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Description

Cone-Rod Dystrophies refer to a group of inherited retinal degenerations (1:30 – 40,000 people) that affect the photoreceptor (light sensing) cells that are responsible for capturing images from the visual field. These cells line the back of the eye in the region known as the retina. Cone photoreceptor cells are present throughout the retina, but are concentrated in the central region (the macula). They are useful for central (reading) vision. Rod photoreceptor cells are present throughout the retina except for the very centre and they help with night vision.

In contrast to typical retinitis pigmentosa (known as the Rod-Cone Dystrophies), which results from the loss of rod cells and later the cone cells, Cone-Rod Dystrophies can reflect the opposite sequence of events, where cone cells are primarily first affected with later loss of rods. The degree of vision loss becomes more severe over time. There are multiple types of Cone-Rod Dystrophies, which are determined by their genetic cause and pattern of inheritance.

Cone-Rod Dystrophies may sometimes present as part of a syndrome, such as Bardet-Biedl syndrome and Spinocerebellar Ataxia Type-7 (SCA7).

Symptoms

In the early stages of this condition, which can occur in childhood, individuals can experience difficulty with the clarity of vision, notice problems with colour vision and light sensitivity. Eventually blind spots in the field of vision can occur. These symptoms present as a result of the deterioration of cone photoreceptor cells. This is followed by a progressive loss of rod photoreceptor cells, which leads to a loss of side vision and night blindness.

In some cases, the rod photoreceptor cells may deteriorate at the same time as cone photoreceptor cells, leading to a more complex presentation of symptoms. With progression of the condition, some individuals may develop nystagmus (involuntary eye movements). Blindness as a result of cone-rod dystrophies typically occurs by mid-adulthood.

The age of onset, progression and severity of Cone-Rod Dystrophies can vary greatly from one person to another, even among individuals with the same type of Cone-Rod Dystrophy. It is therefore very difficult to predict what an individual’s vision will be like at a specific time in the future.

Causes

Cone-Rod Dystrophies are genetic conditions. There are many different types of Cone-Cod Dystrophies, which differ in their genetic cause and the way in which they are inherited (passed on through generations of a family).

There are multiple genes which can cause Cone-Rod dystrophies, with mutations in these leading to a loss of cone and rod photoreceptor cells. Genes linked with this condition include ABCA4, CRX, GUCY2D and RPGR.

As mentioned, Cone-Rod Dystrophies can follow varied inheritance patterns, including autosomal dominant, autosomal recessive and X-linked. Autosomal recessive is the most common pattern of inheritance. If the condition is inherited in an autosomal dominant manner, this means that one copy of a gene doesn’t work properly, giving rise to the condition. In this case, a person will have received one copy of a mutated gene from an affected parent.

If the condition is inherited in an autosomal recessive manner, this means that both copies of a gene linked with the condition don’t work properly, giving rise to the condition.

In this case, the individual’s mother and father have both passed on a mutation in the gene in question. If the condition is inherited in an X-linked manner, this means that if a male has an X-chromosome with the mutated gene, they will develop the condition as they only have one copy of the X-chromosome, containing the gene. As females almost always have another functioning X-chromosome, they typically don’t develop the condition.

Although in rare circumstances, due to the phenomenon of ‘non-random X-chromosome activation’ some females may develop symptoms of the condition.

Some forms of Cone-Rod Dystrophy appear to occur spontaneously for no apparent reason (sporadically). In this case, a new genetic mutation may have occurred, giving rise to the condition.

More information on genetic inheritance can be found at our Genetic Inheritance section.

Diagnosis

Cone-Rod Dystrophies are diagnosed through a number of assessments which will help with providing the correct diagnosis.

The eye doctor will ask about a person’s medical history, including any family history of eye conditions. Individuals will receive a clinical eye examination where they may be asked to read letters off a chart (a Snellen chart). They may also check intraocular pressure and examine visual acuity and the visual field.

An individual may receive a number of imaging tests. Information about the condition may be identified using colour or wide-field fundus photography (which essentially takes photos of the back of the eye). Fundus autofluorescence may be used to identify stress or damage to the retinal pigment epithelium. Optical coherence tomography (OCT) can also be used to assess the various layers at the back of the eye.

An individual may also have an electroretinogram (known as an ERG), which is used to evaluate the functioning of the different types of photoreceptor cells (rods and cones).

A genetic test is also an important component of testing, to ensure the correct condition is diagnosed. For people living in Ireland, genetic testing for cone-rod dystrophies can be performed through the Target 5000 programme.

If a family member is diagnosed with a Cone-Rod Dystrophy, it is strongly advised that other members of the family also have an eye exam by an eye doctor (ophthalmologist) who is specially trained to detect retinal diseases.

For further information, please contact the Research Department on 01 6789004.

Genetic Diagnosis

It’s often impossible to tell which type of retinal disease a person has just by looking into the eye. As such, a genetic test may be necessary to confirm the diagnosis.

The Target 5000 programme provides free genetic and clinical testing to all individuals living in Ireland with a genetic retinal degeneration, including Cone-Rod Dystrophy. Through genetic screening of the person awaiting diagnosis and their family members, the Target 5000 programme will provide more detailed information about the nature and inheritance pattern of the condition.

As gene-specific clinical trials and treatments become available, knowing the genetic mutation associated with a genetic retinal degeneration will become even more important. Taking part in this programme ensures participants are included on a national registry from which participants can be identified for clinical trials and treatments and from which further information about each of the genetic retinal degenerations can be defined.

For further information on the Target 5000 programme, please contact the Research Department on 01 6789004 or email research@fightingblindness.ie.

Treatment

There are no proven treatments for Cone-Rod Dystrophies as of yet, although recent years have noted advances in clinical research and development. To find out more about advances made in this area, please visit the ‘Latest Research’ section.

Maximising an individual’s remaining vision is a crucial first step to take. There are many low vision aids, including telescopic and magnifying lenses, providing plenty of choice for users at all stages of sight loss. This technology has also removed many barriers to education and employment.

Despite the lack of treatments for Cone-Rod Dystrophies, general eye check-ups are important. People with these conditions are still at risk for other kinds of eye problems that may be treatable.

No matter what level of vision a person may have, it is important to look after the eyes. To find out more about what can be done to take care of the eyes on a daily basis, please visit our Tips for Good Eye Health.

For further information, please contact the Research Department on 01 6789004.

Research

Whilst there are currently no proven or effective cures for Cone-Rod Dystrophies, researchers have been seeking ways to change this.

Some researchers are actively gathering as much information (such as the information from clinical tests and genetic testing) as possible to enable a greater understanding of the condition. With time, researchers hope that this information will bring benefits such as yielding new treatments and ways to improve quality of life.

To date, scientists have identified more than 30 genes linked with this condition. These genes provide avenues of therapeutic potential, including for gene therapies. Gene therapy is a therapeutic approach which has proven safe in other retinal conditions. Using this technique, researchers can engineer small, safe viruses to deliver the correct version of the mutated gene to the retina.

Another area of potential for Cone-Rod Dystrophies includes retinal implant technology. This technology aims to provide a means of communication with the brain which can be perceived as vision, where retinal photoreceptor cells are otherwise incapable- due to deterioration, damage or cell death. This technology includes the use of microelectronics and microchip electrodes surgically implanted into the back of the eye to restore the functionality of these damaged cells. A number of clinical trials are now investigating their potential for Cone-Rod Dystrophy.

Information about clinical trials can be found on their website and can be searched by condition and trial location.

Fighting Blindness currently support a number of research initiatives which aim to improve the diagnosis, care and quality of life of individuals living with Cone-Rod Dystrophy.

Target 5000 research, largely funded by Fighting Blindness aims to determine the genetic cause and understand the nature of the condition over time. Through Target 5000, a national registry will also be developed which will greatly improve access to suitable clinical trials and treatments for people living in Ireland with Cone-Rod Dystrophy. For further information, please visit ***(insert link to Target 5000).

Dr Sarah Doyle based in Trinity College Dublin is conducting a study to investigate if a protein known as SARM1 plays a role in retinal degeneration, a key component of Cone-Rod Dystrophy. This work aims to further understand the underlying mechanisms of retinal degeneration and identify potentially new therapeutic targets. To find out more about this study, please visit our latest research section.

A study conducted by Professor Breandán Kennedy is investigating a group of neuroprotective drugs, known as HDAC inhibitors, for their potential to delay vision loss in retinal degenerations. This work seeks to identify new therapeutics which could provide significant benefit to individuals.

A new study being led by Dr Oliver Blacque and Ms Ailís Moran will investigate a small protein, known as Rab28, which is associated with Cone-Rod Dystrophy. This work seeks to further understand this protein and how it relates to the condition.

For further information, please contact the Research Department on 01 6789004.

Support

Receiving a diagnosis can be overwhelming for anyone, but this is not a journey that you have to make alone. There are many groups and resources available to provide support for people living with Cone-Rod Dystrophies.

Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please contact insight@fightingblindness.ie or call 01 6746496.

A mindfulness group is also available on every Wednesday at the Fighting Blindness office at 11am.

For technology support and guidance, the Dublin-based Technology Exchange Club meets every Monday at the Fighting Blindness office at 11am. Another Technology Exchange Club, based in Cork, meet every Saturday in the Cork City Library, Grand Parade, Cork City at 11am. The Cork-based club do not meet on Bank Holiday weekends or on the second Saturday of the month. For further information please contact insight@fightingblindness.ie or call 01 6746496.

RareConnect is an online social network for patients and families. It was created by EURORDIS (European Rare Disease Organisation) and NORD (National Organisation for Rare Disorders) to provide a safe space where individuals and families affected by rare diseases can connect with each other, share vital experiences, and find helpful information and resources. Communities for specific conditions are built in partnership with patient groups who help create, moderate and maintain the forum.

Resources

Féach provides support for parents of children living with sight loss in Ireland.

ChildVision is the national education centre for children with sight loss in Ireland.

NCBI (National Council for the Blind in Ireland) provides support and services for people living with sight loss in Ireland.

Irish Guide Dogs for the blind helps individuals and their families to achieve improved mobility and independence.

 

Last Updated: 4th February 2019