Exactly what is Pre-implantation genetic diagnosis?

Pre-implantation genetic diagnosis (PGD) enables people with an inheritable condition in their family to avoid passing it on to their children. It involves checking the genes and chromosomes of embryos created through IVF.

Preimplantation genetic diagnosis (PGD) refers specifically to when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality.

Because only unaffected embryos are transferred to the uterus for implantation, preimplantation genetic testing provides an alternative to current postconception diagnostic procedures (i.e., amniocentesis or chorionic villus sampling), which are frequently followed by the difficult decision of pregnancy termination if results are unfavorable. PGD and PGS are presently the only options available for avoiding a high risk of having a child affected with a genetic disease before implantation. It is an attractive means of preventing heritable genetic disease, thereby eliminating the dilemma of pregnancy termination following unfavorable prenatal diagnosis.

History Of Pre-implantation genetic diagnosis PGD

Edwards and Gardner successfully performed the first known embryo biopsy on rabbit embryos in 1968. In humans, PGD was created in the United Kingdom in the mid 1980s as an alternative to current prenatal diagnoses. [1] Initially, PGD revolved around determination of gender as an indirect means of avoiding an X-linked disorder. In 1989 in London, uk, Handyside and colleagues reported the first unaffected child born following PGD performed for an X-linked disorder.

As of 2006, more than 15, 000 PGD cycles have been reported. [2] PGD is currently available for most known genetic variations. [3] Though the indications for PGD are well established, PGS is a relatively new, evolving technique and remains controversial.

Condition diagnosed with Pre-implantation genetic diagnosis

PGD should be offered for 3 major groups of disease: (1) sex-linked disorders, (2) solitary gene defects, and (3) chromosomal disorders.

Sex-linked disorders

X-linked diseases are passed to the child through a mother who is a carrier. They are passed by an abnormal X chromosome and manifest in sons, who do not inherit the normal X chromosome from the father. Because the X chromosome is transmitted to offspring/embryos through the mother, affected fathers have sons who are not affected, but their daughters have a 50% risk of being carriers if the mother is healthy. Sex-linked recessive disorders include hemophilia, fragile X syndrome, most neuromuscular dystrophies (currently, >900 neuromuscular dystrophies are known), and hundreds of other diseases. Sex-linked dominant disorders include Rett syndrome, incontinentia pigmenti, pseudohyperparathyroidism, and vitamin D–resistant rickets.

pre-implantation-genetic-diagnosis-diagram

Single gene defects

PGD is employed to distinguish single gene defects such as cystic fibrosis, Tay-Sachs disease, sickle cell,  low blood count, and Huntington disease. In such diseases, the unusualness is detectable with molecular techniques using polymerase strong reaction (PCR) amplification of DNA from a solitary cell. Although progress has happened, some single-gene defects, such as cystic fibrosis, have multiple known mutations. In cystic fibrosis, only 25 mutations are currently routinely tested. Mainly because almost all of these rare mutation are not routinely examined, a parent without the indicators of cystic fibrosis could still be a jar. This allows the opportunity for a parent holding a rare mutation gene to be tested as negative but still are able to pass on the mutant cystic fibrosis gene.

PGD can be used to identify genetic mutations like BRCA -1, which does not cause a specific disease but increases the risk of a collection of diseases.

Chromosomal disorders

The very last group includes chromosomal disorders in which a variety of chromosomal rearrangements, including translocations, inversions, and deletions, can be detected using fluorescent in situ hybridization (FISH). SEAFOOD uses telomeric probes specific to the loci site of interest. Some parents may have never achieved a viable pregnancy without using PGD because prior conceptions resulted in chromosomally unbalanced embryos and were spontaneously miscarried.

How will Pre-implantation genetic diagnosis work?

The treatment for PGD is usually as follows:

  • You undergo normal in vitro fertilisation (IVF) treatment to accumulate and fertilise your eggs.
  • The embryo is cultivated in the laboratory for two to three days until the cells have divided and the embryo involves around eight skin cells.
  • A trained embryologist removes the cells (blastomeres) from the embryo.
  • The cells are tested to see if the embryo from where they were removed contains the gene that causes the genetic indicator in the family.
  • The embryo untouched by the problem is transferred to the womb to allow it to develop.
  • Any suitable left over unaffected embryos can be frozen for later use/ Those embryos that are afflicted by the condition can perish or, with your consent, used for research/

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