dna editing CRISPR human embryos Fredrik Lanner of the Karolinska Institute in Stockholm and his student, Alvaro Plaza Reyes, examine a magnified image of an human embryo they used to attempt to create genetically modified healthy human embryos. Rob Stein/NPR

A scientist in Sweden has begun editing the genes of healthy human embryos for the first time in known history, according to an exclusive report published by NPR.

NPR's Rob Stein watched biologist Fredrik Lanner of the Karolinska Institute and a graduate student thaw five embryos that had been donated for research before having the student inject the embryos with the genome editing tool CRISPR/Cas-9, which can essentially find and cut out or replace sections of DNA to activate or even replace specific genes.

CRISPR basically works like "a molecular scalpel for genomes," as Jennifer Doudna, a biologist frequently credited as one of the co-discoverers of this revolutionary genetic editing system (and one of the first to use it), previously described it to me. "All the technologies in the past were sort of like sledgehammers ... This just gives scientists the capability do something that is incredibly powerful."

Lanner's plan is to use the tool to study early embryonic development, the process by which embryonic cells first begin to divide as an embryo grows during its first days. None of the embryos will be allowed to develop for longer than two weeks.

Still, editing healthy embryos is a big step, as it's the same technology that could permanently alter the human genome. This technology could allow us to eliminate deadly genetic diseases from people before they are born (and remove these genes from the human genetic library, eventually) but could also in theory be used to engineer desired traits into children.

Since Lanner does not plan to implant the embryo into a person, none of that is an issue here. Still, NPR notes that some are concerned that if he shows it's possible to accurately edit human genes in healthy embryos (something we don't know yet, and something that this research could reveal), people could use that knowledge to actually edit and implant embryos in the future. That would make genetically edited human babies possible scientifically, if not legally.

dna editing CRISPR Fredrik Lanner of the Karolinska Institute in Stockholm and his student, Alvaro Plaza Reyes, fill a bucket with liquid nitrogen so they can transfer early human embryos to their lab for experiments aimed at creating genetically modified healthy human embryos. Rob Stein/NPR

In states that don't regulate embryo research in the US, the experiments that Lanner is doing would be legal, since there are no plans to implant edited embryos into people. That sort of procedure — one that could result in an actual birth — would need to be approved by the FDA, and the current budget bill does not allow the agency to accept a proposal to do so.

The National Academies gene editing committee expects to publish a report with specific recommendations on governance of gene editing research for the US government in early 2017.

While Lanner is the first to do this research in healthy human embryos, other researchers have similar plans in the UK. Researchers in China have also already published data on their efforts to edit non-viable human embryos.

You can read NPR's report on the Shots blog or listen to the Morning Edition segment about the experiment below.

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