Genetically enhancing human beings offers infinite potential benefits in health and medicine, but it could also cause significant harm in ways scientists cannot foresee.

For instance, Chinese scientist He Jiankui used CRISPR to genetically edit the genes of twin girls Lulu and Nana in 2018 in a bid to protect them from HIV. Specifically, he modified a gene called CCR5.

Now, new research reveals that he may have also shortened their lives in the process.

The CCR5 Gene

Previous research have suggested that individuals with a CCR5 mutation of two non-working copies of this gene appear to be immune to a common HIV strain. So, He sought to recreate this immunity in the twin babies.

Findings of a new study published in the journal Nature Medicine show that genetic mutations similar to the ones He produced in the CCR5 gene in the babies actually decrease an individual's life expectancy by an average of 1.9 years.

The effect was discovered by University of California, Berkeley population geneticist Rasmus Nielsen while studying data from 400,000 volunteers over the age of 40 in the British gene database known as the UK Biobank.

Nielsen and his team discovered that among the thousands of middle-aged volunteers in the database, those with two non-working CCR5 genes are noticeably fewer. Upon comparing the volunteers' DNA records with death records, they found that people with this double mutation had a higher mortality rate.

It turns out, people with this specific gene mutation are at 21 percent greater risk of dying before the age of 76 than those who don't have the mutation.

"That tells us there is a process that removes individuals with two copies, and that process is probably natural selection. People die," said Nielsen.

On Gene Editing

He's example of inadvertently shaving years off the babies' lives shows how editing genes could cause severe side effects that scientists did not expect.

In February 2019, a study showed how variations in the gene are linked to memory recovery after a stroke. This means that the gene could have associations to brain function.

Mutations in the gene has also been suggested to make people more vulnerable to various infections, including influenza and the West Nile virus.

When He announced the birth of the two babies whose genes he edited, it instantly sparked a global controversy on the ethics of making designer babies.

With the new findings cropping up on just this one gene, it's even more crucial to proceed with caution when it comes to editing the genes of humans.

"There might be a perception that when you have one mutation, you have one effect. But in fact, one mutation might have many different effects," Nielsen explained, adding that the consequences can be difficult to predict as "a mutation that's beneficial in one context is very detrimental in other contexts."

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