Therapy for the Blind

You may have heard in the news last week about a trial that took place to help improve a currently incurable form of blindness. You may also have heard about the newest Big Brother gossip and the latest One Direction shenanigans. Yet you’ve chosen to read this instead, and for that we thank you! So…on with the science!

The one-of-a-kind study used gene therapy techniques to fix a faulty gene in patients with an inherited disease called choroideremia. This is an X-linked recessive condition which means the mutation that causes the disease is found on the X chromosome, and affects males more than females.

Image of an eye affected with choroideremia

Image of an eye affected with choroideremia

This faulty gene means that the light-sensitive cells at the back of our eyes that usually detect light and allow us to see, stop relaying information to the brain about what we’re seeing in the world around us. These rods and cones – the photoreceptors – start to degenerate and cause gradual loss of vision, from night vision to peripheral vision and in some cases eventually leading to total blindness.

The gene that has stopped working in the disease is named CHM and is involved in making a protein called REP1. The gene therapy used by scientists in Oxford and London introduced a fully-functioning version of the faulty gene into choroideremia patients. They did this by using a virus called adeno-associated virus (AAV) to express the healthy gene. This virus is then classed as a vector and can be used as a delivery vehicle for the new gene.

Patients then underwent surgery where the vector was injected into their eye just under the fovea: a part of the retina. By administering this genetically modified vector, normal copies of the CHM gene were expressed and degeneration of photoreceptors was not only stopped, but in some cases reversed.   Results from after the trial suggest that the use of gene therapy was effective at preventing the death of these retinal cells. More importantly, a number of patients that received the treatment showed improvements in vision, even patients who had a more severe form of the disease.

In choroideremia, the retina shrinks and causes vision to decrease. It is hoped, however, that similar gene therapy techniques can be used in the future to help improve sight in patients with other forms of blindness. It’s very early days to know this for sure though.

So there you have it, helping the blind to see one small step at a time. Thanks for reading!

Reference: Retinal gene therapy in patients with choroideremia: initial findings from a phase 1/2 clinical trial

Background info: Boye SE, Boye SL, Lewin AS, & Hauswirth WW (2013). A comprehensive review of retinal gene therapy. Molecular therapy : the journal of the American Society of Gene Therapy, 21 (3), 509-19 PMID: 23358189

Feature Image: adapted from http://www.intechopen.com/books/viral-gene-therapy/harnessing-the-potential-of-adenovirus-vectored-vaccines

Image: http://trialx.com/curebyte/2011/08/27/pictures-for-choroideremia/

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