Retinoschisis 1, X-Linked, Juvenile

A number sign (#) is used with this entry because X-linked retinoschisis is caused by mutation in the retinoschisin gene (RS1; 300839) on chromosome Xp22.

Description

X-linked retinoschisis (XLRS) is a retinal dystrophy that leads to schisis (splitting) of the neural retina leading to reduced visual acuity in affected men. The condition accounts for almost all congenital retinoschisis, with occasional reports of autosomal dominant retinoschisis (see 180270) making up the remainder. The split in the retina occurs predominantly within the inner retinal layers and is very different from retinal detachment, which is a split between the neural retina and the retinal pigment epithelium. In general, carrier females remain asymptomatic (summary by Sikkink et al., 2007).

Clinical Features

Gieser and Falls (1961) observed a macular cyst in 1 eye of a possible female carrier in a kindred with 9 affected males and suggested that it might represent an expression of the carrier state. In contrast to previous reports, Kaplan et al. (1991) concluded that heterozygous carriers frequently express the disease and display peripheral retinal alterations similar to those found in affected males. Retinoschisis is, in the opinion of Gieser and Falls (1961), the same condition as that described by Mann and MacRae (1938) as congenital vascular veil in the vitreous and also the same as the X-linked retinal detachment described by Sorsby et al. (1951). So-called congenital falciform fold of the retina (ablatio falciformis retinae congenita) is probably an expression of the same gene as that for retinoschisis. See 312550.

Weve (1938) observed falciform fold and pseudoglioma in the same family. Forsius et al. (1963) described a family with a homozygous affected female who was the daughter of an affected male and his second cousin. All 3 of the homozygote's sons, by 2 different husbands, were affected. Yanoff et al. (1968) reported the histologic appearance in the eye of a 50-month-old boy whose brother was also affected. The splitting occurred in the sensory retina, predominantly in the nerve fiber layer. Forsius (1977) described a homozygous female, the offspring of an affected male and his second cousin.

Newton et al. (1991) described a family in which there was typical X-linked retinoschisis in 3 generations except that a male born in 1963 had apparently inherited his retinal disease from his unaffected father, born in 1941, who had 2 affected brothers and an affected maternal uncle. Genealogic search revealed, however, that the mother of the man born in 1963 was related as a third cousin once removed to his father and was connected to the original affected individuals in a pattern consistent with X-linked inheritance.

Kato et al. (2001) examined the relationship between ocular axial length and refractive error in patients with X-linked retinoschisis. They found that the refractive error was significantly more hypermetropic and the axial length was significantly shorter in the adult patient group than in the normal adult group (P less than 0.001). The authors concluded that the hypermetropia in patients with X-linked retinoschisis may be axial hypermetropia.

The Mizuo phenomenon, also called the Mizuo-Nakamura phenomenon, is a change in the color of the fundus from red in the dark-adapted state to golden immediately or shortly after exposure to light. The color of the fundus reflex can be either homogeneous or streaky. It has been observed mainly in Oguchi disease (258100) and in X-linked recessive cone dystrophy (304020). De Jong et al. (1991) observed the phenomenon in 4 unrelated males with retinoschisis. They suggested that altered potassium ion flux may be responsible for the phenomenon.

George et al. (1995) provided a review of X-linked retinoschisis. They suggested that the first description was that of Haas (1898), who illustrated the disease in 2 males with a beautiful drawing of the typical radiating cystic maculopathy. Sauer et al. (1997) stated that the disorder has been reported in patients as young as 3 months but may already be present at or before birth. Although foveal retinoschisis occurs in essentially all affected individuals, there is a wide phenotypic variability; approximately 50% of patients have bilateral schisis cavities in the peripheral retina. Typically, in the early stages of the disease, perifoveal radial microcysts form in the deep nerve fiber layer in a cartwheel-like pattern. Although Haas (1898) believed that the changes were inflammatory in origin, Pagenstecher (1913) published a pedigree that showed an X-linked pattern of inheritance.

George et al. (1995) stated that young patients show moderate visual impairment, although some patients have been reported with normal acuity. Most patients retained reasonable vision until their fifth or sixth decades, when some deterioration may occur due to macular atrophy. Total blindness is an exception, although Forsius et al. (1973) reported that all patients over 70 years of age had a visual acuity of less than 6/60. George et al. (1995) suggested that when the molecular defect is identified, the role of the Mueller cell may be defined. A primary defect with the Mueller cell would concur with observations of histopathology and electrophysiology. The Mueller cell, the principal glial cell of the retina, spans the full depth of the retina and is in intimate contact with photoreceptors and cells of the middle retinal layers. Its basement membrane forms part of the inner limiting membrane (ILM). George et al. (1995) presented the cases of 5 male infants with nystagmus and/or strabismus who were found to have bilateral highly elevated bullous retinoschisis involving the macula. There was hemorrhage within the schisis cavity or the vitreous in 4 patients. The bullous retinoschisis eventually reattached spontaneously, leaving pigment demarcation lines. A family history of X-linked retinoschisis was known in 2 of the patients and in the other 3 subsequent investigation showed other male family members to be affected. This uncommon presentation of XLRS is important to recognize so that appropriate genetic counseling can be given. Surgical treatment is not usually indicated and the visual prognosis is better than the initial appearance might suggest.

Mendoza-Londono et al. (1999) reported a Colombian family in which 3 females presented an RS phenotype that was as severe as that in their affected male relatives. All of those affected carried the same mutation in the RS1 gene (639delG), the females in homozygous state.

Eksandh et al. (2000) described the clinical phenotype of juvenile X-linked retinoschisis in 30 patients with 7 different mutations in the XLRS1 gene. The authors concluded that juvenile retinoschisis shows a wide variability in phenotype between, as well as within, families with different genotypes. Electroretinogram (ERG) findings showed reduced b-wave to a-wave ratios of dark-adapted recordings and prolonged implicit times of 30-Hz flicker response. Eksandh et al. (2000) concluded that ERG findings provide a useful marker for confirming the clinical diagnosis. They stressed the importance of complementing the ophthalmologic exam with full-field ERG and molecular genetics in boys with visual failure of unknown etiology to determine the diagnosis early in the course of the disease.

Ozdemir et al. (2004) reported the optical coherence tomographic findings in a child with X-linked familial foveal retinoschisis. The cleavage planes were between the outer plexiform layer and the adjacent nuclear layers of the retina.

Hayashi et al. (2004) described the clinical phenotypes of 4 unrelated Japanese male patients with juvenile retinoschisis. All 4 affected patients showed cystoid- or wheel-like foveal changes with little or no fluorescein leakage and negative ERG b-wave patterns in both eyes. Optical coherence tomography (OCT) showed foveal retinoschisis occurred in the putative fibers of Henle. In 3 patients, the authors identified 3 different missense mutations, 1 of them novel, in the functionally important discoidin domain of the RS1 gene. No nucleotide substitutions were detected in the fourth patient, whose parents were unrelated and asymptomatic. No other member of the fourth family for 3 generations had had juvenile retinoschisis. Although the inheritance pattern was uncertain in the patient without the RS1 mutation, the clinical and ERG findings were indistinguishable from those of patients with RS1 mutations, pointing to possible genetic heterogeneity of juvenile retinoschisis.

Sikkink et al. (2007) reviewed the clinical, pathologic, and electrophysiologic features of X-linked retinoschisis and its molecular basis.

Wang et al. (2015) studied the clinical features of 23 Taiwanese males from 16 families with molecularly confirmed X-linked retinoschisis and found significant inter- and intrafamilial variability. The best-corrected visual acuity ranged from no light perception to 20/25. The typical spoke-wheel pattern in the macula was present in 14 patients (61%), while peripheral retinoschisis was present in 10 (43%). Four eyes presented with vitreous hemorrhage, and 2 eyes presented with leukocoria that mimicked Coats disease (300216). Macular schisis was identified with spectral-domain optical coherence tomography (SD-OCT) in 31 eyes (82%), while foveal atrophy was present in 7 (18%). Concentric areas of high intensity was the most common fundus autofluorescence (FAF) abnormality observed. Seven (58%) of 12 patients showed electronegative full-field ERG findings.

Mapping

Ives et al. (1970) found loose linkage of RS with the Xg locus. Using a cloned DNA sequence, RC8 (DXS9), about 15% recombination was found with RS (Wieacker et al., 1983). RC8 is linked to DMD (300377) at about 15 cM and RS is linked to Xg (314700) at about 25 cM. Thus, the genetic distance between Xg and DMD may be about 55 cM. Dahl et al. (1987) mapped RS distal to both OTC and DMD. Alitalo et al. (1987) demonstrated very close linkage to DXS41 (at Xp22.2-p22.1) and slightly less close linkage to DXS16 (at Xp22). Negative lod scores were observed with DXS85 (at Xp22.3-p22.2). Dahl et al. (1988) confirmed close linkage to DXS41 in four 3-generation families with retinoschisis. No recombination was observed between the RS1 gene and DXS41, DXS43, DXS208, DXS16, DXS207, and DXS28. The maximum lod score in their series was 4.978 at a recombination fraction theta of 0 for DXS43. Gellert et al. (1988) found no recombination with DXS9 (at Xp22); the maximum lod score was 2.66 for theta = 0.0. Sieving et al. (1990) found no recombinants for linkage between RS and DXS9; maximum lod score = 4.93 at theta = 0.0. No evidence for genetic heterogeneity was found. Of the 7 families, 5 individually showed evidence of linkage to at least one of the probes from Xp22.3-p22.1, with a lod score of more than 2.0.

Pawar et al. (1995) provided a refined mapping of the RS1 gene to an interval of about 3.7 cM. By constructing a YAC contig of the Xp22 region, analyzing the marker content of the YACs and deducing the order of the markers, and analyzing key recombinants in families segregating RS, Van de Vosse et al. (1996) refined the critical region for RS to 0.6 Mb, between DXS418 and DXS7161. Huopaniemi et al. (1997) confirmed the localization between these 2 markers and on the basis of YAC clones in this region estimated the physical distance between the markers to be approximately 0.9 Mb. A total of 5 potential CpG islands could be identified. On the basis of linkage-disequilibrium data derived from the genetically isolated Finnish population, they narrowed the critical region for RS to 0.2 to 0.3 cM between markers DXS418 and a new polymorphic microsatellite marker, HYAT1.

Pathogenesis

Although little is known about RS pathogenesis, the lesions are thought to be related to a defect in retinal Mueller cells. Sauer et al. (1997) noted that, as the principal glia of the retina, Mueller cells serve a variety of functions, such as mechanical stability, provision of nutrients to neurons and photoreceptor cells, synthesis and renewal of visual pigment, recycling of neurotransmitters, phagocytosis, neuronal signaling, and clearance of potassium ions from the extracellular space. In particular, a defect in the last-mentioned function of the Mueller cells is thought to contribute to a characteristic electrophysiologic abnormality in RS patients, demonstrated by an absent or near-absent electroretinographic b-wave in the light-adapted eye. As Mueller cells have been shown to aid neurite outgrowth and neuronal connections, failure to establish a proper neuronal interaction may be the indirect result of a Mueller-cell defect. Consequently, it has been suggested (Arden et al., 1988) that RS may be considered a disorder of retinal development rather than a dystrophic process.

Mooy et al. (2002) used immunohistochemical analysis with an RS1-specific antibody to study a blind, painful enucleated eye from a 19-year-old patient from a moderately large Dutch pedigree with X-linked juvenile retinoschisis. They found strong RS1 antibody immunostaining in the inner segments of the photoreceptors and the outer nuclear layer, and moderate immunostaining in the inner nuclear and plexiform layers in the normal retina of an age-matched control's eye. Neither the ganglion cell layer nor the nerve fiber layer stained. The retinoschisis-affected eye with no RS1 antibody staining in the atrophic central area also had markedly reduced staining in the well-preserved peripheral retina. The authors concluded that in an RS-affected human eye, a mutation in the RS1 gene appeared to give rise to a dysfunctional adhesive protein, resulting in defective cellular retinal adhesion that eventually led to schisis formation. They stated that their results contradicted the theory suggesting that the primary defect is in the Muller cells.

Population Genetics

Forsius and Eriksson (1980) stated that more than 200 cases had been found in Finland, whereas up to 1970 only about 100 cases had been reported elsewhere. However, reports since 1970 suggest that it may be more common in the United States and Canada than previously thought. De la Chapelle et al. (1994) stated that the prevalence of RS in Finland is greater than 1 in 17,000.

Alitalo et al. (1991) found that the haplotype association in patients from southwest Finland differed from that in patients from north central Finland, favoring the possibility that the mutations in the 2 groups arose independently. Huopaniemi et al. (1999) studied the haplotypes and mutations in the XLRS1 gene in 55 RS families with about one-third of all RS patients in Finland, including 117 affected males and 1 affected female. Most of the RS families were clustered in the western region of Finland and about one-fifth in the northern region. Haplotype analysis, using 9 microsatellite markers spanning 1 cM in Xp22.2, showed 8 different haplotypes. Representatives from these 8 haplotypes were studied for mutations, and 7 missense mutations were identified. No genotype-phenotype correlation could be found. The western and northern groups possessed different haplotypes; the former carried the glu72-to-lys (accounting for 70% of all RS patients) and the gly74-to-val (6%) founder mutations, whereas the latter carried the gly109-to-arg (19%) founder mutation. Based on genealogic data, the glu72-to-lys founder mutation was estimated to be the oldest, at least 1,000 years old.

Molecular Genetics

Sauer et al. (1997) performed mutation analyses of XLRS1 in affected individuals from 9 unrelated RS families and identified 1 nonsense, 1 frameshift, 1 splice acceptor, and 6 missense mutations (e.g., 300839.0001) segregating with the disease phenotype in the respective families. The gene mutant in retinoschisis was the fourth to be implicated in macular dystrophy and the first one isolated by positional cloning. Mutation in peripherin/RDS (PRPH2; 179605) is associated with a variety of forms of macular dystrophy. The tissue inhibitor of metalloproteinase-3 (TIMP3; 188826) is implicated in autosomal dominant Sorsby fundus dystrophy (136900). A member of the ABC transporter gene family (ABCR; 601691) is involved in autosomal recessive Stargardt disease (248200).

The Retinoschisis Consortium (1998), consisting of a large number of individuals in 6 separate collaborating groups in the Netherlands, Italy, U.S., Finland, Germany, and U.K., screened the RS gene for mutations in 234 familial and sporadic retinoschisis cases and identified 82 different mutations in 214 (91%). Thirty-one mutations were found more than once, i.e., 2 to 10 times, with the exception of the 214G-A mutation (300839.0003) which was found in 34 apparently unrelated cases. The origin of the patients, the linkage data, and the site of the mutations (mainly CG dinucleotides) indicated that most recurrent mutations had independent origins, suggesting the existence of a 'significant' new mutation rate in the gene, which they symbolized XLRS1. The mutations identified covered the entire spectrum, from small intragenic deletions (7%) to nonsense (6%), missense (75%), small frameshifting insertions/deletions (6%), and splice site mutations (6%). Since, regardless of the mutation type, no females with a typical RS phenotype were identified, RS seems to be caused by loss-of-function mutations only. Mutations occurred nonrandomly, with hotspots at several CG dinucleotides and a C6 stretch. Exons 1 to 3 contained few, mainly translation-truncating mutations, arguing against an important functional role for this segment of the protein. Exons 4 to 6, encoding the discoidin domain, contained most, mainly missense mutations. An alignment of 32 discoidin domain proteins was constructed to reveal the consensus sequence and to deduce the functional importance of the missense mutations identified. The mutation analysis revealed a high preponderance of mutations involving or creating cysteine residues, pointing to sites important for the tertiary folding and/or protein function, and highlighted several amino acids that may be involved in XLRS1-specific protein-protein interactions. Despite the enormous mutation heterogeneity, patients have relatively uniform clinical manifestations, although with great intrafamilial variation in age at onset and progression. The 20 retinoschisis cases in which mutations were not identified may have had mutations affecting transcription initiation and mRNA processing, e.g., promoter or intronic mutations. Mutations occurred in 12 of the 26 CpG dinucleotides in the XLRS1 coding region.

Hiriyanna et al. (1999) screened 31 unrelated patients and families for XLRS1 mutations in addition to previously reported mutations for 60 of their families reported by the Retinoschisis Consortium (1998). They found 23 different mutations, including 12 novel ones in 28 patients. Two novel mutations, 38T-C (L13P; 300839.0007) and 667T-C (C223R; 300839.0008), respectively, presented the first genetic evidence for the functional significance of the putative leader peptide sequence and for the functional significance at the carboxy terminal of the XLRS1 protein beyond the discoidin domain. Mutations in 25 of the 28 families were localized to exons 4-6, emphasizing the critical functional significance of the discoidin domain of the XLRS1 protein.

Gehrig et al. (1999) reported a missense mutation (300839.0010) in a Greek family. Two affected boys and their mother were found to carry the mutation, while it was not present in either maternal grandparent. Haplotype analysis suggested that the mutation had arisen on the grandpaternal X chromosome. Gehrig et al. (1999) considered this to be the first molecular evidence of a de novo mutation in RS1.

Inoue et al. (2000) analyzed the XLRS1 gene in 10 Japanese men diagnosed with juvenile retinoschisis. Point mutations in the XLRS1 gene were identified in all 10 patients. Identical mutations were found in 2 pairs of brothers. Six of the point mutations represented missense mutations, 1 was a nonsense mutation, and 1 was a frameshift mutation. Five of the mutations were newly reported. Inoue et al. (2000) stated that these limited data failed to reveal a correlation between mutation and disease phenotype.

Wang et al. (2002) expressed 7 pathologic RS1 mutations in COS-7 cells and investigated their intracellular processing and transport by immunoblotting and confocal fluorescent immunocytochemistry. Transfected cells showed normal secretion of wildtype RS1, but either reduced or absent secretion of mutant RS1 and intracellular retention. RS1 bearing the only mutation of the 7 to occur within the signal peptide was degraded by proteasomes, and in vitro transcription/translation revealed defects in both cleavage of its signal peptide and translocation into the endoplasmic reticulum. Wang et al. (2002) concluded that the pathologic basis of RS1 may be intracellular retention of the majority of mutant proteins, which may explain why disease severity is not mutation-specific.

Saldana et al. (2007) reported a 5-year-old girl with classic findings of X-linked retinoschisis who was heterozygous for a mutation in the RS1 gene (300839.0011). Her affected father and his brother also carried the mutation. Although the authors postulated skewed X-inactivation, such studies were uninformative.

Tsang et al. (2007) described 7 patients with a mutation in the RS1 gene, including 1 with the 214G-A mutation (300839.0003), who had an atypical retinoschisis phenotype. Several of the patients had previously been diagnosed with macular degeneration (see 603075), Stargardt disease, or Goldmann-Favre syndrome (268100). All 7 had fine white dots resembling drusen-like deposits, which were sometimes associated with retinal pigment epithelial abnormalities, in the maculas. An electronegative bright-flash electroretinogram (ERG) configuration was present in all patients tested, and abnormal pattern ERG findings confirmed macular dysfunction. A parafoveal ring of high-density autofluorescence, which had not previously been described in retinoschisis, was present in 3 eyes, and 1 patient showed high-density foci concordant with the white dots. Optical coherence tomography did not show foveal schisis in 3 of 4 eyes. Tsang et al. (2007) concluded that fine white dots in the macula might be the initial fundus feature with RS1 mutations.

In 60 XLRS patients who shared 27 missense mutations in RS1, Sergeev et al. (2010) evaluated possible correlations of the molecular modeling with retinal function as determined by the ERG a- and b-waves. The b/a-wave ratio reflects visual-signal transfer in retina. The majority of RS1 mutations caused minimal structural perturbations and targeted the protein surface. Maximum structural perturbations from either the removal or insertion of cysteine residues or changes in the hydrophobic core were associated with greater difference in the b/a-wave ratio with age, with a significantly smaller ratio at younger ages. The molecular modeling suggested an association between the predicted structural alteration and/or damage to retinoschisin and the severity of XLRS as measured by the ERG analogous to the RS1-knockout mouse.

Duncan et al. (2011) evaluated the macular cone structure in 2 patients with X-linked retinoschisis caused by mutations in exon 6 of the RS1 gene. Two unrelated males, ages 14 and 29, with visual acuity ranging from 20/32 to 20/63, had macular schisis with small relative central scotomas in each eye. The mixed scotopic electroretinogram b-wave was reduced more than the a-wave. Spectral domain optical coherence tomography showed schisis cavities in the outer and inner nuclear and plexiform layers. Cone spacing was increased within the largest foveal schisis cavities but was normal elsewhere. Adaptive optics scanning laser ophthalmoscopy images of the 2 patients revealed increased cone spacing and abnormal cone packing in the macula of each patient, but cone coverage and function were near normal outside of the central foveal schisis cavities. The mutation in each patient occurred within the discoidin domain of the retinoschisin protein.

Genotype/Phenotype Correlations

In a study of 86 patients with X-linked retinoschisis in whom the causative RS1 mutation had been identified, Pimenides et al. (2005) reported no correlation between mutation type and severity of disease, even in patients of similar ages. Visual acuity, foveal changes, peripheral schisis, and disease complications were compared. Mutations were classified into groups including protein truncating, missense, mutations in different exons, discoidin domain mutations and those affecting other residues, and mutations affecting cysteine residues and those affecting other residues.

Clinical Management

To evaluate gene therapy as a possible treatment for XLRS, Dyka and Molday (2007) examined the effect that coexpression of wildtype RS1 with 7 disease-causing mutants has on RS1 expression, oligomerization, and secretion. Myc-tagged wildtype RS1 (myc-RS1) was identical to untagged, wildtype RS1 with respect to cellular localization, disulfide-linked octamer formation, and secretion. When wildtype RS1 was expressed in the same cells as disease-causing mutants, the wildtype protein underwent protein folding, subunit assembly, and secretion independent of all disease-causing RS1 mutants studied except R141H. Dyka and Molday (2007) suggested that gene therapy may be an effective treatment for most persons with XLRS.

Animal Model

To gain insight into the function of the retinoschisin protein and its role in the cellular pathology of RS, Weber et al. (2002) generated knockout mice deficient in Rs1. They showed that the pathologic changes in hemizygous mutant male mice were evenly distributed across the retina, apparently contrasting with the macular-dominated features in human. Similar functional anomalies in human and hemizygous mutant male mice, however, suggested that both conditions are a disease of the entire retina affecting the organization of the retinal cell layers as well as structural properties of the retinal synapse.