When Can Gene Therapy Treat Inherited Blindness Longterm?

Genes themselves are a relatively new discovery, found only about a century ago. Gene therapy, a medical procedure that alters genes to address disease, is in its first 30 years. The subject created a lot of chatter in the medical world about the many diseases it could potentially be used to treat. Because genes are the building blocks of our make up, the ability to tinker with them provides a huge step in our ability to address a large category of rare disease, many of which are often rooted in genetic mutations.

The Previous Research

As reported in Science Daily in source material provided by University of Pennsylvania, two decades ago, scientists discovered the first gene therapy that can be used to treat an inherited, genetic disease: Leber congenital amaurosis, inherited blindness. The treatment option has become available after a trial successfully fixed the vision of a Briad dog with Leber congenital amaurosis, a rare inherited vision disorder with a RPE65 mutation. In 2017 it became the first FDA approved gene therapy to address a rare inherited disease. The new gene therapy has successfully restored the subjects vision, a feat that had never before been possible. However, they had not previously been able to observe the long term results. Now researchers have looked into the next step to ask under what conditions will the vision remain restored, and when does it continue to break down to as it had been before. 
 

What is Leber Congenital Amaurosis?

Leber congenital amaurosis is an inherited eye disorder caused by genes that severely affects vision due to an issue with the retina. The impairment is usually steady, though it can worsen and cause the eyes to become sunken down. It occasionally affects hearing and intellectual development as well.

The New Research

Now, new research out of the University of Pennsylvania dug deeper into under what conditions the vision improved and when the therapy resulted in sustained, longterm recovery. They had previously found that there is a relationship between how well the vision recovered and the degree to which the retina had already degenerated. From this, they wanted to see at what point in the progression of the disease would the treatment have long lasting effects in stopping the disease.
They used dogs again to test the effectiveness of the vision recovery in correlation to the degree at which the photoreceptor cells had already degenerated. The disease affects humans in childhood, when they are often young and unlikely to receive the treatment. For this reason, they tested dogs that had further degeneration because this is more representative of the people who would be receiving the treatment.
They found that the canines that still had 63% of their photoreceptor cells, though non-functional, were able to recover and it seems permanently. Alternatively, the dogs that had less than 63% of the cells remaining, while temporarily also achieving vision, eventually became blinded again and had the disease progress.
These results have both good and bad news. On the one hand, the ability to recover from this disease longterm is an incredible new finding, and shows the potential of gene therapy for the future. Any additional information on when it is effective is useful for knowing how to correctly use the gene therapy. However, because this particular disease effects humans very young, often patients are already past this degree of degeneration by the time the treatment would occur, meaning for many, the treatment will not be effective for life.
For researchers, the next quest is to search for a secondary solution to be paired with the gene therapy to see what may stop the cells from continuing to die after the gene therapy. They also unexpectedly found that the entire retina was strengthened by the therapy, not just the part addressed by the therapy. This means perhaps other diseases could benefit from the same treatment. This too, is promising.

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