US researchers made 40 embryos with eggs from healthy women and sperm from a man with a gene mutation that causes hereditary blindness. They then repaired the blindness-causing mutation using CRISPR/Cas9 genome editing, but instead of the mutation actually being corrected, the researchers found that about half of the embryos ended up missing large parts of the chromosome on which the gene was located, some even losing it entirely.
'If our results had been known two years ago, I doubt that anyone would have gone ahead with an attempt to use CRISPR to edit a gene in a human embryo in the clinic,' said lead author Dr Dieter Egli of Columbia University in New York.
The CRISPR genome editing approach has been praised for enabling researchers to make precise changes to the genome of cultured cells, living tissues, and animal embryos. Its use holds promise for treating disorders, and its discoverers won a Nobel Prize in chemistry last month (see BioNews 1067). The approach was also used in 2018 by now-imprisoned Chinese scientist Dr He Jiankui who controversially created the world's first genome-edited twin babies (see BioNews 1033).
Despite previous studies having shown CRISPR's ability to repair genetic defects in human embryos, Dr Egli warned that more extensive testing needs to be carried out to ensure other uncontrolled changes have not been made – like in this study.
'Our hope is that these cautionary findings should discourage premature clinical application of this important technology but can also guide responsible research to achieve its ultimate safe and effective use,' said Dr Egli.
The study was published in the journal Cell.