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

• Cone-Rod Degeneration
• Retinal Cone-Rod Dystrophy
• Tapetoretinal Degeneration

What is Cone-Rod Dystrophy? (Definition/Background Information)

• Cone-Rod Dystrophy (CRD) is a group of inherited eye disorders that affect the light sensitive cells of the retina called the cones and rods. People with this condition experience vision loss over time as the cones and rods deteriorate
• Initial signs and symptoms that usually occur in childhood may include decreased sharpness of vision (visual acuity) and abnormal sensitivity to light (photophobia)
• These signs are usually followed by blind spots in the central field of vision (scotomas), loss of color perception, and loss of peripheral vision. Most individuals with this condition are legally blind by mid adulthood
• There are over 30 types of CRD caused by mutations in several different genes that can be inherited in many different ways including autosomal recessive, autosomal dominant, X-linked or mitochondrial patterns. Cone-Rod Dystrophies are usually non-syndromic, but they may also be part of several syndromes
• There is no cure for Cone-Rod Dystrophy; however, there may be ways to slow the disease process. Depending on the underlying cause of CRD and other associated symptoms, research may be ongoing to try to identify an effective treatment

(Source: Cone-Rod Dystrophy; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

Who gets Cone-Rod Dystrophy? (Age and Sex Distribution)

• Cone-Rod Dystrophy is a rare congenital disorder, with an estimated prevalence of 1 in 40,000 individuals 
• The presentation of symptoms may occur in childhood
• Both males and females may be affected
• Worldwide, individuals of all racial and ethnic groups may be affected

What are the Risk Factors for Cone-Rod Dystrophy? (Predisposing Factors)

• A positive family history may be an important risk factor, since Cone-Rod Dystrophy is an inherited condition
• Currently, no other risk factors have been clearly identified for the disorder

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 Cone-Rod Dystrophy? (Etiology)

• Cone-Rod Dystrophy is caused by mutations in several different genes, each leading to a different type of the disorder
• The condition may be inherited in an autosomal dominant, autosomal recessive, X-linked, or mitochondrial inheritance patterns

Autosomal dominant: Autosomal dominant conditions are traits or disorders that are present when only one copy of the mutation is inherited on a non-sex chromosome. In these types of conditions, the individual has one normal copy and one mutant copy of the gene. The abnormal gene dominates, masking the effects of the correctly function gene. If an individual has an autosomal dominant condition, the chance of passing the abnormal gene on to their offspring is 50%. Children, who do not inherit the abnormal gene, will not develop the condition or pass it on to their offspring.

Autosomal recessive: Autosomal recessive conditions are traits or disorders that occur when two copies of an abnormal gene have been inherited on a non-sex chromosome. If both parents have an autosomal recessive condition, there is a 100% likelihood of passing on the mutated genes to their children. If, however, only one mutant copy of the gene is inherited, the individual will be a carrier of the condition, but will not be present with any symptoms. Children born to two carriers, have a 25% chance of being homozygous dominant (unaffected), a 50% chance of being heterozygous (carrier), and a 25% chance of being homozygous recessive (affected).

X-linked recessive pattern of inheritance: The gene associated with this condition 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 would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, 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.

Mitochondrial inheritance: In this type of inheritance, the causative gene localizes to the mitochondria, and an individual inherits the disorder only from the mother.

What are the Signs and Symptoms of Cone-Rod Dystrophy?

The signs and symptoms of Cone-Rod Dystrophy may include:

• Very frequently present symptoms in 80-99% of the cases:
  • Abnormality of retinal pigmentation 
  • Nyctalopia
  • Photophobia
• Frequently present symptoms in 30-79% of the cases: Abnormality of color vision
• Occasionally present symptoms in 5-29% of the cases: Visual impairment

(Source: Cone-Rod Dystrophy; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

How is Cone-Rod Dystrophy Diagnosed?

Cone-Rod Dystrophy is diagnosed on the basis of the following information:

• Complete physical examination
• Thorough medical history evaluation
• Assessment of signs and symptoms
• Laboratory tests
• Vision tests 
• Fundus examination
• Electroretinography
• Imaging studies
• Biopsy studies, if necessary

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 Cone-Rod Dystrophy?

The complications of Cone-Rod Dystrophy may include:

• Progressive deterioration in vision acuity
• Permanent loss of vision

Complications may occur with or without treatment, and in some cases, due to treatment also.

How is Cone-Rod Dystrophy Treated?

• Currently, there is no treatment to stop a person with Cone-Rod Dystrophy from losing their vision. However, there may be treatment options that can help slow down the degenerative process, such as light avoidance and the use of low-vision aids
• It is important that people with CRD receive support and resources to help them cope with the social and psychological impact of vision loss

(Source: Cone-Rod Dystrophy; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

How can Cone-Rod Dystrophy be Prevented?

Cone-Rod Dystrophy may not be preventable, since it is a genetic disorder.

• 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
• Regular medical screening at periodic intervals with tests and physical examinations are recommended

What is the Prognosis of Cone-Rod Dystrophy? (Outcomes/Resolutions)

• The prognosis of Cone-Rod Dystrophy is guarded
• It is reported that most affected individuals completely lose their vision by mid-adulthood 

Additional and Relevant Useful Information for Cone-Rod Dystrophy:

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/rare-disorders/