Electrophysiological evaluation of visual loss in Müller cell sheen dystrophy

AUTOSOMAL DOMINANT MÜLLER CELL SHEEN DYSTROPHY: Clinical, Histopathologic, and Genetic Assessment in an Extended Family With Long Follow-Up

BACKGROUND

Autosomal dominant Müller cell dystrophy is a rare condition we described in 1991. It is characterized by a striking sheen appearance on the retinal surface with progressive retinal changes leading to disorganization and atrophy with a decreased b-wave electroretinograms.

MATERIALS AND METHODS

We examined 45 members of a 4-generation family. Fifteen subjects from three generations were found with the disease, without gender predilection. Seven patients underwent ophthalmic examination including fundus examination, intravenous fluorescein angiogram, spectral-domain optical coherence tomography, and electroretinogram. Six patients have a 30-year follow-up. Histopathology examination was performed on eyes of the eldest patient. Whole exome sequencing was done in four affected subjects.

RESULTS

Findings include a decreased visual acuity, abnormal cellophane-like sheen of the vitreoretinal interface, a "plush" nerve fiber layer, and characteristic macular changes. Electroretinogram showed a selective b-wave diminution. Intravenous fluorescein angiogram presented perifoveal hyperfluorescence and capillary leakage. Spectral-domain optical coherence tomography revealed cavitations involving inner and later outer retinal layers with later disorganization. Histopathologic findings included Müller cell abnormalities with cystic disruption of inner retinal layers, pseudoexfoliation in anterior segment, and amyloidosis of extraocular vessels. Pedigree analysis suggests an autosomal dominant inheritance with late onset. DNA analysis demonstrated a previously undescribed heterozygous missense p.Glu109Val mutation in transthyretin.

CONCLUSION

To the best of our knowledge, this is the first family reported with this disorder. Our data support the hypothesis that autosomal dominant Müller cell dystrophy is a distinct retinal dystrophy affecting Müller cells. Mutations in transthyretin gene may manifest as a predominantly retinal disorder.

Loss of Gap Junction Delta-2 (GJD2) gene orthologs leads to refractive error in zebrafish

Myopia is the most common developmental disorder of juvenile eyes, and it has become an increasing cause of severe visual impairment. The GJD2 locus has been consistently associated with myopia in multiple independent genome-wide association studies. However, despite the strong genetic evidence, little is known about the functional role of GJD2 in refractive error development. Here, we find that depletion of gjd2a (Cx35.5) or gjd2b (Cx35.1) orthologs in zebrafish, cause changes in the biometry and refractive status of the eye. Our immunohistological and scRNA sequencing studies show that Cx35.5 (gjd2a) is a retinal connexin and its depletion leads to hyperopia and electrophysiological changes in the retina. These findings support a role for Cx35.5 (gjd2a) in the regulation of ocular biometry. Cx35.1 (gjd2b) has previously been identified in the retina, however, we found an additional lenticular role. Lack of Cx35.1 (gjd2b) led to a nuclear cataract that triggered axial elongation. Our results provide functional evidence of a link between gjd2 and refractive error.

Quint et al. use zebrafish lines deficient in one of two orthologs of the Gap Junction Delta-2 (GJD2) gene, which is associated with myopia by genome-wide association studies. They link gjd2 with refractive error and report evidence to suggest that gjd2a plays a role in ocular biometry whilst gjd2b, previously found in the retina, possesses an additional lenticular role.

Imaging of Muller cell sheen dystrophy

To report a rare case of Muller cell sheen dystrophy and to describe its clinical and diagnostic aspects. A 42-year-old woman presented with unilateral defective vision. Fundus evaluation revealed bilateral glistening retinal reflexes throughout the posterior pole with a wrinkled appearance in the right. Spectral Domain-OCT in the right showed abnormal internal limiting membrane, intraretinal schisis with serous detachment at macula. Angiography revealed staining along vessels. Electroretinogram in the affected eye was negative. At 4 months of follow up, vision dropped and intraretinal schisis increased. Family screening was negative.

Electrophysiological findings show generalised post-photoreceptoral deficiency in macular telangiectasia type 2

BACKGROUND

Photoreceptor damage, reported in single observations, has been suggested to contribute to the disease pathogenesis in macular telangiectasia type 2 (MacTel2). The purpose of this study was to ascertain whether the photoreceptor or post-photoreceptoral function is affected in MacTel2 and could be detected using electrophysiological examination.

METHODS

Thirty-five eyes from 18 patients (15 men, aged 60.1±9.6 years, range 38-77 years) with MacTel2 were included in the study. All patients underwent standard ophthalmic examination followed by pattern electroretinography (PERG) and full-field ERG. The data were compared against 22 normal control subjects (10 men, age 59.83±6.28 years, range 48-76).

RESULTS

Mean PERG P50 amplitude and peak time in patients with MacTel2 did not differ significantly from control values (p>0.2) but P50 amplitude was subnormal in three patients. The mean scotopic rod b-wave amplitude was significantly lower in patients than in healthy controls (p=0.027). A lower dark-adapted 10.0 b-wave (p=0.06) but not a-wave amplitude (p=0.58) was present in patients with MacTel2. Photopic single-flash a-wave and b-wave amplitudes did not differ between patient and control groups (p=0.2 and 0.3), but 30 Hz flicker peak time was significantly later in patients with MacTel2 with no effect on amplitude (p=0.04 and 0.7).

CONCLUSION

Both scotopic (rod system dominated) and photopic ERGs (cone system) are consistent with post-photoreceptoral dysfunction. There was no electrophysiological evidence of dysfunction at the level of the photoreceptor.

Ten-year follow-up of two unrelated patients with Müller cell sheen dystrophy and first report of successful vitrectomy

PURPOSE

To describe clinical characteristics of Müller cell sheen dystrophy (MCSD) in two unrelated patients followed for 10 years.

METHODS

Best-corrected visual acuity (BCVA), kinetic perimetry, biomicroscopy, ophthalmoscopy, fundus photography, fluorescein angiography, fundus autofluorescence, near-infrared reflectance, optical coherence tomography (OCT), and electroretinography (ERG).

RESULTS

Case 1: A 61-year-old woman showed internal limiting membrane (ILM) folds at the posterior pole (OU), and cystoid macular edema (CME) in OD. During follow-up, BCVA decreased from 0.2 to 0.06 (OD) and from 0.7 to hand movements (OS). Fundus presented fluctuant CME and subretinal fluid, and an increase in ILM folds and intraretinal schisis cavities. ERG was negative in OD and initially normal in OS. Case 2: A 60-year-old man was first diagnosed with epiretinal membrane before MCSD with ILM folds was detected. OCT showed schisis cavities in all retinal layers. After vitrectomy with ILM peeling in OD because of visual loss and massive CME, BCVA recovered from 0.05 to 0.4. BCVA in OS remained at 0.6. OD developed negative ERG.

CONCLUSIONS

MCSD presents with late onset, ILM folds, intraretinal schisis cavities, and negative ERG. Visual loss is accompanied by CME and subretinal fluid. Vitrectomy with ILM peeling led to BCVA increase and anatomic improvement.

The role of glia in retinal vascular disease

Retinal vascular diseases collectively represent a leading cause of blindness. Unsurprisingly, pathological characterisation and treatment of retinal 'vascular' diseases have primarily focused on the aetiology and consequences of vascular dysfunction. Far less research has addressed the contribution of neuronal and glial dysfunction to the disease process of retinal vascular disorders. Ample evidence now suggests that retinal vasculopathy only uncommonly occurs in isolation, usually existing in concert with neuropathy and gliopathy. Retinal glia (Müller cells, astrocytes and microglia) have been reported to exhibit morphological and functional changes in both early and advanced phases of almost every retinal vascular disease. It is anticipated that identifying the causes of glial activation and dysfunction, and their contribution to loss of vision in retinal vascular disease, will lead to a better understanding of retinal vascular diseases, which might ultimately be translated into novel clinical therapies.

Adenovirus vectors targeting distinct cell types in the retina

Purpose. Gene therapy for a number of retinal diseases necessitates efficient transduction of photoreceptor cells. Whereas adenovirus (Ad) serotype 5 (Ad5) does not transduce photoreceptors efficiently, previous studies have demonstrated improved photoreceptor transduction by Ad5 pseudotyped with Ad35 (Ad5/F35) or Ad37 (Ad5/F37) fiber or by the deletion of the RGD domain in the Ad5 penton base (Ad5DeltaRGD). However, each of these constructs contained a different transgene cassette, preventing the evaluation of the relative performance of these vectors, an important consideration before the use of these vectors in the clinic. The aim of this study was to evaluate these vectors in the retina and to attempt photoreceptor-specific transgene expression. Methods. Three Ad5-based vectors containing the same expression cassette were generated and injected into the subretinal space of adult mice. Eyes were analyzed for green fluorescence protein expression in flat-mounts, cross-sections, quantitative RT-PCR, and a modified stereological technique. A 257-bp fragment derived from the mouse opsin promoter was analyzed in the context of photoreceptor-specific transgene expression. Results. Each virus tested efficiently transduced the retinal pigment epithelium. The authors found no evidence that Ad5/F35 or Ad5/F37 transduced photoreceptors. Instead, they found that Ad5/F37 transduced Müller cells. Robust photoreceptor transduction by Ad5DeltaRGD was detected. Photoreceptor-specific transgene expression from the 257-bp mouse opsin promoter in the context of Ad5DeltaRGD vectors was found. Conclusions. Adenovirus vectors may be designed with tropism to distinct cell populations. Robust photoreceptor-specific transgene expression can be achieved in the context of Ad5DeltaRGD vectors.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

The negative ERG: clinical phenotypes and disease mechanisms of inner retinal dysfunction

Inner retinal dysfunction is encountered in a number of retinal disorders, either inherited or acquired, as a primary or predominant defect. Fundus examination is rarely diagnostic in these disorders, although some show characteristic features, and careful electrophysiological assessment of retinal function is needed for accurate diagnosis. The ERG in inner retinal dysfunction typically shows a negative waveform with a preserved a-wave and a selectively reduced b-wave. Advances in retinal physiology and molecular genetics have led to a greater understanding of the pathogenesis of these disorders. This review summarizes current knowledge on normal retinal physiology, the investigative techniques used and the range of clinical disorders in which there is predominantly inner retinal dysfunction.

Blindness caused by deficiency in AE3 chloride/bicarbonate exchanger

Background

Vision is initiated by phototransduction in the outer retina by photoreceptors, whose high metabolic rate generates large CO₂ loads. Inner retina cells then process the visual signal and CO₂. The anion exchanger 3 gene (AE3/Slc4a3) encodes full-length AE3 (AE3fl) and cardiac AE3 (AE3c) isoforms, catalyzing plasma membrane Cl⁻/HCO₃⁻ exchange in Müller (AE3fl) and horizontal (AE3c) cells. AE3 thus maintains acid-balance by removing photoreceptor-generated CO₂ waste.

Methodology/Principal Findings

We report that Slc4a3^−/− null mice have inner retina defects (electroretinogram b-wave reduction, optic nerve and retinal vessel anomalies). These pathologic features are common to most human vitreoretinal degenerations. Immunobloting analysis revealed that Na⁺/HCO₃⁻ co-transporter (NBC1), and carbonic anhydrase II and CAXIV, protein expression were elevated in Slc4a3^−/− mouse retinas, suggesting compensation for loss of AE3. TUNEL staining showed increased numbers of apoptotic nuclei from 4–6 months of age, in Slc4a3^−/− mice, indicating late onset photoreceptor death.

Conclusions/Significance

Identification of Slc4a3 as underlying a previously unrecognized cause of blindness suggests this gene as a new candidate for a subset of hereditary vitreoretinal retinal degeneration.

Dysfunction of transmission in the inner retina: incidence and clinical causes of negative electroretinogram

BACKGROUND

Only limited data exist on the incidence of negative electroretinograms (ERG) in clinical practice. The purpose of this study is therefore to determine the incidence and clinical causes of a negative ERG in a tertiary care centre focused on inherited and acquired retinal degenerations.

METHODS

All ERGs recorded (in accordance with ISCEV standards) in our electrophysiological laboratory from 1992 to 2004 were retrospectively reviewed. The negative ERGs (criterion: ERG with b:a wave ratio<or=1 in the scotopic standard combined response in at least one eye) were analysed in the context of further clinical results. The photopic ON- and OFF-responses were recorded with long duration (200 ms) stimuli.

RESULTS

A total of 1999 ERGs from 1644 patients were performed during the study period. 47/1644 patients (2.9%) presented with a negative ERG and were included in the study. Clinical diagnoses included inherited retinal dystrophies [X-linked congenital retinoschisis (XRS) (n=17), congenital stationary night blindness (CSNB) (n=6), retinitis pigmentosa (RP) (n=6), cone (-rod) dystrophy (n=5), choroideremia (n=1), Müller cell sheen dystrophy (MCSD) (n=1)] and acquired retinopathies (melanoma-associated retinopathy (MAR) (n=1), vigabatrin retinotoxicity (n=1)). In nine patients a definitive diagnosis could not be established. Unilateral negative ERGs were seen in 10/37 patients where ERG was bilaterally recorded. The fellow eye presented with a b:a wave ratio >1 (8 eyes) or ERG responses were not detectable (2 eyes). Photopic ON- and OFF-responses were recorded in 38 eyes of 29 patients and 32/38 eyes presented with a negative ERG. The ON-response was reduced in 25/32 eyes, whereas the OFF-response was reduced in only 11/32 eyes.

CONCLUSIONS

The incidence of a negative ERG can differ between the laboratories depending on the causes for ERG recording and was in our laboratory 2.9% in a consecutive series of patients with inherited or acquired retinal degenerations. A disorder characteristically associated with negative ERG (e.g. XRS, CSNB, MAR) was diagnosed in 53% of these patients, whereas in 47% the negative ERG indicated an unexpected post-receptoral dysfunction, e.g. in cone (-rod) dystrophy or RP. The ON-bipolar pathway was affected in most cases.

Blue cone monochromatism: clinical findings in patients with mutations in the red/green opsin gene cluster

BACKGROUND

X-linked blue cone monochromatism (BCM) has to be differentiated from x-linked cone dystrophy and autosomal recessive rod monochromatism.

METHODS

In nine male patients with congenital cone dysfunction (one family, six single cases; age range: 9-55 years), mutations in the red/green opsin gene cluster were confirmed. Clinical findings were analyzed retrospectively.

RESULTS

In one family and three single cases, a single red-green hybrid gene was found carrying a Cys203Arg mutation. Two patients had multiple opsin genes, a red/green hybrid gene and at least one green pigment gene, all carrying the Cys203Arg mutation. In one patient, a large deletion of the locus control region and parts of the red pigment gene were detected. Two patients (ages: 45 and 55 years) complained about progression. Two patients presented with nystagmus. Refractive errors (+8.0 and -11.0 D) and visual acuity were variable (0.05-0.3). Only four patients had a visual acuity > or = 0.1. In two patients, visual acuity could be improved using blue filter glasses. Four of five patients > or = 25 years had dystrophic alterations in the macula. Severe color vision defects and relative central scotoma were present in all patients. In the electroretinogram, residual cone responses were detected in 2/8 patients.

CONCLUSIONS

Hybrid red/green opsin genes carrying the Cys203Arg mutation are a frequent cause of BCM in German patients. Molecular genetic evaluation is mandatory for adequate diagnosis of patients since from the clinical data only two patients were diagnosed as having BCM. In the other patients, either rod monochromatism or cone-rod dystrophy could not be excluded with certainty. The patients should be cautioned that macular dystrophy may develop in adults older than 30 years.

[Molecular genetic findings in patients with congenital cone dysfunction. Mutations in the CNGA3, CNGB3, or GNAT2 genes]

PURPOSE

This study compares clinical and molecular genetic findings in patients with congenital cone dysfunction.

METHODS

In this study 28 patients underwent a basic ophthalmologic examination. Except for a 1-year-old boy, color vision, perimetry, and full-field ERG (ISCEV standard) were evaluated in all patients. Blood samples were taken for molecular genetic analysis of the CNGA3, CNGB3, or GNAT2 genes.

RESULTS

Two patient groups could be distinguished: patients without and with residual cone function in the ERG. In 14 of 17 patients without cone function, mutations in one of the three genes were detected, and except for one patient mutations in both alleles could be determined. In these patients, visual acuity was reduced to 20/400 and color discrimination was absent. In 2 of 11 patients with residual cone function, mutations in one allele of the CNGB3 gene were detected. It is of interest that 6 of 16 patients with mutations perceived their disease as progressive; in three of them we could determine a progression. Only in 4 of 16 patients was the ocular fundus normal. The other patients with mutations presented with central pigment irregularities, attenuated vessels, or pale optic disk.

CONCLUSION

In patients with congenital cone dysfunction without cone function in the ERG, an analysis of the CNGA3, CNGB3, or GNAT2 gene is advisable. In contrast, patients with residual cone function did not show clear association with mutations in one of the three genes. In patients with mutations, retinal alterations and nystagmus are frequent. In contrast to the designation of these disorders as stationary, in some patients with mutations in the CNGA3 and CNGB3 gene slow progression was observed.

Characterization of the intermolecular associations of the dystrophin-associated glycoprotein complex in retinal Muller glial cells

The abnormal retinal neurotransmission observed in Duchenne muscular dystrophy patients has been attributed to altered expression of C-terminal products of the dystrophin gene in this tissue. Muller glial cells from rat retina express dystrophin protein Dp71, utrophin and the members of the dystrophin-associated glycoprotein complex (DGC), namely beta-dystroglycan, delta- and gamma-sarcoglycans and alpha1-syntrophin. The DGC could function in muscle as a link between the cystoskeleton and the extracellular matrix, as well as a signaling complex. However, other than in muscle the composition and intermolecular associations among members of the DGC are still unknown. Here we demonstrate that Dp71 and/or utrophin from rat retinal Muller glial cells form a complex with beta-dystroglycan, delta-sarcoglycan and alpha1-syntrophin. We also show that beta-dystroglycan is associated with alpha-dystrobrevin-1 and PSD-93 and that anti-PSD antibodies coimmunoprecipitated alpha-syntrophin with PSD-93. By overlay experiments we also found that Dp71and/or utrophin and alpha-dystroglycan from Muller cells could bind to actin and laminin, respectively. These results indicate that the DGC could have both structural and signaling functions in retina. On the basis of our accumulated evidence, we propose a hypothetical model for the molecular organization of the dystrophin-associated glycoprotein complex in retinal Muller glial cells, which would be helpful for understanding its function in the central nervous system.