Healthy' genes to replace defective ones.
Choroideremia is a rare genetic disease characterised by progressive degeneration of the retinal pigment epithelium and choroid capillaries. It has an X-linked recessive transmission mode, so it almost exclusively affects male individuals (in 90% of cases). It arises during the first decade of life, with difficulty in night vision, then leads to loss of peripheral vision in adulthood and often to legal blindness around the age of 40.
It is a devastating disease for both affected individuals and their families, and to date no effective cure has been found. Some hope now comes from gene therapy currently undergoing phase II clinical trials at the Royal Alexandra Hospital in Alberta, Canada.
Gene therapy is not a medical therapy per se, as it is rather based on the transfer of human genes. Basically, the incorporation of new DNA into cells to replace a missing or malfunctioning gene is performed. This allows cells to synthesise the corresponding protein. In choroideremia, without the protein produced by the healthy CHM gene, the photoreceptors die over time. To prevent this from happening, explains Dr Ian MacDonald, who leads the research team at the University of Alberta, a therapy is used that relies on the administration of 'customised' viruses to replace the diseased genes with healthy ones.
A viral vector (known as AAV2-REP1), a harmless virus modified to carry the 'good' genes needed to prevent further vision loss and restore some of the visual acuity in already sick patients, is injected in a single administration. Promising results have been reported already after the first month of treatment.
Researchers are convinced that this new approach will allow patients to be treated before many photoreceptors have been lost and can be extended to other degenerative retinal diseases that can lead to blindness, such as retinitis pigmentosa and age-related macular degeneration.
For more information, please visit the choroideremia site of the Choroidermia Research Foundation Canada.
Dr. Carmelo Chines
Direttore responsabile
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