A small study published in Nature Methods has found that the CRISPR-Cas9 gene editing technique may insert hundreds of unexpected mutations into the genome.
“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,” says co-author Stephen Tsang, MD, PhD, associate professor of ophthalmology at Columbia University Medical Center.
Dr. Tsang and his colleagues from the University of Iowa and Stanford University sequenced the entire genome of 2 mice that had previously undergone CRISPR gene editing to fix a defect for retinitis pigmentosa (RP). While CRISPR successfully corrected the defected RP gene, it also induced more than 1,500 single-nucleotide mutations and more than 100 larger deletions and insertions, a significantly higher mutation rate than what was found in a single wildtype control mouse (100 single-nucleotide variants, and 4 larger deletions).
None of these DNA mutations were predicted by the computer algorithms that are widely used by researchers to look for off-target effects.
“Researchers who aren’t using whole genome sequencing to find off-target effects may be missing potentially important mutations,” Dr. Tsang said. “Even a single nucleotide change can have a huge impact.”
The researchers didn’t notice anything obviously wrong with their animals and remain “upbeat” about CRISPR.
“We’re physicians, and we know that every new therapy has some potential side effects—but we need to be aware of what they are,” said corresponding author Vinit Mahajan, MD, PhD, associate professor of ophthalmology at Stanford University, adding that the findings were based on a very small number of animals.
Meanwhile, the first clinical trial to study CRISPR-Cas9 in humans has begun in China, with plans to treat 10 patients with metastatic non-small-cell lung cancer. The NIH also recently approved a study led by the University of Pennsylvania to use CRISPR in patients with several types of cancer, including melanoma and myeloma. Aside from its applications in oncology and RP, CRISPR-Cas9 is also being investigated in corneal diseases.