Three folks stoke DNA advance
A boy with three parents marks a major achievement in genetic science.
A controversial technique that allows parents with rare genetic mutations to have healthy babies has been employed by a US-based team in Mexico.
The boy’s mother carries genes for Leigh disease, a fatal nervous system disorder. Those genes reside in the mitochondria of the DNA, which comes from the mother’s side and carries just 37 genes, the rest of which come from the DNA housed in each cell’s nucleus.
But John Zhang and his team at the New Hope Fertility Center in New York City offered the parents a way to avoid passing on the dangerous genes using sing the so-called “three-parent” technique.
There are a few ways to do this, but Zhang used a particular approach called spindle nuclear transfer, where the nucleus from one of the mother’s eggs is removed and inserted it into a donor egg with its nucleus removed.
The result was an egg with nuclear DNA from the mother and mitochondrial DNA from a donor that was fertilised with the father’s sperm.
The team created five embryos, one of which developed normally and was implanted into the mother.
A different method called ‘pronuclear transfer’ (in which both the mother’s and donor’s eggs are fertilised before being combined) has been approved, but not used, in the UK. However, given that neither method has been approved in the US, Zhang had to perform the procedure in Mexico.
Most of the ethical concerns around the process relate to the amount of embryos that have to be destroyed for it to work. Zhang’s team has been applauded for not having to destroy embryos, and for using a male embryo, so that the resulting child would not pass on any inherited mitochondrial DNA.
There are also safety concerns prompted by earlier attempts at the ‘three-parent baby’ technique in the 1990s, where mitochondrial DNA was injected from a donor into another woman’s egg, and combined with sperm from her partner.
Several babies from these trials developed genetic disorders, leading the technique to be banned, though experts now believe it failed because the babies had mitochondria from two sources.
The researchers have now tested the mitochondria of the boy in the latest trail, and found that less than 1 per cent carried the Leigh syndrome mutation, which should be too low to cause any problems.
The team will describe the findings further at the American Society for Reproductive Medicine’s Scientific Congress in Salt Lake City in October.
Dr Ainsley Newson, Associate Professor of Bioethics at the University of Sydney, has some concerns.
"This couple’s decision to use mitochondrial replacement – after four miscarriages and the deaths of two children – is unlikely to have been taken lightly. They have also chosen to use maternal spindle transfer (MST) as it may lead to less embryo destruction than other forms of mitochondrial replacement.
"Ethical aspects of this technique, such as the cost of the technology and the value of having a genetically related child need to be weighed against the value for this couple. But, the manner of this particular case is disquieting.
"The treatment location seems to have been chosen due to there not being any regulations in place. This is in stark contrast to the UK, where specific regulation was developed after a lengthy process of scientific, legal and public engagement. There has also been less research into MST than other approaches, raising safety aspects.
"While research on some forms of mitochondrial replacement in Australia may be possible under licence, the format of our cloning laws means that performing MST in either a research or clinical setting would be illegal. Given advances in this area, Australia needs to look at how its laws can keep pace with fast-moving technologies like this one."