Britain's decision to allow researchers to edit the genes of human embryos – not to create babies but to start unravelling the earliest stages of development – is raising new questions about the ethics of this hot new technology.
Genome editing is a technique that lets scientists alter the DNA of plants, animals or humans more precisely than ever before, much like a biological cut-and-paste programme. Scientists say one day the technique might help treat devastating inherited diseases, such as muscular dystrophy, or wipe out malaria-carrying mosquitoes.
But one concern is that gene editing also might eventually lead to so-called designer babies. Here's a look at the science and controversy:
What is gene editing ?
While scientists have long been able to find defective genes, fixing them has been so cumbersome that it's slowed development of genetic therapies. With gene editing, scientists home in on a piece of DNA and use molecular tools that act as scissors to snip that spot – deleting a defective gene, repairing it or replacing it.
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There are some older methods but a new tool called CRISPR-Cas9 has been adopted by laboratories worldwide because it's faster, cheaper, simple enough to use with minimal training and allows altering of multiple genes simultaneously.
What it might treat
The biggest use so far is to rapidly engineer animals with human-like disorders for basic research, but promising gene-editing experiments make regular headlines.
Much like a bone marrow transplant, researchers hope to use CRISPR for diseases like sickle cell, correcting the faulty gene in someone's own blood-producing cells rather than implanting donated ones.
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Similarly, doctors in Britain recently treated a 1-year-old with leukaemia using donated immune cells that had been experimentally altered with an older editing method to target her cancer. A California company is testing a non-CRISPR way to make HIV patients' immune cells better resist the virus.
The University of Massachusetts just reported using a CRISPR technique to switch off, rather than cut and repair, a gene in muscle cells that causes one form of muscular dystrophy.
And Harvard researchers recently edited 62 spots in pig DNA, part of work to use the animals to grow organs for human transplant.
The biggest hurdle
Safety is a key question because gene editing isn't always precise enough; there's the possibility of accidentally cutting DNA that's similar to the real target. Out-of-body treatments like altering blood cells get around the fear of fixing one problem only to spark another, and efforts to improve precision are underway.
The ethics controversy
Altering genes in sperm, eggs or embryos can spread those changes to future generations, so-called germline engineering that might one day stop parents from passing inherited diseases to their children.
Read: Scientists question ethics of 'designer babies'
Chinese scientists reported the first-known attempt to edit human embryos last spring, working with leftovers from fertility clinics that never could have developed into foetuses. They aimed to correct a deadly inherited gene, but uncovered problems that will require more research.
Among the ethical concerns are that future generations couldn't consent, and any long-term negative effects might not become apparent for years. There's also concern about babies designed for better intellect, athleticism or appearance rather than to prevent disease.
In December, international scientists and ethicists gathered at the U.S. National Academy of Sciences declared that while gene-editing is nowhere near ready to use for pregnancy, altering early embryos as part of careful laboratory research should be allowed even as society grapples with the ethical questions.
Britain's Human Fertilisation and Embryology Authority announced it was granting permission for that kind of laboratory research at the Francis Crick Institute, a study of the genes human embryos need to develop properly in the first seven days.
Is it legal?
Where you live determines if, or what kind of, research can be performed on embryos. Some countries, especially in Europe, ban germline research.
Others, such as China, have guidelines described as unenforceable. Britain allows basic lab research only.
In the U.S., the NIH won't fund research involving germline editing but private funding is allowed.
Human gene editing aside, there are environmental concerns, too. Experiments are underway to force genetic changes to spread rapidly through populations of animals and plants changes that could wipe out invasive species or disease-carrying insects.
A California team recently reported a first step, hatching malaria-resistant mosquitoes that could easily spread their new protective gene to their offspring.
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Image: Genetics research in a labratory from iStock