The Power of CRISPR

Something amazing can be found in the DNA of bacteria: CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) genes. They allow bacteria to detect and defend themselves against invading viral genetic material, and it looks like there may be a way to use these DNA sequences for human genome editing.

Recent research has been using a simple modified version of the gene, composed of the CRISPR sequence and its associated protein Cas9. The Cas9 protein is itself complexed with a synthetic RNA sequence and cuts the target DNA in a specific location, thus allowing genetic material to be removed and/or added thanks to homology directed repair. Basically, the DNA strand that gets cut uses its homologue strand to repair itself, by adding complementary nucleobases until it is whole again.

A team of Chinese scientists has already experimented with the CRISPR genetic editing tool on human embryos as an attempt at rectifying a mutation in gene MYBPC3 from the father’s sperm. The gene is responsible for hypertrophic cardiomyopathy, a condition which causes the heart muscle to thicken and cause sudden death.

This immediately raises ethical issues: how far can genome editing go? Isn’t it too easy to argue that the technique is “healing” someone and then use it for genetic modifications aiming at human “enhancement”? Couldn’t the side effects of such a process be worse than the condition it frees a patient from? What if the CRISPR tool cuts the targeted DNA in the wrong place? Surely, if you’re deleting and then adding genetic material to someone’s DNA, there is a risk of off-target mutations with catastrophic consequences.

With all these fears in mind however, CRISPR remains revolutionary in molecular biology. In the case of the recent experiments on the mutations in gene MYBPC3, the embryos disregarded the genetic template provided by the researchers to repair the paternal DNA strand, and instead used the mother’s DNA as a model. This suggests that it wouldn’t be yet possible to artificially engineer human DNA, as the body seems to use what is already there rather than exterior guidance to heal itself.

Once fully perfected, applications of this technique could be endless: not only could it be used to study genetic rearrangements but also to track the progression of diseases like cancer and even correct genetically-inherited disorders before birth. With the worryingly increasing number of antibiotic-resistant bacteria, scientists have also been thinking about creating a CRISPR pill which could target harmful bacteria and trigger an autoimmune disease which would cause them to destroy their own genes. The research still has a long way to go, but if used correctly, it could become one of the coolest things in the history of medicine since the invention of penicillin.

[Isabelle Ribe]

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