Humans are able to see the world through the eyes. Many people may have not realised that the ability to have a perfect pair of eyes that can ponder the beauty of everything around them, is a blessing. There are still many people who have abnormal eyes in terms of structure or function. Certain eye diseases may affect a person since they are young and cause eye problems. One of them is Norrie disease. In this DoctorOnCall’s article, we will learn more about Norrie disease.
Norrie disease is an eye disorder which is characterised by blindness that occurs in male babies. This condition can occur at birth or soon after birth. You may wonder why it is male that are most likely to be affected by this condition. To understand this, you have to know that Norrie disease is an inherited disease which means it is associated with genetics. Most specifically, mutation in the NDP gene causes such changes to the eyes with a wide range of retinopathies. NDP gene is responsible for norrin protein that is essential for development of blood vessels. Norrie disease is the most severe form of retinopathy. Roughly, retinopathy are diseases of the retina. Retina is the layer of tissue consisting of the cells that senses light and convey signals to the brain to be interpreted as images. These specific layers is at the back wall inside the eye.
Thus, what makes male more susceptible to getting the disease? Norrie disease is an X-linked condition. There’s just one X chromosome and a Y chromosome in the male. Thus, when there is a faulty X-chromosome such as with Norrie disease, male are definitely affected as there is only one X-chromosome. This is in contrast with females as females have two X chromosomes which means that even if there is one X-chromosome affected by the abnormal gene, the female would only be a carrier. Such a condition translates to a female being a carrier of having 50% chance to pass the gene with Norrie disease to their child.
Norrie disease is considered a rare disease. It is estimated that only 500 cases have been found globally. It is worth noting that this number may have been higher due to unreported cases or undiagnosed properly. Norrie disease causes the abnormal development of the retina and the blood vessels in the eye. Thus, when the retina is affected, it causes symptoms that mainly revolve around visual impairment.
Main symptom is blindness that is often found at birth. The blindness progressed most throughout their childhood. These retinal degradations usually occur by 3 months of age. Apart from this, the abnormal development of the retina can lead to retinal detachment. When this develops, a greyish-yellow mass in the back of the eye can be seen. This mass is known as leukocoria and can be seen clearly when there is illumination from light onto the eyes. Patients may also be presented with cataracts which can be seen when the iris (coloured part of the eyes) turns white or opaque. As the disease progresses, it can cause the eyeball to become smaller (phthisis bulbi) and significant when the patient reaches the age of 10. Eyes may also be abnormally small in size at birth with widened pupils (the hollow part of the eyes allowing light entering the eyes). Iris may be attached to the lens (clear disc behind the iris) or to the cornea (clear part in front of the eyes). This sticking part causes increased pressure in the eyes caused by the blocked flow of fluid flowing throughout inside the eyes.
Symptoms are not entirely limited to the eyes problems. Another symptom associated with Norrie disease is progressive hearing loss. This is because there are also abnormalities of the blood vessels playing part of the inner ear function. Inner ear is one of the important parts of the ear that aids in the hearing process. This begins in early childhood in a mild manner and significant hearing loss can be severe when the patient is around 30 years old, though this can occur between the age 5 to 48 years old.
These visual impairment and hearing loss may resulted in developmental delays which turned to be a learning disability. Developmental delays such as motor skills are greatly affected. Apart from intellectual issues, it may also cause patients to have behavioural issues. Autistic traits may be seen. Last but not least, due to the fact that it may affect the blood vessels, it can cause many other symptoms related to the blood vessels function such as leg ulcers and erectile dysfunction. Ranges and severity of symptoms will vary greatly even if their family members are diagnosed with Norrie disease.
Treatment for Norrie disease will depend on the symptoms. Thus, treatment aim to address the symptoms even if there is no standard care due to the fact it is a rare condition. Treatment can be from surgery, hearing aids and specialised education. For patients and their families, genetic counselling is recommended.
