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CRISPR-Cas9: The science behind the world’s first gene-edited babies

CRISPR-Cas9: The science behind the world’s first gene-edited babies
Health
Designer babies — these words likely conjure up scenes from Hollywood movies like Gattaca or maybe even science fiction books where humans are cloned or modified in the womb to create the ultimate human.

For decades, the possibility of genetically altered babies remained firmly in the realm of science fiction, but in late 2018, it became a reality. The world’s first-ever designer babies were reportedly born in China .

Jiankui He, a scientist at Southern University of Science and Technology in Shenzhen, China, claimed that he had, for the first time, genetically altered embryos.

“I feel a responsibility, not only to make a first but as an example,” said He.

The scientist said he had altered a section of DNA in twin girls named Nana and Lulu. He said he had essentially cut out a section that would have made the twins susceptible to contracting HIV from their father using a technology called CRISPR-Cas9.

“Right after we sent her husband’s sperm into (the mother’s) egg, we also sent in a little bit of protein and instructions for a gene surgery,” said He.

The scientific world reacted to this announcement with shock, horror and cries of unethical practices. For his part, He said he knew there was the possibility of backlash.

“I understand my work will be controversial but I believe families need my technology,” said He.

Sarion Bowers with the Wellcome Sanger Institute in the U.K., one of the world’s premier genomic discovery centres, is among those who disagree with He’s decision to create the gene-edited embryos.

“I think it is quite important to say that what happened in China is pretty much an outlier. He went against a lot of ethical norms, and while genome-editing of embryos might be acceptable in the future, it isn’t really at the moment,” said Bowers.

Most scientists agree that what He claimed to have done was far beyond the current scope of gene-editing technology.

“From the point of view of the investigator in China who did this, he said: ‘In vitro was thought to be unethical, but it has been used routinely around the world, and I am going to build on that and make a breakthrough’ — but he didn’t realize that this was horrible,” said John Bergeron, a medical professor at McGill University. “To go germ-line editing … it’s not just unethical, it’s scientifically inappropriate because just too much is unknown right now.”

It’s that idea of germ-line editing that creates controversy when talking about CRISPR-Cas9.

Neville Sanjana, who works with CRISPR technology at the New York Genome Centre and NYU, explains there is a distinct difference between what was reportedly done in China and how most scientists use CRISPR.

“There’s a fundamental distinction you can make between somatic editing and germ-line editing, and those terms just denote one key difference, that somatic editing is things you do in one organism that is only in that organism, whether it be a plant or an animal,” said Sanjana.  “Germ-line editing is much more serious stuff… When you edit, say, the sperm or the egg cells, that’s something that’s now a heritable mutation that’s passed down to every cell in the next generation and, potentially, for many generations after it,” Sanjana added.

So what, exactly, is CRISPR-Cas9? It’s actually the acronym for clustered, regularly interspaced, short palindromic repeats. Essentially, it’s an editing tool for genes.

“[Scientists] discovered that bacteria have an immune system that prevents viruses from infecting them. These folks did it because they were interested in making yogurt and cheese, and the viruses were killing the bacteria,” said Bergeron.

“People didn’t really realize this was of particular interest to scientists till they realized, actually, that they could take that little system and use it to identify DNA in very specific regions, in any animals or species, basically, and make changes to the DNA as they wished,” added Bowers.

Essentially, CRISPR-Cas9 allows scientists to quickly, easily and more cost-effectively identify and edit genes. Think of it like editing a word document, where you would highlight and edit a misspelled word or remove a word and replace it with another. The same thing happens in CRISPR-Cas9.

CRISPR has two components: the Cas9 protein, which cuts the DNA that scientists want to edit — essentially acting as the scissors — and what’s called a guide RNA, which is really the brains of the operation. The guide RNA recognizes the DNA that needs to be edited.

Using this CRISPR tool, scientists first identify the sequence of DNA they want to edit then create the guide RNA to recognize that piece of DNA. The RNA is then placed in the cutting tool, or Cas9, and it is introduced into the cells. It locates the target DNA sequence and cuts it. Once the cut is made, scientists can then delete, modify or insert an entirely new DNA sequence.

“I think it is amazing, but on the other hand, this is just the latest in a series of tools scientists have been using, and I think it’s really captured the imagination so fast but, actually, scientists have been doing it for quite a long time, just not quite as easily and not as accurately,” said Bowers.

CRISPR may have now been used to edit an embryo, but scientists say it’s just not that simple and won’t soon be used in fertility clinics around the world to make babies to suit parent’s desires.

“If you go on the web, it says it’s simple. That’s like looking at Roger Federer play tennis and (saying): ‘Oh, that looks simple.’ Behind that are thousands of hours of training [and] discipline,” said Bergeron.

Bowers agrees, saying: “It’s not going to be that easy to make someone super strong or give them superhuman eyesight. These are complex genetic traits, and we don’t fully understand them.”

With designer babies off the table, at least for the foreseeable future, CRISPR is being used in everything from creating healthier, stronger crops, like wheat, to finding drugs to treat cancers.

“We have quite new technology at the Sanger Institute, where we take tissue from cancer patients and are able to grow it in culture, and then what we do is we can treat these cells from the patient with CRISPR-Cas9 and we can basically work out which genes are involved in the cancer with that particular patient,” said Bowers.

Sanjana says CRISPR is one of the most promising tools available today and will likely be even more important down the line.

“I think, as we grow this toolbox, there are things that we haven’t even thought about right now that five, 10 years in the future, are going to have a tremendous impact on human health and the health of our planet.”

Bowers believes that although the use of CRISPR-Cas9 to create the world’s first designer babies was unethical, it’s opened an important discussion to the public about a very promising technology.

“I think what’s really interesting is the ethical debate that’s now happening. While what happened in China was irresponsible in the way it was done, I think on the other hand, we are now having a conversation and I think it’s an important conversation to have,” said Bowers.

Sanjana agrees, saying: “It’s important with any new kind of technology that increases human capability in ways that can be both good and bad for us to broadly consider the implications of the technology… As with any new technology, it has to be developed reasonably and responsibly.”
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