Genetically Testing IVF Embryos

Preimplantation genetic screening (PGS) involves testing pre-implantation embryos for chromosomal numerical abnormalities (aneuploidy). Preimplantation genetic diagnosis (PGD) involves genetic testing of embryos for specific genetic conditions. The objective of both PGS and PGD is to identify embryos that are aneuploid or genetically defective so as to selectively transfer the most “competent” so as to improve embryo implantation potential, reduce the risk of miscarriages and minimize the chance of birth defects

PREIMPLANTION GENETIC SCREENING (PGS)

PGS is the process whereby the chromosomes in the cells of an embryo (or the polar body of an egg) are examined (karyotyped). Embryo cells that have all 46 chromosomes intact are termed euploid. Those with additional chromosomal material and those with deficient chromosomal material are aneuploid.

Should PGS be done routinely in IVF? When Levent Keskintepe and I first introduced PGS testing into the clinical IVF arena (2005) initial results were most-encouraging. Embryo implantation rates of >50% and birth rates of 50-60% when up to two euploid blastocysts were transferred, were being reported. In addition, the reported incidence of miscarriages and chromosomal birth defects was likewise greatly reduced.  Initially we believed that a time would come where full embryo karyotyping through PGS would become a routine part of IVF.  Alas, we were soon to be disappointed when following the widespread introduction of PGS testing success rates started dropping. This was especially the case when PGS was performed on embryos derived from the eggs of older women and women with severely diminished ovarian reserve (DOR).  We soon began to recognize that other factors are also operative:

    • The chromosomal integrity of the egg is certainly the most important factor that influences the subsequent ability of an embryo to propagate a viable pregnancy. However, aside from the woman’s age and her ovarian reserve, the type of protocol used for ovarian stimulation and its implementation can also significantly impact on egg/embryo competency.
    • Aside from the embryo’s karyotype, there are likely also epigenetic and metabolic factors (perhaps also influenced by advancing age and DOR) that likely impact egg/embryo competency.
    • Technical skill in performing embryo transfer (ET) varies and, needless to say, the “competency” of the embryo, will not correct for this.
    • There are anatomical and immunologic implantation issues (addressed elsewhere) which, unless addressed, will thwart the ability of even the most competent embryo to implant and propagate a viable pregnancy.
    • Not all PGS-aneuploid embryos are “incompetent”. Some are capable of “autocorrecting” upon being transferred to the uterus (i.e. are “mosaic”. While most embryo aneuploidy (>70%) originates from aneuploidy that occurs during reproductive division (meiosis) of either the egg or the sperm, the vast majority of cases are egg related. Such meiotic aneuploidy is irreversible and is responsible for >80% of IVF failures and early miscarriages. In contrast, in some cases where both the egg and sperm are euploid and upon fertilization propagate a euploid fertilized egg (zygote), during subsequent mitosis where the embryos cells multiply, some undergo “mutation” and become aneuploid while the majority maintain euploid division. This is referred to as embryo “mosaicism”.
    • Upon reaching the uterine environment, mosaic embryos have the potential to leach out their aneuploid blastomeres, while allowing the euploid cells to multiply in an orderly fashion. This results in autocorrection and in most cases, in the subsequent development of a normal, euploid conceptus/baby. Since some mitotically aneuploid (“mosaic”) embryos can, and indeed do “autocorrect’ while meiotically aneuploid embryos cannot, it follows that an ability to reliably differentiate between these two varieties of aneuploidy would potentially be of considerable clinical value. The introduction of a variety of preimplantation genetic screening (PGS) known as next generation gene sequencing (NGS) has vastly improved the ability to reliably and accurately karyotype embryos and thus to diagnose embryo “mosaicism”.
    • The ability of “mosaic embryos” to autocorrect is influenced by the stage at which the condition is diagnosed as well as the percentage of mosaic cells. Many embryos diagnosed as being mosaic while in the earlier cleaved state of development, subsequently undergo autocorrection to the euploid state (normal numerical chromosomal configuration) during the process of undergoing subsequent mitotic cell to the blastocyst stage.
    • Similarly, mosaic blastocysts can also undergo autocorrection after being transferred to the uterus. The lower the percentage of mosaic cells in the blastocyst the greater the propensity to autocorrect and propagate chromosomally normal (euploid) offspring. By comparison, a blastocyst with 10% mosaicism could yield a 30% healthy baby rate with 10-15% miscarriage rate, while with >50% mosaicism the baby rate is roughly halved, and the miscarriage rate doubled.
  • I advise all patients who subsequently conceive after undergoing ET using such “potentially mosaic” embryos to undergo prenatal genetic testing to rule out the development of an aneuploid fetus so that they can terminate affected pregnancies if they so choose.

Gender identification: Potential applications include:

    • Gender selection for nonmedical reasons (see elsewhere). This indication has become the commonest application of PGD with >50% of all such testing being done for this reason. Gender selection done simply for family balancing remains controversial, challenging concern that if it became widely accessible and freely available, such practice could distort the natural sex ratio leading to a population gender imbalance.
    • However, for this to happen, there would have to be a significant population preference for sex selection. However, the contrary seems to apply since studies conducted in western societies discount both of these concerns. In fact, the relatively high cost of IVF with the added cost of gender selection in the United States makes it unlikely that the demand would ever become large enough to impact on population gender bias.
    • In addition, several studies done in Western countries have shown that the majority does not seem to be concerned about the gender of their offspring and that with a few notable exceptions, gender preference does not appear to be slanted in the direction of either male or female. Thus, from a practical standpoint such concerns are overstated.
    • So, given that in the United States most do not care about the sex of their offspring and only a minority are interested in selecting the sex of their children, it is my opinion that freedom of choice should prevail and as such, a service for sex selection for non-medical reasons should be freely available.
  • To prevent non-Mendelian disorders that are significantly more prevalent in one sex.

PREIMPLANTATION GENETIC DIAGNOSIS (PGD):

PGD is used for the genetic, rather than chromosome- profiling of embryos in order to screen for a specific genetic diseases.

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 screening (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/PGS, 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:

    • 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.

Both PGD and PGS, are additional steps in the IVF treatment process.  Performance of PGS is less complex than PGD. The cost is roughly $3,00-=$3500, while PGD which examines individual genes costs $4,000-$6000, depending on the nature and extent of gene assessment.  For a variety of reasons, the results reported following PGS/PGD testing can sometimes be incorrect (very rarely) or inconclusive (about 5% of the time) and neither PGS or PGD are devoid of risk to the embryos. However, the reliability of the test as well as the likelihood of causing damage to embryos is very much dependent on the skill and experience of the embryologist. This having been said, the introduction of PGS/PGD technology has literally changed the entire field of IVF.

2 Comments

jodi

Hi Dr. Sher

Would any of these be transferable in hopes of auto correction. These were tested on day 3 if that matters.
1. 45, XX, -2,-5,+12
2. 47, XY,+13
3. 45, XX, -14
4. 46, XY, -4, +19

reply
Dr. Geoffrey Sher

#2 and # 5 are in my opinion worthy of consideration for FET.

Human embryo development occurs through a process that encompasses reprogramming, sequential cleavage divisions and mitotic chromosome segregation and embryonic genome activation. Chromosomal abnormalities may arise during germ cell and/or preimplantation embryo development and represents a major cause of early pregnancy loss. About a decade ago, I and my associate, Levent Keskintepe PhD were the first to introduce full embryo karyotyping (identification of all 46 chromosomes) through preimplantation genetic sampling (PGS) as a method by which to selectively transfer only euploid embryos (i.e. those that have a full component of chromosomes) to the uterus. We subsequently reported on a 2-3-fold improvement in implantation and birth rates as well as a significant reduction in early pregnancy loss, following IVF. Since then PGS has grown dramatically in popularity such that it is now widely used throughout the world.
Most IVF programs that offer PGS services, require that all participating patients consent to all their aneuploid embryos (i.e. those with an irregular quota of chromosomes) be disposed of. However, there is now growing evidence to suggest that following embryo transfer, some aneuploid embryos will in the process of ongoing development, convert to the euploid state (i.e. “autocorrection”) and then go on to develop into chromosomally normal offspring. In fact, I am personally aware of several such cases occurring within our IVF network. So clearly, summarily discarding all aneuploid embryos as a matter of routine we are sometimes destroying some embryos that might otherwise have “autocorrected” and gone on to develop into normal offspring.
Thus, by discarding aneuploid embryos the possibility exists that we could be denying some women the opportunity of having a baby. This creates a major ethical and moral dilemma for those of us that provide the option of PGS to our patients. On the one hand, we strive “to avoid knowingly doing harm” (the Hippocratic Oath) and as such would prefer to avoid or minimize the risk of miscarriage and/or chromosomal birth defects and on the other hand we would not wish to deny patients with aneuploid embryos, the opportunity to have a baby.
The basis for such embryo “autocorrection” lies in the fact that some embryos found through PGS-karyotyping to harbor one or more aneuploid cells (blastomeres) will often also harbor chromosomally normal (euploid) cells (blastomeres). The coexistence of both aneuploid and euploid cells coexisting in the same embryo is referred to as “mosaicism.”
It is against this background, that an ever-increasing number of IVF practitioners, rather than summarily discard PGS-identified aneuploid embryos are now choosing to cryobanking (freeze-store) certain of them, to leave open the possibility of ultimately transferring them to the uterus. In order to best understand the complexity of the factors involved in such decision making, it is essential to understand the causes of embryo aneuploidy of which there are two varieties:
1. Meiotic aneuploidy” results from aberrations in chromosomal numerical configuration that originate in either the egg (most commonly) and/or in sperm, during preconceptual maturational division (meiosis). Since meiosis occurs in the pre-fertilized egg or in and sperm, it follows that when aneuploidy occurs due to defective meiosis, all subsequent cells in the developing embryo/blastocyst/conceptus inevitably will be aneuploid, precluding subsequent “autocorrection”. Meiotic aneuploidy will thus invariably be perpetuated in all the cells of the embryo as they replicate. It is a permanent phenomenon and is irreversible. All embryos so affected are thus fatally damaged. Most will fail to implant and those that do implant will either be lost in early pregnancy or develop into chromosomally defective offspring (e.g. Down syndrome, Edward syndrome, Turner syndrome).
2. “Mitotic aneuploidy” occurs when following fertilization and subsequent cell replication (cleavage), some cells (blastomeres) of a meiotically normal (euploid) early embryo mutate and become aneuploid. This is referred to as “mosaicism”. Thereupon, with continued subsequent cell replication (mitosis) the chromosomal make-up (karyotype) of the embryo might either comprise of predominantly aneuploid cells or euploid cells. The subsequent viability or competency of the conceptus will thereupon depend on whether euploid or aneuploid cells predominate. If in such mosaic embryos aneuploid cells predominate, the embryo will be “incompetent”). If (as is frequently the case) euploid cells prevail, the mosaic embryo will likely be “competent” and capable of propagating a normal conceptus.
Since some mitotically aneuploid (“mosaic”) embryos can, and indeed do “autocorrect’ while meiotically aneuploid embryos cannot, it follows that an ability to reliably differentiate between these two varieties of aneuploidy would potentially be of considerable clinical value. The recent introduction of a variety of preimplantation genetic screening (PGS) known as next generation gene sequencing (NGS) has vastly improved the ability to reliably and accurately karyotype embryos and thus to diagnose embryo “mosaicism”.
The ability of mosaic embryos to autocorrect is influenced by the stage at which the condition is diagnosed as well as the percentage of mosaic cells. Many embryos diagnosed as being mosaic while in the earlier cleaved state of development, subsequently undergo autocorrection to the euploid state (normal numerical chromosomal configuration) during the process of undergoing subsequent mitotic cell to the blastocyst stage. Similarly, mosaic blastocysts can also undergo autocorrection after being transferred to the uterus. The lower the percentage of mosaic cells in the blastocyst the greater the propensity to autocorrect and propagate chromosomally normal (euploid) offspring. By comparison, a blastocyst with 10% mosaicism could yield a 30% healthy baby rate with 10-15% miscarriage rate, while with >50% mosaicism the baby rate is roughly halved and the miscarriage rate double.
Aneuploidy involves the addition (trisomy) or subtraction (monosomy) of one or part of one chromosome in any given pair. As previously stated, some aneuploidies are meiotic in origin while others are mitotic “mosaics”. Certain aneuploidies involve only a single, chromosome pair (simple aneuploidy) while others involve several pairs (i.e. complex aneuploidy). Aside from monosomy involving the absence of the y-sex chromosome (i.e. XO) which can result in a live birth (Turner syndrome) of a compromised baby, virtually all monosomies involving autosomes (non-sex chromosomes) are likely to be lethal and will rarely result in viable offspring. Some autosomal meiotic aneuploidies, especially trisomies 13, 18, 21, can propagate viable and severely chromosomally defective babies. Other meiotic autosomal trisomies will almost invariably, either not attach to the uterine lining or upon attachment, will soon be rejected. All forms of meiotic aneuploidy are irreversible while as stated, mitotic aneuploidy (“mosaicism) can autocorrect, yielding healthy offspring. Most complex aneuploidies are meiotic in origin and will thus almost invariably fail to propagate viable pregnancies.
Since certain “mosaic” meiotic aneuploid trisomy embryos (e.g. trisomies 13, 18, & 21) can potentially result in aneuploid concepti. For this reason, it is my opinion that unless the woman/couple receiving such embryos is willing to commit to terminating a resulting pregnancy found through amniocentesis or chorionic villus sampling (CVS) to be so affected, she/they are probably best advised not to transfer have them transferred to the uterus. Embryos harboring other autosomal mosaic trisomic embryos, should they not autocorrect in-utero will hardly ever produce a baby and as such there is hardly any risk at all…in transferring such embryos. However, it is my opinion that in the event of an ongoing pregnancy, amniocentesis or CVS should be performed to make certain that the baby is euploid. Conversely, when it comes to mosaic autosomal monosomy, given that virtually no autosomal monosomy embryos are likely to propagate viable pregnancies, the transfer of such mosaic embryos is virtually risk free. Needless to say, in any such cases , it is absolutely essential to make full disclosure to the patient (s) , and to insure the completion of a detailed informed consent agreement which would include a commitment by the patient (s) to undergo prenatal genetic testing (amniocentesis/CVS) aimed at excluding a chromosomal defect in the developing baby and/or a willingness to terminate the pregnancy should a serious birth defect be diagnosed.

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ADDITIONAL INFORMATION!
I strongly recommend that you visit http://www.SherIVF.com. Then go to my Blog and access the “search bar”. Type in the titles of any/all of the articles listed below, one by one. “Click” and you will immediately be taken to those you select. Please also take the time to post any questions or comments with the full expectation that I will (as always) respond promptly.

• A Fresh Look at the Indications for IVF
• The IVF Journey: The importance of “Planning the Trip” Before Taking the Ride”
• Controlled Ovarian Stimulation
• IVF: Factors Affecting Egg/Embryo “competency” during Controlled Ovarian Stimulation(COS)
• The Fundamental Requirements For Achieving Optimal IVF Success
• Use of GnRH Antagonists (Ganirelix/Cetrotide/Orgalutron) in IVF-Ovarian Stimulation Protocols.
• Egg Maturation in IVF: How Egg “Immaturity”, “Post-maturity” and “Dysmaturity” Influence IVF Outcome:
• Blastocyst Embryo Transfers done 5-6 Days Following Fertilization are Fast Replacing Earlier day 2-3 Transfers of Cleaved Embryos.
• Embryo Transfer: The “Holy Grail in IVF.
• IVF: Approach to Selecting the Best Embryos for Transfer to the Uterus.
• Fresh versus Frozen Embryo Transfers (FET) Enhance IVF Outcome
• Frozen Embryo Transfer (FET): A Rational Approach to Hormonal Preparation and How new Methodology is Impacting IVF.
• Genetically Testing Embryos for IVF
• Staggered IVF
• Staggered IVF with PGS- Selection of “Competent” Embryos Greatly Enhances the Utility & Efficiency of IVF.
• Staggered IVF: An Excellent Option When. Advancing Age and Diminished Ovarian Reserve (DOR) Reduces IVF Success Rate
• Embryo Banking/Stockpiling: Slows the “Biological Clock” and offers a Selective Alternative to IVF-Egg Donation
• Preimplantation Genetic Testing (PGS) in IVF: It should be Used Selectively and NOT be Routine.
• IVF: Selecting the Best Quality Embryos to Transfer
• Preimplantation Genetic Sampling (PGS) Using: Next Generation Gene Sequencing (NGS): Method of Choice.
• PGS and Assessment of Egg/Embryo “competency”: How Method, Timing and Methodology Could Affect Reliability
• IVF outcome: How Does Advancing Age and Diminished Ovarian Reserve (DOR) Affect Egg/Embryo “Competency” and How Should the Problem be addressed.
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ADDENDUM:
INTRODUCING SHER FRERTILITY SOLUTIONS (SFS)
Hitherto I have personally performed the actual hands-on treatment of all patients who, seeking my involvement, elected to travel to Las Vegas for my care. However, with the launching of Sher-Fertility Solutions (SFS), I will as of March 31st take on a new and expanded consultation role. Rather than having hands-on involvement with IVF procedures I will, through SFS, instead provide fertility consultations (via SKYPE) to the growing number of patients (from >40 countries) with complex Reproductive Dysfunction (RD) who seek access to my input , advice and guidance. In this way I will be able to be involved in overseeing the care, of numerous patients who previously, because they were unable to travel long distances to be treated by me, were unable to gain access to my input.

Anyone wishing to schedule a Skype consultation with me, can do so by: Calling my concierge (Patti Converse) at 1-800-780-7437 for an appointment,enrolling online on my website, http://www.SherIVF.com, or 702-533-2691; or emailing Patti at concierge@SherIVF.com or . sher@sherivf.com .
I was very recently greatly honored in receiving an award by the prestigious; International Association of Top Professionals (IAOTP). For more information, go to the press release on my website, http://www.sherIVF.com .

PLEASE HELP SPREAD THE WORD ABOUT SFS!

Geoff Sher

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