August 08, 2005.
University of Florida scientists have used a healthy human gene to prevent blindness in mice with a form of an incurable eye disease that strikes one in 5,000 boys in the United States.
Retinoschisis is a rare genetic disorder that is passed from mothers, who retain their sight, to their sons. In boys who inherit the condition, the retina is split into two layers. Central vision is almost always affected, and in about half the cases, some peripheral or side vision is also lost.
Patients have been diagnosed as early as 3 months, but most are identified when they are over the age of 5. Often the first sign of trouble comes when a youngster fails to pass his school vision screening test.
"Currently there is no treatment," said William Hauswirth, UF's Rybaczki-Bullard professor of ophthalmic molecular genetics. "These children lose their sight gradually, often with devastating results."
Writing in the August issue of Molecular Therapy, scientists from the UF Genetics Institute describe how they successfully used gene therapy in mice to treat retinoschisis.
Researchers injected a healthy version of the human RS1 gene to the sub-retinal space of the right eyes of 15-day-old male mice, which, like boys with the disease, didn't have the healthy gene to maintain the retina.
Retinoschisin, or RS1, is a protein which acts like glue to connect the layers of the retina. Without it, the layers separate and tiny cysts form.
Hauswirth said that in terms of disease development, the condition in the treated mice was roughly equivalent to retinoschisis in a 10-year-old boy.
Six months later, researchers looked at the interior of the eyes with a laser ophthalmoscope and found cyst formation was clearly evident in the untreated eyes, but the treated eyes appeared healthy.
The eye's photoreceptor cells — the rods and cones that help the brain process light and color — were spared from the disease and the connections between the layers of the retinas were intact.
The treatment has promising implications for other genetic eye diseases that involve the eye's ability to process light, Hauswirth explained.
Among them is retinitis pigmentosa, which affects about 200,000 people in the United States and is one of the most common inherited causes of blindness in people between the ages of 20 and 60.
"We've been very successful in curing a disease in mice that has a direct copy in humans," said Hauswirth, who, in conjunction with UF, has interest in a biotechnology company that may seek to market some of the research technology.
Hauswirth said results from the animal studies were as good as could be hoped for, and bode well for human trials within a five-year time frame.
"It may take two to five years before we try this in human patients because of the need for safety studies, but we feel based on success so far, we will be able to provide formal evidence for safety that will allow us to get treatment into the clinic."
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