Norrie disease

Norrie disease is a rare disease and genetic disorder that primarily affects the eyes and almost always leads to blindness. It is caused by mutations in the Norrin cystine knot growth factor (NDP) gene, which is located on the X chromosome. In addition to the congenital ocular symptoms, the majority of patients experience a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties among other additional characteristics. Patients with Norrie disease may develop cataracts, leukocoria (where the pupils appear white when light is shone on them), along with other developmental issues in the eye, such as shrinking of the globe and the wasting away of the iris. Around 30 to 50% of them will also have developmental delay or learning difficulties, psychotic-like features, incoordination of movements or behavioral abnormalities. Most patients are born with normal hearing; however, the onset of hearing loss is very common in early adolescence. About 15% of patients are estimated to develop all the features of the disease. Due to the X-linked recessive pattern of inheritance, Norrie disease affects almost entirely males. Only in very rare cases, females have been diagnosed with Norrie disease; cases of symptomatic female carriers have been reported. It is a very rare disorder that is not associated with any specific ethnic or racial groups, with cases reported worldwide (including cases in North America, South America, Europe, Asia and Australasia). While more than 400 cases have been described, the prevalence and incidence of the disease still remains unknown. The most prominent symptoms initially observed in Norrie disease are ocular. Initial characteristics are usually identified at birth or in early infancy, with parents often noticing abnormal eye features or that their child fails to show a response to light. The first visible finding is leukocoria, a grayish-yellow pupillary reflection that originates from a mass of disorganized tissue behind the lens.