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Juvenile X-linked Retinoschisis
X-linked Retinoschisis is an inherited retinal degeneration (IRD) and is often referred to as Juvenile Retinoschisis due to its early onset. As the name suggests, X-linked Retinoschisis has an X-linked pattern of inheritance and primarily affects boys and young men.
Retinoschisis is a condition which affects the the light-sensitive tissue layer at the back of the eye, called the retina. The retina contains rod and cone photoreceptor cells, located primarily at the centre and outer edges of the retina respectively and appear to be equally affected by the condition.
What are the symptoms of X-linked Retinoschisis?
X-linked Retinoschisis is most commonly diagnosed when young boys experience difficulty with central vision and is a form of Juvenile Macular Degeneration. Most boys with Retinoschisis present with a mild decrease in central vision that may be subtle and not noticed which can continue until adulthood, when it begins to stabilise.
People living with X-linked Retinoschisis can also experience farsightedness (hyperopia), eyes looking in different directions (strabismus) and in more severe cases, involuntary eye movements (nystagmus). Affected individuals are also more susceptible to retinal detachment and eye haemorrhage (bleeding) than other people and therefore should have regular examinations with an eye doctor. When detected early, a retinal detachment can be treated with surgical intervention.
What Causes X-linked Retinoschisis?
Mutations in the RS1 gene which makes the retinoschisin protein cause X-linked Retinoschisis to develop. It is suggested that the retinoschisin protein has a role in the retina’s development and maintenance. Mutations in the RS1 gene cause insufficient retinoschisin to be produced, and as a result, the retina splits and tears.
As genes responsible for causing X-linked Retinoschisis are located on the X chromosome, males are primarily affected as they only require one faulty copy of the RS1 gene for the condition to develop. For females to be affected, a faulty RS1 gene copy must exist on both X chromosomes. For this reason, female are mainly “carriers” of the condition and usually have only one faulty RS1 gene copy and typically retain normal vision. However, in rare circumstances, due to the phenomenon of ‘non-random X chromosome inactivation’ some female carriers may have symptoms. Men, on the other hand, will develop sub-optimal vision if they have an affected X chromosome. Affected males cannot pass on the disease to their sons, because they pass on their Y chromosome. Men who have Retinoschisis will pass on the mutated gene to all of their daughters who in turn become carriers of the condition.
A variety of tests can be used to identify and confirm X-linked Retinoschisis, particularly optical coherence tomography tests to visualise the retina tears and electroretinograms, which assess the integrity of the rod and cone photoreceptors by measuring their responsiveness to light. Genetic testing is also a vital part of the diagnostic process as detection of the mutated RS1 gene can confirm that the individual has X-linked Retinoschisis.
What treatments are available?
Currently, there are no medical or surgical treatments available for Retinoschisis. Glasses may improve the overall quality of vision in a patient with Retinoschisis who is also near-sighted or farsighted, but will not repair the nerve tissue damage caused. The first gene-therapy Luxturna is approved for treating a form of Leber Congenital Amaurosis caused by mutations in both RPE65 gene copies. Although this therapy is not suitable for people living with X-linked Retinoschisis, it highlights the potential of a gene-therapy to resolve the mutation in the RS1 gene and may lead to great success.
General eye check-ups are important for people with Retinoschisis, as these men and boys are still at risk for other kinds of eye problems that can affect the general population and may be treatable. They are also more vulnerable to retinal detachments and haemorrhages. Regular visits to your eye doctor can also make you aware of current advances as we learn more about X-linked Retinoschisis.