The 'three blind mice' of song could actually be seeing again after scientists restored vision in breakthrough research that could reverse the condition in people as well.

The hereditary condition retinitis pigmentosa is one of the most common causes of blindness, affecting one in every 4,000 people. Now, researchers in China have used a genome-editing technique to correct a mutation that leads to the condition in both mice and humans.

Not only did the genetic correction lead to the mice regaining their sight, but the mice were shown to retain their sight well into old age.

The study team, from the Wuhan University of Science and Technology, hope this promising new method could soon be used to similarly restore people's vision in years to come.

Retinitis pigmentosa (RP) can be caused by mutations in more than 100 different genes. Symptoms begin with the dysfunction and death of dim light-sensing rod cells, before the disease spreads to cone cells required for color vision. Eventually, RP leads to severe and irreversible loss of vision.

Led by Professor Kai Yao, the team attempted to rescue the vision of mice with RP caused by mutations in the gene encoding a critical enzyme – called PDE6β – by engineering a new use for the CRISPR genome editing tool.

When the system was programmed to target the harmful mutant gene (PDE6β), it was shown to be able to correct the mutation and restore the enzyme's activity in the retinas of the mice.

This correction prevented the death of rod and cone photoreceptors in the eye and helped to restore the mice's normal electrical responses to light.

The authors published the breakthrough study in the Journal of Experimental Medicine, then performed a series of behavioral tests with the mice to evaluate their sight.

They found that the mice were able to navigate their way out of a visually-guided water maze almost as well as those with normal eyesight, and showed typical head movements in response to visual stimuli. The mice retained their good vision even into old age.

Yao praised his team's findings, but tempered their successful experiment by saying that further studies were required.

"The ability to edit the genome of neural retinal cells-particularly unhealthy or dying photoreceptors-would provide much more convincing evidence for the potential applications of these genome-editing tools in treating diseases such as retinitis pigmentosa.

"However, our study provides substantial evidence for the in vivo, a process occurring inside a living organism, applicability of this new genome-editing strategy, and its potential in diverse research and therapeutic contexts-in particular for inherited retinal diseases such as retinitis pigmentosa."

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