Best macular dystrophy, sometimes called Best vitelliform dystrophy or Best dystrophy is a disease of the retina caused by genetic mutations in a gene known as BEST1. It is named after a German ophthalmologist, Friedreich Best, who described the first family in 1905. The clinical disease is uncommon although not rare.
Best disease primarily affects the macula which is a special area of the retina that we use for our best vision. That is because this area contains the highest concentration of rods and cones which are the cells that respond to light stimulation. The macula is located in the central portion of the retina which we use when focusing directly on visual targets (such as printed material). Therefore, any disease which interferes with normal functioning of this portion of the retina will lead to loss of good, sharp vision that we all depend upon for much of our daily activities. This disease is only one of many forms of macular degeneration though. Some, such as Best disease, are inherited, others are related to aging, trauma, and even other retinal disorders.
Best macular dystrophy is caused by a gene change (mutation) that is passed from parent to child. The gene change can result in clinical disease when inherited in a single dose (we all have two copies of our genes, receiving one from each of our parents). The resulting family pattern of retinal disease is called ‘autosomal dominant’. In general, half (50%) of the children born to someone carrying the Best mutation will inherit the mutant gene. But not everyone that inherits the altered gene develops symptoms and among those with macular abnormalities there is much variability in clinical manifestations and disease progression. The severity of disease among parents is not correlated with the nature of clinical disease in their offspring.
Recently several families have been reported in which the parents had no clinical or electrophysiologic evidence of Best disease but the classical signs and symptoms were present in one or more children suggesting that this condition may also be inherited in an autosomal recessive pattern. In this case, the parents have a 25% chance that any subsequent children will have Best disease.
Macular disease, including Best dystrophy, can usually be diagnosed by your ophthalmologist by examination of the retina. A simple test called an EOG (electro-oculogram) can detect the presence of the abnormal BEST1 gene even when the retina and vision are normal (such as occurs in up to 10% of individuals). However, due to the highly variable nature of the disorder, it is simply not possible to predict who may develop symptoms or how rapidly they progress, if at all. Up to a third of patients maintain reading and driving vision through the 5th and 6th decades of life. At any point in time among patients with some degeneration in the macula, nearly two-thirds have vision this good or better. One study found that less than 20% lost vision when followed for a decade. Among other individuals the vision may fluctuate dramatically, sometimes beginning in the first decade, with periods of severe vision loss usually in only one eye and subsequent marked improvement lasting for years. It is important to note that Best disease does not lead to complete blindness although eventually about 10% fit the definition of legal blindness (20/200 or worse using an eye chart).
Best disease does not cause any clinical problems outside of the eye. In addition to the retinal damage, some patients are far-sighted which may lead to crossing of the eyes (strabismus). In some children this can lead to a lazy eye (amblyopia). Glasses can correct the far-sightedness and prevent the lazy eye condition. Even the lazy eye can be treated after it occurs, especially in children. No treatment is available for the retinal disease nor is gene therapy available for the mutation.