Mutations in the XLRS1 gene in Thai families with X-linked juvenile retinoschisis

A large family with inherited optic disc anomalies: a correlation between a new genetic locus and complex ocular phenotypes

Congenital cavitary optic disc anomalies (CODA) is clinically typified by an enlarged excavation of optic disc in diverse degrees. Here, we report the clinical and genetic findings in a four-generation Chinese family with a complicated form of autosomal dominant CODA. Cardinal manifestations included bilateral excavated optic disc with multiple cilioretinal vessels emerging and bilateral retinoschisis with great variability in the range of extension and severity. Other intra-familial phenotypic diversities were also noted, including severity in retinal atrophy, onset age of visual impairment and presence of congenital nystagmus and strabismus. Genome-wide linkage analysis and fine mapping mapped a novel locus for CODA to a 34.3 cM interval between D14S972 and D14S139 at 14q12-q22.1. A maximum multi-point log odds score of 3.901 was reached at D14S275. However, no mutation was identified by exome sequencing or direct sequencing of PAX6 and PAX2 genes, suggesting that the mutation may reside within a regulatory element. In conclusion, we find retinoschisis as a necessary consequence of optic nerve head (ONH) anomalies. The complicated phenotype observed in the family provided additional insights into the inherited ONH anomalies. Mapping of a novel locus, 14q12-q22.1, implies a new disease-causing gene and potential distinct pathogenesis for CODA.

Long-term rearrangement of retinal structures in a novel mutation of X-linked retinoschisis

The aim of the present study was to report a novel mutation in the retinoschisin 1 (RS1) gene in a Caucasian family affected by X-linked juvenile retinoschisis (XLRS) and to describe the long-term modification of retinal structure. Two brothers with an early onset maculopathy were diagnosed with XLRS. Fundus photography, fluorescein angiography, spectral domain optical coherence tomography and electroretinogram analyses were performed. Their sister was also examined. All subjects were screened for mutations in the RS1 gene. XLRS patients demonstrated a marked reduction of best-corrected visual acuity. SD-OCT scans reported a cystic degeneration primarily involving the inner nuclear layer, though some cysts were detected in the outer plexiform layer and in the ganglion cell layer. During the ten-year follow-up, a progressive retinal thickening and coalescence of the cysts was observed. Genetic testing revealed a novel mutation (p.Ile212Asn) in the RS1 gene in both XLRS patients, whereas their sister was not a genetic carrier. Several mutations of the RS1 gene were recognized to be responsible for XLRS. Although the correspondence between genotype and phenotype is still under debate, is reasonable that siblings affected by XLRS could share other genetic and/or epigenetic factors capable to influence clinical course of the disease.

X-linked juvenile retinoschisis: clinical diagnosis, genetic analysis, and molecular mechanisms

X-linked juvenile retinoschisis (XLRS, MIM 312700) is a common early onset macular degeneration in males characterized by mild to severe loss in visual acuity, splitting of retinal layers, and a reduction in the b-wave of the electroretinogram (ERG). The RS1 gene (MIM 300839) associated with the disease encodes retinoschisin, a 224 amino acid protein containing a discoidin domain as the major structural unit, an N-terminal cleavable signal sequence, and regions responsible for subunit oligomerization. Retinoschisin is secreted from retinal cells as a disulphide-linked homo-octameric complex which binds to the surface of photoreceptors and bipolar cells to help maintain the integrity of the retina. Over 190 disease-causing mutations in the RS1 gene are known with most mutations occurring as non-synonymous changes in the discoidin domain. Cell expression studies have shown that disease-associated missense mutations in the discoidin domain cause severe protein misfolding and retention in the endoplasmic reticulum, mutations in the signal sequence result in aberrant protein synthesis, and mutations in regions flanking the discoidin domain cause defective disulphide-linked subunit assembly, all of which produce a non-functional protein. Knockout mice deficient in retinoschisin have been generated and shown to display most of the characteristic features found in XLRS patients. Recombinant adeno-associated virus (rAAV) mediated delivery of the normal RS1 gene to the retina of young knockout mice result in long-term retinoschisin expression and rescue of retinal structure and function providing a 'proof of concept' that gene therapy may be an effective treatment for XLRS.

Mutations in the RS1 gene in a Chinese family with X-linked juvenile retinoschisis

The purpose of our study was to identify the mutations in the retinoschisis 1 (RS1) gene, which was associated with X-linked retinoschisis (XLRS) in a four-generation Chinese family, and to provide the theoretical basis for gene diagnosis and gene therapy. Genomic DNA was extracted from peripheral leukocytes. All six exons and flanking intronic regions were amplified by polymerase chain reaction (PCR), followed by direct sequencing. Through our genetic analysis, one frameshift 573delG mutation was identified in the patients of this four-generation pedigree; however, this mutation was absent in normal or non-carrier subjects. In conclusion, this 573delG mutation is reported in the Chinese population for the first time. This mutation widens the mutational spectrum of RS1 in Asians. Identification of mutations in the RS1 gene and expanded information on clinical manifestations will facilitate early diagnosis, appropriate early therapy, and genetic counseling regarding the prognosis of XLRS.