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Genetics Home Reference: your guide to understanding genetic conditions
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Choroideremia

Reviewed July 2013

What is choroideremia?

Choroideremia is a condition characterized by progressive vision loss that mainly affects males. The first symptom of this condition is usually an impairment of night vision (night blindness), which can occur in early childhood. A progressive narrowing of the field of vision (tunnel vision) follows, as well as a decrease in the ability to see details (visual acuity). These vision problems are due to an ongoing loss of cells (atrophy) in the specialized light-sensitive tissue that lines the back of the eye (retina) and a nearby network of blood vessels (the choroid). The vision impairment in choroideremia worsens over time, but the progression varies among affected individuals. However, all individuals with this condition will develop blindness, most commonly in late adulthood.

How common is choroideremia?

The prevalence of choroideremia is estimated to be 1 in 50,000 to 100,000 people. However, it is likely that this condition is underdiagnosed because of its similarities to other eye disorders. Choroideremia is thought to account for approximately 4 percent of all blindness.

What genes are related to choroideremia?

Mutations in the CHM gene cause choroideremia. The CHM gene provides instructions for producing the Rab escort protein-1 (REP-1). As an escort protein, REP-1 attaches to molecules called Rab proteins within the cell and directs them to the membranes of various cell compartments (organelles). Rab proteins are involved in the movement of proteins and organelles within cells (intracellular trafficking). Mutations in the CHM gene lead to an absence of REP-1 protein or the production of a REP-1 protein that cannot carry out its protein escort function. This lack of functional REP-1 prevents Rab proteins from reaching and attaching (binding) to the organelle membranes. Without the aid of Rab proteins in intracellular trafficking, cells 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 nonfunctional, 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 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.

Related Gene(s)

Changes in this gene are associated with choroideremia.

  • CHM

How do people inherit choroideremia?

Choroideremia is inherited in an X-linked recessive pattern. The CHM gene is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In X-linked recessive inheritance, a female with one mutated copy of the gene in each cell is called a carrier. She can pass on the altered gene, but usually does not experience signs and symptoms of the disorder. Females who carry a CHM mutation may show small areas of cell loss within the retina that can be observed during a thorough eye examination. These changes can impair vision later in life.

Where can I find information about diagnosis or management of choroideremia?

These resources address the diagnosis or management of choroideremia and may include treatment providers.

  • Gene Review: Choroideremia (http://www.ncbi.nlm.nih.gov/books/NBK1337)
  • Genetic Testing Registry: Choroideremia (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0008525)
  • MedlinePlus Encyclopedia: Vision - night blindness (http://www.nlm.nih.gov/medlineplus/ency/article/003039.htm)
  • MedlinePlus Encyclopedia: Visual field (http://www.nlm.nih.gov/medlineplus/ency/article/003879.htm)

You might also find information on the diagnosis or management of choroideremia in Educational resources (http://www.ghr.nlm.nih.gov/condition/choroideremia/show/Educational+resources) and Patient support (http://www.ghr.nlm.nih.gov/condition/choroideremia/show/Patient+support).

General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook. Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).

To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

Where can I find additional information about choroideremia?

You may find the following resources about choroideremia helpful. These materials are written for the general public.

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

What other names do people use for choroideremia?

  • choroidal sclerosis
  • progressive tapetochoroidal dystrophy
  • TCD

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about choroideremia?

Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).

What glossary definitions help with understanding choroideremia?

atrophy ; carrier ; cell ; choroid ; chromosome ; expressed ; gene ; inheritance ; inherited ; intracellular ; mutation ; organelle ; prevalence ; progression ; protein ; recessive ; retina ; sclerosis ; sex chromosomes ; symptom ; tissue ; visual acuity ; X-linked recessive

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).

References

  • 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. (http://www.ncbi.nlm.nih.gov/pubmed/18385043?dopt=Abstract)
  • 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. (http://www.ncbi.nlm.nih.gov/pubmed/12203991?dopt=Abstract)
  • Roberts MF, Fishman GA, Roberts DK, Heckenlively JR, Weleber RG, Anderson RJ, Grover S. Retrospective, longitudinal, and cross sectional study of visual acuity impairment in choroideraemia. Br J Ophthalmol. 2002 Jun;86(6):658-62. (http://www.ncbi.nlm.nih.gov/pubmed/12034689?dopt=Abstract)
  • 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. (http://www.ncbi.nlm.nih.gov/pubmed/12827496?dopt=Abstract)
  • Yau RJ, Sereda CA, McTaggart KE, Sauvé Y, MacDonald IM. Choroideremia carriers maintain a normal electro-oculogram (EOG). Doc Ophthalmol. 2007 May;114(3):147-51. Epub 2007 Mar 1. (http://www.ncbi.nlm.nih.gov/pubmed/17333094?dopt=Abstract)
  • 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. (http://www.ncbi.nlm.nih.gov/pubmed/18087237?dopt=Abstract)

 

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? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: July 2013
Published: November 24, 2014