Incomplete normal retinal angiogenesis is the hallmark of a group of retinal vascular diseases including familial exudative vitreoretinopathy (FEVR). The primary pathological process in FEVR is believed to be a premature arrest of retinal angiogenesis/vasculogenesis or retinal vascular differentiation, leading to incomplete vascularization of the peripheral retina (van Nouhuys 1991). This failure to vascularize the peripheral retina is the unifying feature seen in all affected individuals, but by itself usually causes no clinical symptoms. The visual problems in FEVR result from secondary complications due to the development of hyperpermeable blood vessels, neovascularization and vitreo-retinal traction. These features cause a reduction in visual acuity and in 20% of cases can lead to vitreous hemorrhage and partial or total retinal detachment. We have been using FEVR as a genetic model to understand this group of diseases. FEVR is a well-defined inherited disorder of retinal vessel development (MIM 133780) (Benson 1995, van Nouhuys 1991). It is reported to have a penetrance of 100% but clinical features can be highly variable, even within the same family. Severely affected patients may be blind during the first decade of life, while mildly affected individuals may not even be aware of symptoms and are only diagnosed by fluorescein angiography (Ober et al. 1980). FEVR is genetically heterogeneous, and can be presented as autosomal dominant, autosomal recessive or X-linked traits. Three loci have been mapped and two genes (Frizzled-4 gene, FZD4 , Robitaille et al 2002; LRP5, Toomes et al 2004b) have been identified in dominant FEVR.We are currently working to develop a disease classification and staging system.

Detailed information about FEVR is available on the OMIM, Online Mendelian Inheritance in Man website and at FEVR.net, a site designed to orient patients with the signs and symptoms of FEVR and provide support for patients and families through education, outreach and understanding. You can visit these sites by clicking on the graphics below.