Norrie disease

Norrie disease is a genetic disorder that primarily affects the eye and almost always leads to blindness. In addition to the congenital ocular symptoms, some patients suffer from a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties. Norrie disease is a genetic disorder that primarily affects the eye and almost always leads to blindness. In addition to the congenital ocular symptoms, some patients suffer from a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties. Patients with Norrie disease may develop cataracts, leukocoria (a condition 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. The disease affects almost only male infants, because the disease is inherited X-linked recessive. Only in very rare cases, females have been diagnosed with Norrie disease as well. The exact incidence number is unknown; only a few hundred cases have been reported. It is a very rare disorder that is not associated with any specific ethnic or racial groups. The most prominent symptoms of Norrie disease are ocular. The first visible finding is leukocoria, a grayish-yellow pupillary reflex that originates from a mass of disorganized tissue behind the lens. This material, which possibly includes an already detached retina, may be confused with a tumor and thus is termed pseudoglioma. However, an affected baby may have a normally sized eye globe and inconspicuous iris, anterior chamber, cornea and intraocular pressure. Over the first few months of life, complete or partial retinal detachment evolves. From infancy through childhood, the patient may undergo progressive changes in the disease. These progressions include the formation of cataracts, deterioration of the iris with adhesions forming between the iris and the lens or the cornea, and shallowing of the anterior chamber which may increase intraocular pressure, causing eye pain. As the situation worsens, there is corneal opacification, where the cornea becomes opaque, and band keratopathy. Intraocular pressure is lost and the globe shrinks. In the last stage of Norrie disease, the globes appear small and sunken in (phthisis bulbi) and the cornea appears to be milky. Norrie disease can also have cognitive and behavioral symptoms. Developmental delay or learning difficulties are present in about 30 to 50% of males who have Norrie disease. Psychotic-like features and poorly characterized behavior abnormalities may also be present. Auditory symptoms are common with Norrie disease. Progressive hearing loss starts in early childhood for a majority of males with the condition. Early hearing loss is sensorineural, mild and asymmetric. By adolescence, high-frequency hearing loss begins to appear. Hearing loss is severe, symmetric, and broad-spectrum by the age of 35. However, studies show that while the hearing loss is deteriorating, the ability to speak well is highly preserved. The slowly progressing hearing loss is more problematic to adjust to than the congenital blindness for most people with Norrie disease. Norrie disease is a genetic disorder caused by mutations in the NDP gene, located on Xp11.4 (GeneID: 4693). It is inherited in an X-linked recessive manner. This means that almost only males are affected. Sons of affected men will not have the mutation, while all of their daughters will be genetic carriers of the mutation. They also usually show no clinical symptoms, but will pass the mutation to 50% of their offspring. Daughters with the mutated gene will also be, like their mother, asymptomatic carriers, but 50% of their sons will express clinical symptoms. Females are very unlikely to express clinical signs. One possible scenario leading to this (unlikely) case would be if both of their copies of the NDP gene bear mutations, which could be the case in consanguineous families or due to a spontaneous somatic mutation. Another explanation for affected females could be skewed X-chromosome inactivation. However, there have been a few rare cases where females have shown symptoms associated with Norrie disease such as retinal abnormalities and mild hearing loss.