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Norrie disease
This condition is typically present from birth or early infancy and can also be associated with other health issues, including hearing loss and developmental delay. It is caused by changes in the NDP gene.
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Overview
Norrie disease is a rare genetic condition that primarily affects the eyes, leading to severe vision impairment or blindness from birth or early infancy. The condition predominantly affects males due to its X-linked inheritance pattern. In some individuals, Norrie disease can also be associated with other health problems affecting hearing and development, though the severity of these additional symptoms can vary widely [PMID:31379761]. This condition is classified as a rare disease within the Ophthalmology category.
Symptoms & clinical features
The main symptoms of Norrie disease are severe eye abnormalities, which are often present at birth or develop shortly thereafter. Key features include a white mass behind the lens of the eye, often visible as a 'white pupil' (leukocoria), retinal detachment, and progressive retinal degeneration [PMID:20301710]. These issues typically lead to profound vision loss or complete blindness. In addition to ocular findings, some individuals with Norrie disease may experience progressive sensorineural hearing loss, which can range from mild to severe and often develops during childhood or adolescence. A smaller proportion of affected individuals may also have developmental delay, learning difficulties, or, less commonly, seizures [PMID:31379761]. The extent and severity of these non-ocular symptoms can differ significantly between individuals.
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Affected organs
Norrie disease primarily affects the eyes. The retina, which is the light-sensitive tissue at the back of the eye, is particularly impacted, often detaching or degenerating. Other eye structures like the lens and iris can also be affected. Beyond the eyes, the condition can sometimes affect the auditory system, leading to hearing impairment, and the central nervous system, which may manifest as developmental delay or learning difficulties. The heart and peripheral blood vessels can also be affected in some cases, although this is less common.
Risks & severity
Norrie disease typically presents with severe vision impairment or complete blindness from birth or early infancy. The progression of vision loss is generally rapid and profound. The severity of associated non-ocular features, such as hearing loss or developmental delay, can vary greatly among affected individuals, even within the same family [PMID:20301710]. Some individuals may have only eye involvement, while others experience a broader range of symptoms. Since Norrie disease is rare, the exact prevalence is not well established. Its X-linked inheritance pattern means that males are predominantly affected and typically experience more severe symptoms than carrier females, who are often asymptomatic or may have milder eye changes.
Genetic causes
Norrie disease is caused by pathogenic variants in the NDP gene. The NDP gene provides instructions for making a protein called norrin. Norrin is a signalling molecule that plays a crucial role in the development of blood vessels in the retina, as well as in the development of the inner ear and certain parts of the nervous system [PMID:20301710]. Pathogenic changes in the NDP gene disrupt the normal function of norrin, leading to abnormal development of the eye's blood vessels and subsequent retinal damage. This disruption can also affect other tissues where norrin is important, such as the ear and brain, contributing to the broader range of symptoms seen in some individuals with Norrie disease.
- NDP norrin cystine knot growth factor NDPThe NDP gene provides instructions for making the norrin protein, which is crucial for normal eye development, particularly retinal specialisation and blood vessel formation in the retina and inner ear.
Inheritance pattern
Norrie disease has an X-linked recessive inheritance pattern. This means the NDP gene is located on the X chromosome, one of the two sex chromosomes. Females have two X chromosomes, while males have one X and one Y chromosome. For males, a pathogenic variant on their single X chromosome is sufficient to cause the condition. Females with one affected X chromosome and one unaffected X chromosome are typically carriers. Carrier females usually do not show symptoms or may have very mild eye changes, as their unaffected X chromosome can compensate. Each son of a carrier mother has a 50% chance of inheriting the pathogenic variant and developing Norrie disease, while each daughter has a 50% chance of being a carrier.
X-linked recessive: sons of a carrier mother have a 50% chance of being affected. Daughters have a 50% chance of being carriers.
Diagnosis & testing
Diagnosis of Norrie disease is often suspected based on characteristic eye findings in infancy, such as leukocoria (white pupil) and retinal detachment [PMID:31379761]. Confirmation of the diagnosis is achieved through genetic testing, which identifies pathogenic variants in the NDP gene. In the UK, genetic testing for inherited retinal disorders, including Norrie disease, is available through the NHS Genomic Medicine Service. Referrals for genetic testing are typically made by ophthalmologists, paediatricians, or clinical geneticists, usually following an initial clinical assessment. The relevant NHS National Genomic Test Directory R-code for inherited retinal disorders is R80, which includes testing for NDP.
Management & lifestyle
Management of Norrie disease primarily focuses on supporting individuals with vision loss and addressing any associated symptoms. There is currently no cure for Norrie disease. Ocular management involves regular ophthalmic examinations to monitor the eye condition. Surgical interventions may be considered in some cases, particularly for retinal detachment, though outcomes for vision preservation are often limited. For hearing loss, audiology assessments and hearing aids may be recommended. Developmental support, including early intervention programmes, special educational provision, and therapies (e.g., speech and language therapy, occupational therapy), can be beneficial for individuals with developmental delay. All management plans should be individualised and coordinated through multidisciplinary teams within the NHS, often involving specialists in ophthalmology, audiology, paediatrics, and clinical genetics. Genetic counselling is an important part of care, providing information about inheritance patterns, risks to family members, and reproductive options.
UK care pathway
In the UK, individuals suspected of having Norrie disease would typically enter the NHS Genomic Medicine Service pathway. This often begins with a referral from a specialist, such as an ophthalmologist or paediatrician, to a Clinical Genetics service. Clinical geneticists and genetic counsellors work together to assess the family history, offer genetic testing (under NHS National Genomic Test Directory R-codes like R80 for inherited retinal disorders), and provide information and support. This pathway ensures access to specialist diagnostic services and ongoing genetic counselling.
Frequently asked questions
Is Norrie disease always associated with blindness?
Yes, individuals with Norrie disease typically experience severe vision impairment or complete blindness, usually from birth or early infancy, due to profound retinal abnormalities.
Can females be affected by Norrie disease?
Norrie disease primarily affects males. Females are typically carriers due to the X-linked inheritance pattern, meaning they carry the genetic change but usually do not develop symptoms or have very mild eye changes.
Are there treatments for Norrie disease?
There is currently no cure for Norrie disease. Management focuses on supporting individuals with vision loss and addressing any associated health issues, such as hearing loss or developmental delay, through specialist NHS services.
How is Norrie disease diagnosed?
Norrie disease is typically diagnosed based on characteristic eye findings in infancy, such as a white pupil, and is confirmed by genetic testing to identify pathogenic variants in the NDP gene.
What support is available for families affected by Norrie disease?
Families can access support through NHS clinical genetics services, genetic counselling, and specialist paediatric and ophthalmology teams. Patient advocacy groups and charities also offer valuable resources and community support.
References
- Shastry BS. SNPs: impact on gene function and phenotype. Methods in molecular biology (Clifton, N.J.). 2009. PMID: 19768584
- Adam MP, Bick S, Mirzaa GM. NDP-Related Retinopathies. 1993. PMID: 20301506
- Kanukollu VM, Tripathy K. Leukocoria. 2023. PMID: 32809629
- De Silva SR, Arno G, Robson AG. The X-linked retinopathies: Physiological insights, pathogenic mechanisms, phenotypic features and novel therapies. Progress in retinal and eye research. 2021. PMID: 32860923
- Sızmaz S, Yonekawa Y, T Trese M. Familial Exudative Vitreoretinopathy. Turkish journal of ophthalmology. 2015. PMID: 27800225
- Ho HH. The tale of capturing Norrin. eLife. 2024. PMID: 38814685
- Denzer L, Muranyi W, Schroten H. The role of PLVAP in endothelial cells. Cell and tissue research. 2023. PMID: 36781482
- Özdek Ş, Özdemir Zeydanlı E, Baumal C. Avascular Peripheral Retina in Infants. Turkish journal of ophthalmology. 2023. PMID: 36847634