After several years of setbacks, gene therapy is once again yielding promising results. One area in which it is proving its potential is in restoring vision to patients who have been losing it since birth.

Between 2008 and 2011 Jean Bennett, a neuroscientist at the University of Pennsylvania, and her colleagues used gene therapy to treat blindness in 12 adults and children with Leber’s congenital amaurosis (LCA). LCA is a rare inherited eye disease that destroys vision by killing photoreceptors—light-sensitive cells in the retina at the back of the eye. Typically afflicted children start life with poor vision, which worsens as more and more photoreceptors die.

The treatment grew out of the understanding that people with the disorder become blind because of genetic mutations in retinal cells. Once such mutation prevents the production of an enzyme needed to break down retinol, a form of vitamin A, into a substance that photo­receptors need to detect light and send signals to the brain.

In their original study, Bennett and her colleagues treated each of the 12 patients in one eye; six improved so much they no longer met the criteria for legal blindness. In a subsequent study published in February in Science Translational Medicine, the researchers injected functional genes into the previously untreated eye in three of the women from the first group and followed them for six months. The women’s vision in their previously untreated eye improved as soon as two weeks after the operation: they could avoid obstacles in dim light, read large print and recognize faces.

Bennett showed that not only were the women’s eyes much more sensitive to light, their brains were much more responsive to optical input as well. Functional magnetic resonance imaging showed regions of their visual cortex lighting up that had been offline before gene therapy began. Surprisingly, the second round of gene therapy further strengthened the brain’s response to the initially treated eye, as well as the newly treated one, perhaps “because the two eyes act in concert, and some aspects of vision rely on binocularity,” she says.

Bennett thinks the therapy will work even better in younger patients who have not lost as many photoreceptors. The results “really bode well” for restoring meaningful vision to people with LCA and other forms of inherited blindness, Bennett says.

This article was published in print as "Hopeful Vision."