Q: What is Crispr-Cas9?
A: An incredibly powerful gene-editing tool that is transforming the way DNA is manipulated and modified. First demonstrated in 2013, it is based on a system bacteria use to defend themselves against invading viruses.
Q: How does Crispr-Cas9 work?
A: In its most basic form, the gene editing ‘tool kit’ consists of a small piece of RNA – a genetic molecule closely related to DNA – and an enzyme protein called Cas9.
The RNA component is programmed to latch onto a specific DNA sequence. Then Cas9 slices through the strands of DNA, like a pair of molecular scissors.
Q: What can Crispr-Cas9 do?
A: By cutting away precisely targeted elements of DNA, active genes can be switched off. Defective parts of a gene can also be removed, allowing the fault to be repaired.
Q: How are defective genes fixed?
A: Here, nature comes into play. Once a piece of DNA has been snipped out in a cell, natural repair systems kick in to try to repair the damage.
More advanced gene editing systems include additional ‘template’ DNA the cell can use to mend the break, making it possible to re-write the genetic code.
This was what the scientists conducting the new research planned to do. In the event, the embryos went their own way.
Instead of adopting the researchers’ template, their cells exploited the fact that only one copy of the gene – carried by sperm – was defective.
They based their repairs on the other, functioning, copy of the gene inherited from the women who donated their eggs for the research.
Q: Does this mean gene editing of embryos could eliminate inherited diseases?
A: A lot more research has to be done before the technique is shown to be safe and effective enough to be used in the clinic.
Also, altering nuclear DNA in a developing embryo is currently illegal.
A change in the law would be needed before such treatments can be considered, and this would involve addressing some profound ethical questions.
If in future gene editing of embryos is given the green light, it could potentially prevent thousands of diseases being passed onto future generations.