A particular case of gene therapy is based on gene editing, a recent technology that intervenes in a precise manner to find and correct genetic errors in DNA, even at a single-letter level.
Genetic editing is viewed as very promising for the gene therapy of the future, because it could enable faulty genes to be corrected without providing a healthy copy externally, and simultaneous action on the genome at several points, therefore also working on conditions caused by mutations in several genes.
Gene editing was already being discussed at the beginning of this century, when the most popular techniques were zinc-finger nucleases and TALENs, which could target specific genomes but required long process times.
The real revolution in this field came in 2012 with the discovery of the Crispr-Cas9 system, which is naturally present in numerous bacteria and is able to modify any type of plant or animal cell, human cells included, even at a single-letter level. Above all, this is a 'programmable' system that does not require everything to be redefined from the start to target a new gene, facilitating a considerable reduction in costs as a result, and accelerating research. Scientists from all over the world soon started to study its potential treatment applications in numerous areas, including rare genetic conditions (Duchenne muscular dystrophy, thalassemia, haemophilia B, X-SCID, cystic fibrosis), tumours, neurological conditions such as Alzheimer's and Parkinson's, and infectious diseases such as AIDS. As in the case with gene therapy, in vivo and ex vivo techniques can be used with CRISPR.