Complete Congenital Stationary Night Blindness Research Articles

Cryo-EM structure of human class C orphan GPCR GPR179 involved in visual processing

GPR179, an orphan class C GPCR, is expressed at the dendritic tips of ON-bipolar cells in the retina. It plays a pivotal role in the initial synaptic transmission of visual signals from photoreceptors, and its deficiency is known to be the cause of complete congenital stationary night blindness. Here, we present the cryo-electron microscopy structure of human GPR179. Notably, the transmembrane domain (TMD) of GPR179 forms a homodimer through the TM1/7 interface with a single inter-protomer disulfide bond, adopting a noncanonical dimerization mode. Furthermore, the TMD dimer exhibits architecture well-suited for the highly curved membrane of the dendritic tip and distinct from the flat membrane arrangement observed in other class C GPCR dimers. Our structure reveals unique structural features of GPR179 TMD, setting it apart from other class C GPCRs. These findings provide a foundation for understanding signal transduction through GPR179 in visual processing and offers insights into the underlying causes of ocular diseases.

Loss of ON-Pathway Function in Mice Lacking Lrit3 Decreases Recovery From Lens-Induced Myopia.

To determine whether the Lrit3-/- mouse model of complete congenital stationary night blindness with an ON-pathway defect harbors myopic features and whether the genetic defect influences the recovery from lens-induced myopia. Retinal levels of dopamine (DA) and 3,4 dihydroxyphenylacetic acid (DOPAC) from adult isolated Lrit3-/- retinas were quantified using ultra performance liquid chromatography after light adaptation. Natural refractive development of Lrit3-/- mice was measured from three weeks to nine weeks of age using an infrared photorefractometer. Susceptibility to myopia induction was assessed using a lens-induced myopia protocol with -25 D lenses placed in front of the right eye of the animals for three weeks; the mean interocular shift was measured with an infrared photorefractometer after two and three weeks of goggling and after one and two weeks after removal of goggles. Compared to wild-type littermates (Lrit3+/+), both DA and DOPAC were drastically reduced in Lrit3-/- retinas. Natural refractive development was normal but Lrit3-/- mice showed a higher myopic shift and a lower ability to recover from induced myopia. Our data consolidate the link between ON pathway defect altered dopaminergic signaling and myopia. We document for the first time the role of ON pathway on the recovery from myopia induction.

Characterizing Retinal Sensitivity and Structure in Congenital Stationary Night Blindness: A Combined Microperimetry and OCT Study.

To investigate the characteristics of microperimetry and optical coherence tomography (OCT) in congenital stationary night blindness (CSNB), as well as their structure-function association. This cross-sectional study included 32 eyes from 32 participants with CSNB, comprising 18 with complete CSNB and 14 with incomplete CSNB, along with 36 eyes from 36 CSNB-unaffected controls matched for age, sex, and spherical equivalent. Using MP-3 microperimetry, central retinal sensitivity was assessed within a 20° field, distributed across six concentric rings (0°, 2°, 4°, 6°, 8°, and 10°). OCT was used to analyze retinal and choroidal thickness. The study aimed to assess the overall and ring-wise retinal sensitivity, as well as choroidal and retinal thickness in CSNB and CSNB-unaffected controls, with a secondary focus on the relationship between retinal sensitivity and microstructural features on OCT. In comparison with CSNB-unaffected subjects, the overall and ring-wise retinal sensitivity as well as choroidal thickness were reduced in patients with CSNB (P < 0.001). Moreover, the central sensitivity in incomplete CSNB group was lower than in complete CSNB group (25.72 ± 3.93 dB vs. 21.92 ± 4.10dB; P < 0.001). The retinal thickness in the CSNB group was thinner outside the fovea compared with the CSNB-unaffected group. Multiple mixed regression analyses revealed that point-to-point retinal sensitivity was significantly correlated with BCVA (P = 0.002) and the corresponding retinal thickness (P = 0.004). Examination of retinal sensitivity and OCT revealed different spatial distribution profiles in CSNB and its subtypes. In CSNB eyes, retinal sensitivity on microperimetry was associated with retinal thickness on OCT.

Congenital Stationary Night Blindness: Structure, Function and Genotype–Phenotype Correlations in a Cohort of 122 Patients

To examine the molecular causes of Schubert-Bornschein (S-B) congenital stationary night blindness (CSNB), clinically characterize in detail, and assess genotype-phenotype correlations for retinal function and structure. Retrospective, longitudinal, single-center case series. One hundred twenty-two patients with S-B CSNB attending Moorfields Eye Hospital, United Kingdom. All case notes, results of molecular genetic testing, and OCT were reviewed. Molecular genetics, presenting complaints, rates of nystagmus, nyctalopia, photophobia, strabismus, color vision defects and spherical equivalent refraction (SER). Retinal thickness, outer nuclear layer (ONL) thickness, and ganglion cell layer+ inner plexiform layer (GCL+IPL) thickness from OCT imaging. X-linked (CACNA1F and NYX) and autosomal recessive (TRPM1, GRM6, GPR179 and CABP4) genotypes were identified. The mean (± standard deviation) reported age of onset was 4.94 ± 8.99 years. Over the follow-up period, 95.9% of patients reported reduced visual acuity (VA), half had nystagmus, and 64.7% reported nyctalopia. Incomplete CSNB (iCSNB) patients more frequently had nystagmus and photophobia. Nyctalopia was similar for iCSNB and complete CSNB (cCSNB). Color vision data were limited but more defects were found in iCSNB. None of these clinical differences met statistical significance. There was no significant difference between groups in VA, with a mean of 0.46 logarithm of the minimum angle of resolution, and VA remained stable over the course of follow-up. Complete congenital stationary night blindness patients, specifically those with NYX and TRPM1 variants, were more myopic. CACNA1F patients showed the largest refractive variability, and the CABP4 patient was hyperopic. No significant differences were found in OCT structural analysis during the follow-up period. Retinal structure in CSNB is stationary and no specific genotype-structure correlates were identified. Visual acuity seems to be relatively stable, with rare instances of progression. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Compound heterozygous mutations in GRM6 causing complete Schubert-Bornschein type congenital stationary night blindness

BackgroundTo explore the genetic defects of a Chinese family with complete Schubert-Bornschein type congenital stationary night blindness (CSNB). MethodsA Chinese family with complete Schubert-Bornschein type CSNB was enrolled in this study. The detailed ocular presentations of the patient were recorded. Targeted gene sequencing including 156 genes related to retinal diseases was used to detect the gene mutation. Sanger sequencing was performed to validate the potential pathogenic variants, and segregation analysis was performed on all available family members. Bioinformatics analysis was performed to predict the impact of the mutations. ResultsBy targeted gene sequencing and Sanger sequencing, we identified compound heterozygous mutations in GRM6: c.152G>T (p.Gly51Val) and c.727delG (p.Val243SerfsX21). Segregation analysis demonstrated that the mother of the proband carried the missense mutation (c.152G>T) while her father carried the frameshift mutation (c.727delG), indicating CSNB was autosomal recessively inherited in this family. Several bioinformatics prediction programs revealed the mutations were “Damaging” or “Disease Causing” and conservation analysis showed both the codons Gly51 and Val243 were highly conserved among species, suggesting the changes were pathogenic. ConclusionBy targeted gene sequencing and Sanger sequencing, we detected compound heterozygous mutations (c.152G>T, p.Gly51Val and c.727delG, p.Val243SerfsX21) in GRM6. The mutations co-segregated with the phenotype of the family members and are considered to be responsible for complete Schubert-Bornschein type CSNB. However, functional experiments in the future are needed to confirm the pathogenicity of the variants and to elucidate their exact molecular mechanisms causing CSNB.

Do differentially expressed genes explain high myopia in congenital stationary night blindness?

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signalling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON‐bipolar cell signal transmission defect and is also associated with high myopia. The purpose of this work was to identify the molecular cause of myopia present in cCSNB. A whole transcriptome sequencing (RNA‐seq) approach was performed using retina from three mouse lines with cCSNB, Gpr179−/−, Lrit3−/− and Grm6−/− and the expression data compared to data of age‐matched wild‐type littermates (n = 5). DEGs with fold changes of at least 1.2, P‐values of ≤0.01, an expression value of at least 5 transcripts per million reads and appearing in at least two cCSNB mouse lines were investigated in detail. A meta‐analysis was performed by a) comparing our data with published transcriptome data from purified retinal cells and single cell RNA‐Seq data, b) pathway analyses, c) myopia databases and publications concerning their role in normal vision. Several of the DEGs were validated by RT‐qPCR experiments and analysed by western blot and immunolocalization studies. More than 50 DEGs were found in at least two cCSNB mouse lines. Expression of those was found in different retinal cell types. The difference in expression was independent of the number of nuclei present in wild‐type and mutant inner retina. Pathway analysis revealed that mitogen‐activated protein kinase pathways, synaptic signalling, G protein‐coupled receptor ligand binding pathways, and proteins implicated in eye, endoderm and connective tissue development were affected in cCSNB. More than half of the genes were already associated with myopia. Our study reveals DEGs in all retinal cell types of cCSNB models, previously associated with myopia and novel candidates. These studies combined with pathway analyses provide the basis for the development of pharmacological and optical myopia therapies.

LRIT3 expression in cone photoreceptors restores post-synaptic bipolar cell signalplex assembly and partial function in Lrit3−/− mice

Complete congenital stationary night blindness (cCSNB) is a heterogeneous disorder characterized by poor dim-light vision, myopia, and nystagmus that is caused by mutations in genes critical for signal transmission between photoreceptors and depolarizing bipolar cells (DBCs). One such gene, LRIT3, is required for assembly of the post-synaptic signaling complex (signalplex) at the dendritic tips of DBCs, although the number of signalplex components impacted is greater in cone DBCs (all components) than in rod bipolar cells (only TRPM1 and Nyctalopin). Here we show that rAAV-mediated expression of LRIT3 in cones results in robust rescue of cone DBC signalplex components and partially restores downstream visual function, as measured by the light-adapted electroretinogram (ERG) b-wave and electrophysiological recordings of bipolar cells (BCs) and RGCs. These data show that LRIT3 successfully restores partial function to cone DBCs most likely in a trans-synaptic manner, potentially paving the way for therapeutic intervention in LRIT3-associated cCSNB.

Shedding light on myopia by studying complete congenital stationary night blindness.

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare progressive and stationary inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in a variety of biological processes including eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signaling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON-bipolar cell signal transmission defect and is also associated with high myopia. Thus, it represents also an interesting model to identify myopia-related genes, as well as disease mechanisms. While the origin of night blindness is molecularly well established, further research is needed to elucidate the mechanisms of myopia development in subjects with cCSNB. Using whole transcriptome analysis on three different mouse models of cCSNB (in Gpr179-/-, Lrit3-/- and Grm6-/-), we identified novel actors of the retinal signaling cascade, which are also novel candidate genes for myopia. Meta-analysis of our transcriptomic data with published transcriptomic databases and genome-wide association studies from myopia cases led us to propose new biological/cellular processes/mechanisms potentially at the origin of myopia in cCSNB subjects. The results provide a foundation to guide the development of pharmacological myopia therapies.

Mice Lacking Gpr179 with Complete Congenital Stationary Night Blindness Are a Good Model for Myopia.

Mutations in GPR179 are one of the most common causes of autosomal recessive complete congenital stationary night blindness (cCSNB). This retinal disease is characterized in patients by impaired dim and night vision, associated with other ocular symptoms, including high myopia. cCSNB is caused by a complete loss of signal transmission from photoreceptors to ON-bipolar cells. In this study, we hypothesized that the lack of Gpr179 and the subsequent impaired ON-pathway could lead to myopic features in a mouse model of cCSNB. Using ultra performance liquid chromatography, we show that adult Gpr179-/- mice have a significant decrease in both retinal dopamine and 3,4-dihydroxyphenylacetic acid, compared to Gpr179+/+ mice. This alteration of the dopaminergic system is thought to be correlated with an increased susceptibility to lens-induced myopia but does not affect the natural refractive development. Altogether, our data added a novel myopia model, which could be used to identify therapeutic interventions.

Shedding light on myopia by studying complete congenital stationary night blindness

AbstractPurpose: Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signalling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON‐bipolar cell signal transmission defect and is also associated with high myopia. The purpose of this work was to identify the molecular cause of myopia present in cCSNB.Methods: A whole transcriptome sequencing (RNA‐seq) approach was performed using retina from three mouse lines with cCSNB, Gpr179−/−, Lrit3−/− and Grm6−/− and the expression data compared to data of age‐matched wild‐type littermates (n = 5). DEGs with fold changes of at least 1.2, p‐values of ≤0.01, an expression value of at least 5 transcripts per million reads and appearing in at least two cCSNB mouse lines were investigated in detail. A meta‐analysis was performed by (a) comparing our data with published transcriptome data from purified retinal cells and single cell RNA‐Seq data, (b) pathway analyses, (c) myopia databases and publications concerning their role in normal vision. Several of the DEGs were validated by RT‐qPCR experiments and analysed by western blot and immunolocalization studies.Results: More than 50 DEGs were found in at least two cCSNB mouse lines. Expression of those was found in different retinal cell types. The difference in expression was independent of the number of nuclei present in wild‐type and mutant inner retina. Pathway analysis revealed that mitogen‐activated protein kinase pathways, synaptic signalling, G protein‐coupled receptor ligand binding pathways, and proteins implicated in eye, endoderm and connective tissue development were affected in cCSNB. More than half of the genes were already associated with myopia.Conclusions: Our study reveals DEGs in all retinal cell types of cCSNB models, previously associated with myopia and novel candidates. These studies combined with pathway analyses provide the basis for the development of pharmacological and optical myopia therapies.

Establishment and measurement of myopia in mice with ON‐bipolar cell defects

AbstractPurpose: Myopia is a multifactorial eye disorder caused by genetic and environmental factors and is inhibited by light exposure. Complete congenital stationary night blindness (cCSNB) a group of genetically and clinically heterogeneous retinal disorders associated with high myopia in patients. Mutations in cCSNB‐associated genes have been found to disrupt the transmission of ON‐bipolar cells (ON‐BC) in the retina. As ON‐BCs are responsible for the retinal integration of the perception of surrounding light intensity, which is disrupted in myopia, we seek to determine whether cCSNBs models are more susceptible to develop myopia.Methods: We evaluated the levels of retinal Dopamine (DOPA) and its metabolite 3,4‐Dihydroxyphenylacetic acid (DOPAC), commonly used markers of myopia, in three cCSNB mouse models lacking Grm6, Gpr179 or Lrit3. Using an eccentric infrared photorefractometer, we measured the refractive development of two cCSNB mouse models lacking Gpr179 or Lrit3. To assess the sensitivity of cCSNB mouse lines to myopia induction, we developed a lens‐induced myopia (LIM) model and measured the induced refractive error in mice lacking Gpr179 or Lrit3.Results: Our preliminary data revealed decreased levels of both retinal DOPA and DOPAC in all tested cCSNB mouse models. All tested groups presented the same kinetic of refractive development. Mice lacking Gpr179 displayed a higher sensitivity to LIM as shown by an increase in the mean interocular shift compared to wild‐type littermates. Mice lacking Lrit3 with LIM will be measured to document the refractive errors induced by the ON‐BC defect.Conclusions: These results suggest that disruption of the ON‐BC pathway contributes to the development of myopia and that mouse models of cCSNB represent good models to study myopia. Our data strengthen the hypothesis of an impact of ON‐BC dysfunction upon the onset of myopia. These findings provide the basis for the development of pharmacological and optical therapies.

Congenital Stationary Night Blindness: Clinical and Genetic Features.

Congenital stationary night blindness (CSNB) is an inherited retinal disease (IRD) that causes night blindness in childhood with heterogeneous genetic, electrophysical, and clinical characteristics. The development of sequencing technologies and gene therapy have increased the ease and urgency of diagnosing IRDs. This study describes seven Taiwanese patients from six unrelated families examined at a tertiary referral center, diagnosed with CSNB, and confirmed by genetic testing. Complete ophthalmic exams included best corrected visual acuity, retinal imaging, and an electroretinogram. The effects of identified novel variants were predicted using clinical details, protein prediction tools, and conservation scores. One patient had an autosomal dominant CSNB with a RHO variant; five patients had complete CSNB with variants in GRM6, TRPM1, and NYX; and one patient had incomplete CSNB with variants in CACNA1F. The patients had Riggs and Schubert-Bornschein types of CSNB with autosomal dominant, autosomal recessive, and X-linked inheritance patterns. This is the first report of CSNB patients in Taiwan with confirmed genetic testing, providing novel perspectives on molecular etiology and genotype-phenotype correlation of CSNB. Particularly, variants in TRPM1, NYX, and CACNA1F in our patient cohort have not previously been described, although their clinical significance needs further study. Additional study is needed for the genotype-phenotype correlation of different mutations causing CSNB. In addition to genetic etiology, the future of gene therapy for CSNB patients is reviewed and discussed.

Clinical and genetic findings in TRPM1-related congenital stationary night blindness.

Congenital stationary night blindness (CSNB) is a heterogeneous group of Mendelian retinal disorders that present in childhood. Biallelic variants altering the protein-coding region of the TRPM1 gene are one of the commonest causes of CSNB. Here, we report the clinical and genetic findings in 10 unrelated individuals with TRPM1-retinopathy. Study subjects were recruited through a tertiary clinical ophthalmic genetic service at Manchester, UK. All participants underwent visual electrodiagnostic testing and panel-based genetic analysis. Study subjects had a median age of 8 years (range: 3-20 years). All probands were myopic and had electroretinographic findings in keeping with complete CSNB. Notably, three probands reported no night vision problems. Fourteen different disease-associated TRPM1 variants were detected. One individual was homozygous for the NM_001252024.2 (TRPM1):c.965 + 29G>A variant and a mini-gene assay highlighted that this change results in mis-splicing and premature protein termination. Additionally, two unrelated probands who had CSNB and mild neurodevelopmental abnormalities were found to carry a 15q13.3 microdeletion. This copy number variant encompasses seven genes, including TRPM1, and was encountered in the heterozygous state and in trans with a missense TRPM1 variant in each case. Our findings highlight the importance of comprehensive genomic analysis, beyond the exons and protein-coding regions of genes, for individuals with CSNB. When this characteristic retinal phenotype is accompanied by extraocular findings (including learning and/or behavioural difficulties), a 15q13.3 microdeletion should be suspected. Focused analysis (e.g. microarray testing) is recommended to look for large-scale deletions encompassing TRPM1 in patients with CSNB and neurodevelopmental abnormalities.

Substantial restoration of night vision in adult mice with congenital stationary night blindness

Complete congenital stationary night blindness (cCSNB) due to mutations in TRPM1, GRM6, GPR179, NYX, or leucine-rich repeat immunoglobulin-like transmembrane domain 3 (LRIT3) is an incurable inherited retinal disorder characterized by an ON-bipolar cell (ON-BC) defect. Since the disease is non-degenerative and stable, treatment could theoretically be administrated at any time in life, making it a promising target for gene therapy. Until now, adeno-associated virus (AAV)-mediated therapies lead to significant functional improvements only in newborn cCSNB mice. Here we aimed to restore protein localization and function in adult Lrit3−/− mice. LRIT3 localizes in the outer plexiform layer and is crucial for TRPM1 localization at the dendritic tips of ON-BCs and the electroretinogram (ERG)-b-wave. AAV2-7m8-Lrit3 intravitreal injections were performed targeting either ON-BCs, photoreceptors (PRs), or both. Protein localization of LRIT3 and TRPM1 at the rod-to-rod BC synapse, functional rescue of scotopic responses, and ON-responses detection at the ganglion cell level were achieved in a few mice when ON-BCs alone or both PRs and ON-BCs, were targeted. More importantly, a significant number of treated adult Lrit3−/− mice revealed an ERG b-wave recovery under scotopic conditions, improved optomotor responses, and on-time ON-responses at the ganglion cell level when PRs were targeted. Functional rescue was maintained for at least 4 months after treatment.

A New Mouse Model for Complete Congenital Stationary Night Blindness Due to Gpr179 Deficiency.

Mutations in GPR179 lead to autosomal recessive complete congenital stationary night blindness (cCSNB). This condition represents a signal transmission defect from the photoreceptors to the ON-bipolar cells. To confirm the phenotype, better understand the pathogenic mechanism in vivo, and provide a model for therapeutic approaches, a Gpr179 knock-out mouse model was genetically and functionally characterized. We confirmed that the insertion of a neo/lac Z cassette in intron 1 of Gpr179 disrupts the same gene. Spectral domain optical coherence tomography reveals no obvious retinal structure abnormalities. Gpr179 knock-out mice exhibit a so-called no-b-wave (nob) phenotype with severely reduced b-wave amplitudes in the electroretinogram. Optomotor tests reveal decreased optomotor responses under scotopic conditions. Consistent with the genetic disruption of Gpr179, GPR179 is absent at the dendritic tips of ON-bipolar cells. While proteins of the same signal transmission cascade (GRM6, LRIT3, and TRPM1) are correctly localized, other proteins (RGS7, RGS11, and GNB5) known to regulate GRM6 are absent at the dendritic tips of ON-bipolar cells. These results add a new model of cCSNB, which is important to better understand the role of GPR179, its implication in patients with cCSNB, and its use for the development of therapies.

Restoration of mGluR6 Localization Following AAV-Mediated Delivery in a Mouse Model of Congenital Stationary Night Blindness.

PurposeComplete congenital stationary night blindness (cCSNB) is an incurable inherited retinal disorder characterized by an ON-bipolar cell (ON-BC) defect. GRM6 mutations are the third most prevalent cause of cCSNB. The Grm6−/− mouse model mimics the human phenotype, showing no b-wave in the electroretinogram (ERG) and a loss of mGluR6 and other proteins of the same cascade at the outer plexiform layer (OPL). Our aim was to restore protein localization and function in Grm6−/− adult mice targeting specifically ON-BCs or the whole retina.MethodsAdeno-associated virus-encoding Grm6 under two different promoters (GRM6-Grm6 and CAG-Grm6) were injected intravitreally in P15 Grm6−/− mice. ERG recordings at 2 and 4 months were performed in Grm6+/+, untreated and treated Grm6−/− mice. Similarly, immunolocalization studies were performed on retinal slices before or after treatment using antibodies against mGluR6, TRPM1, GPR179, RGS7, RGS11, Gβ5, and dystrophin.ResultsFollowing treatment, mGluR6 was localized to the dendritic tips of ON-BCs when expressed with either promoter. The relocalization efficiency in mGluR6-transduced retinas at the OPL was 2.5% versus 11% when the GRM6-Grm6 and CAG-Grm6 were used, respectively. Albeit no functional rescue was seen in ERGs, relocalization of TRPM1, GPR179, and Gβ5 was also noted using both constructs. The restoration of the localization of RGS7, RGS11, and dystrophin was more obvious in retinas treated with GRM6-Grm6 than in retinas treated with CAG-Grm6.ConclusionsOur findings show the potential of treating cCSNB with GRM6 mutations; however, it appears that the transduction rate must be improved to restore visual function.

The X-linked retinopathies: Physiological insights, pathogenic mechanisms, phenotypic features and novel therapies.

X-linked retinopathies represent a significant proportion of monogenic retinal disease. They include progressive and stationary conditions, with and without syndromic features. Many are X-linked recessive, but several exhibit a phenotype in female carriers, which can help establish diagnosis and yield insights into disease mechanisms. The presence of affected carriers can misleadingly suggest autosomal dominant inheritance. Some disorders (such as RPGR-associated retinopathy) show diverse phenotypes from variants in the same gene and also highlight limitations of current genetic sequencing methods. X-linked disease frequently arises from loss of function, implying potential for benefit from gene replacement strategies. We review X-inactivation and X-linked inheritance, and explore burden of disease attributable to X-linked genes in our clinically and genetically characterised retinal disease cohort, finding correlation between gene transcript length and numbers of families. We list relevant genes and discuss key clinical features, disease mechanisms, carrier phenotypes and novel experimental therapies. We consider in detail the following: RPGR (associated with retinitis pigmentosa, cone and cone-rod dystrophy), RP2 (retinitis pigmentosa), CHM (choroideremia), RS1 (X-linked retinoschisis), NYX (complete congenital stationary night blindness (CSNB)), CACNA1F (incomplete CSNB), OPN1LW/OPN1MW (blue cone monochromacy, Bornholm eye disease, cone dystrophy), GPR143 (ocular albinism), COL4A5 (Alport syndrome), and NDP (Norrie disease and X-linked familial exudative vitreoretinopathy (FEVR)). We use a recently published transcriptome analysis to explore expression by cell-type and discuss insights from electrophysiology. In the final section, we present an algorithm for genes to consider in diagnosing males with non-syndromic X-linked retinopathy, summarise current experimental therapeutic approaches, and consider questions for future research.

Ring analysis of multifocal oscillatory potentials (mfOPs) in cCSNB suggests near-normal ON-OFF pathways at the fovea only.

To investigate the center-periphery distribution of ON and OFF retinal responses in complete congenital stationary night blindness (cCSNB). Photopic full-field flash ERGs (photopic ffERGs) and OPs (photopic ffOPs) and slow m-sequence (to enhance OP prominence) mfERGs (and filtered mfOPs) evoked by a 37 hexagon stimulus array were recorded from normal subjects and cCSNB patients. Discrete wavelet transform (DWT) analysis of photopic ffERGs and mfERGs was also performed in order to assess the contribution of the ON and OFF retinal pathways (i.e., OFF-to-ON ratio) in both cohorts. As expected, the photopic ffERG (and ffOPs) responses in cCSNB were devoid of the first two of the three OPs (i.e., OP2 and OP3 and OP4) normally seen on the ascending limb of the b-wave. A similar finding was also noted in the mfERGs (and mfOPs) of ring 4. In contrast, the mfERGs (and mfOPs) of ring 1 included all three OPs. DWT analysis revealed that while in normal subjects, the OFF-to-ON ratio of mfERGs slightly increased from rings 1 to 4 (from 0.61 ± 0.03 to 0.78 ± 0.04; p < 0.05; median: from 0.62 to 0.79; p < 0.05), in cCSNB this ratio increased significantly more [from 0.73 ± 0.13 (ring 1) to 1.18 ± 0.17 (ring 4); p < 0.05; median: 0.78 to 1.22; p < 0.05], hence from a normal ON-dominated ratio (central ring) to an OFF-dominated ratio (peripheral ring). Our results show a clear discrepancy of ON and OFF mfOP components in cCSNB. Responses originating from the most central ring (i.e., ring 1) disclosed a near-normal electrophysiological contribution (as revealed with the presence of OP2, OP3 and OP4 as well as with the DWT OFF-to-ON ratio) of the retinal ON and OFF pathways in mfERG (and mfOPs) responses compared to responses from the more peripheral ring (and ffOP) which are devoid of the ON OPs (i.e., OP2 and OP3).

Optical coherence tomography and fundus autofluorescence in children with infantile nystagmus syndrome and early-onset retinal dystrophy

Background: The purpose of the study was to compare morphological retinal differences in children with infantile nystagmus syndrome (INS) and early-onset retinal dystrophies (EORD) with healthy controls in order to evaluate the diagnostic value of optical coherence tomography (OCT) and fundus autofluorescence (FAF). Material and methods: Twenty-six children (mean age 10.0 years) were ophthalmologically and electrophysiologically diagnosed as INS and EORD. Their SD-OCT and FAF imaging was prospectively performed and compared with 36 controls (mean age 7.2 years). Results: Optical coherence tomography imaging was successfully completed in 17/26 (mean age 9.7 years) and FAF in 15/26 (mean age 11.1 years) children with EORD. OCT imaging was completed in 29/36 (mean age 8.9 years) and FAF in 15/19 (mean age 8.7 years) control children. In all six children with Leber congenital amaurosis (LCA) photoreceptor layer abnormalities were seen in the peripheral retina using SD-OCT, but macular images could not be obtained. In 5/5 children with congenital stationary night blindness (CSNB) retinal thinning was found in all regions except the fovea. 2/6 children with achromatopsia showed ellipsoid zone disruption with macula thinning. In 1/1 child with blue cone monochromatism reduced macular thickness was observed. In 5/5 children with cone-rod dystrophy the outer retinal signal intensity was decreased. In 2/3 children with complete CSNB, slight foveal hypoautofluorescence was indicated. 1/4 children with achromatopsia showed a central hyperautofluorescent ring. In 1/1 child with blue cone monochromatism slight foveal hypoautofluorescence was observed. 2/7 children with cone-rod dystrophy showed a central hyperautofluorescent ring, and additionally in 1/7 a macular hypoautofluorescence in one eye and an additional patch of hyperautofluorescence centrally in the other eye were found. Conclusion: The study demonstrated OCT and FAF as a non-invasive and fast diagnostic tool that defines morphological changes in early-onset retinal dystrophies in young children with nystagmus.

Presynaptic LRIT3 Expression Trans-Synaptically Organizes Postsynaptic Trafficking of TRPM1 in Rod Bipolar Cells and Restores Vision in Dim Light

Synaptic function requires the precise alignment of pre and post-synaptic signaling complexes. At the first synapse in the retina, each rod photoreceptor connects via an invaginating ribbon synapse to two postsynaptic partners, rod bipolar cells (RBCs) and horizontal (HCs) cells. The RBCs signal rod-mediated changes in synaptic glutamate using a signalplex initiated by the metabotropic glutamate receptor 6, mGluR6, and culminating with modulation of the transient receptor potential cation channel, melastatin subfamily 1 (TRPM1) channel. One member of this signalplex, LRIT3, when deleted eliminates signaling and causes complete congenital stationary night blindness (cCSNB). The mechanism by which LRIT3 impacts the signalplex and its subcellular location are unknown. Using in situ hybridization, and restoring expression to Lrit3-/- mice by the use of recombinant adenoassociated virus (rAAV) vector-mediated transduction, we show LRIT3 is expressed in rod photoreceptors. This presynaptic restoration restores postsynaptic TRPM1 expression to the RBC dendrites, and scotopic, but not photopic, retinal visual function. Thus, LRIT3 acts as a trans-synaptic organizer of the RBC signalplex.