Gene editing is used to make targeted genetic modifications in all types of cells, using specific molecular scissors, to repair genes that cause diseases.
We refer to gene editing when we are looking to correct, replace, insert or remove one or more pieces of DNA of a genome. To do this, researchers use molecular scissors – known as nucleases – which have the ability to cut the DNA double helix at a chosen point.
These cuts trigger DNA repair mechanisms that will enable the desired modification to take place.
CRISPR-Cas9 and other molecular scissors
There are four main families of nucleases, or molecular scissors. Today the best known are the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas9 scissors, which recently won a Nobel Prize.
The CRISPR/Cas9 system lets you cut DNA at a precise point of the genome, in any cell. A “guide RNA” is created, which targets a particular DNA sequence, associated with the Cas9 enzyme, which cuts the DNA.
Once the DNA sequence has been cut, the cell repair systems will re-bind the ends of the two DNA pieces created by cutting. Then, depending on the protocol, the targeted gene can then be corrected, repaired or deactivated.
Its simplicity of use has enabled this technique to be very rapidly deployed throughout the scientific community.
Three other families of molecular scissors are also used: meganucleases, zinc-finger nucleases (or ZFNs) and transcription activator-like effector nucleases (or TALEN).
More recently, “BASE editing”, an adaptation of the CRISPR system, has been developed. This precise editing method involves changing single nucleotides. It has the advantage of not requiring DNA strands to be broken, which avoids the insertions and deletions associated with breakage of DNA strands. Base editing is suitable only for precise editing but proves very effective for this type of editing.
First applications in neuromuscular diseases and other rare diseases
In terms of neuromuscular diseases, several studies conducted in a laboratory using the CRISPR/Cas9 system have been published, including by researchers from Genethon in Duchenne muscular dystrophy and in Steinert disease, as well as in diseases of the blood (thalassemia) and some metabolic diseases.
The teams at Genethon are also working on developing safe and effective approaches for gene editing to alter hematopoietic stem cells ex vivo, for the treatment of rare genetic diseases.
More research must be done before application in humans, in particular to ensure that this approach is safe to use.