Gene therapy offers hope for a common cause of mitochondrial blindness

A new approach to the treatment of patients with Leber Hereditary Optic Neuropathy (LHON) has shown encouraging results in a clinical study at Moorfields Eye Hospital.

The study involved injecting a gene therapy vector into one eye of patients with LHON, to explore if it improves vision in both eyes.

The study, published in the journal Science Translational Medicine, saw researchers inject a viral vector containing modified cDNA into the back of one eye of 37 patients who had suffered vision loss from LHON for 6 to 12 months. Their other eye received a placebo sham injection. The therapeutic approach, involving allotopic gene expression and mitochondrial targeting, was optimised for LHON by the Institut de la Vision in Paris, France, and licensed to GenSight Biologics.

78% of treated patients in the trial experienced visual improvement in both eyes following the same trajectory over 2 years of follow-up. The study suggests that the improvement in vision in untreated eyes could be due to the transfer of viral vector DNA from the injected eye into the untreated eye. Importantly, patients reported that the treatment had a positive impact on their quality of life and well-being. Subject to further trials, the treatment could help thousands of people affected with LHON across the world to regain and retain more of their sight.

LHON affects a specific type of retinal cells, known as retinal ganglion cells, causing optic nerve degeneration and rapidly worsening vision in both eyes. Within a few weeks of disease onset, the vision of most people affected deteriorates to levels at which they are considered legally blind. The majority of patients carry the m.11778G>A mutation in the MT-ND4 gene. Treatment options for this condition remain limited.

Dr Patrick Yu-Wai-Man, consultant ophthalmologist at Moorfields Eye Hospital and Honorary Associate Professor at the UCL Institute of Ophthalmology, said: “By replacing the defective gene, this treatment rescues the retinal cells from the destructive effects of the mutation, preserving function and improving the patient’s visual outcome. This has been life-changing for some patients.”

“Saving sight with gene therapy is now a reality. The treatment has been shown to be safe and we are currently exploring the optimal way to deliver this new treatment.”