London, UK - Fertility regulators in the UK have paved the way for the introduction of a radical form of gene therapy in which babies are created using cellular material from three people.
The Human Fertilisation and Embryology Authority (HFEA) advised the government recently that there is no evidence "mitochondrial replacement" - an advanced form of in-vitro fertilisation - is unsafe, and ministers will now decide whether to proceed with the technique.
"Once you cross the Rubicon, it becomes difficult not to move to the next stage - full-fledged enhancement, genetic engineering."
- Dr David King, Human Genetics Alert
Critics say the move is the first step on a slippery slope towards the creation of "designer babies" built to order that heralds a new era of "consumer eugenics" - with potentially disastrous implications for humankind.
"There has been a consensus for some time in about 50 or 60 countries that we should not manipulate the human 'germline' - that is, the cells that give rise to a new individual," said Dr David King, director of the group Human Genetics Alert.
"This is the first time that there has been official approval for crossing that line and, once you cross the Rubicon, it becomes difficult not to move to the next stage - full-fledged enhancement, genetic engineering."
Mitochondria are cigar-shaped components of body cells that provide them with energy. If they are defective, it can starve the body of energy, leading to muscle weakness, blindness, deafness, epilepsy, heart failure, early dementia and even death.
Some form of mitochondrial disease affects about one in 200 children born each year - or a few dozen babies in Britain.
The proposed therapy targets women who harbour harmful mitochondrial DNA mutations, but who want to have their own genetic offspring instead of relying on a donated egg.
The treatment would take a donated egg cell then remove its nucleus and chromosomes containing the genetic information, but retain its healthy mitochondria. The nucleus from the egg of an affected mother would be inserted into it - either before or after fertilisation - and the fertilised egg would then be implanted in the mother's womb.
A baby born as a result should be free of the mother's mitochondrial defects - and that child's own eventual offspring should also be free of these, changing the genetic line for ever.
HFEA said the technique is safe and consultations at the end of last year had found widespread public support for it.
Those consulted said that ethical concerns were outweighed by the potential benefits to families at risk of genetic disorders.
"Although some people have concerns about the safety of these techniques, we found that they trust the scientific experts and the regulator to know when it is appropriate to make them available to patients," HFEA chairwoman Lisa Jardine said.
British laws on fertilisation and embryology do not allow germline or inheritable gene therapy, but in 2008 these were changed to allow mitochondrial techniques.
These therapies are not yet ready to be performed in practice, but it is thought that scientists in the United Kingdom and United States are nearing the point where it will become possible.
HFEA acknowledges there are concerns about whether this technique has the potential to confuse a child over his or her identity, because it would result in babies having DNA from two parents, plus some from a third person. The authority is advising ministers that there should be no right for the child to know the identity of the egg donor. Advocates of the procedure say mitochondrial DNA contains just 37 of the estimated 20,000 genes in the human genome, making concerns about identity a non-issue.
A panel of scientists dismissed fears that switching genetic material from one egg cell to another would change how genes behave in a different cell - so-called "epigenetic" changes that could have far-reaching effects on health. The panel, however, called for more experiments to ensure that the technique would not cause long-term harm to either the baby or future generations.
However, critics insist HFEA is downplaying important safety concerns over epigenetic risks by dressing up the technique as a tool to fight disease, which the public cannot possibly object to.
'Serious health risks'
"These techniques go far beyond anything existing in both invasiveness to the embryo and complexity, so it's not surprising that they pose serious health risks to the child, risks that the HFEA refuses to properly address," said Dr King, who presented evidence to the regulator against the technique.
But most of the heat generated in the debate has been about whether the technique heralds a new era of "eugenics" - the practice of nurturing desirable human traits through reproduction that has often been associated with political and racial extremism.
In its report, HFEA acknowledged that "some participants suggested that the use of these techniques might be seen as 'playing God' and could result in a 'slippery slope' to 'designer babies' and 'aborting disabled people'".
Stuart Newman, professor of cell biology and anatomy at New York Medical College, is a trenchant critic of any move to use mitochondrial replacement.
"Eventually this could turn into a form of consumer genetics," he says. "Once the door is open to using genetic manipulation to alter the biological properties of future people, who's to rule on whether what those involved want is a necessity or a frivolous charateristic? If you lift the taboo of genetically engineering future people, everything is going to be up for grabs."
Newman argues the technique is simply not medicine - aiming to cure the sick - but an effort to improve future people that goes even beyond ideas underpinning forced sterilisation programmes in Nazi Germany.
"Some people think it will open up a Pandora's Box of 'designer babies', but it doesn't have to be that way. Perhaps as a society we can decide where to draw the line."
- Sarah Fecht, Genetic Literacy Project
He said the commercial potential of this technique - and the desire of scientific institutions to attract generous research funding from governments and corporations - may be encouraging the UK scientific establishment's support for this untested procedure.
'Not a slippery slope'
Bioethicists have been dismissive of these concerns, and Jardine has insisted the therapy would be used only for mitochondrial disorders.
"This is not a Rubicon or a slippery slope," Jardine told a recent public meeting.
John Harris, professor of bioethics at the University of Manchester, argues what HFEA is recommending is merely that the scope of the permitted use of reproductive technologies be widened.
"Every parent wishes for a healthy child and if wish fulfillment were a form of eugenics, then eugenics would be universal," Harris said.
"Really one can consider this technology as a way of fulfilling that wish in a very limited range of cases, where a future child would almost certainly have mitochondrial disease. So it's a very limited door that is being opened. I don't believe in slippery slopes - it is a false fear."
Harris said the ethical debates society is now having and appropriate regulation should prevent future misuse of this form of therapy.
Sarah Fecht, a writer and editor with the Genetic Literacy Project in the US, agrees.
"Some people think it will open up a Pandora's Box of 'designer babies', but it doesn't have to be that way. Perhaps as a society, we can decide where to draw the line.
"With mitochondrial replacement, we're not talking about 'designer babies', we're talking about life versus death."