When Can Gene Therapy Treat Leber Congenital Amaurosis for Good?

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 a concept a few decades old. 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 is a huge step in our ability to address a large category of rare diseases, many of which are often rooted in genetic mutations.

The Previous Research

As reported in Science Daily from source material provided by University of Pennsylvania, two decades ago, scientists developed the first gene therapy that can be used to treat an inherited, genetic disease: Leber congenital amaurosis, an inherited condition that causes blindness. The treatment has become available after a trial successfully fixed the vision of a Briard 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 can successfully restored the subject’s vision, a feat that had never before been possible. However, researchers had not previously been able to observe the long term results. Now, researchers have begun asking new questions. Under what conditions will the vision remain restored? When does the condition continue to progress as it had before?

What is Leber Congenital Amaurosis?

Leber congenital amaurosis is an inherited eye disorder caused by genetic mutations that severely affect 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 digs deeper into the conditions during which vision improved and when the therapy results 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 that the treatment would have long lasting effects in stopping the disease. 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 and were able to recover see permanent benefit. However, the dogs that had less than 63% of the cells remaining eventually saw disease progression.
These results have both good and bad news. On the one hand, the ability to recover from this disease long term 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 at a young age, older patients are already past the threshold of degeneration used in the study by the time the treatment occurs. This means that 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 treatment. They also unexpectedly found that the entire retina was strengthened by the treatment. This means perhaps other diseases could benefit from the same treatment.

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