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Genetic editing against retinitis pigmentosa

The CRISPR technique has permitted partial recovery of retinal function in guinea-pigs or a deceleration of cellular degeneration

dna-animazio6b00-176ce.gifOphthalmology is at the forefront of gene therapies. This is confirmed by a study conducted at Columbia University (U.S.A.): a pioneering treatment for retinitis pigmentosa has just been described in the online version of Ophthalmology, the journal of the American Academy of Ophthalmology.

Even if tested only on lab rats, the CRISPR correction technique – which allows an automatic replacement of faulty DNA sequences – according to the researchers “can restore retinal function” or at least slow down the degeneration of nerve cells.

To get a better idea of how it works, it’s as if a word typed incorrectly was replaced throughout a text with the correct word through the tool “find and replace”. However, there is also the potential risk that genetic sequences, which do not cause retinal pathology could modified; therefore the side effects of CRISPR will have to be further evaluated. The same genetic therapeutic strategy can be used for hundreds of other pathologies (such as Huntington’s disease, Marfan syndrome, corneal dystrophy).

The American Academy of Ophthalmology write:

Retinitis pigmentosa is a group of rare inherited genetic disorders caused by one of more than 70 genes. It involves the breakdown and loss of cells in the retina, the light sensitive tissue that lines the back of the eye. It typically strikes in childhood and progresses slowly, affecting peripheral vision and the ability to see at night. Most will lose much of their sight by early adulthood and become legally blind by age 40. There is no cure. It is estimated to affect roughly 1 in 4,000 people worldwide.

At Columbia University researchers are studying how to treat the autosomal dominant form of retinitis pigmentosa. It is believed that different types of genetic mutation can lead to the same ocular pathology. For instance, any mutation of the rhodopsin gene (an indispensable molecule for the correct functioning of the retina) can cause retinitis pigmentosa). Using two guide RNAs instead of just one increased the probability of replacing defective genes from 30 to 90 percent, always using the flu virus (adenovirus) preventively rendered harmless. The results were then evaluated with an electroretinogram, which can be considered the analogue of a retinal “electrocardiogram”.

The American Academy of Ophthalmology explain:

Previous CRISPR studies for retinal diseases have relied on a less objective measure that involves evaluating how often the mouse turns its head in the direction of a light source. Dr. Stephen H. Tsang used electroretinography to show that retinal degeneration slowed in treated eyes compared with untreated eyes.

Sources: AAO, Ophthalmology

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