Tuesday, January 24, 2012

Gene therapy found to correct blindness

Not being able to see can have many causes. A common form of blindness, found in young and old, is caused by a defective gene, and can be inherited. Scientists from the University of Florida have shown the defect can be repaired in animals, which paves the way for human testing. If it proves to work, hundreds of thousands could get their vision restored.

X-linked retinitis pigmentosa, as this particular form of blindness is known, is caused by a defect in a single gene, which in itself is quite remarkable: most diseases with a genetic component rely on a complex network of gene dysfunction. There is more than one gene that can cause the disease, but patients typically show one dysfunctional gene. X-linked means the defect is found on the X chromosome, and it is one of the most common forms of gene-induced blindness. Because something on the X chromosome is causing the problems, males have a much higher chance to acquire the disease. While females have two X chromosomes, males only possess one, so they have no 'backup' if there is a defect. Additionally, because the disease is genetic in origin, onset is fairly early in life. It is marked by increased pigmentation of the retina, which can be observed. Additionally, light-sensitive cells die.
In order to repair the defect, the researchers developed a virus loaded with a functional copy of the gene. Because viruses naturally function by infecting our cells and inserting their genetic material in our genome to promote the cell to make copies of them, they are a well-suited vehicle to deliver a therapeutical genetic load. Scientists commonly use a simple, harmless virus that is not able to spread any further after infecting the cell. After all, we do not want the cell to die after infection. In addition to a functional copy, a promoter that enables transcription of the gene was also loaded into the virus.

Animal testing
After trying to infect animals that naturally develop this particular form of blindness with a viral load, scientists noted that vision was restored. Fortunately, the genes were only inserted where they were needed, and did not spread throughout the body. That means the therapy is well targeted. Because viruses only care about spreading themselves, it means the scientists were able to train them well. In summary, the therapy was found to be both effective and safe.

If the gene therapy proves to work, many people could regain their vision. Sadly, retinitis pigmentosa can be caused by defects in a few other genes not present on the X chromosome, which the newly developed treatment cannot cure. However, one could imagine that treating patients with the same viral load, but a different gene could prove to be functional. 

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