Gene therapy for rare cause of blindness shows promise …

An experimental gene therapy has improved eyesight in patients with a rare, inherited eye disease that can cause blindness, according to its developer, Spark Therapeutics Inc.

The company said it plans to apply to the Food and Drug Administration next year for approval to market the treatment. If accepted, this would be the first gene therapy to win approval in the United States.

"We saw substantial restoration of vision in patients who were progressing toward complete blindness," Dr. Albert M. Maguire, principal investigator in the trial and professor of ophthalmology at the Perelman School of Medicine of the University of Pennsylvania, said in a statement.

There were no serious adverse effects associated with the treatment, the company reported.

The news comes about a week after a hospital in the U.K. announced it had performed a pioneering human embryonic stem cell operation on a patient with the aim of curing a different, more common cause of blindness known as macular degeneration.

Gene therapy involves injecting genetic material into a person's cells to treat or prevent a disease. While research in this area has been going on since the late 1990's, no such treatment has been approved in the U.S. The European Commission approved the Western world's first gene therapy in 2012 for an extremely rare disease in patients with a particular enzyme deficiency.

Spark's treatment, called SPK-RPE65, is targeted at mutations in a gene called RPE65, which plays a role in maintaining the health of the photoreceptors in the eye. The condition can progress to complete blindness.

The Phase III trial included a total of 31 participants, 21 of whom were given the treatment and 10 of whom weren't. Researchers evaluated the participants at multiple points over the course of a year for their performance in navigating a mobility course under a variety of light levels. These levels ranged from the equivalent of a "moonless summer night" to a brightly lit office, according to the statement.

"The majority of the subjects given SPK-RPE65 derived the maximum possible benefit that we could measure on the primary visual function test, and this impressive effect was confirmed by a parallel improvement in retinal sensitivity," Maguire said. "If approved, SPK-RPE65 should have a positive, meaningful impact on the lives of patients with this debilitating condition."

But much still remains unknown at this time. Spark has not yet made the actual trial data public, and it is unclear what it will take for the FDA to approve the treatment. The company said it plans to present additional data from the trial in a series of scientific meetings in the coming months.

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