What is Pre-implantation genetic diagnosis (PGD)?
PGD is a method to detect genetic abnormalities in embryos prior to implantation and pregnancy.
PGD was developed with the primary intention to identify genetic abnormalities within embryos. Its ultimate goal is to improve success rates in in vitro fertilization (IVF). In particular, it reduces the chances of failed pregnancies and risky late pregnancy termination. Traditional prenatal diagnoses methods include chorionic villus sampling (CVS) and amniocentesis. However, since they are highly invasive and confer risk to both the mother and the fetus, PGD is often used as an alternative.
One point worth noting is that PGD was not designed to alter DNA. However, it can detect various types of disorders. These include single-gene disorders such as cystic fibrosis and sickle cell anaemia, and sex-linked disorders such as haemophilia and fragile X syndrome. Today, PGD is able to identify up to 10,000 genetic conditions.
To parents who are both carriers of genes for debilitating conditions, PGD offers them a miracle by ensuring their child is unaffected. In the situation of late pregnancy, PGD ensures children will not develop sporadic chromosomal abnormalities that lead to conditions such as Down’s Syndrome or Turner’s Syndrome. Couples who experienced repeated IVF failures and recurrent pregnancy losses can also benefit from PGD. The method avoids the associated physical and psychological risk of undergoing an abortion.
How far can we push the boundaries of PGD?
The conditions mentioned all impart definite morbidity onto the child. However, PGD has since expanded to filter embryos with genes that merely confer risk (as opposed to absolute causation) such as BRCA (predisposes to breast cancer) and adult onset diseases such as Huntington’s disease.
A more controversial use of PGD is its role in producing a child with perfectly matched HLA-types to their siblings suffering from thalassemia. This ‘saviour child’ is conceived healthy and acts as a bone marrow donor to save the affected sibling.
PGD has also been used in non-medical sex selection – sex selection with no medical justification and solely for the purpose of ‘family balancing’.
While few would dispute using PGD to avoid life-threatening genetic diseases, the ethical lines became blurry for some other scenarios. Does PGD skirt the borders of eugenics? Does accepting the logic of PGD lead to a slippery slope where our moral stand posts eventually disappear?
In Hong Kong, PGD was first performed by the Assisted Reproduction Unit at Queen Mary Hospital in 2001. Currently, couples who want to undergo PGD are required to consult a trained genetic counsellor. MIMS
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