Saviour siblings: have we slipped down the slope?

The Human Fertilisation and Embryology Authority (HFEA) has announced a relaxation of the rules surrounding PGD (preimplantation genetic diagnosis) and tissue typing, otherwise known as saviour siblings treatment. Predictably, the decision prompted a rash of media comment. But, perhaps unpredictably, nearly all the comment was positive and in support of the HFEA's decision to let this form of treatment go ahead.

However, amongst the critics, one very familiar idea kept coming up. It wasn't the idea of the designer babies (everyone, supporters and critics alike, uses this misleading, lazy term), but the slippery slope. In the Daily Mail, the leader comment warned that the 'genie is out of the bottle'. 'As sure as night follows day', it continued, 'this paper predicts that yesterday's development will lead inexorably to a much looser interpretation of the rules, with babies 'designed' for particular intellectual or physical characteristics in a brave new world where 'perfection' becomes the rule.'

The idea of the slippery slope is by no means new. In the context of assisted reproduction, it has been common parlance since the very beginning IVF, more than a quarter of a century ago. In the specific case of PGD, critics of the technique have worried from the start that giving permission to screen for one disease would make it increasingly difficult to resist requests for embryo screening for ever more trivial reasons.

Part of the concern underpinning the slippery slope argument is that the relaxation of a particular rule will make a technique widely available to whoever wants it. And the implication is that demand for that technique will be enormous. But, as many people have pointed out, demand for PGD with tissue typing is likely to remain low, just as demand for normal PGD has remained low, because the circumstances that lead parents to request it are, thankfully, relatively rare.

But despite the small number of couples who might seek PGD and tissue typing, is this relaxation evidence we have slipped down the slope? PGD was first developed for couples at high risk of having a child with a serious genetic disease, to allow them to start a pregnancy knowing that their future child would be free from that disease. And so, whilst this genetic screening is still the overriding motivation for requesting PGD, tissue typing has expanded the applications of the procedure. This is also the first time that PGD has been used to screen in a particular characteristic, rather than to screen one out.

Allowing PGD for tissue typing alone, without testing for a genetic disease, is a departure. But it's not a slip. The HFEA has by no means made a speedy or ill-considered decision: many have argued that it has taken rather too long to develop this policy. And so, if timing is anything to go by, this decision does not represent a downhill slide, but rather an uphill struggle.