The classic nursery rhyme Three Blind Mice might need to be rewritten thanks to researchers from the Friedrich Miescher Institute (FMI) and the Institut de la Vision in Paris. Using gene therapy, the scientists have have restored sight in mice by repairing the function of cone photoreceptors made defective by a genetic eye condition.

The condition, retinitis pigmentosa, is a form of inherited retinal degeneration that affects over one million people worldwide and is manifested by a progressive loss of sight, eventually leading to blindness. It affects the photoreceptors – a specialized type of nerve cell found in the eye’s retina that convert light into nervous impulses that are processed by the retina and are transmitted along the nerve fibers to the brain.

As the disease progresses, it initially leads to degeneration of the rods – the photoreceptors responsible for night vision – and is followed by degeneration of the cones – the photoreceptors that are adapted to detect colors and function well in bright light. Whereas the rods are destroyed, the cones survive in the organism for extended periods, even after the occurrence of blindness. It was this fact that inspired the researchers to develop a genetic therapy to restore the visual function of the cones that were dormant, but remained in the eye.

At the stage of the disease where the researchers have intervened, the defective cones no longer possess the ability to respond to a luminous stimulation, but they do still retain some electrical properties. They also retain their connections with the neurons of the inner retina, which normally transmit visual information to the brain. It was this fact that allowed them to be activated artificially through the introduction of a protein using gene therapy.

The researchers say the results of the technique are very promising, particularly as they have been confirmed by researchers at the Institut de la Vision using human retina in cultures and therapeutic vectors for which human compatibility has already been demonstrated.

As good as this news is potentially for those affected by retinitis pigmentosa, somehow Three Formerly Blind Mice doesn’t have the same ring to it.