Novel NR2E3 Mutations (R104Q, R334G) Associated with a Mild Form of Enhanced S-Cone Syndrome Demonstrate Compound Heterozygosity

Evaluating therapeutic potential of NR2E3 doses in the rd7 mouse model of retinal degeneration

Retinitis Pigmentosa is a leading cause of severe vision loss. Retinitis Pigmentosa can present with a broad range of phenotypes impacted by disease age of onset, severity, and progression. This variation is influenced both by different gene mutations as well as unique variants within the same gene. Mutations in the nuclear hormone receptor 2 family e, member 3 are associated with several forms of retinal degeneration, including Retinitis Pigmentosa. In our previous studies we demonstrated that subretinal administration of one Nr2e3 dose attenuated retinal degeneration in rd7 mice for at least 3 months. Here we expand the studies to evaluate the efficacy and longitudinal impact of the NR2E3 therapeutic by examining three different doses administered at early or intermediate stages of retinal degeneration in the rd7 mice. Our study revealed retinal morphology was significantly improved 6 months post for all doses in the early-stage treatment groups and for the low and mid doses in the intermediate stage treatment groups. Similarly, photoreceptor function was significantly improved in the early stage for all doses and intermediate stage low and mid dose groups 6 months post treatment. This study demonstrated efficacy in multiple doses of NR2E3 therapy.

Bilateral helicoid peri-papillary sub-retinal fibrosis due to a biallelic NR2E3 mutation: Describing variable expressivity of a mutation

BACKGROUND

To describe different clinical presentations of a same NR2E3 recessive mutation in two families and within one family.

DESIGN

Interventional family study.

RESULTS

Our first case was a one-year-old male child with high hyperopia and refractive accommodative esotropia. In retinal examination, peri-papillary sub-retinal fibrosis with a helicoid configuration was observed in both eyes. The parents and the only sibling had no pathologic findings in the eyes. The child showed to have severely reduced responses in both photopic and scotopic electroretinogram components. In the genetic investigation, a homozygous autosomal recessive mutation in the NR2E3 gene (IVS1-2A > C) was discovered in the affected child, while the other family members were heterozygous for this mutation. We followed up with the patient for 3 years and no new lesion developed during this period. The second case was a 13-year-old male child referred to the retina clinic for decreased vision in the right eye. In retina examination, there were nummular pigmentary changes at the level of retinal pigment epithelium and along the vascular arcades with foveo-schitic changes in both eyes. A choroidal neovascularization (CNV) was noticed in the macula of his right eye. The genetic evaluation proved the same mutation in the NR2E3 gene as in the first case. Family history was remarkable for an uncle, an aunt, and two cousins with night blindness.

CONCLUSION

Same NR2E3 gene mutation can cause heterogeneous clinical manifestations such as slight retinal changes in the absence of any visual symptoms to high hyperopia associated with helicoid peri-papillary sub-retinal fibrosis.

Nuclear Receptor Subfamily 2 Group E Member 3 (NR2E3): Role in Retinal Development and Disease

NR2E3 is a nuclear hormone receptor gene required for the correct development of the retinal rod photoreceptors. Expression of NR2E3 protein in rod cell precursors suppresses cone-specific gene expression and, in concert with other transcription factors including NRL, activates the expression of rod-specific genes. Pathogenic variants involving NR2E3 cause a spectrum of retinopathies, including enhanced S-cone syndrome, Goldmann-Favre syndrome, retinitis pigmentosa, and clumped pigmentary retinal degeneration, with limited evidence of genotype-phenotype correlations. A common feature of NR2E3-related disease is an abnormally high number of cone photoreceptors that are sensitive to short wavelength light, the S-cones. This characteristic has been supported by mouse studies, which have also revealed that loss of Nr2e3 function causes photoreceptors to develop as cells that are intermediate between rods and cones. While there is currently no available cure for NR2E3-related retinopathies, there are a number of emerging therapeutic strategies under investigation, including the use of viral gene therapy and gene editing, that have shown promise for the future treatment of patients with NR2E3 variants and other inherited retinal diseases. This review provides a detailed overview of the current understanding of the role of NR2E3 in normal development and disease, and the associated clinical phenotypes, animal models, and therapeutic studies.

Recognizable Patterns of Submacular Fibrosis in Enhanced S-Cone Syndrome

PURPOSE

To highlight recognizable patterns of subretinal fibrosis in enhanced S-cone syndrome (ESCS).

DESIGN

Retrospective case series.

PARTICIPANTS

Forty-seven patients with subretinal fibrosis identified from 101 patients with clinically diagnosed ESCS, confirmed by full-field electroretinography (35/47), genetic testing (34/47), or both.

METHODS

Multimodal retinal imaging, electroretinography, and genetic analysis.

MAIN OUTCOME MEASURES

Patterns of subretinal fibrosis with angiographic, OCT, and genetic correlations.

RESULTS

Eighty-five eyes of 47 patients (24 male patients; 36 unrelated consanguineous families) had subretinal fibrosis. Mean age at presentation was 14 years. Best-corrected visual acuity ranged from 20/20 to hand movements. All 34 genetically tested patients were homozygous for pathogenic NR2E3 variants. Subretinal fibrosis was always in the macular area, although it extended beyond in some patients. Six recurrent patterns of submacular fibrosis were noted: central unifocal nodular, circumferential unifocal nodular, multifocal nodular, arcuate, helicoid, and thick geographic. Some patients showed a combination of patterns. Previous misdiagnosis as inflammatory disease was common. Fibrosis was fairly symmetrical in a given patient but not always present or identical in other affected individuals with a given homozygous mutation from the same or other families.

CONCLUSIONS

These recognizable patterns of submacular fibrosis are part of the ESCS phenotypic spectrum and strongly suggest the disease. In addition to facilitating diagnosis, recognition of these patterns can spare patients unnecessary workup for an inflammatory cause.

Enhanced S-Cone Syndrome: Spectrum of Clinical, Imaging, Electrophysiologic, and Genetic Findings in a Retrospective Case Series of 56 Patients

PURPOSE

To describe the detailed phenotype, long-term clinical course, clinical variability, and genotype of patients with enhanced S-cone syndrome (ESCS).

DESIGN

Retrospective case series.

PARTICIPANTS

Fifty-six patients with ESCS.

METHODS

Clinical history, examination, imaging, and electrophysiologic findings of 56 patients (age range, 1-75 years) diagnosed with ESCS were reviewed. Diagnosis was established by molecular confirmation of disease-causing variants in the NR2E3 gene (n = 38) or by diagnostic full-field electroretinography findings (n = 18).

MAIN OUTCOME MEASURES

Age at onset of visual symptoms, best-corrected visual acuity (BCVA), quantitative age-related electrophysiologic decline, and imaging findings.

RESULTS

Mean age at onset of visual symptoms was 4.0 years, and median age at presentation was 20.5 years, with mean follow-up interval being 6.1 years. Six patients were assessed once. Disease-causing variants in NR2E3 were identified in 38 patients. Mean BCVA of the better-seeing eye was 0.32 logarithm of the minimum angle of resolution (logMAR) at baseline and 0.39 logMAR at follow-up. In most eyes (76% [76/100]), BCVA remained stable, with a mean BCVA change of 0.07 logMAR during follow-up. Nyctalopia was the most common initial symptom, reported in 92.9% of patients (52/56). Clinical findings were highly variable and included foveomacular schisis (41.1% [26/56]), yellow-white dots (57.1% [32/56]), nummular pigmentation (85.7% [48/56]), torpedo-like lesions (10.7% [6/56]), and circumferential subretinal fibrosis (7.1% [4/56]). Macular and peripheral patterns of autofluorescence were classified as (1) minimal change, (2) hypoautofluorescent (mild diffuse, moderate speckled, moderate diffuse, or advanced), or (3) hyperautofluorescent flecks. One patient showed undetectable electroretinography findings; quantification of main electroretinography components in all other patients revealed amplitude and peak time variability but with pathognomonic electroretinography features. The main electroretinography components showed evidence of age-related worsening over 6.7 decades, at a rate indistinguishable from that seen in unaffected control participants. Eighteen sequence variants in NR2E3 were identified, including 4 novel missense changes.

CONCLUSIONS

Enhanced S-cone syndrome has a highly variable phenotype with relative clinical and imaging stability over time. Most electroretinography findings have pathognomonic features, but quantitative assessment reveals variability and a normal mean rate of age-related decline, consistent with largely nonprogressive peripheral retinal dysfunction.

Novel Pathogenic Sequence Variants in NR2E3 and Clinical Findings in Three Patients

A retrospective review of the clinical records of patients seen at the Oxford Eye Hospital identified as having NR2E3 mutations was performed. The data included symptoms, best-corrected visual acuity, multimodal retinal imaging, visual fields and electrophysiology testing. Three participants were identified with biallelic NR2E3 pathogenic sequence variants detected using a targeted NGS gene panel, two of which were novel. Participant I was a Nepalese male aged 68 years, and participants II and III were white Caucasian females aged 69 and 10 years old, respectively. All three had childhood onset nyctalopia, a progressive decrease in central vision, and visual field loss. Patients I and III had photopsia, patient II had photosensitivity and patient III also had photophobia. Visual acuities in patients I and II were preserved even into the seventh decade, with the worst visual acuity measured at 6/36. Visual field constriction was severe in participant I, less so in II, and fields were full to bright targets targets in participant III. Electrophysiology testing in all three demonstrated loss of rod function. The three patients share some of the typical distinctive features of NR2E3 retinopathies, as well as a novel clinical observation of foveal ellipsoid thickening.

Why the macula?

The regional susceptibility of the retina to diseases has been well known by clinicians for many years. It is surprising that the implications of these observations have not spawned major research efforts to characterise the structural and functional attributes of the outer retina in different regions of a foveate retina. Without such an effort, the understanding of the disease mechanisms in retinal dystrophies will remain limited and may hamper therapeutic efforts. That outer retinal disease is responsible for over 50% of blind registration in the western world underlines the importance of these considerations.

Identifying mutations in Tunisian families with retinal dystrophy

Retinal dystrophies (RD) are a rare genetic disorder with high genetic heterogeneity. This study aimed at identifying disease-causing variants in fifteen consanguineous Tunisian families. Full ophthalmic examination was performed. Index patients were subjected to IROme analysis or whole exome sequencing followed by homozygosity mapping. All detected variations were confirmed by direct Sanger sequencing. Mutation analysis in our patients revealed two compound heterozygous mutations p.(R91W);(V172D) in RPE65, and five novel homozygous mutations: p.R765C in CNGB1, p.H337R in PDE6B, splice site variant c.1129-2A > G and c.678_681delGAAG in FAM161A and c.1133 + 3_1133 + 6delAAGT in CERKL. The latter mutation impacts pre-mRNA splicing of CERKL. The other changes detected were six previously reported mutations in CNGB3 (p.R203*), ABCA4 (p.W782*), NR2E3 (p.R311Q), RPE65 (p.H182Y), PROM1 (c.1354dupT) and EYS (c.5928-2A > G). Segregation analysis in each family showed that all affected individuals were homozygotes and unaffected individuals were either heterozygote carriers or homozygous wild type allele. These results confirm the involvement of a large number of genes in RD in the Tunisian population.

New truncation mutation of the NR2E3 gene in a Japanese patient with enhanced S-cone syndrome

PURPOSE

The enhanced S-cone syndrome (ESCS) is a rare hereditary retinal degeneration that has enhanced short wavelength-sensitive cone (S-cone) functions. The longitudinal clinical course of this disease has been rarely reported, and the genetic aspects of ESCS have not been well investigated in the Japanese population. In this report, we present our clinical and genetic findings for 2 patients with ESCS.

PATIENTS AND METHODS

The patients were 2 unrelated Japanese men. Standard ophthalmic examinations and mutation screening for the NR2E3 gene were performed.

RESULTS

Patient 1 was a 36-year-old man, and his clinical findings were typical of ESCS. His decimal best-corrected visual acuity (BCVA) was 1.0 OD and 0.5 OS after removal of cataracts. Genetic investigations revealed a homozygous truncation frameshift, the p.I307LfsX33 mutation. Patient 2 was an 11-year-old boy when he was first examined by us. His clinical findings were typical of ESCS except for uveitis in the left eye. His decimal BCVA at the age of 39 years was maintained at 1.5 in each eye, although the retinal degeneration and visual field impairments had progressed during the follow-up period. The genetic investigations revealed homozygous mutations of p.R104Q in the NR2E3 gene.

CONCLUSIONS

The frameshift mutation, p.I307LfsX33, in the NR2E3 gene is a new causative mutation for ESCS. The clinical observations for patient 2 are the longest ever reported. The retinal degeneration caused by this mutation is slowly progressive, and these patients maintained good vision with maintenance of the foveal structure until their late thirties.

Differential dimerization of variants linked to enhanced S-cone sensitivity syndrome (ESCS) located in the NR2E3 ligand-binding domain

NR2E3 encodes the photoreceptor-specific nuclear hormone receptor that acts as a repressor of cone-specific gene expression in rod photoreceptors, and as an activator of several rod-specific genes. Recessive variants located in the ligand-binding domain (LBD) of NR2E3 cause enhanced short wavelength sensitive- (S-) cone syndrome (ESCS), a retinal degeneration characterized by an excess of S-cones and non-functional rods. We analyzed the dimerization properties of NR2E3 and the effect of disease-causing LBD missense variants by bioluminescence resonance energy transfer (BRET(2) ) protein interaction assays. Homodimerization was not affected in presence of p.A256V, p.R039G, p.R311Q, and p.R334G variants, but abolished in presence of p.L263P, p.L336P, p.L353V, p.R385P, and p.M407K variants. Homology modeling predicted structural changes induced by NR2E3 LBD variants. NR2E3 LBD variants did not affect interaction with CRX, but with NRL and rev-erbα/NR1D1. CRX and NRL heterodimerized more efficiently together, than did either with NR2E3. NR2E3 did not heterodimerize with TLX/NR2E1 and RXRα/NR2C1. The identification of a new compound heterozygous patient with detectable rod function, who expressed solely the p.A256V variant protein, suggests a correlation between LBD variants able to form functional NR2E3 dimers and atypical mild forms of ESCS with residual rod function.

Disruption of the human cone photoreceptor mosaic from a defect in NR2E3 transcription factor function in young adults

BACKGROUND

Enhanced S-cone syndrome is an orphan disease caused by mutations in the NR2E3 gene which result in an increased number of S-cones overpopulating the retina. Although the characteristic onset of enhanced S-cone syndrome can be well-documented by current ophthalmic imaging modalities, techniques such as spectral-domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) fail to provide sufficient details regarding the microstructure of photoreceptors in retinal diseases. Adaptive optics (AO) provides a unique opportunity to analyze the effects of genetic mutations on photoreceptors by compensating aberrations of human eyes.

METHODS

Three eyes of three young adults with enhanced S-cone syndrome were studied by clinical examination, genetic screening, fundus autofluorescence (FAF) imaging, SD-OCT, and electroretinography (ERG). Cone mosaic imaging was accomplished by an AO-SLO equipped with a dual crystal on silicon spatial light modulator. Qualitative image analyses and genetic findings were investigated in each patient.

RESULTS

The diagnosis of patients was confirmed by ERG finding. Genetic screening confirmed the presence of two disease-causing mutations in the NR2E3 gene in each study patient, as well as identified a novel mutation (202 A > G, S68G). Fundus photograph, FAF, and SD-OCT found rosette-like lesion within the mid-periphery along the vascular arcades of the retina. In all AO-SLO images of patients, sparse distribution and asymmetric size of cone mosaic pattern were found within central retina. There were regions of dark space between groups of photoreceptors, distinguishable from shadowing and artifacts.

CONCLUSIONS

AO-SLO provided an in-depth window into the retina of live enhanced S-cone syndrome patients beyond the ability of other current imaging modalities. Dark lesions within the central retina in each patient contain structurally dysfunctional cones which account for retinal mosaic disorganization, and may predispose affected areas to other abnormalities such as rosette lesions. AO-SLO can be an efficient diagnostic tool in clinics for examining cellular-level pathologies in various retinal dystrophies.

The crystal structure of the orphan nuclear receptor NR2E3/PNR ligand binding domain reveals a dimeric auto-repressed conformation

Photoreceptor-specific nuclear receptor (PNR, NR2E3) is a key transcriptional regulator of human photoreceptor differentiation and maintenance. Mutations in the NR2E3-encoding gene cause various retinal degenerations, including Enhanced S-cone syndrome, retinitis pigmentosa, and Goldman-Favre disease. Although physiological ligands have not been identified, it is believed that binding of small molecule agonists, receptor desumoylation, and receptor heterodimerization may switch NR2E3 from a transcriptional repressor to an activator. While these features make NR2E3 a potential therapeutic target for the treatment of retinal diseases, there has been a clear lack of structural information for the receptor. Here, we report the crystal structure of the apo NR2E3 ligand binding domain (LBD) at 2.8 Å resolution. Apo NR2E3 functions as transcriptional repressor in cells and the structure of its LBD is in a dimeric auto-repressed conformation. In this conformation, the putative ligand binding pocket is filled with bulky hydrophobic residues and the activation-function-2 (AF2) helix occupies the canonical cofactor binding site. Mutations designed to disrupt either the AF2/cofactor-binding site interface or the dimer interface compromised the transcriptional repressor activity of this receptor. Together, these results reveal several conserved structural features shared by related orphan nuclear receptors, suggest that most disease-causing mutations affect the receptor's structural integrity, and allowed us to model a putative active conformation that can accommodate small ligands in its pocket.

Overexpression of retinal degeneration slow (RDS) protein adversely affects rods in the rd7 model of enhanced S-cone syndrome

The nuclear receptor NR2E3 promotes expression of rod photoreceptor genes while repressing cone genes. Mice lacking NR2E3 (Nr2e3^rd7/rd7 referred to here as rd7) are a model for enhanced S-cone syndrome, a disease associated with increased sensitivity to blue light and night blindness. Rd7 retinas have reduced levels of the outer segment (OS) structural protein retinal degeneration slow (RDS). We test the hypothesis that increasing RDS levels would improve the Rd7 phenotype. Transgenic mice over-expressing normal mouse peripherin/RDS (NMP) in rods and cones were crossed onto the rd7 background. Disease phenotypes were assessed in NMP/rd7 eyes and compared to wild-type (WT) and rd7 eyes at postnatal day 30. NMP/rd7 retinas expressed total RDS (transgenic and endogenous) message at WT levels, and NMP protein was correctly localized to the OS. NMP/rd7 retinas have shorter OSs compared to rd7 and WT and significantly reduced number of rosettes. NMP/rd7 mice also exhibited significant deficits in scotopic ERG amplitudes compared to rd7 while photopic amplitudes remained unaffected. Protein levels of rhodopsin, RDS, and the RDS homologue ROM-1 were significantly reduced in the NMP/rd7 retinas compared to rd7. We show that correcting the levels of RDS gene expression does not improve the phenotype of the rd7 suggesting that RDS deficiency is not responsible for the defect in this model. We suggest that the specific rod defect in the NMP/rd7 is likely associated with ongoing problems in the rd7 that are related to the expression of cone genes in rod cells, a characteristic of the model.

Enhanced S-cone syndrome with preserved macular structure and severely depressed retinal function

We present ophthalmic features and genetic analysis findings of a 44-year-old croatian patient with enhanced S-cone syndrome (ESCS). Complete ophthalmic examination, Ishihara colour vision test, dark adaptometry, spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence imaging, Goldmann visual field and automated perimetry, full-field electroretinography (ERG), multifocal ERG, S-cone ERG and ON-OFF ERG were performed. Mutation screening of the NR2E3 gene, which encodes a photoreceptor-specific orphan nuclear receptor, was performed with polymerase chain reaction amplification and direct sequencing. The patient has good visual acuity and normal colour vision. Fundus examination showed normal posterior pole and nummular pigment depositions at the level of the retinal pigment epithelium in the mid-periphery of the retina. The SD-OCT images showed normal macular structure and thickness. The ERG showed characteristic findings: photopic and scotopic responses to the same stimulus had a similar waveform and were dominated by short-wavelength-sensitive mechanisms. Mutation analysis revealed the known NR2E3 mutation c.481delA (p.Thr161HisFsX18) and the novel NR2E3 variant c.1120C > T (p.Leu374Phe). To the best of our knowledge, this is the only ESCS patient older than 40 years who phenotypically has preserved macular structure, good central visual acuity and severely depressed full-field ERG as well as the first reported patient with NR2E3 mutation from Croatia.

A novel mutation (Cys83Tyr) in the second zinc finger of NR2E3 in enhanced S-cone syndrome

BACKGROUND

Enhanced S-cone syndrome (ESCS) is an autosomal recessive retinal disorder characterized by an increased number of S-cones over L/M cones and rods. Mutations in the NR2E3 gene, encoding a photoreceptor-specific nuclear receptor, are identified in patients with ESCS. The purpose of this study is to report the ophthalmic features of a 25-year-old Portuguese male with a typical ESCS phenotype and a novel homozygous NR2E3 mutation.

METHODS

The patient underwent a detailed ophthalmic examination including fundus photography, fluorescein angiography (FAF), fundus autofluorescence imaging (FAI), and spectral domain optical coherence tomography (SD-OCT). Full-field electroretinography (ERG), S-cone ERG, and multifocal ERG were performed. Mutation screening of the NR2E3 gene was performed with polymerase chain reaction amplification and direct sequencing.

RESULTS

The patient had poor visual acuity but good color vision. Funduscopy showed degenerative changes from the vascular arcades to the midperipheral retina. The SD-OCT revealed macular schisis and cystoid changes that had no fluorescein leakage. The posterior pole showed diffusely increased autofluorescence compared with eccentric areas in both eyes. International-standard full-field ERG showed the typical pathognomonic changes associated with ESCS and the short-wavelength flash ERG was simplified, delayed, and similar to the standard photopic flash ERG. Multifocal ERG showed widespread delay and reduction. Genetic analysis revealed a novel homozygous mutation (p.C83Y), which resides in the second zinc finger of the DNA-binding domain.

CONCLUSIONS

This homozygous mutation is likely to affect binding to target DNA sites, resulting in a non-functional behavior of NR2E3 protein. It is associated with a typical form of ESCS with a nondetectable rod response and reduced/delayed mfERG responses at all eccentricities.

NR2E3 mutations in enhanced S-cone sensitivity syndrome (ESCS), Goldmann-Favre syndrome (GFS), clumped pigmentary retinal degeneration (CPRD), and retinitis pigmentosa (RP)

NR2E3, also called photoreceptor-specific nuclear receptor (PNR), is a transcription factor of the nuclear hormone receptor superfamily whose expression is uniquely restricted to photoreceptors. There, its physiological activity is essential for proper rod and cone photoreceptor development and maintenance. Thirty-two different mutations in NR2E3 have been identified in either homozygous or compound heterozygous state in the recessively inherited enhanced S-cone sensitivity syndrome (ESCS), Goldmann-Favre syndrome (GFS), and clumped pigmentary retinal degeneration (CPRD). The clinical phenotype common to all these patients is night blindness, rudimental or absent rod function, and hyperfunction of the "blue" S-cones. A single p.G56R mutation is inherited in a dominant manner and causes retinitis pigmentosa (RP). We have established a new locus-specific database for NR2E3 (www.LOVD.nl/eye), containing all reported mutations, polymorphisms, and unclassified sequence variants, including novel ones. A high proportion of mutations are located in the evolutionarily-conserved DNA-binding domains (DBDs) and ligand-binding domains (LBDs) of NR2E3. Based on homology modeling of these NR2E3 domains, we propose a structural localization of mutated residues. The high variability of clinical phenotypes observed in patients affected by NR2E3-linked retinal degenerations may be caused by different disease mechanisms, including absence of DNA-binding, altered interactions with transcriptional coregulators, and differential activity of modifier genes.

A novel haplotype with the R345W mutation in the EFEMP1 gene associated with autosomal dominant drusen in a Japanese family

PURPOSE

To describe ophthalmic and molecular genetic findings in a family of Japanese patients with Malattia leventinese (ML)/Doyne honeycomb retinal dystrophy (DHRD), also known as autosomal dominant drusen.

METHODS

Four patients with ML/DHRD, including a 42-year-old female proband, were ascertained. The proband underwent complete ophthalmic examinations, including fundus and electrodiagnostic investigations, and Humphrey visual field (VF) perimetry. Mutation screening of the EFEMP1 gene and haplotype analysis were performed in the family, an Indian ML/DHRD family, and a branch of 1 of 39 ML/DHRD families in the United States, in which all affected patients shared a common haplotype.

RESULTS

A heterozygous missense mutation (p.R345W) was identified in all four Japanese patients and in affected patients of the other two families. This mutation was the only mutation that has been exclusively found in the gene. The disease haplotype in the Japanese family was different from those of the other two families. Clinically, central retinas were prominently affected in the proband and her mother, and subsequently the proband developed subfoveal choroidal neovascularization in the left eye, whereas her younger sister with the mutation, who was asymptomatic, exhibited only fine macular drusen. Long-term follow-up of Humphrey VF and multifocal-electroretinography (mfERG) in the proband also revealed progressive attenuation of macular function in the right eye.

CONCLUSIONS

This is the first report to describe a Japanese family with variable expressivity of ML/DHRD, in which a novel disease haplotype was identified. Humphrey VF and mfERG testing may be helpful in determining the long-term outcome of macular function.

Mutations in the DNA-binding domain of NR2E3 affect in vivo dimerization and interaction with CRX

Background

NR2E3 (PNR) is an orphan nuclear receptor essential for proper photoreceptor determination and differentiation. In humans, mutations in NR2E3 have been associated with the recessively inherited enhanced short wavelength sensitive (S-) cone syndrome (ESCS) and, more recently, with autosomal dominant retinitis pigmentosa (adRP). NR2E3 acts as a suppressor of the cone generation program in late mitotic retinal progenitor cells. In adult rod photoreceptors, NR2E3 represses cone-specific gene expression and acts in concert with the transcription factors CRX and NRL to activate rod-specific genes. NR2E3 and CRX have been shown to physically interact in vitro through their respective DNA-binding domains (DBD). The DBD also contributes to homo- and heterodimerization of nuclear receptors.

Methodology/Principal Findings

We analyzed NR2E3 homodimerization and NR2E3/CRX complex formation in an in vivo situation by Bioluminescence Resonance Energy Transfer (BRET²). NR2E3 wild-type protein formed homodimers in transiently transfected HEK293T cells. NR2E3 homodimerization was impaired in presence of disease-causing mutations in the DBD, except for the p.R76Q and p.R104W mutant proteins. Strikingly, the adRP-linked p.G56R mutant protein interacted with CRX with a similar efficiency to that of NR2E3 wild-type and p.R311Q proteins. In contrast, all other NR2E3 DBD-mutant proteins did not interact with CRX. The p.G56R mutant protein was also more effective in abolishing the potentiation of rhodospin gene transactivation by the NR2E3 wild-type protein. In addition, the p.G56R mutant enhanced the transrepression of the M- and S-opsin promoter, while all other NR2E3 DBD-mutants did not.

Conclusions/Significance

These results suggest different disease mechanisms in adRP- and ESCS-patients carrying NR2E3 mutations. Titration of CRX by the p.G56R mutant protein acting as a repressor in trans may account for the severe clinical phenotype in adRP patients.

Cellular origin of fundus autofluorescence in patients and mice with a defective NR2E3 gene

AIM

To characterise new clinical features in a family with enhanced S-cone syndrome (ESCS) and investigate the pathogenesis of these clinical features in the homozygous Nr2e3(rd7) (rd7) mutant mice.

METHODS

Four patients from an affected family were included for genotypic and phenotypic study. Eye tissues from rd7 mice were used to detect a possible relationship between macrophages and autofluorescent material by immunohistochemistry (IHC) staining.

RESULTS

Homozygous mutation in R311Q in NR2E3 was detected in this family. Colour photographs revealed that white dots do not correlate to hyperautofluorescent spots seen in autofluorescence imaging of the macula. OCT showed rosette-like lesions similar to those found in rd7 mice histology sections. From IHC analysis, we observed that F4/80 (a pan macrophage marker) and autofluorescence were colocalised to the same cells within the retina rosettes.

CONCLUSIONS

The retinal structure of a young ESCS patient with homozygous R311Q mutation in the NR2E3 gene is similar to that seen in the rd7 mice. The macrophages were found to contain autofluorescent materials in the retinal rosettes of rd7 mice. These data are consistent with macrophage infiltration contributing to the hyperautofluorescent spots found in our patients.

Mutations in NR2E3 can cause dominant or recessive retinal degenerations in the same family

NR2E3, a photoreceptor-specific nuclear receptor (PNR), represses cone-specific genes and activates several rod-specific genes. In humans, mutations in NR2E3 have been associated with the recessively-inherited enhanced short-wavelength sensitive S-cone syndrome (ESCS) and, recently, with autosomal dominant (ad) retinitis pigmentosa (RP) (adRP). In the present work, we describe two additional families affected by adRP that carry a heterozygous c.166G>A (p.G56R) mutation in the NR2E3 gene. Functional analysis determined the dominant negative activity of the p.G56R mutant protein as the molecular mechanism of adRP. Interestingly, in one pedigree, the most common causal variant for ESCS (p.R311Q) cosegregated with the adRP-linked p.G56R mutation, and the compound heterozygotes exhibited an ESCS-like phenotype, which in 1 of the 2 cases was strikingly "milder" than the patients carrying the p.G56R mutation alone. Impaired repression of cone-specific genes by the corepressors atrophin-1 (dentatorubral-pallidoluysian atrophy [DRPLA] gene product) and atrophin-2 (arginine-glutamic acid dipeptide repeat [RERE] protein) appeared to be a molecular mechanism mediating the beneficial effect of the p.R311Q mutation. Finally, the functional dominance of the p.R311Q variant to the p.G56R mutation is discussed.

Nr2e3-directed transcriptional regulation of genes involved in photoreceptor development and cell-type specific phototransduction

The retinal transcription factor Nr2e3 plays a key role in photoreceptor development and function. In this study we examine gene expression in the retina of Nr2e3(rd7/rd7) mutants with respect to wild-type control mice, to identify genes that are misregulated and hence potentially function in the Nr2e3 transcriptional network. Quantitative candidate gene real time PCR and subtractive hybridization approaches were used to identify transcripts that were misregulated in Nr2e3(rd7/rd7) mice. Chromatin immunoprecipitation assays were then used to determine which of the misregulated transcripts were direct targets of NR2E3. We identified 24 potential targets of NR2E3. In the developing retina, NR2E3 targets transcription factors such as Ror1, Rorg, and the nuclear hormone receptors Nr1d1 and Nr2c1. In the mature retina NR2E3 targets several genes including the rod specific gene Gnb1 and cone specific genes blue opsin, and two of the cone transducin subunits, Gnat2 and Gnb3. In addition, we identified 5 novel transcripts that are targeted by NR2E3. While mislocalization of proteins between rods and cones was not observed, we did observe diminished concentration of GNB1 protein in adult Nr2e3(rd7/rd7) retinas. These studies identified novel transcriptional pathways that are potentially targeted by Nr2e3 in the retina and specifically demonstrate a novel role for NR2E3 in regulating genes involved in phototransduction.

Dual role of Nr2e3 in photoreceptor development and maintenance

Nr2e3 is a photoreceptor-specific nuclear receptor believed to play a role in photoreceptor development, differentiation, and survival. Much research has focused on the interaction of Nr2e3 with other transcription factors in determining the milieu of target gene expression in photoreceptors of the neonatal and adult retina. To investigate the downstream targets of Nr2e3 and thereby shed light on the functional pathways relevant to photoreceptor development and maintenance, expression profiling was performed on retinas from two different mouse knockout lines, one containing a targeted disruption of the Nr2e3 gene (Nr2e3 -/-), the other containing a spontaneous null allele of the Nr2e3 locus (rd7). Using whole genome microarrays, mRNA expression profiles of retinas from the two mutant strains were compared to those of wildtype C57BL/6 mice over a time course that ranged from postnatal day (p) 2 to 6months of age (p180). Additionally, expression profiling was performed on retinal explants treated with a putative NR2E3 agonist. The molecular profiling of Nr2e3 -/- and rd7/rd7 retinas identified 281 putative Nr2e3-dependent genes that were differentially expressed between wildtype and mutant retinas during at least one time point. Consistent with previous reports that Nr2e3 is necessary for the repression of cone-specific genes, increased expression of cone-specific genes was observed in the mutant samples, thereby providing proof-of-concept for the microarray screen. Further annotation of these data sets revealed ten predominant functional classes involved in the Nr2e3-mediated development and/or maintenance of photoreceptors. Interestingly, differences in the expression of Nr2e3-dependent genes exhibited two distinct temporal patterns. One group of genes showed a sustained difference in expression as compared to wildtype over the entire time course of the study, whereas a second group showed only transient differences which were largest around p10. Comparison of gene expression changes in Nr2e3 -/- and rd7/rd7 retinas with those uncovered by treating retinal explants with a putative NR2E3 agonist revealed four genes that were down-regulated in mutant retinas that lack Nr2e3 function but were up-regulated in agonist-treated explants. These results strongly suggest that the four genes may be direct targets of Nr2e3. Our identification of two sets of Nr2e3-regulated genes provides further evidence of a dual role for Nr2e3 in specification of photoreceptor fate during development as well as photoreceptor maintenance in the adult.

Atypical mild enhanced S-cone syndrome with novel compound heterozygosity of the NR2E3 gene

PURPOSE

To report mild enhanced s-cone syndrome (ESCS) associated with a novel heterozygous mutation of the NR2E3 gene.

DESIGN

Observational case report.

METHODS

Clinical examination, optical coherence tomography (OCT), electroretinography (ERG), genetic analysis, and protein homology modeling.

RESULTS

Examination of a 9-year-old girl with acute visual loss of the left eye showed visual acuity of 20/30 in the right eye and 20/200 in the left eye; OCT revealed a choroidal neovascular membrane (CNVM) in the left fovea and cystic maculopathy in the right eye. Full-field ERG showed supranormal s-cone responses, reduced rod response, and characteristic ESCS waveform in photopic cone response but not in scotopic bright-flash response. Sequence analysis revealed heterozygous mutations in the NR2E3 gene, c.767C-->T yielding a substitution p.Ala256Val, and a mutation in the splice site before exon 2, c.119-2 A-->C.

CONCLUSIONS

The p.Ala256Val mutation affects the ligand binding domain of the NR2E3 nuclear receptor only, resulting in modestly impaired ESCS ERG results.

Familial partial lipodystrophy phenotype resulting from a single-base mutation in deoxyribonucleic acid-binding domain of peroxisome proliferator-activated receptor-gamma

CONTEXT

Familial partial lipodystrophy (FPLD) results from coding sequence mutations either in LMNA, encoding nuclear lamin A/C, or in PPARG, encoding peroxisome proliferator-activated receptor-gamma (PPARgamma). The LMNA form is called FPLD2 (MIM 151660) and the PPARG form is called FPLD3 (MIM 604367).

OBJECTIVE

Our objective was to investigate whether the clinical phenotype of this proband is due to mutation(s) in PPARgamma.

DESIGN

This is a case report. Patient and Setting: A 31-yr-old female with the clinical phenotype of FPLD3, i.e. lipodystrophy and early childhood diabetes with extreme insulin resistance and hypertriglyceridemia leading to recurrent pancreatitis, was assessed at an academic medical center.

RESULTS

The proband was heterozygous for a novel C-->T mutation in the PPARG gene that led to the substitution of arginine 194 in PPARgamma2 isoform, a conserved residue located in the zinc finger structure involved in DNA binding, by tryptophan (R194W). The mutation was absent from the genomes of 100 healthy Caucasians. In vitro analysis of the mutated protein showed that R194W (and R166W in PPARgamma1 isoform) could not bind to DNA and had no transcriptional activity. Furthermore, R194W had no dominant-negative activity.

CONCLUSIONS

The R194W mutation in PPARG disrupts its DNA binding activity and through haploinsufficiency leads to clinical manifestation of FPLD3 and the associated metabolic disturbances.

A novel homozygous GRK1 mutation (P391H) in 2 siblings with Oguchi disease with markedly reduced cone responses

PURPOSE

The only mutations reported to date in Japanese patients with Oguchi disease, a rare form of stationary night blindness with autosomal recessive transmission, have been in the SAG (arrestin) gene. The objective of this study was to describe the ophthalmic features and a novel mutation in the GRK1 (rhodopsin kinase) gene in 2 Japanese patients with Oguchi disease.

DESIGN

Molecular genetic and observational case study.

PARTICIPANTS

A consanguineous family including 2 siblings with Oguchi disease (a 35-year-old man and a 31-year-old woman).

METHODS

Best-corrected visual acuity (BCVA), fundus examinations, Goldmann perimetry, color vision tests, and full-field electroretinograms (ERGs) were evaluated. Mutation screening of the SAG and GRK1 genes was performed with polymerase chain reaction amplification and direct sequencing.

MAIN OUTCOME MEASURES

Mutations in the GRK1 gene, BCVA, color vision, fundus photographs, visual fields, and ERG findings.

RESULTS

Molecular analysis revealed a novel homozygous missense mutation (p.P391H) in the GRK1 gene in both patients. Proline 391 is not only within the functionally important catalytic domain, but is also a phylogenetically conserved amino acid residue among GRK1 orthologs and homologs. No mutation was found in the SAG gene. The unaffected parents were heterozygous carriers of the mutation. Both patients had night blindness, 1.5 BCVA for each eye, normal color vision, and typical fundus appearance with golden-yellow discoloration. The visual fields were normal in the male sibling. The ERGs showed no rod B waves, reduced standard combined responses, and markedly reduced single-flash cone and 30-Hz flicker responses in both patients.

CONCLUSIONS

A novel homozygous GRK1 mutation (p.P391H) was found in 2 Japanese siblings with Oguchi disease. Visual function in the 2 patients has not deteriorated with age, indicating that the disease is stationary. This is the first report of any patient with GRK1-associated Oguchi disease with markedly reduced cone responses.