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Description

Best disease, also known as vitelliform macular dystrophy, is a rare (1:15,000) inherited retinal degeneration affecting the portion of the retina known as the macula. The macula is the central part of the retina containing the photoreceptor cells known as cone cells, which are responsible for central vision, fine visual detail and colour perception.

Best disease is usually diagnosed during the teenage years, but vision does not generally deteriorate until later in life. Side (also known as peripheral) vision and dark adaption usually remains unaffected. Therefore, people with Best disease do not generally have issues with independent mobility.

Symptoms

The first symptoms of Best disease can vary from person to person but always involves central vision. In the initial stages, a yellow accumulation of metabolic by-products builds up in the cells underneath the macula. Over time, the abnormal accumulation of this substance can damage the cone cells located in the macula, leading to a blurring or distortion of central vision. Individuals may also experience challenges in distinguishing between or recognising colours.

Best disease generally doesn’t affect peripheral or side vision. It does not always affect both eyes equally and clearer vision is sometimes retained in one eye. In rare cases, individuals may not experience symptoms, known as asymptomatic.

Causes

Best Disease is a genetic condition caused by mutations in the BEST1 gene (also known as VMD2 gene) which produces the protein Bestrophin-1.

Best disease is most commonly passed down through families by an autosomal dominant pattern of inheritance, although rare cases of autosomal recessive inheritance have been reported. If the condition is inherited in an autosomal dominant manner, this means that a person has one copy of the BEST1 gene which doesn’t work properly, giving rise to the condition. In this case, a person will have received one copy of the mutated gene from an affected parent.

If the condition is inherited in an autosomal recessive manner, this means that both copies of the BEST1 gene don’t work properly, giving rise to the condition. In such cases, the individual’s mother and father have both passed on a mutation in the BEST1 gene.

Owing to the variable expression of the BEST1 mutation some people who have the mutation may have very mild, or in rare cases no, symptoms.

Diagnosis

Best disease is diagnosed through a number of assessments which are important for providing the correct diagnosis.

The eye doctor will ask about an individual’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 (Snellen chart). They may also check intraocular pressure and examine visual field and visual acuity.

The retina (light-sensitive layer at the back of the eye) is examined for the presence of a characteristic yellow mass on the macula (section of the retina important for central, detailed, colour vision). A test called an electrooculogram (EOG) may be performed, which measures the difference in electrical charge between the front and the back of the eye using electrodes placed on the skin near the eye. This is typically abnormal in Best disease. An individual may have an electroretinogram (known as an ERG), which is used to evaluate the functioning of photoreceptor cells.

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.

Genetic testing is another important component of making a diagnosis of Best disease and ensures that the correct diagnosis is given. The Target 5000 genetic testing programme is available for anyone living in Ireland to assist in the diagnosis of Best disease.

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 Best Disease. 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

Currently, there is no treatment for Best disease, but researchers have made significant advances in understanding the condition and developing treatments for it. To find out more about these advances, please visit the ‘Latest Research’ section.

Maximising the remaining vision that an individual has is a crucial step to take, and there are many low vision aids such as telescopic and magnifying lenses which may be of benefit. The wide range of assistive technologies for people with visual impairments provides plenty of choice for users at all stages of sight loss and this technology has also removed many barriers to education and employment.

General eye check-ups are important for people living with Best Disease, as these individuals may still be at risk of developing other kinds of eye problems that affect the general population, some of which 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

There are promising research efforts underway for Best Disease.

Since identifying the BEST1 gene as causative for Best disease, researchers have been working on understanding the function of this gene in the retina and seeking ways to target it for treatment, with the latest research delivering significant potential.

Gene therapy is a therapeutic approach which has proven safe in other retinal conditions and has shown promise for the treatment of Best Disease. With this technique, researchers have engineered small, safe viruses to deliver the correct version of the BEST1 gene to the retina in experimental models. In the US, recently published findings describe how BEST1 gene therapy was found to improve visual function and prevent disease progression in a canine model of Best disease.

Although further study is required to investigate its potential in humans, these results indicate the potential for gene therapy to benefit those living with Best disease in the future.

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 Best Disease.

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 Best Disease. For further information, please visit the Target 5000 section.

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 Best Disease. 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 Meet your researchers 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. To find out more about this study, please visit our Meet you researchers section.

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 Best Disease.

Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please email 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.

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