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New Gene Therapy Cures Blindness

October 21, 2017

Gene Therapy Cures Leber's Congenital Amaurosis Retinitis PigmentosaAn FDA advisory panel recommends approval for Luxturna, a novel gene therapy for the treatment of two inherited retinal diseases which cause blindness.  Both Leber's congenital amaurosis and retinitis pigmentosa 20 are rare types of retinal blindness caused by a defective RPE65 gene.

The FDA will not officially consider approval of Luxturna until January 2018.

Spark Therapeutics manufactures voretigene neparvovec (the generic name for Luxturna).  The drug will be administered as a single injection to each eye, exposing the retina to the sight saving drug.

Mutant Gene Produces Defective Protein

Genes make proteins.

Normally, the RPE65 gene produces a protein which integral to a functioning and normal vision cycle that occurs in the rods and cones of the retina.  The vision cycle is responsible for converting light into electrical signals which are sent to the brain.  The brain interprets these electrical signals as "vision."

Mutant RPE65 genes produce mutated proteins.  These defective proteins prevent the natural process of the vision cycle.  Retinal cells, without the necessary RPE65 protein, are unable to translate light into electrical signals.

Patients with Leber's congenital amaurosis (LCA) and retinitis pigmentosa 20 have defects in RPE65.  There are many types of retinitis pigmentosa, but only retinitis pigmentosa 20 is treated by Luxurna.

Gene Therapy Allows Normal Protein

Luxturna will be administered via intraocular injection and will lead to insertion of functional (aka "normal") DNA into the retinal cells, thus allowing retinal cells to produce a normal protein product.

The normal protein now allows a normal vision cycle to occur, that is, the retinal cells can return to normal function by sending electrical signals to the brain.

Priority Review

Neither LCA nor retinitis pigmentosa 20 presently have a treatment or cure.  Both lead to progressive blindness.

Luxturna has been given "priority review" by the FDA.  Drugs under "priority review" can be fast tracked through the approval process as these drugs are highly likely to have a great impact on the treatment of disease.

As a measure of vision improvement, patients involved in the trials were rated on their ability to navigate through a maze under varying lighting conditions (multi-luminance mobility testing - MLMT) .  The maze was reconfigured to prevent memorization as light levels were changed.

Most patients still showed an improvement in "MLMT" and maintained that improvement for over a year.  Improvements have been maintained for 2-4 years in many of the patients receiving treatment.

Inherited Retinal Diseases

Inherited retinal diseases are rare and can cause blindness.  There are more than 220 different genes which cause blindness from inherited retinal diseases.

Leber's congenital amaurosis and retinitis pigmentosa 20 are just two examples of inherited retinal diseases caused by defective RPE65 gene.

Note:  This article is for informational purposes only.  The medicine is not available to the public and is not FDA approved.  FDA approval is pending.

Shilpa Rose, M.D.
Vision Correction & Dry Eye Specialist

Mark Whitten, M.D.
Vision Correction Surgeon
LASIK, Cataract & Raindrop

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