MEDICAL GENETICS

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Medical Genetics

Basic outline of genetic testing of the embryo :

1st step –Genetic counselling to determine if the couple needs genetic test of the embryo & which type of test should be done.

2nd step –IVF /ICSI procedure to get embryos.

3rd step –Blastocyst culture to get embryos with best implantation potential.

4th step –Embryo biopsy : Collection of 5-7 cells from blastocyst stage embryo using special microsurgical instruments.

– Implantation & future growth potential of the embryo is not compromised when biopsy is done on blastocyst stage embryos.

5th step – The genetic material , DNA is extracted from these cells & tested for genetic diseases using specially made genetic test probes.

6th step – Transfer of normal embryo in womb

-In most cases cryopreservation of embryo is required till the final result of genetic test is available

There are 3 type of embryo genetic testing :
(1) Preimplantation Genetic Testing for Aneuploidies ( PGT-A):
  • Earlier it was called Preimplantation Genetic Screening ( PGS ).
  • The aim is to look for presence of any aneuploidies ( extra or missing chromosome ) of the embryo.
  • It can help to select the embryos with normal chromosomal pattern which will have highest chance of becoming healthy babies.
  • It is done when there is no known evidence of a genetic abnormality in either parent.
Who can benefit from PGT-A ?
  • Female partner age 38 or older.
  • Couples interested in single embryo transfer.
  • History of repeated pregnancy loss.
  • History of repeated failed IVF.
  • Couple with more number of embryos can choose to select the normal embryo to decrease ‘ time to pregnancy ‘.
(2) Pre Implantation Genetic Testing for Monogenic Diseases (PGT-M):
  • It was earlier called Preimplantation Genetic Diagnosis( PGD ).
  • It is recommended when there is known risk of passing down a genetic abnormality to future offspring.
  • Genetic test report of affected family member is analysed in details to plan treatment for the couple.
Who can benefit from PGT-M ?
  • Personal or family history of single-gene defects—such as cystic fibrosis, haemophilia, sickle cell anaemia, muscular dystrophy, citrullinemia , multiple exostosis etc.
(3) Pre Implantation Genetic tests for Structural Rearrangement ( PGT- SR )
  • Chromosomal structural rearrangements are translocations , inversions ,duplications or deletions of part of chromosome.
  • Many time carriers of structural rearrangement are apparently healthy individuals.
  • Most of the times structural rearrangements are suspected & detected only when such individual suffer from repeated IVF failure, repeated miscarriage or birth defects in their babies.
Who can benefit from PGT-SR ?
  • In known carriers of chromosomal structural rearrangement normal embryos can be selected by PGT SR.
Hope this was helpful for basic understanding. The aim of this discussion is to make anyone with curious mind to understand these condition better. It is not equivalent to detailed in person individualised consultation. Please contact us if you want to understand your treatment options.