no chromosomes
A slide fixation error such that cells are lost
Unknown detection failure
Failure to amplify the gene due to technical problems at IVF lab, PGD lab or an embryo
With degraded DNA
Contamination with foreign DNA
Other limitations and challenges to consider are as follow:
There may be few or no normal embryos available for transfer.
There are generally no embryos available for cryopreservation requiring another fresh IVF cycle
Cryopreserved biopsied embryos appear to have a lower implantation rate than non biopsied cryopreserved embryos.
There is no guarantee of pregnancy even in otherwise fertile couples with the transfer of normal good quality embryos.
Embryos can only be diagnosed as “normal” for the defect(s) tested
There is a very low risk ~ 0.1% of damage to the embryo as a result of the biopsy
Analysis of a single cell has limitations and an error rate (5-10%) that allows for a small percentage of misdiagnosis. Therefore if a pregnancy results prenatal testing in the form of chorionic villus sampling or amniocentesis are still required.
Patients who come to an infertility practice for PGD are very often different from infertility patients. They generally are not infertile and may already have children.They may have a child who is affected by a condition they are trying to prevent in another child. They may or may not have a true understanding of what IVF and PGD entail. They may have no understanding of the time frame involved in a PGD cycle and the many steps involved. They may have no information on the cost or coverage of the PGD cycle. They are generally referred by someone who may or may not have started the educational process of how and why PGD may be beneficial to them.
Infertility patients may also require PGD for reasons identified as part of their infertility workup ( both identified as carriers of CF gene mutation) or treatment (multiple failed IVF cycles). Depending on the reason for PGD the first consult for these patients may be with the reproductive endocrinologist or with the genetics counselor. Additionally, they will need to meet with financial and nursing and their cycle will also require the involvement of the embryology lab at the practice and a PGD lab.
Every patient needs genetics counseling before their PGD cycle. The genetics counselor can review the genetic basis for the particular clinical situation the patient presents. Discussion may include an overview of the diagnosis, transmission of disorders, likelihood of transmission and ways to test for it. Family and personal medical histories may be discussed and previous genetic testing reviewed. Meeting with the counselor is an integral part of the “informed consent process” for patients undergoing PGD. Genetics counselors are the experts in discussing genetics with patients.
The physician meets with the patients to discuss their clinical situation and the application of IVF with PGD. Risks and benefits of IVF, polar body/blastomere biopsy, FISH or PCR testing as well as the possibilities of no embryos to transfer, pregnancy rates and follow up testing all need to be discussed. Consents for all of the above procedures need to be signed. Very often the PGD testing will be done at a laboratory that is a separate entity from the infertility practice with a separate set of consents to be signed. The physician will need to discuss the most effective method for biopsy and testing with the embryology and PGD lab and clearly document what will be tested, where and how.
Very often the PGD lab is not part of the infertility practice and may even be in another state. The relationship between the practice and the PGD lab needs to be clearly spelled out with defined roles in each entity and a communication plan for the various steps in the process. Financial issues need to be clearly documented so that all parties involved understand the costs and who is responsible for payment and to whom. Some PGD labs provide embryologists who come to the center to perform the actual polar body or blastomere biopsy while other infertility practices have their own embryologists do the biopsy, prepare the cells and ship to the PGD lab for analysis. Patients may have very little interaction with the lab that will do their genetic testing.
Most PGD labs have the final say as to when a patient is clear to start their cycle based on receipt of consents, pretesting and preparation of probes etc., completion of genetic counseling and financial arrangements. Depending on the reason for PGD it may take 8-12 weeks for all of the testing and preparation to be completed. The PGD lab generally needs to be notified of:
Start of stimulation
Anticipated biopsy date
HCG and egg retrieval dates
Number of eggs retrieved
Number of embryos to be biopsied
All information regarding shipment of the specimens, generally by Fed Ex or another predetermined courier.
There needs to be a defined plan for communication within the PGD team at the infertility practice. The embryology lab needs to be involved in plans for upcoming PGD cycles including cycle starts and coordination with the PGD lab for egg retrieval and biopsy dates as well as information regarding eggs and embryos, transport of biopsied cells and communication of results and embryo transfer. There needs to be flexibility within the embryology staff as expected egg retrieval dates may change based on response to stimulation. Embryology needs to know how and who to get in touch with at the PGD lab at any time.
Patients need to meet with the Financial Department at the infertility center to discuss the cost of the procedures they will undergo. Some patients may have coverage for some of the pretesting involved and some for the IVF cycle. Very few patients will have insurance coverage for the actual PGD process which can cost somewhere between $2000 to $5000.
Patients who are planning IVF and PGD can certainly benefit from a consultation with a psychological counselor. They may have issues that need to be discussed in light of their diagnosis and previous experiences. Counselors can help to reinforce the commitment that patients make when planning a PGD cycle in terms of time, money and emotions. Counselors should be available throughout the cycle to help patients cope with the emotional issues treatment can raise.
Nurses play an intricate role in the very precise and detail oriented coordination of PGD cycles. Perhaps the most important word for everyone involved in these cycles to remember is communication. This refers both to the verbal communication that is essential between all the parties involved as well as written communication in the form of documentation of all that has been discussed, agreed to and planned. Nurses are pivotal figures in that they generally have the most contact with the patients and are the point person that patients, physicians, embryologists and the PGD lab all look to for assurance that all the appropriate steps have been followed and documented to allow the cycle to proceed successfully. Some might assume that a PGD cycle is simply an IVF cycle with a few additional laboratory procedures in between egg retrieval and embryo transfer. That is a very simplistic and unrealistic assumption for many reasons.
The nursing consult orients patients to the process of IVF and PGD. Very often patients do not expect that they will need the same basic workup (day 3 hormones, infectious disease testing, uterine evaluation, semen analysis) as infertility patients because they don’t consider themselves to be infertility patients. They may need additional bloodwork or records of previous genetic testing done in order for the PGD lab to develop testing specific for their clinical situation. Much of the infertility nurses’ role is patient education. Despite the fact that these patients have generally met with various other members of the “PGD team” and been counseled and consented, it is very often the nurse who answers the questions that remain unasked or unanswered. The nurse fills in all the details of the journey from point A to point B in the process of IVF and PGD. Medications are discussed and ordered, the stimulation process and protocol are outlined, monitoring is arranged and the expected time table is covered. It is essential that the nurse has a reasonable understanding of polar body biopsy, blastomere biopsy, FISH and PCR so that they can be explained in terms that patients can understand. Nurses need open communication with the physician regarding the clinical plan for each patient. Some practices may designate specific nurses to handle PGD patients in the same way that there are usually specific donor egg nurses.
Most patients are anxious to get started and may be overwhelmed and disappointed when they realize all that needs to be done before they can go ahead with the cycle. The nurse reassures and coordinates the various steps. The nurse is, in some respect, the gatekeeper who insures that all the i’s are dotted and t’s crossed so that the patient fulfills all the obligations necessary to get the go ahead from the PGD lab to start their cycle. As the gatekeeper the nurse is very often the key communicator between the physician, embryology lab, PGD lab and the patients.
It takes expertise, cooperation, organization, communication and documentation on everyone’s part to make a successful PGD program. It takes empathy, compassion and patience to care for the people who can benefit from these technologies. Defined roles, team meetings and ongoing evaluation of results can help to keep everyone on the same page.
A PGD program can raise issues that may require ethical consideration and discussion. Professor Robert Edwards eloquently summarizes some of these moral issues that PGD forces us to consider:
“A constant worry is the oft repeated charge that these techniques introduce eugenics to human populations rather than helping to avoid inherited diseases in fetuses. Great care is essential to avoid any impression that averting genetic disease in embryos casts any reflection of the value and equality of the handicapped in a modern society. And a final challenge to the democracy of science is that the rich will benefit most from these new advances because health authorities in many countries still crassly decline to fund IVF and PGD despite their overwhelming advantages to so many couples. All these issues have stemmed from the belief that the social advantages of trying to avert genetic disease in children far outweigh the cost of their technologies. There is no doubt that preimplantation genetic diagnosis and other means of averting or alleviating serious inherited disease are bound to offer ever widening opportunities while demanding the closest of ethical attention.”
“An Atlas of Preimplantation Genetic Diagnosis”
Verlinsky and Kuliev Parthenon Publishing 2000
The Genetics and Public Policy Center, www.dnapolicy.org, released the result of their public opinion survey toward genetic testing on February 18, 2005. This is believed to be the largest public opinion survey ever conducted on the topic and was funded by The Pew Charitable Trusts. It included 21 focus groups, 62 in-depth interviews, and 2 surveys with a combined sample size of more than 6,000 people and both in person and on line town meetings. The report states that:
“A majority of Americans believes it is appropriate to use reproductive genetic testing to avoid having a child with a life-threatening disease, or to test embryos to see if they will be a good match to provide cells to help a sick sibling. However, most Americans believe it would be wrong to use genetic testing to select the sex or other non-health related, genetic characteristics of a child. Focus groups and town hall meetings revealed that Americans don’t fear technology per se, but rather fear that unrestrained human selfishness and vanity will drive people to use reproductive genetic testing inappropriately such as to select for non-medical but socially desirable characteristics.”
According to the report, Americans “fear a world in which children are expected to be perfect, and parents are expected to do everything possible to prevent children with genetic disease from being born. For many participants, these technologies raise concerns about how society might treat individuals with disabilities in a world where the birth of disabled persons might be preventable, and where the cost of testing and treatment might lead to disparities in who can afford them.”
A majority of those surveyed also “wants and expects oversight to ensure safety, accuracy and quality of reproductive genetic testing” but 70 percent of respondents are also “concerned about government regulators invading private reproductive decisions”. Only 38% “support the idea of the government regulating PGD based on ethics and morality.”
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18. Biology The Unity and Diversity of Life Ninth Edition 2001 Brooks/Cole Thompson Learning Publishers.
19. www.dnapolicy.org assessed 2/18/05
1. Preimplantation genetic diagnosis testing must always be done in conjunction with an
Answer is A
2. Polar body biopsy involves the removal of one or two polar bodies from:
A. an oocyte
B. a day 1 embryo
C. a day 3 embryo
D. a blastocyst
Answer is A
3. Polar body biopsy tests for
A. paternal genetic contribution
B. maternal genetic contribution
C. both paternal and maternal genetic contribution
D. sex of the embryo
Answer is B
4. Blastomere biopsy is usually done:
A. as soon as fertilization is confirmed.
B. after ICSI insemination with sperm.
C. on day 3 after egg retrieval when there are generally 8 cells.
D. on day 5 at the blastocyst stage.
Answer is C
5. FISH involves the use of:
A. probes which are small pieces of DNA.
B. a fluorescent microscope to count the chromosomes analyzed.
C. microscope slides and coverslips.
D. all of the above.
6. FISH can be used to test for aneuploidy of polar bodies, sperm or embryos.
Answer is A
7. Polymerase chain reaction allows for:
A. multiplication of chromosomes.
B. insertion of news genes to replace defective genes.
C. amplification of specific DNA sequences
D. removal of defective genes from embryos so they can be transferred.
Answer is C
8. PGD for aneuploidy:
A. uses fluorescent probes to identify the number of specific chromosomes being tested for.
B. cannot test for every chromosome simultaneously at the present time.
C. may help to increase implantation rates in patients with repeated IVF failure.
D. all of the above.
Answer is D
9. PGD eliminates the need for either chorionic villus sampling or amniocentisis.
Answer is B
10. Each embryo that has undergone a blastomere biopsy will have a definitive
Answer is B