US scientists have used gene therapy to successfully treat mice with a rare genetic disorder that causes blindness, called retinoschisis. The researchers, based at the University of Florida Genetics Institute, say their method could eventually be used to treat a range of eye diseases in humans.
Retinoschisis causes the retina to split in the middle, leading to gradual sight loss in affected children. There is currently no cure for the disorder, which is usually first detected in boys between five and ten years of age. In healthy eyes, the cells of the retina usually make a protein called retinoschisin, which acts like glue to stick the layers of the retina together. But in children with retinoschisis, this protein is missing, so the layers separate and tiny cysts form, causing blindness.
In the latest study, the scientists used mice with symptoms of retinoschisis equivalent to those of a ten-year-old boy affected by the disease. They injected a healthy copy of the human RS1 gene- which makes the retinoschisin protein - into the right eyes of the mice. Six months later, the team used a laser opthalmoscope to look at the inside of the animals' eyes, and found that while cysts had appeared in the untreated eyes, the treated eyes appeared healthy. The light-detecting rod and cone cells were unaffected, and the layers of the retina were intact.
The researchers, who published their findings in the journal Molecular Therapy, say that the protein made by the therapeutic gene could move within the retina to its target sites, and that the beneficial changes appeared to be long-lasting. They say that it may now take two to five years to try out the treatment in human patients, because of the need for safety studies. The team also say the work has promising implications for other genetic eye diseases that affect the eye's ability to process light, such as retinitis pigmentosa.
Meanwhile, US researcher Katherine High predicts that a successful gene therapy treatment for the blood clotting disorder haemophilia could be available in five years time. 'It has taken approximately 5-8 years to move from a cure for haemophilia in mice to a cure in dogs', she said, adding that the studies carried out on dogs had identified problems that had to be solved before trying the approach in humans. Professor High presented the latest findings last week at a meeting held in Sydney, Australia.