Best disease is also known as early-onset vitelliform macular dystrophy. It usually appears in childhood, but the onset of symptoms and the severity of vision loss can vary widely. The adult-onset form of Best disease begins later, usually in mid-adulthood, and tends to cause vision loss that worsens slowly over time. The two forms of Best disease each have characteristic changes in the macula that can be detected during an eye examination. In the early stages, pictures of the retina look like an egg yolk. Later they look like scrambled egg. There is also an accumulation of lipofuscin deposits (a waste material) which can be seen as yellowish flecks in the macula. It does not affect side (peripheral) vision or the ability to see at night.
How is Best disease inherited?
Best disease is a genetic condition inherited in the dominant form. This means that Best disease is caused by a faulty gene from one parent. This parent will have Best disease and there is a 50 per cent chance that they will pass this gene on to their child. If the child does not inherit the faulty gene they cannot pass it on to their children. The genes, which can cause Best disease, include BEST1, RDS/PRPH2 and IMPG1.
What are the symptoms?
Symptoms of Best disease can include blurring or distortion of central vision. In some cases Best disease can be asymptotic and may not cause vision loss. However, some people will lose a degree of central vision in one eye, or less commonly, both eyes.
There is currently no treatment for Best disease. Treatment can only be given for new blood vessel growth, as in wet age-related macular degeneration, and this would involve anti-VEGF injections such as Avastin® or Lucentis®. If there is fluid under the retina, some patients might benefit from drops or tablets.
Scientists are creating models of Best disease by reprogramming adult skin cells into stem cells. By using cells from people with severe Best disease researchers are able to create a model of the disease and look at the effects of the mutations on the BEST1 protein. This may give us more insight into how the condition develops. Importantly, these cells give us the opportunity to efficiently test new potential treatments and therapies, without the lengthy process of clinical trials, at least initially. These include new genetic therapies using viruses or DNA cutting to replace or edit defective genes.