Polar body biopsy

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Polar body biopsy is the sampling of a polar body of an oocyte. It was first applied clinically in humans in 1987 after extensive animal studies. [1] A polar body is a small haploid cell that is formed concomitantly as an egg cell during oogenesis, but which generally does not have the ability to be fertilized.

Contents

After sampling of a polar body, subsequent analysis can be used to predict viability and pregnancy chance of the oocyte, as well as the future health of a person resulting from such a pregnancy. The latter use makes it a form of preimplantation genetic screening (PGS). Compared to a blastocyst biopsy, a polar body biopsy can potentially be of lower costs, less harmful side-effects, and more sensitive in detecting abnormalities. [2]

Techniques

The first polar body is removed from the unfertilised oocyte, and the second PB from the zygote, shortly after fertilization. The biopsy and analysis of the first and second polar bodies can be completed before fertilization, which is the moment from which the zygote is generally considered[ who? ] an embryo and may become protected by law[ citation needed ].

By screening the first polar body for chromosomal anomalies, non-viable eggs can be reliably identified, though eggs with normal first polar bodies can still be affected by errors. This method was initially performed with fluorescence in situ hybridization (FISH), then by hybridizing a sample into lymphocytes to observe it in metaphase, and more recently by microarrays, which are fully automated and make it easier to distinguish between chromosome vs. chromatid abnormalities. [3]

The main advantage of the use of polar bodies in PGD is that they are not necessary for successful fertilisation or normal embryonic development, thus ensuring no deleterious effect for the embryo. One of the disadvantages of PB biopsy is that it only provides information about the maternal contribution to the embryo, which is why cases of autosomal dominant and X-linked disorders that are maternally transmitted can be diagnosed, and autosomal recessive disorders can only partially be diagnosed. Another drawback is the increased risk of diagnostic error, for instance due to the degradation of the genetic material or events of recombination that lead to heterozygous first polar bodies. It is generally agreed that it is best to analyse both polar bodies in order to minimize the risk of misdiagnosis. This can be achieved by sequential biopsy, necessary if monogenic diseases are diagnosed, to be able to differentiate the first from the second polar body, or simultaneous biopsy if FISH is to be performed.

In theory, molecular analysis of polar bodies may include epigenetic profiling in the near future. [4]

Target diseases

Aneuploidy

Several studies have suggested that polar body screening for aneuploidy may not be optimal. When the majority of errors occur in chromatids rather than entire chromosomes (a condition correlated with the age of the mother), screening only the first polar body will fail to detect a large percentage of defective eggs. As mentioned earlier, chromosomal abnormality in the first polar body can result in a healthy embryo, meaning that eggs may in fact be wasted as a result of the screening. Polar body testing will also be unable to detect post-zygotic errors in an oocyte. [3]

Because euploid polar bodies contain the same chromosomes as the oocyte, they can be used as a source of genetic material that is easily accessed without destroying the egg. This presents a research advantage by minimizing damage to the oocytes under investigation. [5]

Usage

Polar body biopsy is used mainly by two PGD groups in the USA [6] [7] and by groups in countries where cleavage-stage embryo selection is banned. [8]

Related Research Articles

<span class="mw-page-title-main">Meiosis</span> Cell division producing haploid gametes

Meiosis is a special type of cell division of germ cells and apicomplexans in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome (haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a cell with two copies of each chromosome again, the zygote.

<span class="mw-page-title-main">Zygote</span> Diploid eukaryotic cell formed by fertilization between two gametes

A zygote is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.

<span class="mw-page-title-main">Intracytoplasmic sperm injection</span> In vitro fertilization procedure

Intracytoplasmic sperm injection is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of embryos that may be transferred to a maternal uterus. With this method, the acrosome reaction is skipped.

<span class="mw-page-title-main">Nondisjunction</span> Failure to separate properly during cell division

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis/meiosis). There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).

<span class="mw-page-title-main">Preimplantation genetic diagnosis</span> Genetic profiling of embryos prior to implantation

Preimplantation genetic diagnosis is the genetic profiling of embryos prior to implantation, and sometimes even of oocytes prior to fertilization. PGD is considered in a similar fashion to prenatal diagnosis. When used to screen for a specific genetic disease, its main advantage is that it avoids selective abortion, as the method makes it highly likely that the baby will be free of the disease under consideration. PGD thus is an adjunct to assisted reproductive technology, and requires in vitro fertilization (IVF) to obtain oocytes or embryos for evaluation. Embryos are generally obtained through blastomere or blastocyst biopsy. The latter technique has proved to be less deleterious for the embryo, therefore it is advisable to perform the biopsy around day 5 or 6 of development.

In biology, a blastomere is a type of cell produced by cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals.

Sex selection is the attempt to control the sex of the offspring to achieve a desired sex. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at childbirth. It has been marketed under the title family balancing.

<span class="mw-page-title-main">Assisted reproductive technology</span> Methods to achieve pregnancy by artificial or partially artificial means

Assisted reproductive technology (ART) includes medical procedures used primarily to address infertility. This subject involves procedures such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), cryopreservation of gametes or embryos, and/or the use of fertility medication. When used to address infertility, ART may also be referred to as fertility treatment. ART mainly belongs to the field of reproductive endocrinology and infertility. Some forms of ART may be used with regard to fertile couples for genetic purpose. ART may also be used in surrogacy arrangements, although not all surrogacy arrangements involve ART. The existence of sterility will not always require ART to be the first option to consider, as there are occasions when its cause is a mild disorder that can be solved with more conventional treatments or with behaviors based on promoting health and reproductive habits.

<span class="mw-page-title-main">Designer baby</span> Genetically modified human embryo

A designer baby is a baby whose genetic makeup has been selected or altered, often to exclude a particular gene or to remove genes associated with disease. This process usually involves analysing a wide range of human embryos to identify genes associated with particular diseases and characteristics, and selecting embryos that have the desired genetic makeup; a process known as preimplantation genetic diagnosis. Screening for single genes is commonly practiced, and polygenic screening is offered by a few companies. Other methods by which a baby's genetic information can be altered involve directly editing the genome before birth, which is not routinely performed and only one instance of this is known to have occurred as of 2019, where Chinese twins Lulu and Nana were edited as embryos, causing widespread criticism.

<span class="mw-page-title-main">Human fertilization</span> Union of a human egg and sperm

Human fertilization is the union of a human egg and sperm, occurring primarily in the ampulla of the fallopian tube. The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the 19th century.

<span class="mw-page-title-main">Polar body</span> Byproduct of oogenesis

A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized. It is named from its polar position in the egg.

Preimplantation genetic haplotyping (PGH) is a clinical method of preimplantation genetic diagnosis (PGD) used to determine the presence of single gene disorders in offspring. PGH provides a more feasible method of gene location than whole-genome association experiments, which are expensive and time-consuming.

A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there is an atypical number of chromosomes, or as structural abnormalities, where one or more individual chromosomes are altered. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. Chromosome abnormalities may be detected or confirmed by comparing an individual's karyotype, or full set of chromosomes, to a typical karyotype for the species via genetic testing.

The genetics and abortion issue is an extension of the abortion debate and the disability rights movement. Since the advent of forms of prenatal diagnosis, such as amniocentesis and ultrasound, it has become possible to detect the presence of congenital disorders in the fetus before birth. Specifically, disability-selective abortion is the abortion of fetuses that are found to have non-fatal mental or physical defects detected through prenatal testing. Many prenatal tests are now considered routine, such as testing for Down syndrome. Women who are discovered to be carrying fetuses with disabilities are often faced with the decision of whether to abort or to prepare to parent a child with disabilities.

<span class="mw-page-title-main">Yury Verlinsky</span> Russian-American medical researcher (1943–2009)

Yury Verlinsky was a Russian-American medical researcher specializing in embryonic and cellular genetics. He is best known as a pioneer in prenatal diagnosis for detecting genetic and chromosomal disorders six weeks earlier than standard amniocentesis. The founding father of pre-implantation genetic diagnosis (PGD) and embryo analysis prior to in-vitro fertilization (IVF), Verlinsky used his polar body biopsy technique to detect potential birth defects in offspring. It is now accepted worldwide as the standard for the most efficient and effective means of analyzing the chromosomal status of an embryo.

Oocyte selection is a procedure that is performed prior to in vitro fertilization, in order to use oocytes with maximal chances of resulting in pregnancy. In contrast, embryo selection takes place after fertilization.

46,XX/46,XY is a chimeric genetic condition characterized by the presence of some cells that express a 46,XX karyotype and some cells that express a 46,XY karyotype in a single human being. The cause of the condition lies in utero with the aggregation of two distinct blastocysts or zygotes into a single embryo, which subsequently leads to the development of a single individual with two distinct cell lines, instead of a pair of fraternal twins. 46,XX/46,XY chimeras are the result of the merging of two non-identical twins. This is not to be confused with mosaicism or hybridism, neither of which are chimeric conditions. Since individuals with the condition have two cell lines of the opposite sex, it can also be considered an intersex condition.

Embryo quality is the ability of an embryo to perform successfully in terms of conferring a high pregnancy rate and/or resulting in a healthy person. Embryo profiling is the estimation of embryo quality by qualification and/or quantification of various parameters. Estimations of embryo quality guides the choice in embryo selection in in vitro fertilization.

Dmitri Dozortsev is a Russian-American physician scientist, inventor and researcher. Dozortsev's contributions in research and publications are mostly in the areas of human reproductive medicine and biology. In particular, he is best known for his studies of in vitro fertilisation and embryo transfer. Dozortsev currently serves as President of the American College of Embryology and as Director of Omni-Med laboratories.

Oocytes are immature egg cells that develop to maturity within a follicle in the ovary. Oocyte abnormalities can occur due to several factors, including premature ovarian insufficiency (POI), other maturation abnormalities, maternal ageing, and mitochondrial abnormalities.

References

  1. ↑ Galst, Joann Paley; Verp, Marion S. (2015-08-26). Prenatal and Preimplantation Diagnosis: The Burden of Choice. ISBN   9783319189116.
  2. ↑ "Delivery of a chromosomally normal child from an oocyte with reciprocal aneuploid polar bodies". Scott Jr, Richard T., Nathan R. Treff, John Stevens, Eric J. Forman, Kathleen H. Hong, Mandy G. Katz-Jaffe, William B. Schoolcraft. Journal of Assisted Reproductive Genetics Vol. 29 pp. 533-537. 2012.
  3. 1 2 "Is the polar body approach best for pre-implantation genetic screening?" Delhanty, Joy. Placenta Vol. 32, pp. 268-270. 2011.
  4. ↑ Wei, Y.; Schatten, H.; Sun, Q.-Y. (2014). "Environmental epigenetic inheritance through gametes and implications for human reproduction". Human Reproduction Update. 21 (2): 194–208. doi: 10.1093/humupd/dmu061 . ISSN   1355-4786. PMID   25416302.
  5. ↑ Jia ZX, et al. (2012). "Age-associated alteration of oocyte-specific gene expression in polar bodies: potential markers of oocyte competence". Fertility and Sterility. 98 (2): 480–486. doi:10.1016/j.fertnstert.2012.04.035. PMC   3409302 . PMID   22633262.
  6. ↑ Verlinsky Y, Ginsberg N, Lifchez A, Valle J, Moise J, Strom CM (Oct 1990). "Analysis of the first polar body: preconception genetic diagnosis". Hum. Reprod. 5 (7): 826–9. doi:10.1093/oxfordjournals.humrep.a137192. PMID   2266156.
  7. ↑ Munné S, Dailey T, Sultan KM, Grifo J, Cohen J (Apr 1995). "The use of first polar bodies for preimplantation diagnosis of aneuploidy". Hum. Reprod. 10 (4): 1014–20. doi:10.1093/oxfordjournals.humrep.a136027. PMID   7650111.
  8. ↑ Montag M, van der Ven K, Dorn C, van der Ven H (Oct 2004). "Outcome of laser-assisted polar body biopsy and aneuploidy testing". Reprod. Biomed. Online. 9 (4): 425–9. doi: 10.1016/S1472-6483(10)61278-3 . PMID   15511343 . Retrieved 2015-02-26.[ dead link ]
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