A genetic therapy offers a glimmer of hope for patients with a rare form of blindness.
In a clinical study conducted in Oxford University in the United Kingdom, the therapy restored vision in the patients for as long as four years, potentially benefiting not only those with the type of genetic blindness but also those afflicted by common causes of vision loss.
The technique involves injecting a working copy of the gene into the eye to help cells regenerate and to replace a key missing gene for choroideremia, a disorder affecting young men whose cells in the eyes used for light detection are dying due to a fault in the gene CHM.
Until today there is still no treatment for its sufferers, currently about one in 50,000 individuals in the UK. The patients slowly turn blind as the disease progresses and destroys photoreceptors in the retina.
The trial, where doctors examined the vision of six persons up to four years after they received gene therapy, is the first choroideremia procedure in the world. While designed to slow or stop loss of vision, two patients had significant vision improvement sustained for at least four years, although their untreated eye declined over the same period.
Three more patients maintained vision in their treated eye during the trial, with the sixth patient – who received a lower therapy dose – experiencing slow deterioration of vision in both eyes.
The team considers this the strongest proof so far of the potentially permanent benefits of gene therapy, which is also hoped to cure other forms of genetic blindness including retinitis pigmentosa and age-related macular degeneration.
“[N]ow we have unequivocal proof that [gene therapy] effects following a single injection of viral vector are sustained,” said lead investigator and professor Robert MacLaren. “Even sharpening up the little bit of central vision that these patients have can give them considerable independence.”
The key, MacLaren added, is correcting a faulty gene even before a disease sets in. In this particular case, they saw lasting benefits because the viral DNA was optimally designed and the viral vector delivered in the right spot using advanced surgery.
Bristol-based retired barrister Jonathan Wyatt, the first in the world to receive this gene therapy, still has impaired sight but doubled his level of vision in the treated left eye – a gain he has sustained for four years now.
Suffering vision issues since age 20, the 68-year-old patient could now read 44 letters in eye chart tests, which used to be just 23 letters before his operation. According to him, the improvement has made him more independent, particularly during train rides when he would likely be “tapping with a white stick” if it weren’t for the surgery.
The news was welcomed by UK charity RP Fighting Blindness, which funds groundbreaking medical research and assists people with genetic retinal dystrophies and related conditions.
“This is fabulous news. The advances made in genetic therapies are extremely encouraging . . . Our patient community is excited,” said chief executive Tina Houlihan in a report with The Guardian.
The findings are published in The New England Journal of Medicine.
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