|Locus||Gene (OMIM)||Genomic Location||Inheritance||Key Reference (Pubmed)|
|NDP1||NDP||Xp11.3||X-linked Recessive||Berger et al., 1992; Chen et al., 1992|
The diagnosis of Norrie disease can be difficult. Classic features include specific ocular symptoms (pseudotumor of the retina, retinal hyperplasia, hypoplasia and necrosis of the inner layer of the retina, cataracts, phthisis bulbi), progressive sensorineural hearing loss, and mental disturbance, although less than one-half of patients are hearing impaired or mentally retarded. The Norrie gene encodes for a protein of 133 amino acids that has homologies at the C-terminus to a group of proteins including mucins. The high proportion of new mutations is an expected finding for an X-linked disorder with greatly reduced male reproductive fitness ( Berger et al., 1992 ). It was suggested that the norrin protein regulates vascularization of the cochlea and retina ( Rehm et al, 2002 ).