What are genome editing and CRISPR-Cas9?
Genome editing (also called gene editing) is a set of technologies that enable scientists to change the genetic code in the living cells of an organism. They make it possible to make specific changes to a particular location in the genome in a controlled way. One of the approaches is known as CRISPR-Cas9.
The “Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein 9”, or CRISPR-Cas9 for short, was discovered by a team of CRISPR pioneers led by biochemists Emmanuelle Charpentier from France and Jennifer Doudna from the US. CRISPR-Cas9 is a genome editing system that occurs naturally in bacteria, which use it to protect themselves against viruses.
CRISPR-Cas9 applications in humans
An adapted CRISPR-Cas9 system can act also on the genome of higher organisms, including humans. Researchers generate a small piece of ribonucleic acid (RNA) with a short guiding sequence that attaches to a specific target sequence of DNA in a genome. The Cas9 enzyme is also bound to the RNA. As in bacteria, modified RNA is used to recognize a target DNA sequence, and the Cas9 enzyme cuts the deoxyribonucleic acid (DNA) at the intended location. Enzymes other than Cas9 may also be used for this process. After the target DNA is cut out, researchers make use of the DNA repair machinery of the cell in order to introduce changes in the DNA by replacing an existing segment with the desired DNA sequence.
Most of the applications in humans are limited to somatic cells, which are cells other than egg and sperm cells. Although changes in the germline would be passed on to the next generation, germline modifications are forbidden in most countries.
Relevance for science
This approach creates a pathway to cures for unwanted changes in human genes. The approach is being explored in a wide variety of diseases, in particular previously untreatable single-gene disorders (monogenic diseases), such as Leber congenital amaurosis 10, which causes blindness.