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Gene editing technique improves vision in rats with inherited blindness

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A Cedars-Sinai study has revealed that a research team at the Cedars-Sinai Board of Governors Regenerative Medicine Institute has discovered a new technique that has the potential to treat inherited diseases by removing genetic defects has been shown for the first time to hinder retinal degeneration in rats with a type of inherited blindness.

The focus of the researchers was on inherited retinitis pigmentosa – a degenerative eye disease with no known cure that can lead to blindness.  A technique called CRISPR/Cas9 was used by the researchers to remove a genetic mutation that causes the blindness disease.  The technique CRISPR/Cas9 (CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeat, the type of DNA sequences involved in this process) is adapted from a strategy used by bacteria to fight invading viruses. The study was carried out in mice, however the finding are significant as they have potential implication sin humans as well. The details of the study findings were published recently in the journal Molecular Therapy.

Shaomei Wang, MD, PhD, a research scientist in the institute’s Eye Program and associate professor of Biomedical Sciences and the study's senior author remarked that their data show that with further development, it may be possible to use this gene-editing technique to treat inherited retinitis pigmentosa in patients.

As per the National Institutes of Health, retinitis pigmentosa is a class of diseases characterized by night blindness in the early stages, atrophy and pigment changes in the retina, constriction of the visual field and eventual blindness. It affects about 1 in 4,000 people in the U.S. and Europe and is one of the most common inherited diseases of the retina.

The technique – CRISPR/Cas9 has been in use by genetic researchers for less than five years and in this time, it has transformed the science of genome editing by making the process easier, more dependable and less expensive.

Bacteria are capable of disabling invading virus by deploying a unique system. Inspired from this system the researchers adapted the technique used in the study. The bacteria first copy part of the invader’s genetic code into a special sequence of ribonucleic acid (RNA), which acts a messenger to carry out the code’s instructions. When the virus returns, the RNA binds to a protein called Cas9, and guides it to the matching gene in the virus, where the protein disables the gene.

The researchers modified the system and programed Cas9 to turn selected genes on or off, or rewrite the genetic code. They designed the CRISPR/Cas9 system to remove a mutated gene that causes photoreceptor cell loss in the eye. This system was injected into young laboratory rat's model with a type of inherited retinitis pigmentosa known as autosomal dominant, which involves this mutated gene. It was seen that even after a single injection, the rats were able to see better compared with controls, as measured by optomotor reflex, which involves turning the head in response to moving stripes of varying degrees of brightness.

Improvement in the effectiveness and consistency of these results can be done by modifying elements of the CRISPR/Cas9 system and using new viral delivery techniques remarked Clive Svendsen, PhD, a co-author on the study. He is also of the opinion that after more research a reliable genome editing system can be developed which may provide a means to correct a wide range of inherited diseases in patients.

Svendsen who is also a director of the Board of Governors Regenerative Medicine Institute and the Kerry and Simone Vickar Family Foundation Distinguished Chair in Regenerative Medicine remarked that it is the first time CRISPR/Cas9 gene editing has been used to prevent vision loss in a living animal. It is a truly remarkable result and paves the way for more exciting studies and translation to the clinic in the future.