The experiment with human embryos was dreaded, yet widely anticipated. Scientists somewhere, researchers said, were trying to edit genes with a technique that would permanently alter the DNA of every cell so any changes would be passed on from generation to generation.
Those concerns drove leading researchers to issue urgent calls in major scientific journals last month to halt such work on human embryos, at least until it could be proved safe and until society decided if it was ethical.
Now, scientists in China report that they tried it.
The experiment failed, in precisely the ways that had been feared.
The Chinese researchers did not plan to produce a baby — they used defective human embryos — but did hope to end up with an embryo with a precisely altered gene in every cell but no other inadvertent DNA damage. None of the 85 human embryos they injected fulfilled those criteria. In almost every case, either the embryo died or the gene was not altered. Even the four embryos in which the targeted gene was edited had problems. Some of the embryo cells overrode the editing, resulting in embryos that were genetic mosaics. And speckled over their DNA was a sort of collateral damage — DNA mutations caused by the editing attempt.
...
But some researchers worry that this paper is just an initial sally and that attempts will continue with clinical applications in mind. They fear the result will be the birth of babies whose every cell has been altered by scientists in a rush to be first. This could happen well before researchers know enough about the consequences of editing genes, before they know how to edit safely and before society can debate if such procedures are even acceptable.
Breaking the Chain
A complex immune system found in bacteria is already proving useful in editing DNA and may lead to future therapies.
Snippet
RNA
Short, repeating
block of DNA
Enzyme
Cut
Repair
Edit
Cut
Spacer
RNA
Matching
sequence
of DNA
RNA made
from one
spacer
Disabled
gene
Double helix
opened
STORAGE Researchers in the 1980s noticed that bacteria had small blocks of palindromic DNA repeated many times, with nonrepeated spacers of DNA stored in between. This pattern is a sophisticated immune system known by the acronym Crispr, for “clustered regularly interspaced short palindromic repeats.”
RECOGNITION These spacers match pieces of DNA from viral invaders that bacteria or their ancestors have faced before. When needed, the DNA contained in the spacer is converted to RNA. An enzyme and a second piece of RNA latch on, forming a structure that will bind to strands of DNA that match the spacer’s sequence.
CUTTING When a matching strand of DNA is found, the enzyme opens the double helix and cuts both sides. The double cut breaks the strand and disables the viral DNA. If a bacterium survives an attack by an unfamiliar virus, it will make and store a new spacer, which can be inherited by future generations.
EDITING Researchers are learning how to use synthetic RNA sequences to control the cutting of any piece of DNA they choose. The cell will repair the cut, but an imperfect repair may disable the gene. Or a snippet of different DNA can be inserted to fill the gap, effectively editing the DNA sequence.
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