Jane McCredie: Life-changing edit

JUST how far should we go in editing the human genome?

 

Researchers grappled with some thorny ethical issues last week at an international summit on human gene editing hosted by the US National Academy of Sciences.

 

Emerging technologies are making gene editing easier, cheaper and more effective, raising obvious potential applications for the treatment or prevention of heritable diseases.

 

Editing the genes of an individual person or fetus is one thing, but what if the editing is done in the reproductive or germ cells, meaning any changes may become heritable, thus altering the course of evolution?

 

That prospect is being raised by innovations such as the much discussed CRISPR technology, which can be used to edit human germ cells, among others.

 

The technology could potentially allow scientists to edit germ cell genes to eradicate diseases like cystic fibrosis and Huntington disease, not just in the individual concerned, but in any future descendants.

 

That certainly sounds like a good thing, but there is often a reason why harmful gene mutations survive.

 

The best known example is probably that linked to sickle cell disease: the serious blood disorder reduces life expectancy in those who inherit two copies of the mutation, but the gene also offers protection against malaria in carriers and is more common in malaria-prone regions as a result.

 

For most diseases, the genetic influence is less straightforward. Many genes may be involved, and environmental and epigenetic factors will also come into play.

 

When you start thinking about editing genes to eradicate the hereditary risk of, say, Alzheimer disease, it’s not hard to imagine how things could go badly wrong.

 

Do that in a single person and you’re only risking their future wellbeing, but when you start editing germlines you could end up changing a whole species.

 

Professor Jennifer Doudna, a participant at the Washington summit and pioneer of CRISPR research, warned of that risk in Nature last week, saying the technology could have “profound implications for permanent alteration of the human genome”.

 

Although she welcomes the potential of the technologies to eradicate genetic diseases, she argues we simply don’t know enough yet to be venturing into creating heritable mutations.

 

“Human-germline editing for the purposes of creating genome-modified humans should not proceed at this time”, she writes, “partly because of the unknown social consequences, but also because the technology and our knowledge of the human genome are simply not ready to do so safely”.

 

For the time being, genetic editing should be confined to non-reproductive cells while a regulatory framework is put in place to guide future developments, she argues.

 

Prominent geneticist Professor George Church, also a participant at the summit, disagrees.

 

“Banning human-germline editing could put a damper on the best medical research and instead drive the practice underground to black markets and uncontrolled medical tourism, which are fraught with much greater risk and misapplication”, he writes, also in Nature.

 

A ban would do little to prevent the techniques being used to create “enhanced” humans through non-therapeutic modifications such as those designed to improve intelligence or athletic performance, he argues.

 

“To think that there is not already a cadre of IVF clinicians poised to engage in such practices, perhaps even supported by governments, is to ignore, for example, the history of doping in sport”, he writes. “These kinds of ambitious individuals and institutions are unlikely to be dissuaded by an agreement made on their behalf by others with a different view.”

 

Ultimately, the summit concluded it would be irresponsible to proceed with any clinical use of human germline editing until relevant safety and efficacy issues had been resolved and there was a broad societal consensus in favour of the move.

 

The statement from the organising committee did leave the door open though, saying “the clinical use of germline editing should be revisited on a regular basis”.

 

Although the new technologies are giving us unprecedented power to control the human genome, to some extent these dilemmas are not new.

 

As Egyptian historian Ismail Serageldin, from the Library of Alexandria, said in an opening address to the summit reported in the Washington Post: “We have been playing god ever since we domesticated plants and animals”.