How Gene Drives Could Save the World
Malaria has dogged humanity throughout all of recorded history.
Hippocrates wrote of periodic fevers, describing the recurring waves of symptoms that are a hallmark of the disease. The disease comes in waves, causing symptoms ranging from fever and tiredness to seizures, comas, and death. Malaria was so common in Rome that it was known as “Roman fever”, and may have even contributed to the decline and fall of the Roman Empire. Malaria has plagued humanity for at least 10,000 years, and even attacks our distant relatives, such as chimpanzees.
And it hasn’t gone away. In 2017, there were an estimated 218 million cases of malaria worldwide, with approximately 439,000 deaths stemming from the disease. This occurred despite global spending of roughly $3.1 billion on prevention and eradication.
More people have malaria than the entire population of Brazil — or more people than the populations of England, France, and Italy combined. If any disease could be described as the true scourge of humanity, it might be malaria.
But what if we could eradicate it completely? What if we could wipe an eraser across the planet, removing an entire species, in a single generation?
Such an action could mean the difference between life and death for hundreds of thousands of malaria sufferers — but that action, if used on the wrong target, could spell disaster for our planet’s fragile ecosystems.
This is the power, the promise — and the concern — of gene drives.
In its most basic definition, a gene drive is any mechanism that spreads a specific gene (or suite of genes) across a population by altering the probability that the gene will be passed on to offspring.
If you remember high school biology, most genes are normally passed on at a 50% rate. For each gene in your body, you have two copies — one that you inherited from your mother, and one that you inherited from your father. When you have a child, there’s a 50% chance that you’ll give your child the gene copy from your mother, and a 50% chance that you’ll give your child the gene copy from your father.
A gene drive, however, doesn’t follow that 50% distribution.
A gene drive, at the molecular level, is a bit of DNA that has the ability to copy itself into another location, overwriting whatever was there previously. If you inherit a gene drive from your mother, that drive sequence will delete the gene copy you inherited from your father, replacing it with another copy of itself.
The end result is that, even though you inherited one drive sequence and one normal sequence, the gene drive replaces the normal sequence with a copy of itself, and you end up with two drive sequences instead. The version of the gene that came from your father is gone, and you’re guaranteed to pass on your mother’s version of the gene to any offspring.
The result of introducing a gene drive in a population? Just like a meme on the internet, the altered gene spreads. Instead of having a coin-flip chance of being passed on to descendants, it’s always passed on, thanks to its ability to overwrite the normal version of that gene. In just a few generations, the gene drive can spread throughout an entire population.
Imagine if the altered gene that the gene drive affects is responsible for the development of the mouth-parts of a mosquito. A mosquito with the gene drive doesn’t have its mouth grow properly, and can’t bite humans. Additionally, females with this gene drive can’t lay eggs. The male offspring can still reproduce, so that mutation spreads throughout the entire mosquito population.
In just a handful of years, all the mosquitos (at least, all the ones in that breeding population) have mouths that can’t bite humans, and the inability to lay eggs leads to their rapid extinction from the area.
No biting means no mosquitos, which means no spread of malaria.
This is what’s being tested for use in parts of Africa, right now.
A gene drive could be the solution to eliminating mosquitos, and thus eliminating disease, but it’s also an incredibly powerful tool — one whose effects can’t be easily reversed.
Here’s a nightmare scenario — imagine that a gene drive is released to eliminate mosquitos. It works, incredibly well — but it turns out that the gene drive gets transferred by a virus from mosquitos to bees.
Suddenly, not only is the mosquito population being wiped out, but so is the native bee population. No bees means no pollination, which destroys huge swaths of the global food production apparatus.
This is a frighteningly plausible outcome, and concerns like this one have led to calls for the United Nations to ban the possible use of gene drives. But other groups, like the Gates Foundation, argue that the possible benefits of gene drives outweigh the potential for something going wrong, and are pushing for gene drive use to expand.
Gene drives have already been tested in several environments. Mosquitos with gene drives were released in 2016 in the Cayman Islands, and led to a 62% suppression rate of mosquitos carrying dangerous viruses, with egg laying rates down by 88%. Similarly altered mosquitos were okayed by the FDA to be released in the Florida Keys, but local opposition led to the project being canceled.
Gene drives aren’t just being used against mosquitos. Groups in Texas and New Zealand are pushing for gene drives to target mice, which are destructive pests in both locations. California researchers hare designing a gene drive to attack fruit flies that destroy hundreds of millions of dollars of fruit crops every year.
Supporters of gene drives argue that the method requires thousands of individuals with the gene drive to be released into a single area, and point out that a couple individuals who escape to other areas won’t be enough for the gene drive to spread. After all, especially in short-lived organisms like mosquitos, mice, and fruit flies, the majority of individuals don’t ever get to breed and have any offspring.
Opponents, on the other hand, point out that the gene drive could mutate, or could jump from an invasive species to attack a closely related native species. In many regions, native and invasive species interbreed — the gene drive could hop from the invasive pest to a beneficial, protected native species through this cross-breeding.
Strong arguments exist both for and against gene drives. Do we make a bold move to combat deadly diseases or ecosystem-destroying invasive species, despite the possible risks? Or should we refrain from blindly believing that we understand Nature well enough to alter it?
Whenever a new genetic technology appears, it’s quickly followed by a question: could it be used on humans?
A couple articles have suggested that gene drives could be used as a sort of genetic switch in humans, allowing us to turn a gene on or off at will. However, the more likely application of gene drives in humans would be to eliminate inherited genetic diseases. There are many rare inherited genetic diseases that are easily to test, but impossible to cure.
Each of these diseases is progressive, incurable, deadly — and caused by very specific genetic mutations in only one or two locations. Intervening with a gene drive would not only ensure that somebody’s children don’t inherit this disease. It could also eliminate this disease entirely from that family’s genetic line.
Imagine being told that you’re a carrier for Tay-Sachs. You’re concerned, knowing that, if your spouse is also a carrier, your children have a 1 in 4 chance of being born with this incurable disease, and a 50% chance of being a carrier of the disease. “Not a problem,” your doctor assures you. “We can give you a gene drive that guarantees that none of your children, nor their children, will never have to worry about Tay-Sachs popping up again.”
Is it tempting? Definitely. But, like any other genetic intervention, it carries risks. Additionally, any genetic treatment that affects the germline — sperm and egg cells — receives extra scrutiny, because a messed-up treatment could be passed to future generations.
Gene drives currently aren’t being tested in humans yet — the first tests are only just now being conducted on non-human mammals (mice). If gene drives ever do become a possibility for humans, they’ll have to go through very rigorous testing and examination by groups like the FDA before they’re ever prescribed by a doctor.
But science moves fast — and perhaps gene drives will one day be a tool in our arsenal to fight genetic diseases.
Humanity has struggled with malaria for thousands of years, quite possibly ever since we first started standing upright and walking on two legs. We’ve searched for cures for centuries, trying everything from mosquito netting to opium to a wide range of small-molecule drugs. We have antimalarials, drugs that prevent a person from contracting malaria, but they’re designed for use only for days to weeks, not for years. We have no vaccine or cure for malaria.
Gene drives offer a powerful new solution — not by targeting malaria itself, but by cutting off its method of transmission to humans. It’s mosquito netting for the twenty-first century, taking a flyswatter to an entire species.
It’s incredibly powerful — but as Uncle Ben stated, “with great power comes great responsibility.” As scientists, we need to be responsible and make sure that we fully test every aspect of a gene drive before we release it into the wild.
Gene drives could save humanity from malaria — or could introduce an atom bomb’s worth of damage on a continent’s ecosystem.
We’ll never be able to fully predict the effect of letting one loose on the wild — but we can improve our confidence in our guesses. We, as a species, will need to decide whether the reward is worth the risk.
How Gene Drives Could Save the World
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