This therapy isnt perfect, but its a cool start!
‘Choroideremia‘ is a kind of blindness caused by deletion of a gene called REP1. Because REP1 is on the X-chromosome, there is no ‘second chance gene’ on the other chromosome in men. They have no functional REP1, so, men with this deletion get choroideremia.
This makes treating choroideremia with gene therapy attractive because we know what is going on. It is not an overly complex network– its a deleted gene that is causing the trouble. We can make a virus to deliver a functional copy of that gene. Heck, it is even great the gene is actually deleted instead of just mutated– the ‘new’ functional gene wont be competing with junk REP1 RNA.
Choroideremia is also attractive in that though it shows itself when people are rather young (night blindness), someone can have the deleted REP1 gene and have normal-ish vision until they are middle aged. That means in contrast with a disease like Lebers congenital amaurosis, where patients are going blind, damage is occurring from the day they are born, with choroideremia, they have a long window where scientists might be able to treat patients BEFORE they lose their vision. And boy to choroideremia patients lose their vision. Its like the whole back of their eye disintegrates :-/
Choroideremia derives its name from the almost complete loss of the retina, choroid, and retinal pigment epithelium that leads to exposure of the underlying white sclera…
So choroideremia provides scientists with a novel opportunity– A disease caused by one defective gene, gene test/screening is readily available, symptoms show up early, severe damage does not occur until late.
Can scientists deliver a functional copy of REP1 early and prevent REP1-negative men from developing choroideremia?
From the paper, it was the two patients who had the most damage pre-treatment that got the most benefit. BUT, since the disease takes so long to develop, maybe the remaining patients will see a benefit in 10, 20, 30 years.
But it is a very cool first step and a novel way to study what gene therapy can do.
They also used a freaking cool GMO virus
- AAV2 core.
- Chicken β actin promoter. Yes, chicken.
- Human REP1 gene.
- Woodchuck hepatitis virus post-translational regulatory element. Yes, a woodchuck virus.