With this new spacer now available in the CRISPR loci, the next time a bacteria encounters the same attack it will recognize the foreign DNA and send out a secondary Cas protein to target, bind, and splice out the DNA thereby inactivating the invader, analogous to the way in which our bodies produce antibodies against repeated infections
It’s this ability to identify, isolate, and splice out a specific piece of DNA that has captured the imagination of scientists.
The CRISPR/Cas system can now be hijacked to accurately target genetic errors in DNA and remove them. Once removed repair systems kick in to fix the sequence. This can be done either of two ways: non-homologous end-joining which simply connects the two ends together or the more sophisticated homology-directed repair.
Applying this to Rett Syndrome we can use the following example. The most common mutation in MECP2 is the T158M where a cytosine to thymine
error at nucleotide base number 473 swaps a methionine amino acid for a threonine. One could envision using the CRISPR/Cas technology to introduce a cut at nucleotide base number 473, splice out the thymine and provide a cytosine base via a template. Cas enzymes and base repair templates would be delivered via gene therapy vectors.
So where does the technology currently stand to be able to achieve this? Inducing the break in DNA can now be achieved efficiently and effectively however the repair step using templates is not yet ready for prime time as efficiency rates (the number of cells that actually achieve repair) are still quite small. Before the technology can be considered for therapeutic applications it also needs to be shown that the CRISPR/Cas machinery only cuts the DNA at desired sites as additional “off target” breaks could be damaging.
The encouraging news is that progress with CRISPR/Cas technology is occurring at lightning speed with thousands of laboratories around the world working to improve the process. It is not difficult to imagine the immense possibilities for treating genetic disease. No wonder there is so much excitement with scientists themselves routinely referring to this new technology as revolutionary.