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X-linked retinoschisis (XLRS) is a genetic ocular disease that is characterized by reduced visual acuity in males due to juvenile macular degeneration.
Its prevalence is estimated to range between 1/5,000-1/25,000 males worldwide.
XLRS is a symmetrical bilateral macular disorder with onset in the first decade of life. It manifests with poor vision and reading difficulties. In severe cases, nystagmus may also be observed. Severe cases involve full-thickness retinal detachment that leads to impaired vision or blindness. In more advanced stages of the disease, vitreous hemorrhage, retinal detachment, and neovascular glaucoma, which may induce severe loss of vision, can be seen. Female carriers rarely have any vision impairment.
The disease is caused by mutations on the RS1 gene (Xp22.2-p22.1), including missense, nonsense, and splice site mutations, deletions, and insertions. RS1 codes for retinoschisin, an adhesive protein that is believed to participate in the structural and functional integrity of the retina.
The diagnosis of XLRS can be made clinically, based on fundus appearance. Fundus examination shows microcystic changes of the macular region of the retina and areas of splitting within the nerve fiber layer, or schisis (spoked-wheel pattern), and vitreous veils. Electroretinogram (ERG) shows a reduction in the amplitude of the beta-wave and a relative preservation of the negative alpha-wave in scotopic ERG (electronegative rods and mixed ERG) and a normal photopic ERG. Optical coherence tomography (OCT) shows schisis areas in the macular region. There is also a family history consistent with X-linked inheritance. Molecular genetic analysis by direct sequencing of the RS1 gene detects mutations in approximately 90% of patients.
Differential diagnosis includes retinitis pigmentosa and Goldmann-Favre syndrome (see these terms). The autosomal recessive inheritance, severe nyctalopia, pigmentary retinopathy, and reduced alpha- and beta-waves on the electroretinogram (ERG) help to differentiate Goldmann-Favre syndrome from XLRS.
XLRS is inherited in an X-linked manner, with a carrier female having a 50% chance of transmitting the mutation to her offspring. Carrier testing for at-risk female relatives and prenatal diagnosis for pregnancies at increased risk are possible if the mutation has been identified in an affected family member.
Management and treatment
Management includes periodic ophthalmologic examination to monitor progression of XLRS. Additionally, patients are informed about possible ophthalmic complications that can be surgically treated (i.e., retinal detachment, vitreous hemorrhage, cataracts or strabismus). Therefore, patient education and close follow-up are the only clinical alternatives to early identification and treatment of vision-threatening complications.
In XLRS, vision slowly decreases until adolescence, and then in most patients remains relatively stable during young adulthood. The disease does not progress again until the fouth or fifth decade of life, when a significant decline in visual acuity typically occurs.