Gene therapy fixes (night) blindnessMonday, 28 April, 2008
Those bionic eyes I blogged about have some competition – from genetic engineering. A form of blindness known as Leber’s congenital amaurosis is caused by a lack of a key gene, RPE65, in cells of the pigment epithelium cells. These are the cells just behind the photoreceptors, and they produce a key pigment molecule called 11-cis-retinal. This pigment is used primarily in rod photoreceptors, because the cones can make a similar molecule known 11-cis-retinaldehyde without relying on the pigment epithelium cells. However, the cones degenerate, meaning that Leber’s congenital amaurosis can cause blindness by middle-age.
Gene therapy was trialled on young adults (17-23), who still have reasonable colour vision thanks to functional cones. However, cone cells require more light to be stimulated, so the rod cells (which only show light and dark, or shades of gray) are used primarily in low-light conditions (and in peripheral vision).
The researchers used the common viral vector AAV (adeno-associated virus) plus an adeno 5 helper virus. This vector contained the DNA of the human RPE65 gene, including its promoter sequence (the terminator sequence was different though – bovine growth hormone polyadenylation sequence was used). They injected these into the subretinal space of one eye.
Unfortunately, though three patients underwent the surgery (at least, three were included in the study – I think it has been trialled on others), only one showed improvement. It was a dramatic improvement though – improved visual mobility, as measured by a navigation in a simulated street scene in low-light conditions – from 77seconds to 14 seconds, without bumping into the wall eight times like he did before the surgery. The researchers believe this lack of improvement in the other patients was due to their retinal degeneration being more severe, which if true would mean that this therapy should be targeted at children with the condition.
View full article in the New England Journal of Medicine.
Now the race is on. I wonder which will end up curing blindness first – bionics or genetics. This race is going to be in many areas aside from vision research, such as in giving mobility back to amputees (can we regrow limbs before we get fully functional prosthetics?). Personally, I’m willing to let both fields work, so that those who want it can be enhanced from both directions.