How Do Retinal Gene Therapies Work?

Retinal gene therapy is a treatment for a rare disease that causes retinal degeneration (dystrophy) due to inherited mutations in a gene known as RPE65. RPE65 encodes retinal pigment epithelial 65-kDa (RPE65), a protein that plays an essential role in the visual cycle. Retinal gene therapy delivers a healthy copy of RPE65 to the retinal cells.

Visual or retinoid cycle is the biological conversion of a light particle (photon) into an electrical signal by the retinal cells. The retina sends the electrical signal to the brain through the optic nerve, enabling vision. Mutations in the RPE65 gene can cause reduced levels or lack of RPE65 protein, leading to retinal dystrophy, progressive vision loss and ultimately, complete blindness.

Retinal gene therapy is a treatment in which a normal copy of the RPE65 gene is injected into the retinal cells. The RPE65 gene is delivered in an adeno-associated virus whose DNA is modified to carry the gene. The normal RPE65 copy enables the production of functional RPE65 protein and prevents vision loss.

In December 2017, the FDA approved retinal gene therapy for patients with confirmed biallelic (both maternal and paternal copies of the gene) RPE65 mutation-associated retinal dystrophy. The patients must also have viable retinal cells for the therapy to be administered.

Retinal gene therapy is an expensive treatment costing USD 850,000 for both eyes. RPE65 mutation-associated retinal dystrophy affects approximately 1000 to 2000 Americans.

Retinal gene therapy is a one-time treatment for patients with biallelic RPE65 mutation-associated retinal dystrophy, who have viable retinal cells. Retinal gene therapy is administered as a subretinal injection in one eye at a time, in close intervals but separated at least by six days. Oral corticosteroids are started three days before treatment of each eye, and tapered in 10 days.

Side effects of retinal gene therapy may include:

Ocular side effects

• Cataract
• Conjunctival hyperemia (dilation of blood vessels in the conjunctiva, the clear membrane over the whites of the eye and inner eyelid surfaces)
• Increased intraocular pressure (pressure inside the eye)
• Retinal tear
• Eye inflammation
• Corneal dellen (thinning of the corneal stroma, cornea’s supportive layer)
• Macular hole (hole in the macula, the central portion of the retina)
• Subretinal deposits
• Maculopathy (wrinkling on the macular surface)
• Eye irritation
• Eye pain
• Foveal thinning and loss of function (fovea is a tiny pit in the center of macula)
• Endophthalmitis (inflammation of the intraocular cavities)
• Foveal dehiscence (separation of fovea from the retina)
• Retinal hemorrhage

Systemic side effects

• Mouth ulceration
• Inflammation of the mouth and lips (stomatitis)

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand name of FDA-approved retinal gene therapy drug is:

• Voretigene neparvovec-rzyl (Luxturna)