Genetic modification may be a contentious topic, but scientists have been doing it successfully for years. Researchers can precisely chop and change genes in microbes, human cells, plants and even animal embryos. There is no denying that it’s an incredibly important technique, but at what stage should we draw the line on what is ethically acceptable? This is an ongoing debate among both scientists and the public, but arguments were recently reignited by rumors that Chinese scientists are modifying the genomes of human embryos. Of course, the whispers have now turned out to be true, and you can read about this landmark study in the journal Protein & Cell.

There are several reasons that editing human embryos is such a hotly debated topic. First of all, the individual obviously cannot consent to the procedure, but if the embryo or subsequent human would not survive without it, then arguably this is not an issue. Flags have also been raised because of possible unintended consequences that may not immediately be apparent. Furthermore, as Nature points out, since the changes would be passed on to offspring, once again it is difficult to predict what effects they may have on future generations.

But those in favor of the technique argue that it could offer a way to eliminate genetic diseases, like cystic fibrosis, Tay-Sachs and Huntington’s disease. With this idea in mind, researchers from Sun Yat-sen University in Guangzhou began investigating the possibility of altering the faulty gene responsible for a potentially fatal inherited blood disorder called beta thalassemia, in which sufferers don’t produce enough hemoglobin, the molecule which carries oxygen round the body.

To do this, the researchers first collected donor embryos from a fertility clinic that were non-viable, i.e. would not have survived to term. Although these were intended for use in IVF, they ended up with too many chromosomes because they were fertilized by multiple sperm, so they couldn’t have resulted in a live birth.

They then used a well-established gene-editing technique called CRISPR/Cas9, which is a complex of bacterially-derived enzymes that behave like a pair of molecular scissors, specifically binding to target stretches of DNA and snipping them out. After injecting these enzymes into 86 embryos, the researchers replaced the gaps with healthy genes and monitored their development.

Some of the embryos did not continue to develop, but the team selected 54 of the survivors and then tested them further to see if the editing had been successful. They found that the faulty gene, HBB, had only been removed in 28 of the embryos, and only a few of these contained the healthy replacement gene they tried to insert. Furthermore, the enzymes also added in numerous mutations, suggesting that the system is acting in an imprecise manner and is thus far too immature to be used to eradicate diseases at this stage. But the researchers are not deterred by this setback, and plan to continue their work in order to improve the technique.

[Via Protein & Cell and Nature]