A look at gene editing and why it is controversial

He Jiankui, a Chinese scientist, has claimed that he helped make the world’s first genetically edited babies — twin girls whose DNA he altered with a tool called CRISPR. Here’s a look at gene editing and why it is controversial:

WHAT IS GENE EDITING?
Gene editing is a technique through which genes can be deleted or replaced from one’s genome. It is like removing a word in a sentence completely or replacing it with another related or unrelated word, but which would give a meaningful sentence.


Eg: Sundays are good days for work
Sundays are bad days for work

The most widely used technique of gene editing is called CRISPR, which is an adaptation of methods that bacteria use to kill invading viruses.

HOW DOES CRISPR WORK?
When a virus invades a bacterial cell, it keeps a copy of a part of the virus gene within its own DNA. When a similar virus attacks the bacteria, it uses this copy to make a molecule called RNA, similar to the attacking viral gene, which will go and deactivate the virus.

Scientists use similar RNA as a guide to a gene, and bind it with a protein — called Cas9 – which will cut the unrequired gene shown by the guide RNA. Once it is cut, the cell itself repairs the DNA. Or, scientists can place another piece of DNA there with a required function.

WHY IS CRISPR SO USEFUL?
It is a cheap, quick and easy way of editing genes. Many diseases are caused by a single defective gene, and they can in theory be cured by deleting or changing a single gene. Examples are sickle cell disease, where blood cells cannot carry enough oxygen; cystic fibrosis, where the defective gene causes build-up of mucus — mostly — in the lungs and makes it difficult to breathe; and Huntington’s disease, a degenerative disease of the brain.

WHY IS IT CONTROVERSIAL?
No one has really found a fool-proof method of editing specific genes. Recent studies have shown that CRISPR is not as precise as scientists had once thought. For example, scientists do think that a patient with edited genes stands a higher risk of getting cancer in his/her lifetime. Editing in embryos can pass on harmful changes to the next generation. Which is why scientists themselves have imposed a moratorium on gene editing in embryos.

WHY DOES THE SCIENTIFIC COMMUNITY CONDEMN THE WORK OF THE CHINESE SCIENTIST?
He Jainkui, a scientist working at the Southern University of Science and Technology in Shenzen, edited embryos to provide babies immunity from HIV. He did it because the father had HIV infection. Biologists believe that he cannot guarantee that the procedure is safe, and so he has exposed future generations to defects inadvertently carried out during editing. This is unethical because informed consent is not possible from a future generation. They also think that there were other methods of making sure that the children do not get HIV.