Review: Clinical findings and genetic characterization of children affected with X-linked retinoschisis in the Spanish population

X-linked retinoschisis (XLRS) is an inherited retinal disorder due to mutations in retinoschisin 1, characterized by impaired central vision secondary to parafoveal cystic cavities and visual field loss by splitting through the retinal nerve fibre layer in the peripheral retina. It is the leading cause of juvenile macular degeneration in males, and currently there is no approved treatment but carbonic anhydrase inhibitors can be used. A retrospective review of the medical records of 17 children with confirmed XLRS seen in the Paediatric Ophthalmology Department of La Paz University Hospital from the 1st of January 2009 to the 1st of June of 2023 was conducted. Complete ophthalmological studies, genetic testing and full-field electroretinogram were performed. Topical brinzolamide was given to patients with foveoschisis, adding oral acetazolamide in those who did not improve with topical treatment alone or with very extensive foveoschisis at diagnosis. Surgical treatment was performed in retinal detahment (RD) or in no clearing hemovitreous cases. Mean age at diagnosis was 5,86 years and the most common reason for consultation was strabismus, followed by RD. The most frequently affected retinal later on Optic coherence tomography was the inner nuclear layer and throughout the follow-up we observed a decrease in central macular thickness. We found some genotype-phenotype correlation in our series and more severe phenotypes if the first amino acid of the protein is affected or in frameshift mutations. We found that medical treatment (topical and oral) improves foveoschisis, and that surgery shows poor outcomes, especially in younger patients.

A Carrier Female Manifesting an Unusual X-Linked Retinoschisis Phenotype Associated with the Pathogenic Variant c.266delA, p.(Tyr89LeufsTer37) in RS1, and Skewed X-Inactivation

X-linked retinoschisis (XLRS) is the most common juvenile macular degeneration in males. Unlike most other X-linked retinal dystrophies, carrier heterozygous females are very rarely reported to show clinical features of the disease. Herein, we describe unusual retinal features in a 2-year-old female infant with family history and genetic testing consistent with XLRS.

Clinical and genetic study of a pseudo-dominant retinoschisis pedigree: the first female patient reported in Chinese population

BACKGROUND

The inheritance pattern of genetically confirmed hereditary juvenile retinoschisis reported so far is X-linked recessive with limited number of female cases. We identified a female patient with retinoschisis, and this study reports the clinical features as well as the underlying genetic defect of this family.

MATERIALS AND METHODS

Detailed family history and pedigree analysis were performed. All affected subjects underwent detailed ophthalmic examinations, including best corrected visual acuity (BCVA), dilated fundoscopy, optical coherent tomography (OCT) and fundus autofluorescence (FAF). DNA sample of the proband was sequenced by next-generation sequencing (NGS). Sanger sequencing was performed for validation and segregation.

RESULTS

Three affected subjects including one female and two males were confirmed in this consanguineous family. The BCVA ranged from 20/50 to hand motion. Foveoschisis, hyperopia, subcapsular cataracts, vitreous opacity, retinal pigmentation, and macular atrophy were present in all three patients, with variable severity. Nystagmus, esotropia, and retinal vessels transposition were noted in the female patient. Retinal detachment occurred in the female patient and her affected brother. A small deletion in RS1 gene c.97delT (p.W33Gfs*93) (NM_000330.3) was found, which was co-segregated in the pedigree.

CONCLUSIONS

Consanguineous family having XLRS female patient could manifest as pseudo-dominant inheritance. Significant intrafamilial phenotypic variation was revealed.

Whole-exome sequencing identifies an RS1 variant in a Chinese family with X-linked retinoschisis

A notable behavioural feature of X-linked retinoschisis (XLRS) is extensive structural schisis (splitting) of the outer plexiform and inner nuclear layers of the neurosensory retina, which is partly combined with complications related to vitreous hemorrhage, macular holes and retinal detachment. The present study aimed to identify the pathogenic gene mutation in a three-generation Chinese family with XLRS by whole-exome sequencing (WES). The clinical information of a three-generation Chinese family with cases of XLRS was collected. WES was performed for the proband. A comparison with the human reference genome sequence (hg38) and bioinformatic analysis were performed to reveal putative variants and Sanger sequencing was applied to verify mutations in this family and healthy control participants. Intraretinal cystic spaces were detected by optical coherence tomography imaging. Structures of the wild-type and mutant retinoschisin 1 (RS1) protein were modelled by PyMol. Almost all patients had a history of vision loss and abnormal blue-purple colour vision; however, the phenotypes of the 4 patients were distinctly different. There was no linear correlation between phenotypic severity and age. A recurrent RS1 (Xp22.2) mutation (NM_000330: c.559C>T) was detected, resulting in the p.Q187X variant. According to the protein model, this variant is likely pathogenic. The present study was the first to report that RS1:c.559C>T induces XLRS in a three-generation Chinese pedigree, with the mutation leading to premature termination of translation of the RS1 protein. WES was able to diagnose XLRS, which has the characteristics of clinical and genetic heterogeneity.

Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling

X-linked Retinoschisis (XLRS) is an early-onset transretinal dystrophy, often with a prominent macular component, that affects males and generally spares heterozygous females because of X-linked recessive inheritance. It results from loss-of-function RS1 gene mutations on the X-chromosome. XLRS causes bilateral reduced acuities from young age, and on clinical exam and by ocular coherence tomography (OCT) the neurosensory retina shows foveo-macular cystic schisis cavities in the outer plexiform (OPL) and inner nuclear layers (INL). XLRS manifests between infancy and school-age with variable phenotypic presentation and without reliable genotype-phenotype correlations. INL disorganization disrupts synaptic signal transmission from photoreceptors to ON-bipolar cells, and this reduces the electroretinogram (ERG) bipolar b-wave disproportionately to photoreceptor a-wave changes. RS1 gene expression is localized mainly to photoreceptors and INL bipolar neurons, and RS1 protein is thought to play a critical cell adhesion role during normal retinal development and later for maintenance of retinal structure. Several independent XLRS mouse models with mutant RS1 were created that recapitulate features of human XLRS disease, with OPL-INL schisis cavities, early onset and variable phenotype across mutant models, and reduced ERG b-wave to a-wave amplitude ratio. The faithful phenotype of the XLRS mouse has assisted in delineating the disease pathophysiology. Delivery to XLRS mouse retina of an AAV8-RS1 construct under control of the RS1 promoter restores the retinal structure and synaptic function (with increase of b-wave amplitude). It also ameliorates the schisis-induced inflammatory microglia phenotype toward a state of immune quiescence. The results imply that XLRS gene therapy could yield therapeutic benefit to preserve morphological and functional retina particularly when intervention is conducted at earlier ages before retinal degeneration becomes irreversible. A phase I/IIa single-center, open-label, three-dose-escalation clinical trial reported a suitable safety and tolerability profile of intravitreally administered AAV8-RS1 gene replacement therapy for XLRS participants. Dose-related ocular inflammation occurred after dosing, but this resolved with topical and oral corticosteroids. Systemic antibodies against AAV8 increased in dose-dependent fashion, but no antibodies were observed against the RS1 protein. Retinal cavities closed transiently in one participant. Technological innovations in methods of gene delivery and strategies to further reduce immune responses are expected to enhance the therapeutic efficacy of the vector and ultimate success of a gene therapy approach.

X-Linked Retinoschisis in Females in a Consanguineous Family: A Rare Entity

X-linked juvenile retinoschisis (XLRS) is a disease considered characteristic for males. In this study we report a consanguineous family in which 3 daughters were diagnosed with XLRS. Typical signs of XLRS were detected in 2 girls, aged 4 and 15. Fundoscopic examination of the father and the oldest daughter (age 17) revealed bilateral atrophic macula and retinal thinning. Although rare and considered characteristic for males, XLRS can be seen in females in Middle-East countries that have a high rate of consanguineous marriage. It can be overlooked by ophthalmologists and these patients may be misdiagnosed.

Mouse models of X-linked juvenile retinoschisis have an early onset phenotype, the severity of which varies with genotype

X-linked juvenile retinoschisis (XLRS) is an early-onset inherited condition that affects primarily males and is characterized by cystic lesions of the inner retina, decreased visual acuity and contrast sensitivity and a selective reduction of the electroretinogram (ERG) b-wave. Although XLRS is genetically heterogeneous, all mouse models developed to date involve engineered or spontaneous null mutations. In the present study, we have studied three new Rs1 mutant mouse models: (1) a knockout with inserted lacZ reporter gene; (2) a C59S point mutant substitution and (3) an R141C point mutant substitution. Mice were studied from postnatal day (P15) to 28 weeks by spectral domain optical coherence tomography and ERG. Retinas of P21-22 mice were examined using biochemistry, single cell electrophysiology of retinal ganglion cells (RGCs) and by immunohistochemistry. Each model developed intraretinal schisis and reductions in the ERG that were greater for the b-wave than the a-wave. The phenotype of the C59S mutant appeared less severe than the other mutants by ERG at adult ages. RGC electrophysiology demonstrated elevated activity in the absence of a visual stimulus and reduced signal-to-noise ratios in response to light stimuli. Immunohistochemical analysis documented early abnormalities in all cells of the outer retina. Together, these results provide significant insight into the early events of XLRS pathophysiology, from phenotype differences between disease-causing variants to common mechanistic events that may play critical roles in disease presentation and progression.