X-linked juvenile retinoschisis (RS) is a genetic disorder affecting males. Major symptoms include poor eyesight and degeneration of the retina. The retina consists of membrane layers in the eye that receive visual images. It is composed of supportive and protective structures, nervous system components and layers including "rods" and "cones." RS is due to splitting of the retina, which, in turn, causes slow, progressive loss of parts of the fields of vision corresponding to the areas of the retina that have become split. Often, RS is associated with the development of cysts (sac-like blisters) in the retina.
Symptoms of X-linked juvenile retinoschisis (RS) may include poor eyesight, detachment of all or part of the retina from the rest of the eye, and eventually complete retinal atrophy (wasting away) with hardening of the choroid (the membrane between the white part of the eye and the retina).
The patient may develop cysts in the macula (an oval area of the retina) and other areas of the retina. The cysts lead to splits within the retina. The cystic manifestations may also appear in other family members. Bleeding within the eye may occur.
Problems with vision may be mild up until the age of 40 or 50, after which the condition may slowly worsen. In other cases, vision may decline rapidly during childhood.
X-linked juvenile retinoschisis (XJRS) is inherited as an X-linked recessive trait. The change (mutation) responsible for this disorder is located on the X chromosome (Xp22.2-p22.1).
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome Xp22.2-p22.1” refers to a region between bands 22.1 and 22.2 on the short arm of the X chromosome. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother. All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is “turned off”. A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
X-linked juvenile retinoschisis is a rare disorder present at birth. The disorder affects males, although cases have been reported of females born with this disorder who are children of close relatives who marry. Although some cases have been reported in younger children, most cases are diagnosed at age 6 or older.
In recent years, diagnosis of this disorder has become easier and more certain through the application of electroretinography (ERG) and optical coherence tomography (OCT).
Electroretinography measures the response of the cones and rods (photoreceptor cells of the retina) under light- and dark-adapted conditions. Electrodes, in the form of contact lenses, are placed in the eye while other electrodes are applied to the forehead and earlobe. The patient looks at a flashing light and the electrodes measure the retinal responses.
Optical coherence tomography creates high-resolution color images of the parts of the eye. It is a non-invasive technique that measures the thickness of the macula and/or the nature of the nerve fibers and/or reflections of any particles that may be in the jelly-like substance that fills the interior of the eyeball.
Treatment is generally symptomatic and supportive. Genetic counseling may be of benefit for patients with X-linked juvenile retinoschisis and their families.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
The National Eye Institute is recruiting (2005) patients for a study exploring eye problems related to X-linked juvenile retinoschisis in young males. Patients nine months of age and older, as well as females who are suspected carriers of the gene responsible for this disease, may be eligible to participate. It is hoped that a better understanding of the disorder will lead to improved treatments. For information about this study, visit the Clinical Trials web site or contact the NIH Patient Recruitment Office listed above.
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FROM THE INTERNET
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