Pre-implantation genetic testing (PGT) in IVF can help prevent the transference of your inherited genetic diseases to the next generation. So, what is PGT and which genetic diseases can be prevented with IVF-PGT?

What is the PGT test in IVF used for?

If your doctor mentions PGD (pre-implantation genetic diagnosis), don’t get all confused by the terminology.

Back in 2018, the major reproductive health societies (including ASRM, ESHRE, and ICMART) came together to rename the genetic testing procedures, so as to represent what they do more accurately and bring about a standardization in terminology:

Indications for IVF-PGT

Pre-implantation genetic diagnosis is now:

  • Pre-implantation genetic testing for monogenic (single-gene) defects (PGT-M): is performed to find specific inherited conditions controlled by a single gene such as autosomal recessive, autosomal dominant or X-linked disorders
  • Pre-implantation genetic testing for chromosomal structural rearrangements (PGT-SR): is used to test for inherited chromosomal anomalies such as chromosomal inversions, reciprocal translocations, Robertsonian translocations, etc.

PGD looks for specific inherited anomalies in the embryo and it is used to detect either inherited genetic diseases or inherited chromosomal rearrangements.

The new terminology allows better distinction between the two kinds of PGT, which are applicable for different kinds of patients and employ different technology platforms.

What diseases does PGT screen for?

Even if the parents do not have any genetic disease, they might be carriers who can pass it to their offspring.

That’s why it is important to know the family history of genetic disorders to see what problems were present in the family tree that may be passed to the new babies.

The most commonly diagnosed conditions with PGT include:

  1. Cystic fibrosis
  2. Hemophilia A
  3. Sickle cell anemia
  4. Spinal muscular atrophy
  5. Duchenne muscular atrophy
  6. Fragile X syndrome
  7. Myotonic dystrophy
  8. BRAC 1 & BRAC 2 genetic mutations
  9. Huntington’s disease
  10. Tay-Sachs disease

Family history of X-linked disease

Monogenic diseases that are passed through an X-linked inheritance are usually discovered while taking family history or at the birth of a child who is affected.

X-linked recessive diseases usually only affect males as they have only one X chromosome and any mutation to the genes on that will cause the disorder. That’s why conditions like Hemophilia, Fragile X syndrome, etc. are more common in men.

If a woman has the affected gene on one X chromosome, its effect is masked by the normal X chromosome. However, they will still be carriers and may pass it to their children. If the child is a boy, the disease will likely show and if it is a girl, she might become a carrier too.

Late on-set disorders

Some genetic diseases are present at birth while others develop later during your childhood or adult life. These include cardiomyopathies, predisposition to cancer, neurodegenerative conditions such as Alzheimer’s and Huntington’s.

The usage of PGT is now being extended to check for gene mutations that may cause late-onset disorders.

While it may be beneficial, experts urge to exercise caution against the overuse of PGT, which may have people investing in unnecessary procedures to detect a problem that may or may not occur later in life (1).

Inherited predisposition to cancer

Genes that raise the risk of developing breast and ovarian cancer in women can be identified with PGT but women who don’t have any fertility issues or the need for expensive reproductive methods, are not encouraged to do it.

When is PGT recommended?

Dr. Lam, one of the leading IVF experts in Malaysia, who works at Asia’s top IVF clinic for genetic testing, discusses the indications for PGD in the below video:

(Note: Pre-implantation genetic screening (PGS), which is now named as Preimplantation Genetic Testing for Aneuploidies (PGT-A) is a different technique, which has other applications that are not covered here.)

What are the other reasons to use PGT in IVF?

Create a sibling for HLA matching

PGT combined with human leukocyte antigen or HLA typing is used as a method for creating a baby that can serve as a hematopoietic stem cell (HSC) donor to its sibling, who is in need of a stem cell transplant.

PGT is used to ensure the HLA of the new-born matches that of their affected sibling.

The process of creating a donor child is obviously somewhat controversial but considering there is no harm to the baby by donating cord blood or bone marrow to its sick sibling, it is being practiced.

However, experts have urged the need for clear guidelines as to what should and should not be allowed in PGT-HLA procedure to assuage the ethical concerns (2).

The indications for PGT are expanding slowly as the technology becomes more refined and its usage becomes applicable to more situations.

PGD testing has been established as a safe and effective technique to check the embryos for genetic problems and prevent the transference of faulty genes to the next generation. It is a sophisticated technology that must be performed carefully at a well-equipped lab so the integrity of the embryos is protected and the results are accurate.

Unexplained Infertility

Even the embryos that are found perfectly healthy under simple microscopic evaluation embryo grading may not be capable of producing a healthy pregnancy. Beyond the superficial appearance of an embryo, there is a genetic code that determines their potential and it can be examined with the help of PGT.

If you’re unable understand the reason for repeated miscarriages or IVF failure and are simply given the frustrating diagnosis of unexplained infertility, PGT might be helpful in examining the genetic composition of embryos.

Male factor infertility

Almost half of all infertility cases are attributed to sperm problems and while a simple semen analysis can reveal morphologic and motility problems, it is not enough. You can get sperm DNA fragmentation analysis before IVF to check the genetic integrity of the sperm.

However, if the father is a carrier of genetic diseases, PGT may be helpful in screening the embryos to identify the healthiest ones.

Genes linked to male infertility and spermatogenesis are present on the Y chromosome and while PGT cannot detect all Y-chromosome-related diseases, it can detect some like Retinitis Pigmentosa.

History of chromosomal problems in previous children

If you have children with genetic diseases, PGT may help prevent them in future pregnancies. Genetic testing of embryos is a better alternative to Chorionic villus sampling (CVS) or Amniocentesis because it screens the embryos before the pregnancy thus avoiding the distress of pregnancy termination, if anomalies are found later.

Chromosomal translocations

Reciprocal translocation is the exchange of two terminal segments of different chromosomes and it is seen in around one in 600 live births. It may result in physical and mental disability in the offspring or just be the reason for infertility.

Couples with high-risk translocations will benefit from PGT; but for those, who have only a low risk of conceiving a chromosomally abnormal baby, natural conception may be advised.

According to a study in the European Journal of Human Genetics (3), with the use of PGT, miscarriage rate was reduced from 85% to 33% in 59 couples carrying reciprocal translocations.

If you need more information about PGT testing in IVF or need a medical advice over which genetic diseases can be screened with IVF-PGT, get in touch using the red contact button on this page.
References
  1. Noble, R., Bahadur, G., Iqbal, M., & Sanyal, A. (2008). Pandora’s box: ethics of PGD for inherited risk of late-onset disorders. Reproductive biomedicine online17 Suppl 3, 55–60. https://doi.org/10.1016/s1472-6483(10)60332-x
  2. Devolder K. Preimplantation HLA typing: having children to save our loved ones. Journal of Medical Ethics 2005; 31:582-586. http://dx.doi.org/10.1136/jme.2004.010348
  3. Scriven, P., Flinter, F., Khalaf, Y. et al. Benefits and drawbacks of preimplantation genetic diagnosis (PGD) for reciprocal translocations: lessons from a prospective cohort study. Eur J Hum Genet21,1035–1041 (2013). https://doi.org/10.1038/ejhg.2013.9

Featured: Dr. Lam Wei Kian, IVF expert, Malaysia

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