Were I writing this article a couple of years ago, I would assume that anyone reading it had been born to two biological parents – but this may no longer be the case. So-called three-parent babies are now a reality, not just a far-fetched-sounding sci-fi idea.
Back in 2016, the first of the ‘three-parent babies’ was born in New York City’s New Hope Fertility Centre. A team led by Dr John Zhang created a controversial technique to prevent the transmission of mitochondrial genetic diseases from mother to baby. This technique involves first removing the nucleus from the healthy donor’s egg and replacing it with the nucleus of the prospective mother’s egg cell. Now we have an egg cell that contains the genetic material of the prospective mother in a healthy donor’s egg cytoplasm where the mitochondria are located. This modified egg cell is then fertilised with the father’s sperm and implanted back into the mother’s uterus.
More recently, a similar technique developed by researchers in the Newcastle Fertility Centre has been approved by authorities in the UK to treat two women who carry mutations in a gene that can cause MERRF Syndrome. For those who are interested in neurology will know that MERRF stands for Myoclonic Epilepsy with Ragged Red Fibres and it is an extremely rare mitochondrial disease. It is a multi-system disorder characterised by myoclonus, followed by generalised epilepsy, ataxia, weakness, and dementia. These women were picked because neither of them was suitable for a procedure called pre-implantation genetic diagnosis which is part of the whole in vitro fertilisation procedure. This requires at least some healthy embryos to be successful. However, since mitochondrial DNA are transmitted solely from the mother to the child, all embryos will contain the mutated gene in mitochondrial DNA.
A Perfect Solution?
However, these techniques weren’t perfect. In his paper, Zhang reported finding traces of the mother’s mitochondrial DNA still being passed onto the child, with the amount passed on differing between different tissues. For example, they found 2% of the mutated mitochondrial DNA of cells in the child’s urine, but found 9% in the child’s circumcised foreskin.
Also, the long-term effects of such techniques were unknown especially when the parents refused to let their child undergo any further mitochondrial testing unless there is a genuine medical necessity. You can imagine how having a ‘three-parent baby’ can cause a lot of ethical dilemmas as well – not least amongst them being the fact that the unborn child has not given consent to have the mitochondrial replacement treatment. Medicine has since moved on from paternalism and even though it may sound beneficial and a no-brainer to replace the diseased mitochondrial DNA for the good of the unborn child, we still don’t know the long-term effect of such technique and it may cause even worse side effects, for instance. Only time will tell.