Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by the incomplete development of the retinal vasculature. Its clinical appearance varies considerably, even within families, with severely affected patients often registered as blind during infancy, whereas mildly affected patients with few or no visual problems may have such a small area of avascularity in their peripheral retina that it is visible only by fluorescein angiography. It is believed that this peripheral avascularity is the primary anomaly in FEVR and results from defective retinal angiogenesis. The sight-threatening features of the FEVR phenotype are considered secondary to retinal avascularity and develop because of the resulting retinal ischemia; they include the development of hyperpermeable blood vessels, neovascularization, vitreoretinal traction, retinal folds, and retinal detachments (summary by Poulter et al., 2010). In 31 Chinese pedigrees clinically diagnosed with FEVR, Rao et al. (2017) analyzed 6 FEVR-associated genes and identified mutations in 12 of the probands, including 5 (16.1%) in LRP5, 3 (9.7%) in NDP, 2 (6.5%) in FZD4, and 1 (3.2%) in TSPAN12. In addition, a mutation in the KIF11 gene (148760) was identified in a patient who also exhibited microcephaly (MCLMR; 152950). The authors noted that their detection rate did not exceed 50%, suggesting that other FEVR-associated genes remained to be discovered. Genetic Heterogeneity of Familial Exudative Vitreoretinopathy Also see EVR2 (305390), caused by mutation in the NDP gene (300658) on chromosome Xp11; EVR3 (605750), mapped to 11p13-p12; EVR4 (601813), caused by mutations in the LRP5 gene (603506) on 11q13.4; EVR5 (613310), caused by mutation in the TSPAN12 gene (613138) on 7q31; EVR6 (616468), caused by mutation in the ZNF408 gene (616454) on 11p11; and EVR7 (617572), caused by mutation in the CTNNB1 gene (116806) on chromosome 3p22.

Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by the incomplete development of the retinal vasculature. Its clinical appearance varies considerably, even within families, with severely affected patients often registered as blind during infancy, whereas mildly affected patients with few or no visual problems may have such a small area of avascularity in their peripheral retina that it is visible only by fluorescein angiography. It is believed that this peripheral avascularity is the primary anomaly in FEVR and results from defective retinal angiogenesis. The sight-threatening features of the FEVR phenotype are considered secondary to retinal avascularity and develop because of the resulting retinal ischemia; they include the development of hyperpermeable blood vessels, neovascularization, vitreoretinal traction, retinal folds, and retinal detachments (summary by Poulter et al., 2010). For a discussion of genetic heterogeneity of familial exudative vitreoretinopathy, see EVR1 (133780).

Familial exudative vitreoretinopathy is a hereditary disorder that can cause vision loss that worsens over time. This condition affects the retina, the specialized light-sensitive tissue that lines the back of the eye. In people with this disorder, blood vessels do not fully develop at the outer edges (periphery) of the retina, which reduces the blood supply to this tissue. This prolonged reduction in blood supply (chronic ischemia) causes continued damage to the retina and can lead to worsening of the condition. \n\nThe signs and symptoms of familial exudative vitreoretinopathy vary widely, even within the same family. In many affected individuals, the retinal abnormalities never cause any vision problems. Other people with this condition develop abnormal vessels that leak. This  causes chronic inflammation which, over time, can lead to fluid under the retina (exudate). A reduction in the retina's blood supply causes the retina to fold, tear, or separate from the back of the eye (retinal detachment). The resulting retinal damage can lead to vision loss and blindness. Other eye abnormalities are also possible, including eyes that do not look in the same direction (strabismus) and a visible whiteness (leukocoria) in the normally black pupil.\n\nSome people with familial exudative vitreoretinopathy also have a condition known as osteoporosis-pseudoglioma syndrome, which is characterized by reduced bone density. People with this condition have weakened bones and an increased risk of fractures.