Understanding pre-implantation embryo genetic testing

Kurt Sansone explains what pre-implantation genetic testing is and in which scenarios its used 

File photo
File photo

People with serious hereditary genetic diseases live in constant fear of passing on the disorder or illness to their children.

The changes being proposed to the IVF law will now make it possible for these people to have a measure of comfort by allowing genetic testing of embryos before these are implanted in the womb.

This proposal marks a significant departure from the restrictions of existing legislation, which although allows diagnostic tests to take place, prohibits any further action.

The details of what genetic tests will be allowed and who is eligible are not in the law proper but will be listed in a protocol the Embryo Protection Authority has drawn up. This protocol has not been published yet but based on what Health Minister Chris Fearne said, MaltaToday has drawn up a Q&A to try and answer some of the salient questions surrounding pre-implantation genetic testing.

What is PGT?

PGT stands for pre-implantation genetic testing. It used to be called PGD (pre-implantation genetic diagnosis). In a nutshell, it is when genetic tests are carried out on embryos formed through in-vitro fertilisation (IVF) before these are implanted in the womb.

What is the purpose of PGT?

PGT is used to determine whether embryos are at risk of genetic disease.

Who will be eligible for PGT?

Although the details of the protocol are not known, Fearne has indicated that PGT will be offered to prospective parents who have a history of serious hereditary genetic disorders. In the UK, PGT can be offered if the woman has ended previous pregnancies because of a serious genetic condition; if the woman already has a child with a serious genetic condition and wants to avoid this happening again; if there is a family history of a serious genetic condition; or if there is a family history of chromosome problems.

Is PGT currently available in Malta?

Not quite. The IVF law as it stands now does allow doctors to carry out “clinical interventions” on embryos, however these have to be “exclusively diagnostic or therapeutic”. The law also makes it a condition that any such interventions are “in the interests of the health and development of the embryo itself”. So, any diagnostic test could theoretically be carried out, however in practice these are not done because the law imposes other limitations. The proposed changes will make it possible for PGT to be offered as part of the IVF treatment in particular cases.

What happens if the genetic test flags an abnormality?

In jurisdictions where PGT testing is allowed, the embryo with a genetic abnormality is normally discarded or kept frozen and given up for scientific research. Only healthy embryos are transferred to the womb. The proposed legislative changes in Malta will allow the prospective parents the option to freeze these genetically abnormal embryos and only transfer the healthy ones to the womb or if there aren’t any, proceed with a fresh cycle of IVF to fertilise more eggs.

Can embryos be discarded in Malta?

Malta’s law prohibits embryos from being discarded. It also prohibits embryo use for scientific research. This will not change.

Which genetic defects are tested for?

In theory, tests can be carried out for all known genetic disorders. However, it depends also on what the legislator allows. Although the EPA protocol dictating what will be allowed in Malta has not been published yet, Fearne has said PGT will be used to test for monogenic or single gene disorders (the process will be known as PGT-M). The examples he gave of such disorders include Huntington Disease and Finnish Nephrotic Syndrome. In the UK, the Human Fertilisation and Embryology Authority, a regulator, allows testing to take place for over 600 genetic conditions.

What genetic disorders can be identified with PGT-M?

According to the UK’s HFEA, PGT-M can be used to find one of hundreds of rare genetic conditions in embryos, including Haemophilia A and B, Macular Dystrophy, Downs Syndrome, Parkinson’s disease 1 and 4, sickle cell anaemia, Cystic Fibrosis, early onset Alzheimer’s, Thalassemia, Huntington Disease, ALS, muscular dystrophy, Fragile X Syndrome and many others. It remains to be seen what genetic disorders will be testable in Malta.

Does PGT alter the embryo genetically?

No. Its purpose is to test embryos for genetic defects.

What can couples, in Malta, who are at risk of passing on an inherited disorder do to decrease the risk?

Once the law changes, if the inherited disorder is listed as a testable condition, these couples can choose to undergo IVF treatment and use PGT to select the healthy embryos for transfer into the womb.

They can also choose to undergo IVF with donated gametes, adopt somebody else’s frozen embryo, adopt a child, or remain childless.

They can also opt to conceive naturally and accept the risk of their child inheriting the genetic condition.

Another option is to conceive naturally and undergo conventional prenatal diagnosis (PND) following conception. Two such tests are chorionic villus sampling or amniocentesis and are carried out at around 12 and 15 weeks after conception. If the foetus is found to have the genetic condition of concern, the parents have to make difficult decisions about whether or not to terminate the pregnancy or continue with it. However, given that abortion is illegal in Malta, this can only be done abroad.