How CRISPR is Being Used to Edit Human Genes to Cure Disease
Since the discovery and manipulation of the CRISPR-cas9 system it has been used for research development and clinical treatments.
Earlier this month the first in vivo experiment was performed on an individual born with a rare condition called Leber congenital amaurosis which causes blindness. Individuals with this condition have a mutation in the gene IMPDH1 which makes a protein necessary for the conversion of light to brain signals. By deleting the mutation in the IMPDH1 gene, doctors hope to allow for the production of the wildtype protein and allow individuals to see.
Previous treatments, such as gene therapy, have been unsuccessful because the replacement gene is too large to be carried and delivered by the disabled virus used in gene therapy. Using the CRISPR-cas9 system instead allows the genes found in the retinal cells to be directly edited rather than adding the functional gene.
The CRISPR-cas9 system was delivered to the patient using a hair width tube, and three droplets containing the CRISPR-cas9 genes were placed beneath the retina to access the photoreceptors.
Although the results of this surgery are still ongoing it is believed that this treatment could be a permanent cure for Leber congenital amaurosis. Using experiments in animal models researchers found that only one third of the cells need to be edited in order to restore vision.
The risks that this treatment could pose, like many applications of CRISPR, is the possibility of off-target deletions. The CRISPR system uses a guide RNA to target the appropriate gene however there is a possibility of off-target cuts if there is an error in the CRISPR system. To minimize this risk, the CRISPR-cas9 system used was tested in animal models and found they were able to edit one half of the photoreceptors to restore the wildtype gene. This was more than the estimated one third required to restore vision.
Not only could this treatment be used to cure blindness in similar disorders but this system could be further manipulated to actively edit genes in vivo for other diseases.
Charles Arnorld the chief scientific officer of Editas medicine describes the true impact that this treatment could have on the future of medicine.
“We believe that the ability to edit inside the body is going to open entire new areas of medicine and lead to a whole new class of therapies for diseases that are not treatable any other way”