- The condition
- Current research in choroideremia
- Practical advice
- Referral to a specialist centre
- Further information and support
- A patient’s perspective
- Choroideremia: for professionals
Choroideremia is a rare disease affecting 1 in 50,000 to 100,000 people. It is caused by genetic changes to the CHM gene, resulting in the degeneration of the retina and choroid layers of the eye over time. It begins in early childhood with difficulties in night vision, followed by loss of peripheral vision and then loss of central vision from late middle age onwards. Males are mainly affected due to its X-linked recessive inheritance pattern.
The earliest symptom patients notice is difficulty seeing at night (night blindness) starting from early childhood. It then progresses to loss of peripheral vision, leading to “tunnel vision”. The remaining central vision is eventually lost from late middle age onwards. Some patients may experience issues with their colour vision and contrast vision despite having good central vision. The symptoms can vary in severity between patients, even within the same family.
Choroideremia is caused by mutations in the CHM gene. This gene instructs cells to produce a protein called Rab escort protein 1 (REP-1). REP-1 helps to transport proteins within cells. When the CHM gene is not working properly, proteins cannot reach their correct destination. This malfunction leads to high levels of oxidative stress, which causes damage in the retina and subsequently cell death. This is what causes loss of vision in choroideremia.
How is it diagnosed?
Choroideremia is suspected based on the symptoms, family history and clinical evaluation of the retina. The diagnosis is confirmed with genetic testing by identifying mutations in the CHM gene.
How is it inherited?
1) X-linked recessive pattern
Affected father and the mother is healthy:
- None of the sons will be affected
- All daughters will be carriers
Female carriers and the father is healthy:
- Each son has a 50% chance of being affected
- Each daughter has a 50% chance of being a carrier like the mother
These risks apply to every new pregnancy.
As choroideremia is a hereditary condition, it is advisable to see a genetic counsellor to obtain more information and advice on inheritance and family planning options.
Is there any treatment?
There is currently no available treatment for choroideremia but researchers are exploring various approaches, some of which have entered clinical trials. In the meantime, here is some useful advice to help limit additional damage to the retina:
- A healthy diet consisting of fresh fruit and green leafy vegetables
- Wear UV protected sunglasses in bright light
- Use blue light screen protectors on mobile devices or computer screens*
- Avoid smoking
*Current available evidence shows that blue light emitted from screens do not damage the retina but it can disrupt our sleep cycle. The screen protectors are used as a precautionary measure.
Current research in choroideremia
1) Gene therapy
Gene therapy aims to halt retinal degeneration by replacing the mutated gene with a normal healthy copy. This enables the affected cells to regain some of their function and produce functioning proteins.
In choroideremia, a normal copy of the CHM gene is “packaged” into a harmless virus which is then injected into the retina. This way, the affected retinal cells will have maximum exposure to the viruses containing the normal CHM gene.
Currently, most gene therapy trials in choroideremia are at phase 1 or phase 2 stages. The following are links to scientific summaries of gene therapy trials in choroideremia:
- Xue and colleagues 2018, UK (NCT 01461213)
- Lam and colleagues 2019, USA (NCT 02553135)
- Dimopoulous and colleagues 2018, Canada (NCT 02077361)
- Aleman and colleagues 2019, USA (NCT02341807)
2) Nonsense suppression therapy
Nonsense suppression therapy is a new drug-based treatment targeting conditions caused by nonsense mutations. A nonsense mutation introduces an abnormal “stop” signal into a gene that halts protein production prematurely, resulting in a protein which is too short and not functional. A drug called ataluren (Translarna™) modifies the affected cell to “ignore” these abnormal “stop” signals and produce normal full-length functioning protein. 
About 30%  of choroideremia patients have nonsense mutations. Ataluren has shown to reduce oxidative stress, prevent retinal cell death and regain function in animal and human cell models of choroideremia. However, it has not been studied in patients yet. If proven to be beneficial in clinical trials, ataluren could potentially offer a non-surgical alternative to gene therapy for choroideremia patients.
3) Other potential therapies
- Research Opportunities at Moorfields Eye Hospital UK
- Searching for current clinical research or trials
Living with choroideremia
Patients are still able to lead fairly independent lives through maximising their available vision and having access to social support. Here are some ideas:
- Attending the low vision clinic which provides access to low vision specialists, Eye Clinic Liaison Officers (ECLOs), visual aids and visual rehabilitation services
- Utilising assistive technologies can improve quality of life
- Contacting the local council’s social services department for access to rehabilitation services and assessment of your individual needs to help you remain independent
- Getting in touch with the local education authority for access to qualified teachers for children with visual impairment (QTVI)
- Registering as sight impaired (SI) or severely sight impaired (SSI) if eligible for access to social support and financial concessions
- Getting in touch with national or local charities for advice and peer support
- Coping with sight loss
- Education and learning
- Employment support
- Family support service
- Driving and alternative transport
Referral to a specialist centre
If you are based in the UK and would like to be seen in the nearest specialist centre for your eye condition, either to receive a more comprehensive genetic management or just to find out more about current research, you can approach your GP to make a referral or alternatively arrange for a private appointment.
More information can be found in our “How to see a genetic eye specialist?” page
Further information and support
- Retina UK
- Choroideremia Research Foundation
- Royal National Institute of Blind People (RNIB)
- Guide Dogs for the Blind Association
- Look UK
A patient’s perspective
- Orphanet. Choroideremia. https://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=180. Published 2011. Updated 27 October 2019.
- Richardson R, Smart M, Tracey-White D, Webster AR, Moosajee M. Mechanism and evidence of nonsense suppression therapy for genetic eye disorders. Exp Eye Res. 2017;155:24-37
- Moosajee M, Ramsden SC, Black GC, Seabra MC, Webster AR. Clinical utility gene card for: choroideremia. Eur J Hum Genet. 2014;22(4)