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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed July 2013

What is the official name of the CHM gene?

The official name of this gene is “choroideremia (Rab escort protein 1).”

CHM is the gene's official symbol. The CHM gene is also known by other names, listed below.

What is the normal function of the CHM gene?

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.

How are changes in the CHM gene related to health conditions?

choroideremia - caused by mutations in the CHM gene

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.

Where is the CHM gene located?

Cytogenetic Location: Xq21.2

Molecular Location on the X chromosome: base pairs 85,861,180 to 86,047,562

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The CHM gene is located on the long (q) arm of the X chromosome at position 21.2.

The CHM gene is located on the long (q) arm of the X chromosome at position 21.2.

More precisely, the CHM gene is located from base pair 85,861,180 to base pair 86,047,562 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about CHM?

You and your healthcare professional may find the following resources about CHM helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the CHM gene or gene products?

  • choroideremia
  • DXS540
  • FLJ38564
  • GGTA
  • HSD-32
  • MGC102710
  • REP-1
  • REP-1, Rab escort protein 1
  • TCD

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding CHM?

cell ; expressed ; gene ; intracellular ; prenylation ; protein ; retina ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Garcia-Hoyos M, Lorda-Sanchez I, Gómez-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. (
  • MacDonald IM, Sereda C, McTaggart K, Mah D. Choroideremia gene testing. Expert Rev Mol Diagn. 2004 Jul;4(4):478-84. Review. (
  • 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. (
  • NCBI Gene (
  • 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. Review. (
  • 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. Epub 2003 Jun 25. (
  • 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. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: July 2013
Published: February 1, 2016