In a recent press statement on the use of preimplantation genetic testing (PGT) of human embryos, the Human Fertilisation and Embryology Authority (HFEA) stated that ‘Embryo selection is only legal in the UK to avoid serious inherited illnesses, usually by means of pre-implantation genetic diagnosis authorised by the HFEA, known as PGT-M or PGT-SR.’ This drab, jargon-loaded declaration, which the HFEA has yet to clarify, is more remarkable than it seems, and may not be correct.
Here are four recognised types of PGT:
- PGT-A: testing for aneuploidy embryos (those with an abnormal number of chromosomes). Aneuploidy is a major cause of failed implantation for pregnancy, miscarriage and of birth defects in children, though the benefits of PGT-A are unknown and the focus of some debate.
- PGT-M: testing for monogenic (single gene) conditions that one (or both) of the parents is known to carry.
- PGT-SR: testing for structural rearrangements of chromosomes, such as deleted, duplicated or inverted segments. Embryos affected by structural rearrangements are less likely to result in a live birth.
- PGT-P: calculating a polygenic risk score to predict the likelihood of the child resulting from the embryo being at risk of complex diseases. This is not permitted in the UK.
The HFEA’s press statement came in response to widely reported warnings issued in relation to polygenic risk scores used for preimplantation testing (see BioNews 1130), by the European Society of Human Genetics (ESHG), which described them as unproven and unethical in a paper in the European Journal of Human Genetics last year. It is clear that this type of PGT, PGT-P, is unlawful in the UK but the implications of the HFEA’s declaration for the three other types of PGT is ambiguous.
To read the full article, please see the BioNews website here.