The decision by British MPs to allow the Human Fertilisation and Embryology Authority to license mitochondrial replacement therapies, popularly known as “three-parent” or “three-person” IVF, should be welcomed.

Mitochondrial disease can have devastating effects on children and their families, causing premature death and severe disability. At least one affected mother in this country has seen seven of her children die. Fundamentally then this decision is about giving families whose lives would otherwise be blighted by mitochondrial disease an opportunity to have healthy children.

When making policy decisions of this magnitude, however, it is always advisable to look beyond the immediate beneficiaries and to ask whether there are any ethical objections. Two of the main ones considered yesterday and in the build-up to the debate were the suggestion that allowing mitochondrial replacement therapies would be to set out down a slippery slope to other less acceptable things such as human enhancement or “designer babies”; and the argument that what’s proposed constitutes germline genetic modification (genetic modification that can be passed onto future generations).

The specious slippery slope

It is important to note that not all “slippery slope” arguments are specious. Sometimes what starts off as a relatively innocuous exception to an established principle leads, through a process of incremental progression, to something much more serious or dangerous.

Take university tuition fees, for example. When these were introduced at a low level in England in the late 1990s, some critics argued that, although £1,000 might be affordable and reasonable, the fees were bound to increase substantially over time as governments sought ways to contain spending, and so the initial £1,000 was the start of a slippery slope to far higher tuition fees. Therefore, these critics argued, the principle of free higher education should be maintained in order to avoid setting out down the slippery slope to high fees. Given that many students now pay £9,000, it looks as if this argument may have had some merit.

But does it apply to mitochondrial replacement? There are two reasons for answering no. One is that mitochondrial replacement is technically different from modifying nuclear DNA. And it is nuclear DNA that most people are thinking of when they express concerns about parents micromanaging the characteristics of their future children (height, eye colour, intelligence, musicality, and so on). Mitochondrial replacement simply won’t deliver this. All it does is allow us to avoid mitochondrial disease.

The other (related) reason is that if scientists wanted to create a child whose nuclear DNA had been modified they would not be able to do so under current law. This would require a separate debate in parliament and it is difficult to see any reason why future MPs would feel compelled to approve it.

MPs vote.PA Wire

Mitochondrial replacement will also be closely monitored by the HFEA with specific licences needed in each case. So it is not as if MPs have voted to allow clinicians and scientists to do whatever they like in this area; what each clinic does will still need to be monitored and licensed.

Germline genetic modification

Then there is the argument that what’s proposed constitutes germline genetic modification. A germline genetic modification is one that can be passed onto future generations. So, in the case of mitochondrial replacement, the worry is that when children created using this technique later go on to have children of their own, any unforeseen genetic abnormalities created by the technique may be passed onto the next generation, and then the next.

Against this, it can be argued that mitochondrial replacement isn’t genetic modification as such, but rather donation. The mitochondria are imported wholesale from an egg donor and indeed are ones that, if the egg donor were to have her own children, would be passed onto them anyway. So nothing really new is being added to the human gene pool.

When we consider any concerns about harm and risk, it is important also to reflect on what the alternatives are: in particular, what would happen if prospective patients tried to have children “naturally”. In many cases, if they proceed in this way, we can be confident that their children will inherit mitochondrial disease. So even if there is a small risk of passing on some unforeseen genetic problem to one’s children and grandchildren, this is surely better than a near certainty of passing on a serious mitochondrial disorder.

The decision in favour by MPs was, as public health minister Jane Ellison put it, a “bold step”. So it was important to consider fully the potential ethical pitfalls. There also needs to be serious ethical debate in the coming months and years, not so much about whether to use mitochondrial replacement therapies, but about how to use and regulate them. The UK bill still needs approval by the House of Lords and a further Commons vote on any amendments before becoming law. But overall the decision is good news – not only for affected families but also for British clinicians, scientists and regulators.

Stephen Wilkinson holds a Wellcome Trust Senior Investigator Award