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Normal Function
The CHM gene provides instructions for producing the Rab escort protein-1 (REP-1), which is active (expressed) throughout the body. As an escort protein, REP-1 attaches (binds) to one of a number of Rab proteins. Following a chemical modification, REP-1 then directs the Rab protein to the membrane of one of the cell's compartments (organelles). While attached to the membrane, the Rab protein plays a role in directing the movement of proteins and organelles within cells (intracellular trafficking). After the Rab protein has reached its destination, it is released by REP-1 which then attaches to another Rab protein to begin the process again.
Health Conditions Related to Genetic Changes
Choroideremia
More than 140 mutations in the CHM gene have been found to cause choroideremia. Nearly all of these mutations lead to the production of an abnormally small, nonfunctional REP-1 protein. Other gene mutations result in a decrease in the protein's function or delete part or all of the gene and abolish REP-1 protein production. A lack of normal REP-1 disrupts the ability of Rab proteins to aid in intracellular trafficking. The immobility of proteins and organelles within the cell cause the cell to die prematurely.
The REP-1 protein is active (expressed) throughout the body, as is a similar protein, REP-2. Research suggests that when REP-1 is absent or not functioning properly, REP-2 can perform the protein escort duties of REP-1 in many of the body's tissues. Very little REP-2 protein is present in the light sensitive-tissue at the back of the eye (the retina), however, so it cannot compensate for the loss of REP-1 in this tissue. Loss of REP-1 function and subsequent misplacement of Rab proteins within the cells of the retina causes the progressive vision loss characteristic of choroideremia.
More About This Health ConditionOther Names for This Gene
- choroideremia
- choroideremia (Rab escort protein 1)
- DXS540
- FLJ38564
- GGTA
- HSD-32
- MGC102710
- RAE1_HUMAN
- REP-1
- REP-1, Rab escort protein 1
- TCD
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Garcia-Hoyos M, Lorda-Sanchez I, Gomez-Garre P, Villaverde C, Cantalapiedra D, Bustamante A, Diego-Alvarez D, Vallespin E, Gallego-Merlo J, Trujillo MJ, Ramos C, Ayuso C. New type of mutations in three spanish families with choroideremia. Invest Ophthalmol Vis Sci. 2008 Apr;49(4):1315-21. doi: 10.1167/iovs.07-1169. Citation on PubMed
- MacDonald IM, Sereda C, McTaggart K, Mah D. Choroideremia gene testing. Expert Rev Mol Diagn. 2004 Jul;4(4):478-84. doi: 10.1586/14737159.4.4.478. Citation on PubMed
- McTaggart KE, Tran M, Mah DY, Lai SW, Nesslinger NJ, MacDonald IM. Mutational analysis of patients with the diagnosis of choroideremia. Hum Mutat. 2002 Sep;20(3):189-96. doi: 10.1002/humu.10114. Citation on PubMed
- Preising M, Ayuso C. Rab escort protein 1 (REP1) in intracellular traffic: a functional and pathophysiological overview. Ophthalmic Genet. 2004 Jun;25(2):101-10. doi: 10.1080/13816810490514333. Citation on PubMed
- van den Hurk JA, van de Pol DJ, Wissinger B, van Driel MA, Hoefsloot LH, de Wijs IJ, van den Born LI, Heckenlively JR, Brunner HG, Zrenner E, Ropers HH, Cremers FP. Novel types of mutation in the choroideremia ( CHM) gene: a full-length L1 insertion and an intronic mutation activating a cryptic exon. Hum Genet. 2003 Aug;113(3):268-75. doi: 10.1007/s00439-003-0970-0. Epub 2003 Jun 25. Citation on PubMed
- Yip SP, Cheung TS, Chu MY, Cheung SC, Leung KW, Tsang KP, Lam ST, To CH. Novel truncating mutations of the CHM gene in Chinese patients with choroideremia. Mol Vis. 2007 Nov 27;13:2183-93. Citation on PubMed
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