Two decades ago, Dolly proved that it was possible to use the nucleus of an adult somatic cell to generate a new organism with the same genetic material. At the time, one of the greatest fears was that cloning technology would be used for the development of human clones. Two decades later, the fears haven’t materialized. However, other groundbreaking advances in biotechnology are forcing societies to deal with unprecedented ethical dilemmas. ‘Molecular scissors’ that edit DNA and children with three parents are two themes at the center of today’s bioethical debate.
Mitochondria are small structures that exist inside cells and have genetic material of their own. Unlike the DNA in the cell nucleus, which passes to the next generation in a 50/50 proportion (half father and half mother), mitochondrial DNA is transmitted exclusively by the mother, inside the oocyte. This means that if a mother has a genetic disease associated with mitochondria, she will pass it on to her children. Mitochondrial replacement therapy (MRT), pioneered by scientists at the University of Newcastle, consists of an in vitro fertilization technique that uses oocytes from a woman with healthy mitochondria (emptied of nuclear DNA). This oocyte then joins the DNA of the parents of the future baby. The baby will, therefore, inherit a small portion of the genetic material from the mitochondrial donor. MRT can help prevent mitochondrial diseases – which affect one in every 6,500 children – while giving new hope to infertile couples.
The first country to legalize mitochondrial replacement therapy was the UK in March 2015. Since then, at least two 3-parent babies have been born: a boy in Mexico (2016) and a girl in Ukraine (2017). However, there are concerns that MRT might open the door for genetic manipulation or eugenics.
Genome engineering and editing
CRISPR/Cas9 is a molecular device discovered in bacteria, serving as an immune system against hostile viruses. This discovery surprised the scientific community in 2006, but it didn’t take long until the molecular mechanism was turned into a DNA-editing tool. With CRISPR/Cas9, scientists can choose specific DNA targets and cut them. The medical benefits are tremendous: changing the dangerous variant of a gene that increases the risk of Alzheimer’s disease to a harmless variant should be possible by editing the corresponding ‘letter’. It has recently been shown that CRISPR/Cas9 can be used to edit these ‘letters’.
This innovative technique is moving very fast to clinics. However, there are concerns that it could be employed to modify the human germline. Changing a gene from the reproductive cells — oocytes from women and spermatozoa from men — changes the genetic identity of offspring forever.