Norrie Disease (ND) is a rare hereditary condition that is inherited in an X-linked recessive pattern - seen almost exclusively in males. From the retina perspective, it has some similarities to familial exudative vitreoretinopathy (FEVR). In general, the retina is less well developed in ND than in FEVR. As in FEVR, scar tissue may develop which – as it contracts – can detach the retina and result in visual loss. Vision loss may also occur as consequence of poor retinal development, or as a result of abnormal leaking blood vessels (exudation).
Symptoms: Patients with Norrie disease have profound bilateral visual impairment, small eyes and “white pupils” due to scar tissue present immediately behind the iris/pupil. Hearing loss and mental impairment occur in approximately 30% of patients. Ocular findings include poor retinal development, retinal detachment, bleeding into the gel that fills the eye (vitreous hemorrhage), and findings typical of persistent fetal vasculature (PFVS). The peripheral retina often lacks normal development of retinal blood vessels.
The Norrie disease protein (NDP) has an important role in the Wnt pathway. Similar to FEVR, the genetic abnormality in Wnt signaling impacts on growth and development of retina and retinal blood vessels.
Causes and Risk Factors: Apart from heredity, there are no specific risk factors.
Diagnostic Testing: Genetic testing is available for Norrie’s disease. As with many diseases known to be under genetic control, there may be several mutations. Norrie’s disease testing will confirm the diagnosis in 80% of the cases, leaving 20% of children where a mutation cannot be found, but clinical examination confirms Norrie’s disease. See Norrie’s website at: http://www.norriedisease.org/
Treatment/Prognosis: Unlike FEVR, ND generally presents in more advanced stages. Historically, no treatment has been offered to mitigate the untreated natural history of progression to blindness. For these more advanced stages surgery can be performed to remove or interrupt scar tissue and release traction. This encourages reattachment of the retina, which can stabilize or improve vision. We have shown that Norrie disease patients maintain at least light perception vision in one eye after vitrectomy surgery.
Once stable, individuals with ND are usually followed every 6 months. Like FEVR, ND is a life-long disease.