Much of the enthusiasm around gene-editing techniques, particularly the CRISPR-Cas9 technology, centers on the ability to insert or remove genes or to repair disease-causing mutations. A major concern of the CRISPR-Cas9 approach, in which the double-stranded DNA molecule is cut, is how the cell responds to that cut and how it is repaired. With some frequency, this technique leaves new mutations in its wake with uncertain side effects.

In a paper appearing in the journal Cell on December 7, scientists at the Salk Institute report a modified CRISPR-Cas9 technique that alters the activity, rather than the underlying sequence, of disease-associated genes. The researchers demonstrate that this technique can be used in mice to treat several different diseases.

"Cutting DNA opens the door to introducing new mutations," says senior author Juan Carlos Izpisua Belmonte of the Salk Institute for Biological Studies whose laboratory developed the new technique. "That is something that is going to stay with us with CRISPR or any other tool we develop that cuts DNA. It is a major bottleneck in the field of genetics -- the possibility that the cell, after the DNA is cut, may introduce harmful mistakes."