Fix one gene from a pair

Stephen H. Tsang and his colleagues from Columbia University have developed a tool based on CRISPR technology for the treatment of retinitis pigmentosa, a degenerative disease of the retina that leads to irreversible vision loss. The method was successfully tested on mice.

Retinitis pigmentosa is a hereditary disease that begins in childhood with a gradual loss of peripheral vision. It progresses, capturing larger and larger areas of the retina, and on average leads to blindness by the age of 40. There is no therapy that would cure, stop or at least slow down the course of the disease. Retinitis develops as a result of a defect in one of the genes responsible for the function of the retina. The worldwide prevalence is 1:4000.

Patients with autosomal recessive disorders inherit two copies of the mutant gene. In this case, it is sufficient to replace the defective gene with gene therapy methods. Currently, there are six pharmaceutical companies engaged in gene therapy for the recessive form of retinitis pigmentosa; none of them is developing a method for treating the dominant form of the disease, in which only one of a pair of genes has a defect. In this case, the mutant allele suppresses the normal work, and therefore the disease or its signs are more pronounced. This complicates the use of CRISPR technology, since the Cas9 enzyme must cut off only the defective gene, and its healthy pair must be preserved.

Tsang and colleagues have developed an ablate-and-replace technique that allows you to edit several mutations in a defective gene at once without affecting its healthy copy. This is especially important in diseases that can develop with several types of mutations. Thus, retinitis pigmentosa is caused by any of 150 mutations in the gene responsible for the synthesis of the visual pigment rhodopsin.

The classical CRISPR editing system uses a single guide RNA that points the Cas9 enzyme to the target gene that needs to be deleted. The authors of the study strengthened the system of another guide RNA, which increased the effectiveness of therapy from 30 to 90%. Adeno-associated viral vectors were used to deliver a healthy gene to cells.

Another advantage of the new technology is the possibility of its application in non-dividing cells, such as in the retina, brain, heart. In the classic version, CRISPR mainly targets the genes of dividing cells.

The method was tested on mice. To assess the effectiveness of the intervention, electroretinography was used – recording the electrical potentials of retinal cells. The process of degeneration in the eyes that underwent "gene surgery" slowed down.

As the authors write, human trials will be conducted in three years. With a positive result, it will be possible to treat not only retinitis pigmentosa, but also other diseases with an autosomal dominant type of inheritance.

Article by Y.-T. Tsai et al. Clustered Regularly Interspaced Short Palindromic Repeats-Based Genome Surgery for the Treatment of Autosomal Dominant Retinitis Pigmentosa is published in the journal Ophthalmology.

Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of the American Academy of Ophthalmology: Genome Surgery for Eye Disease Moves Closer to Reality.