What are the other Names for this Condition? (Also known as/Synonyms)

• CHM (Choroideremia)
• Choroidal Sclerosis
• Progressive Tapetochoroidal Dystrophy

What is Choroideremia? (Definition/Background Information)

• Choroideremia (CHM) is a rare, congenital, eye disorder that is inherited in an X-linked recessive manner. It involves the tissues of the choroid and retina (retinal pigment epithelium or RPE), leading to their gradual deterioration and loss of function
• The choroid is a portion of the uvea (part of the eye structure) that is predominantly made up of the blood vessels. The choroid provides nutrients to the retina keeping it healthy. Choroideremia occurs due to degeneration of small blood vessels of both the choroid and retina
• The cause of Choroideremia is a mutation in the CHM gene that encodes for a certain protein, which is necessary for normal eye function. Since, the condition is inherited, a positive family history is a key risk factor
• Choroideremia results in signs and symptoms that include night vision difficulties, blind spots in the eye, altered color perception. The condition is progressive and ultimately results in total vision impairment
• A healthcare provider can use various physical (eye) exams, blood tests, and imaging studies to diagnose Choroideremia. Currently, there is no treatment available to manage the condition and the prognosis of Choroideremia is poor

Who gets Choroideremia? (Age and Sex Distribution)

• Choroideremia is a congenital condition and the onset of signs and symptoms is seen in early childhood
• The condition is X-linked, and hence, a vast majority of the affected individuals are males
• Individuals of different racial and ethnic backgrounds can be affected
• The prevalence of CHM varies between 1 in 50,000 to 1 in 100,000 making it a rare disorder

What are the Risk Factors for Choroideremia? (Predisposing Factors)

• The main risk factor for Choroideremia is a positive family history of the condition

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Choroideremia? (Etiology)

Choroideremia is a genetic disorder that is inherited in an X-linked recessive manner.

• It is caused by CHM gene mutation, which results in an abnormal protein, namely the rab escort protein 1 (RAP1)
• The RAP1 protein is required for the normal functioning of the choroid and retina
• Choroideremia develops due to the degeneration of small blood vessels of both the choroid and retina

X-linked recessive: X-linked recessive conditions are traits or disorders that occur when two copies of an abnormal gene are inherited on a sex chromosome (X or Y chromosome). All X-linked recessive traits are fully evident in males, because they have only one copy of the X chromosome. This means that there is no normal gene present to mask the effects of the mutant copy. All males who are affected will pass the mutated gene onto their female offspring, because they must inherit one copy of the X chromosome from each parent. This means that they will be unaffected carriers. Females are rarely affected by X-linked recessive disorders because they have two copies of the X chromosome. In the rare case that they inherit two mutated copies of the gene, they will inherit the condition.

What are the Signs and Symptoms of Choroideremia?

The signs and symptoms of Choroideremia are initially observed in young children. It may vary from one child to another and is a progressive condition. The signs and symptoms may include:

• The key symptom is difficulty in night vision or dim-light vision (nyctalopia)
• Blind spots affecting the vision, or scotoma
• Alteration of color perception
• The condition affects both the eyes (bilateral presentation); the signs and symptoms of one eye may be worse than the other
• Loss of vision field: The peripheral vision is lost, while the central vision may remain unaffected. This is termed as tunnel vision

A gradual deterioration of vision is observed as the child grows and develops; over time, this results in severe vision impairment (by the time the individual reaches age 60 years).

How is Choroideremia Diagnosed?

A healthcare professional may diagnose Choroideremia using the following tests and procedures:

• Physical examination and analysis of previous medical history
• Eye examination by an eye specialist
• Fundoscopic (ophthalmoscopic) examination by an eye specialist, who examines the back part of the eye (or the fundus)
• Visual acuity test using a special and standardized test chart (Snellen chart)
• Slit-lamp examination: Examination of the eye structure using a special instrument called a slit-lamp. In this procedure, the pupils are dilated and the internal eye structure is examined
• Tonometry: Measurement of intraocular pressure or eye fluid pressure, especially to detect conditions such as glaucoma
• Fundus fluorescein angiography (FFA): In this technique, the eye blood vessels are examined using a fluorescein dye
• Fundus autofluorescence (FAF) imaging: It is a diagnostic technique to examine the fundus of the eye using a fluorescent dye
• Indocyanine green (ICG) angiography: It is used to examine the blood vessels of the choroid using a dye, called indocyanine green, particularly to study the choroid
• B-scan ultrasonography: Special ultrasound scan of the eye through a non-invasive diagnostic tool, to assess health of the eye structures
• Electroretinogram (ERG): It is a technique to measure electrical activities in the retinal cells
• Optical coherence tomography (OCT) of eye: Radiological imaging technique to visualize the eye structure
• Blood tests that include:
  • Complete blood count (CBC) with differential
  • Erythrocyte sedimentation rate (ESR)
  • Testing for CHM gene mutation on a blood sample

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Choroideremia?

The complications of Choroideremia may include:

• Complete retinal atrophy
• Total blindness due to relentless progression of the condition

How is Choroideremia Treated?

• Currently, there is no treatment modality available for Choroideremia and the condition is progressive and terminates with a complete loss of vision
• Gene therapy as a treatment tool is currently being researched upon
• Rehabilitation, vocational, or occupational therapy may be provided to the affected individuals

The healthcare provider may recommend the best treatment options based upon each individual’s specific circumstances.

How can Choroideremia be Prevented?

• Currently, there are no specific methods or guidelines to prevent Choroideremia, since it is a genetic condition
• Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
• If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as Choroideremia

What is the Prognosis of Choroideremia? (Outcomes/Resolutions)

The prognosis of Choroideremia is poor and the condition leads to a gradual loss of complete vision, when the individual reaches the age of around 60 years.

Additional and Relevant Useful Information for Choroideremia:

Choroideremia can be confused with X-linked reticulate pigmentosa; however, both conditions are completely different.

Please visit our Eye & Vision Health Center for more physician-approved health information:

http://www.dovemed.com/health-topics/vision-center/