Gene-altering technology aimed at preventing deadly diseases such as cancer from entering the DNA chain may not be as accurate as first thought, with a new study suggesting CRISPR-Cas9 editing risks accidental mutations.

Heralded as a way to change sections of DNA code, for example replacing damaged cells, the CRISPR-Cas9 process has been the subject of a number of experiments involving mice or fish.

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In 2014, the process, which uses a Cas9 enzyme and ribonucleic acid to slice and bind sections of DNA, was shown capable of performing “targeted” gene deletion by researchers from the Fudan University Shanghai Cancer Center.

#InTheNews: CRISPR. What is it and how does it work? We answer 9 of your burning questions here https://t.co/GiZi3bVe5Q (2/2) pic.twitter.com/d7d8F0HysX — Cancer Research UK (@CR_UK) May 30, 2017

Their work raised the prospect that parts of cells compromised by tumours could be deleted and replaced. The first treatment based on that research took place on a patient with lung cancer in China last year, according to Nature.

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However, a new study raises questions over the safety of the medical process following results of altering genomes in mice. While researchers observed that the genes causing blindness had been repaired, some 1,500 accidental mutations were also found in the test subjects.

Consequences of DNA mutations range from the relatively minor to the extreme, like death.

“We feel it’s critical that the scientific community consider the potential hazards of all off-target mutations caused by CRISPR, including single nucleotide mutations and mutations in non-coding regions of the genome,” said co-author of the study, Stephen Tsang of the Columbia University Medical Center, according to Phys.org.

University of Iowa professor, Alexander Bussak, who was also involved in the study, says the alterations caused by CRISPR-Cas9 must be better scrutinised.

“These predictive algorithms seem to do a good job when CRISPR is performed in cells or tissues in a dish, but whole genome sequencing has not been employed to look for all off-target effects in living animals,” Bussak said.