A genetic technology discovered in 2012 made news again this month when some researchers at the Salk Institute’s Gene Expression Laboratory were successful in removing the HIV virus (which causes AIDS) from cells that had been attacked. HIV subverts the cell’s own mechanisms to make copies of itself, and embeds itself in the cell’s DNA. Patients have to keep taking drugs for HIV, because it can crop up again years later. The new technique removes the active HIV within the cell but also “snips” it out of the DNA, suggesting it could provide a permanent cure (though the success rate isn’t 100% yet).

The technique has been called “DNA scissors” because it really targets specific segments of DNA and cuts them out. A lot of DNA has repeat sequences known as CRISPRs with spacer DNA between. Cas proteins are special enzymes able to cut DNA, especially the enzyme Cas9 which can target specific spots in a sequence and make a break. The cell’s repair systems then re-splice the DNA strand with the cut segment removed.

The use of CRISPR-Cas9 technology to remove HIV sounds like fantastic news, but the same method can also be used to target and “edit out” other pieces of DNA just as well. That opens up a whole new can of worms.

There are many human afflictions that have been linked to a specific gene or genetic mutation. Presumably, CRISPR-Cas9 could be used to remove many undesirable bits of DNA and cure a variety of chronic genetic conditions like Cystic Fibrosis or Haemophilia. But the question of what is “undesirable” can be very subjective. HIV is bad, but are exceptionally long limbs also bad? What about freckles? Where is the line drawn? There are serious ethical concerns that this technology will be used for “non-therapeutic” purposes. Think of all the money that’s spent on purely cosmetic medical services, trying to achieve a ridiculous standard of beauty. And, of course, the spectre of engineering “ethnically pure” babies raises its ugly head again.

For another thing, although we’ve learned a lot about genetics in recent decades, there’s a lot more to learn, especially about the interconnectedness of our body systems. Only 2% of human DNA codes for the production of proteins that make our cells. The other 98% of non-coding DNA includes instructions and triggers that direct how the coding DNA behaves. There is still much to know about that.

A “slip of the scissors” could cause errors that might have far-reaching consequences: mutations that might be viable but unwelcome or outright dangerous (X-men-type superhuman abilities notwithstanding). And even if no mistakes are made, our deliberate interventions will almost certainly have long-term repercussions. In one of my novel manuscripts I have extremists use an engineered virus to “snip out” the pieces of the human genome connected to violent behaviour, creating a pacifist race. Some might think that would be a great result, but the consequences of such a thing are unknowable. We might find real cause to regret it. The same could be said about eradicating many conditions we generally consider undesirable. We don’t know the long term consequences. There’s no way we can know them.

Think of DNA as building plans. No-one wants unsightly extra nails sticking out to catch the unwary, but removing the wrong nails in the ridge beam of a peaked roof, a lintel of a doorway, or the top of a staircase could spell disaster.

I’m not against technological progress. But I am very much in favour of being sure we have the knowledge to reverse our tampering before we go ahead and do it.

Let’s know more about where all the nails should go before we start pulling them out and the roof falls in.