Choroideremia affects about 1 in 50,000, and people who have this condition get progressively worse vision, eventually becoming completely blind around middle age.
Blindness in people with choroideremia is caused by the degenration of the rods and cones (or "photoreceptors") in the eye's retina that send visual information to the brain, and there is no treatment available to correct this.
As part of the first phase of a clinical trial, six male patients aged between 35 and 63 with choroideremia were injected with a genetically engineered, harmless virus (called a "vector") containing a normal, healthy copy of the CHM gene.
The researchers hoped that this functioning gene would stop the cells in the patients' photoreceptors from dying. The patients in the study were not blind, but the choroideremia was more advanced in some patients than in others.
Six months after the injections, the team conducting the trial found the retinas in all of the patients had improved sensitivity to light and that two patients had substantially improved vision.