Choroideremia Research Foundation Inc.
Written by Dr. Ian MacDonald
The choroideremia gene product is called REP-1 (for Rab escort protein-1).
This protein functions to bring other small proteins (thinking of them as signals) into association with an enzyme that adds 20-carbon long chains to the small signals. These signal proteins can then fit into the lipid membrane that surrounds the cell. The small signals are thought to play a role in allowing nurtients to pass across cells. Imagine that this process occurs constantly at the back of the eye as special nutrients are required to keep the biochemical pathways of vision operating at capacity while our eyes are open. Apparently there is another protein called REP-2 in all other cells except the eye that allows normal cell function IF REP-1 is not present. Unfortunately the male patient with choroideremia makes a defective REP-1 protein that is rapidly lost from the eye and REP-2 is not able to replace its function. You recall that the gene is on the X-chromosome. Males only have one X and so only 1 copy of the gene that makes the protein. If the gene copy is changed,there is no other normal copy around to mask the effect of not having the normal protein available. Research is trying hard to find ways of getting the cells in the eye to make the normal protein. Having an animal model of choroideremia will be very important to test if the animal can be successfully treated before trying this in the human condition.