Gene therapy restores sight to mice

A team of University of Florida researchers has restored sight to mice with hereditary blindness by using a harmless virus to deliver therapuetic genes. In a paper published in Nature Medicine, the scientists describe how their research proved it was possible to target and rescue cone cells, the cells vital for visual sharpness and colour vision in people.

The team studied mice with achromatopsia, a hereditary disease that affects about 1 in 30,000 Americans, and that results in complete colour blindness and poor central vision. The mice were then given two months of gene therapy in the form of an injection into the subretinal space, followed by tests to measure the electrical activity in the retinas. The researchers found that 19 out of 21 treated eyes responded to the therapy, and 17 of the 19 had electrical recordings from their retinas on a par with those taken from normal sighted mice.

The tests used on the mice were analogous to that of a human eyesight test, with the mice surrounded by computer monitors that stimulated the experience of being inside a moving drum that had vertical stripes on the walls. Sighted mice would naturally move their heads in the same direction as the stripes, and by reducing the size of the stripes, scientists could determine how sharply the mice could see. Lead researcher John Alexander, of University of Florida, said that 'what makes this test so fantastic is that it involves an animal's natural response, and the results tell us that the animals' brains are involved in the process, that the are actually seeing something'.

The discovery that cone cells could be successfully targeted with gene therapy has huge implications for all diseases that result in blindness, according to William Hauswirth, the Rybaczki-Bullard professor of ophthalmic molecular genetics in the College of Medicine and member of the University of Florida Genetics Institute. He continued, 'even in two very common types of blindness, age-related macular degeneration and diabetic retinopathy, if you can target cones you might be able to rescue that vision'.

Richard Weleber, professor of molecular and medical genetics at Oregon Health and Sciences University, who was not involved in the research, agreed with Professor Hauswirth. He said that the study 'validates the concept that it is possible to deliver a gene therapy targeting the cone system, and that is incredibly important for a number of degenerative diseases'.