Norrie Genetic Disease Paper Example

Introduction

Norrie disease is a genetically inherited eye disorder experienced in male mostly in birth or after birth. It leads to blindness in male, but the effect varies from one individual to another in the same family (Pagon, 2007). An affected individual shows symptoms such as abnormality of the retinal vasculature, blindness, clouding of the lens of the eye, and abnormal morphology. They also develop a hearing problem and may lead to slowness mental development such as behavioral issues, and delays in the development of some body parts. Early establishment of specific symptoms ensures treatments directed towards recognized signs of the affected individual (Shapiro, 2010). These help in conducting individual therapy and special education to the affected children to ensure they reach their potential in life. It does not link to any society, race or ethical group and its rare disorder. This paper will discuss in detail all the area of Norrie disease.

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Description

Causes of Norrie disease are lack of proper functioning of norrin protein found in the NDP gene. NDP gene gives a directive for producing norrin protein. Norrin protein plays a critical role in the growth of retinal cell and blood supply to tissues of the retina in the eye and growth of other body systems. Changes in the NDP gene may prevent the proper working of the norrin protein leading to symptoms of Norrie disease. X-chromosome contain NDP gene thus mutation of the gene lead Norrie disease in males, gotten genetically through X- linked recessive pattern. Males are mostly at high risk of being affected by X-linked recessive disorder than females since it causes two mutated copied of the genes in female thus putting male at high risk of being affected by Norrie disease (Chamney, McLoone, & Willoughby, 2011).

Norrie disease affects the healthy development of the retina cell that senses light and color, leading to undeveloped retinal cells occupying at the back of the eye. These result in the white appearance of the pupil when light shines to them. These may result in the shrinking and deteriorate of the irises or eyeballs mostly in the first month of life and development of the cloudiness in the lens of the eye. The result of the infection leads to blindness in male infants.

The affected individuals with Norrie disease develop continuing hearing loss (Abeshi, et al., 2017). They also experience delays in the development of some normal motor skills such as walking, talking, sitting up, and other behavioral issues. Some of the other problems that may affect an individual with Norrie disease include intellectual disability, breathing problems, psychosis, growth failure, reproduction, or erectile dysfunction, digestion problem and abnormalities that affect blood circulation. Other disorders associated with a change in NDP gene that is related to Norrie disease include persistent hyperplastic primary vitreous, coats disease, X-linked familial exudative, and retinopathy prematurity

Molecular Genetics

The short arm of X-chromosome contains Norrie disease gene. The NDP gene is small in structure and contains three exons. Norrie disease gene mutation occurs in second and third exons since they are full of protein chains known as Norrin. Studies show that an NDP protein has the same structure with a carboxy-terminal that provides recognition in targeting of retinal connection (Abeshi et al., 2017). Norrin receives instruction from NDP gene that assists in sending molecular signal pathway that influences the development of tissues in the body. The role of signaling by norrin affects cell division, migration, and other cell activities. The pathways alter the molecular processes that are critical in normal eye development and other body parts.

Clinical Features

Norrie disease is X-linked recessive disorder with features such as the development of hearing loss as time goes mostly with the ten years after birth. The affected individuals also develop blindness after birth or shortly after birth (Smith, Mullen, Graham, Sims, & Rehm, 2012). White appearance of the pupils of affected person when the light is shined to them. The eyeball and the colored part the eyes may start to shrink shortly after birth. A patient may obtain cataract of the eye that is the cloudiness in the lenses of the eye. The affected individual is said to experiences delays in the development of motor skills for example walking, crawling, and sitting up. It gently develops mental retardation and intellectual inability. Some of the patients also develop psychological and cognitive disorder such as psychosis. Others symptoms associated with Norrie disease include digestion, excretion, growth failure, breathing, and blood circulation problems.

Mode of Inheritance

The disease passed through X-linked recessive arrangement. The disorder is only valid if the mutated gene that initiates the condition found on the X-chromosome. The body has an approximate forty-six chromosome with two X and Y sex chromosome. Males have both Y and X -chromosome and only one malformed copy of the gene in every cell is adequate to trigger the disease. A female has two X- chromosome and the two must be malformed in both copies of the gene to trigger the disorder. These are the reason female are less affected by the disease.

The features of the X- Linked do not allow a father to pass the traits to their sons thus need carriers who are their daughters. It is because of male pass Y-chromosome to son offspring and X- chromosome to their daughter offspring. The X-linked recessive inheritances use one altered copy of the gene in every cell in female as a carrier to pass the traits (Chamney, McLoone, & Willoughby, 2011). The female passes the gene to the male infants but does not necessarily show or experiences any sign of the disorder. It only under minimum cases the female carrier has shown symptoms such as hearing loss problems and developing retinal abnormalities involved with Norrie disease.

Diagnosis

Making a diagnosis, the doctors mostly review the medical history, physical examining, related symptoms and test result from the laboratory to decide on the diagnosis (Dubucs et al., 2018). It also involves looking at family history to ascertain if it had experiences any inheritance of the X-linked gene. Genetically related diseases confirmed through conducting a molecular genetic test show to identify the mutation of the NDP gene in X- chromosome. There is a need to perform a series of differential diagnosis to ascertain if the sign disorder related to other NDP mutations such as persistent hyperplastic primary vitreous other than Norrie disease (Abeshi et al., 2017). There is also a need to conduct parental testing such as at-risk pregnancies if there is a family history of the disease in either of the sides.

Management of Disease

Norrie disease has no specific treatment established, but there are measures to minimize the effect. Medical treatment requires different specialist such as those who asses the retinal treatment, a specialist who treats hearing loss among other professional to have a comprehensive plan on effective treatment. Individuals identified with cataracts, surgery may be appropriate to remove it that might control and prevent eyeballs from shrinking. A cochlear implant may be useful in where the hearing is significantly impaired. Also, the hearing aid may be helpful to individuals affected with hearing loss.

Early identification of the Norrie disease is a great benefit to the child since they will be enrolled in appropriate special education (Chow et al., 2010). These ensure the children appreciate their status and can attain their highest potential. It also guarantees the children benefits from other medical and social services. Providing guidance and counseling of genetic issues to families helps in mitigating the risk associated with genetic inheritances (Pagon, 2007). Lastly finding a specialist who experienced in the area will assist in the management of the disease.

Prognosis

Most of the research has concluded that life span of individual affected with Norrie disease may reduce due to a general risk connected with hearing loss problems, blindness, intellectual disability such as breathing problem and increased risk of trauma. Also, studies show that hearing loss and blindness may develop at adulthood mostly after ten years from birth.

Conclusion

Norrie disease is a genetically inherited eye disorder that is known to cause blindness mostly in males infants at birth or shortly after birth. It is causes mutation of the NDP gene on X- chromosome leading to malfunctioning of norrin protein. Norrin is involved in cell division in the retina and blood supply thus enhancing normal growth of the eye cell. Norrie disease is characterized by blindness, hearing loss problems, shrinking of an eyeball, development of cataract and whitening of the pupils. Patients are also associated with a delay in the development of motor skills, psychological, behavioral disorder, breathing problem, and reproduction.

The disease inherited through an X-linked recessive manner. The traits are passed from father to daughter offspring since he donates X- chromosome to a daughter while Y- chromosome to a son. Inheritance is through altered copies of the gene in every cell of a female carrier. Diagnosis of the disease is through a close review of medical history, sign, and laboratory test. Molecular genetic analysis is carried out to confirm the gene. The condition has no identified treatment and measures taken to manage the disease-directed toward the symptoms. Norrie disease reduces the life span of the affected patient.

References

Abeshi, A., Marinelli, C., Beccari, T., Dundar, M., Ziccardi, L., & Bertelli, M. (2017). Genetic testing for Norrie disease. The EuroBiotech Journal, 1(s1), 77-79. doi:10.24190/issn2564-615x/2017/s1.24

Chamney, S., McLoone, E., & Willoughby, C. E. (2011). A mutation in the Norrie disease gene (NDP) associated with familial exudative vitreoretinopathy. Eye, 25(12), 1658-1658. doi:10.1038/eye.2011.226

Chow, C. C., Kiernan, D. F., Chau, F. Y., Blair, M. P., Ticho, B. H., Galasso, J. M., & Shapiro, M. J. (2010). Laser Photocoagulation at Birth Prevents Blindness in Norrie's Disease Diagnosed Using Amniocentesis. Ophthalmology, 117(12), 2402-2406. doi:10.1016/j.ophtha.2010.03.057

Dubucs, C., Merveille, M., Kessler, S., Sevely, A., Chassaing, N., & Calvas, P. (2018). Prenatal diagnosis of Norrie disease based on ultrasound scan findings. Ultrasound in Obstetrics & Gynecology. doi:10.1002/uog.20097

Pagon, R. A. (2007). GeneTests: Integrating Genetic Services into Patient Care*. The American Journal of Human Genetics, 81(4), 658-659. doi:10.1086/521407

Smith, S. E., Mullen, T. E., Graham, D., Sims, K. B., & Rehm, H. L. (2012). Norrie disease: Extraocular clinical manifestations in 56 patients. American Journal of Medical Genetics Part A, 158A(8), 1909-1917. doi:10.1002/ajmg.a.35469