Best vitelliform macular dystrophy is an early-onset autosomal dominant disorder characterized by large deposits of lipofuscin-like material in the subretinal space, which creates characteristic macular lesions resembling the yolk of an egg ('vitelliform'). Although the diagnosis of Best disease is often made during the childhood years, it is more frequently made much later and into the sixth decade of life. In addition, the typical egg yolk-like lesion is present only during a limited period in the natural evolution of the disease; later, the affected area becomes deeply and irregularly pigmented and a process called 'scrambling the egg' occurs, at which point the lesion may appear as a 'bull's eye.' The disorder is progressive and loss of vision may occur. A defining characteristic of Best disease is a light peak/dark trough ratio of the electrooculogram (EOG) of less than 1.5, without aberrations in the clinical electroretinogram (ERG). Even otherwise asymptomatic carriers of BEST1 mutations, as assessed by pedigree, will exhibit an altered EOG. Histopathologically, the disease has been shown to manifest as a generalized retinal pigment epithelium (RPE) abnormality associated with excessive lipofuscin accumulation, regions of geographic RPE atrophy, and deposition of abnormal fibrillar material beneath the RPE, similar to drusen. Occasional breaks in the Bruch membrane with accompanying neovascularization have also been reported, although Best disease is not noted for extensive choroidal neovascularization. [From OMIM]