<unk>  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<unk>  cystine knot growth factor (NDP) gene, which is located on the X chromosome. In addition to the congenital ocular symptoms, the majority of patients suffer from a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties among other additional characteristics. Patients with<unk>  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/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,<unk>  affects almost entirely males. Only in very rare cases, females have been diagnosed with<unk> ; 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.
Norrie disease
Waldmann disease
Karak syndrome
Camisa disease
Batten disease
Leber congenital amaurosis
Gleich's syndrome
Zaki syndrome