What is it?
Choroideremia is a genetic disease that leads to damage to the retina and eventually blindness. Having trouble seeing in darkness is the first symptom. Later the affected lose their ability to detect distance, and their visual field starts to decrease from the edges until it is altogether lost. Choroideremia typically starts in youth and progresses to blindness in the 40s. The disease is rare, affecting about 1 in 50 000 people.
What causes it?
Choroideremia is caused by a non-functioning gene called REP-1 in the X chromosome. This is why it is almost exclusively seen in men. Men get only one X chromosome, so whatever genes are in that single chromosome will determine their attributes. Women get two X chromosomes, so even if they get the faulty chromosome from one of their parents, the gene in the healthy chromosome from their another parent can compensate.
What happens during it?
Most of our proteins are not ready to function the second they are produced. They might need help to get them to fold in the right manner, or something might have to be added to them or taken away from them.
The protein produced by the REP-1 gene, the REP-1 enzyme, is supposed to help add a certain molecular group to certain proteins that would allow them to be anchored to the cell membrane. In the cell membrane these proteins are supposed to regulate vital mechanism like the movements of the cell’s “skeleton”. It is though that the dysfunction of REP-1 leads to an insufficient production of these proteins, which in turn leads to cell death.
This finding raised questions – if the proteins are important in all cells, why do only the cells of the retina die? The answer to this lies in another gene called REP-2 found in chromosome 1. It resembles REP-1 and is thought to be able to compensate for the loss of it. There are a number of proteins that need the help of the REP enzymes, and the researchers started to wonder whether some of these proteins prefer the 1 over the 2. They did, in fact, find that one of these proteins didn’t have the necessary molecular group attached to it, and this protein happens to be especially common in the cells that die in choroideremia patients.
How can it be treated?
There is currently no widely used cure for choroideremia. However, one treatment with very promising results is being trialled. Viruses are specialized in getting their genetic material inside cells, and in this treatment, the correct version of REP-1 is put inside viruses and the viruses are then allowed to infect the cells in the retina. This technique has been able to slow down, and maybe even stop, the progression of the disease.
Sources: https://en.wikipedia.org/wiki/Choroideremia, https://en.wikipedia.org/wiki/Prenylation, https://www.youtube.com/watch?v=-P55BU9vsEM, https://www.google.fi/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjCyfT9qNXPAhVmEpoKHZQNC_AQFghfMAc&url=http%3A%2F%2Fwww.tandfonline.com%2Fdoi%2Fpdf%2F10.3109%2F13816819609057869&usg=AFQjCNGKIvvR-_pTbMrDH-F-6YntIDl9Qg&sig2=1GhX_fADrPsEffLvh0zZBw