SSBP1-Disease Update: Expanding the Genetic and Clinical Spectrum, Reporting Variable Penetrance and Confirming Recessive Inheritance

Purpose

To report novel genotypes and expand the phenotype spectrum of SSBP1-disease and explore potential disease mechanism.

Methods

Five families with previously unsolved optic atrophy and retinal dystrophy underwent whole genome sequencing as part of the National Institute for Health Research BioResource Rare-Diseases and the UK's 100,000 Genomes Project. In silico analysis and protein modelling was performed on the identified variants. Deep phenotyping including retinal imaging and International Society for Clinical Electrophysiology of Vision standard visual electrophysiology was performed.

Results

Seven individuals from five unrelated families with bilateral optic atrophy and/or retinal dystrophy with extraocular signs and symptoms in some are described. In total, 6 SSBP1 variants were identified including the previously unreported variants: c.151A>G, p.(Lys51Glu), c.335G>A p.(Gly112Glu), and c.380G>A, p.(Arg127Gln). One individual was found to carry biallelic variants (c.380G>A p.(Arg127Gln); c.394A>G p.(Ile132Val)) associated with likely autosomal recessive SSBP1-disease. In silico analysis predicted all variants to be pathogenic and Three-dimensional protein modelling suggested possible disease mechanisms via decreased single-stranded DNA binding affinity or impaired higher structure formation.

Conclusions

SSBP1 is essential for mitochondrial DNA replication and maintenance, with defects leading to a spectrum of disease that includes optic atrophy and/or retinal dystrophy, occurring with or without extraocular features. This study provides evidence of intrafamilial variability and confirms the existence of an autosomal recessive inheritance in SSBP1-disease consequent upon a previously unreported genotype.

Expanding the clinical phenotype in patients with disease causing variants associated with atypical Usher syndrome

Atypical Usher syndrome (USH) is poorly defined with a broad clinical spectrum. Here, we characterize the clinical phenotype of disease caused by variants in CEP78, CEP250, ARSG, and ABHD12.Chart review evaluating demographic, clinical, imaging, and genetic findings of 19 patients from 18 families with a clinical diagnosis of retinal disease and confirmed disease-causing variants in CEP78, CEP250, ARSG, or ABHD12.CEP78-related disease included sensorineural hearing loss (SNHL) in 6/7 patients and demonstrated a broad phenotypic spectrum including: vascular attenuation, pallor of the optic disc, intraretinal pigment, retinal pigment epithelium mottling, areas of mid-peripheral hypo-autofluorescence, outer retinal atrophy, mild pigmentary changes in the macula, foveal hypo-autofluorescence, and granularity of the ellipsoid zone. Nonsense and frameshift variants in CEP250 showed mild retinal disease with progressive, non-congenital SNHL. ARSG variants resulted in a characteristic pericentral pattern of hypo-autofluorescence with one patient reporting non-congenital SNHL. ABHD12-related disease showed rod-cone dystrophy with macular involvement, early and severe decreased best corrected visual acuity, and non-congenital SNHL ranging from unreported to severe.This study serves to expand the clinical phenotypes of atypical USH. Given the variable findings, atypical USH should be considered in patients with peripheral and macular retinal disease even without the typical RP phenotype especially when SNHL is noted. Additionally, genetic screening may be useful in patients who have clinical symptoms and retinal findings even in the absence of known SNHL given the variability of atypical USH.

X-Linked Retinoschisis: Deep Phenotyping and Genetic Characterization

PURPOSE

To examine the genetic and clinical features in children and adults with X-linked retinoschisis (XLRS).

DESIGN

Single-center consecutive, retrospective, observational study.

PARTICIPANTS

Adults and children with molecularly confirmed XLRS followed up between 1999 and 2020.

METHODS

Analysis of genetic, clinical, and retinal imaging findings, including OCT and fundus autofluorescence (FAF), cross-sectionally and longitudinally, was performed.

MAIN OUTCOMES MEASURES

RS1, variants, type of variants and phenotype correlations, age of onset, complications rates and types, fundoscopy findings, OCT metrics, FAF patterns, correlations including between best corrected visual acuity (BCVA) and age, and OCT characteristics.

RESULTS

One hundred thirty-two male patients were identified harboring 66 retinoschisin 1 variants, with 7 being novel. The mean age at onset was 16.5 years (range, 0-58 years). Seventy-one patients (71/75 [94.7%]) were symptomatic at presentation; all had decreased best-corrected visual acuity (BCVA). Funduscopy findings were symmetric in 104 patients (104/108 [96.3%]), with the most common finding being macular schisis (82.4%), whereas peripheral retinoschisis was present in 38.9% and macular atrophy was present in 11.1%. Twenty patients (18.5%) demonstrated complications (vitreous hemorrhage, retinal detachment, or both). Mean BCVA was 0.65 logarithm of the minimum angle of resolution (logMAR; Snellen equivalent, 20/89) in the right eye and 0.64 logMAR (Snellen equivalent, 20/87) in the left eye. Mean BCVA change over a mean interval of 6.7 years was 0.04 and 0.01 logMAR for right and left eyes, respectively. A normal FAF pattern was identified in 16 of 106 eyes (15.1%); 45 eyes (42.5%) showed a spoke-wheel pattern, 13 eyes (12.3%) showed foveal hyperautofluorescence, and 18 eyes (17.0%) showed a central reduction in signal. In total, 14 patients demonstrated evidence of progression on FAF over time. On OCT, foveoschisis was observed in 172 eyes (172/215 [80%]), parafoveal schisis was observed in 171 eyes (171/215 [79.5%]), and foveal atrophy was observed in 44 eyes (44/215 [20.5%]). Cystoid changes were localized to the inner nuclear layer (172/181 eyes [95%]), the outer nuclear layer (97/181 [53.6%]), and the ganglion cell layer (92/181 [50.8%]). Null variants were associated with worse final BCVA and aforementioned complications.

CONCLUSIONS

X-linked retinoschisis is highly phenotypically variable, but with relative foveal and BCVA preservation until late adulthood, allowing more accurate prognostication. The slowly (often minimally) progressive disease course may pose a challenge in identification of early end points for therapeutic trials aimed at altering the kinetics of degeneration.

100,000 Genomes Pilot on Rare-Disease Diagnosis in Health Care - Preliminary Report

BACKGROUND

The U.K. 100,000 Genomes Project is in the process of investigating the role of genome sequencing in patients with undiagnosed rare diseases after usual care and the alignment of this research with health care implementation in the U.K. National Health Service. Other parts of this project focus on patients with cancer and infection.

METHODS

We conducted a pilot study involving 4660 participants from 2183 families, among whom 161 disorders covering a broad spectrum of rare diseases were present. We collected data on clinical features with the use of Human Phenotype Ontology terms, undertook genome sequencing, applied automated variant prioritization on the basis of applied virtual gene panels and phenotypes, and identified novel pathogenic variants through research analysis.

RESULTS

Diagnostic yields varied among family structures and were highest in family trios (both parents and a proband) and families with larger pedigrees. Diagnostic yields were much higher for disorders likely to have a monogenic cause (35%) than for disorders likely to have a complex cause (11%). Diagnostic yields for intellectual disability, hearing disorders, and vision disorders ranged from 40 to 55%. We made genetic diagnoses in 25% of the probands. A total of 14% of the diagnoses were made by means of the combination of research and automated approaches, which was critical for cases in which we found etiologic noncoding, structural, and mitochondrial genome variants and coding variants poorly covered by exome sequencing. Cohortwide burden testing across 57,000 genomes enabled the discovery of three new disease genes and 19 new associations. Of the genetic diagnoses that we made, 25% had immediate ramifications for clinical decision making for the patients or their relatives.

CONCLUSIONS

Our pilot study of genome sequencing in a national health care system showed an increase in diagnostic yield across a range of rare diseases. (Funded by the National Institute for Health Research and others.).

AN ASSOCIATION BETWEEN STELLATE NONHEREDITARY IDIOPATHIC FOVEOMACULAR RETINOSCHISIS, PERIPHERAL RETINOSCHISIS, AND POSTERIOR HYALOID ATTACHMENT

PURPOSE

Stellate nonhereditary idiopathic foveomacular retinoschisis is a disorder characterized by splitting of the retina at the macula, without a known underlying mechanical or inherited cause. This study investigates demographic, anatomical, and functional characteristics of subjects with stellate nonhereditary idiopathic foveomacular retinoschisis, to explore potential underlying mechanisms.

METHODS

In this single-site, retrospective, and cross-sectional, observational study, data were collected from 28 eyes from 24 subjects with stellate nonhereditary idiopathic foveomacular retinoschisis. Descriptive statistics were reported, based on the observed anatomico-functional features.

RESULTS

The visual acuity remained stable (median 20/20) in all subjects over a median follow-up of 17 months. All cases demonstrated foveomacular retinoschisis within Henle's fiber layer, at the junction of the outer plexiform and outer nuclear layers. This schisis cavity extended beyond the limits of the macular OCT temporally in all eyes. In most affected eyes, there were documented features of peripheral retinoschisis and broad attachment of the posterior hyaloid at the macula. Functional testing in a cross-sectional subset demonstrated normal retinal sensitivity centrally but an absolute scotoma peripherally.

CONCLUSION

Stellate nonhereditary idiopathic foveomacular retinoschisis seems to be associated with peripheral retinoschisis and anomalous or incomplete posterior hyaloid detachment. Despite chronic manifestation, this does not significantly affect central visual function but can manifest with profound loss of peripheral visual function.

Comparison of in silico strategies to prioritize rare genomic variants impacting RNA splicing for the diagnosis of genomic disorders

The development of computational methods to assess pathogenicity of pre-messenger RNA splicing variants is critical for diagnosis of human disease. We assessed the capability of eight algorithms, and a consensus approach, to prioritize 249 variants of uncertain significance (VUSs) that underwent splicing functional analyses. The capability of algorithms to differentiate VUSs away from the immediate splice site as being 'pathogenic' or 'benign' is likely to have substantial impact on diagnostic testing. We show that SpliceAI is the best single strategy in this regard, but that combined usage of tools using a weighted approach can increase accuracy further. We incorporated prioritization strategies alongside diagnostic testing for rare disorders. We show that 15% of 2783 referred individuals carry rare variants expected to impact splicing that were not initially identified as 'pathogenic' or 'likely pathogenic'; one in five of these cases could lead to new or refined diagnoses.

KCNV2-Associated Retinopathy: Detailed Retinal Phenotype and Structural Endpoints-KCNV2 Study Group Report 2

PURPOSE

To describe the detailed retinal phenotype of KCNV2-associated retinopathy.

STUDY DESIGN

Multicenter international retrospective case series.

METHODS

Review of retinal imaging including fundus autofluorescence (FAF) and optical coherence tomography (OCT), including qualitative and quantitative analyses.

RESULTS

Three distinct macular FAF features were identified: (1) centrally increased signal (n = 35, 41.7%), (2) decreased autofluorescence (n = 27, 31.1%), and (3) ring of increased signal (n = 37, 44.0%). Five distinct FAF groups were identified based on combinations of those features, with 23.5% of patients changing the FAF group over a mean (range) follow-up of 5.9 years (1.9-13.1 years). Qualitative assessment was performed by grading OCT into 5 grades: (1) continuous ellipsoid zone (EZ) (20.5%); (2) EZ disruption (26.1%); (3) EZ absence, without optical gap and with preserved retinal pigment epithelium complex (21.6%); (4) loss of EZ and a hyporeflective zone at the foveola (6.8%); and (5) outer retina and retinal pigment epithelium complex loss (25.0%). Eighty-six patients had scans available from both eyes, with 83 (96.5%) having the same grade in both eyes, and 36.1% changed OCT grade over a mean follow-up of 5.5 years. The annual rate of outer nuclear layer thickness change was similar for right and left eyes.

CONCLUSIONS

KCNV2-associated retinopathy is a slowly progressive disease with early retinal changes, which are predominantly symmetric between eyes. The identification of a single OCT or FAF measurement as an endpoint to determine progression that applies to all patients may be challenging, although outer nuclear layer thickness is a potential biomarker. Findings suggest a potential window for intervention until 40 years of age.

A rare canonical splice-site variant in VPS13B causes attenuated Cohen syndrome

BACKGROUND

To describe a patient with a history of obesity, retinal dystrophy, type II diabetes, and mild cognitive impairment; found to harbour biallelic splice-site variants in VPS13B.

MATERIALS & METHODS

A complete ophthalmic evaluation was performed at Moorfields Eye Hospital (London, United Kingdom), consisting of measurement of best-corrected visual acuity (BCVA), slit lamp and dilated fundus evaluation, colour, autofluorescence and near-infrared retinal imaging, spectral domain-optical coherence tomography, and electroretinogram (ERG). Whole-genome sequencing was performed as part of the UK's 100,000 Genomes Project.

RESULTS

A 26-year-old Pakistani man with normal appearance, stature, and head size presented with decreased BCVA and severely constricted visual fields to our Ophthalmic Genetics clinic. He had a history of obesity, type II diabetes, and mild cognitive impairment. His evaluation showed retina-wide, severe photoreceptor dysfunction in both eyes, with undetectable scotopic and photopic ERG waveforms. Genomic analysis identified a homozygous rare splice donor variant in the VPS13B gene (c.5024+2T>C) that was demonstrated to lead to skipping of the in-frame exon 31 (p.Gln1607_Ser1675delinsHis).

CONCLUSIONS

Exon 31 skipping in VPS13B may lead to a hypomorphic change, with partial gene function and an incomplete, mild Cohen syndrome-like phenotype.

Clinical and preclinical therapeutic outcome metrics for USH2A-related disease

USH2A variants are the most common cause of Usher syndrome type 2, characterized by congenital sensorineural hearing loss and retinitis pigmentosa (RP), and also contribute to autosomal recessive non-syndromic RP. Several treatment strategies are under development; however, sensitive clinical trial endpoint metrics to determine therapeutic efficacy have not been identified. In the present study, we have performed longitudinal retrospective examination of the retinal and auditory symptoms in (i) 56 biallelic molecularly confirmed USH2A patients and (ii) ush2a mutant zebrafish to identify metrics for the evaluation of future clinical trials and rapid preclinical screening studies. The patient cohort showed a statistically significant correlation between age and both rate of constriction for the ellipsoid zone length and hyperautofluorescent outer retinal ring area. Visual acuity and pure tone audiograms are not suitable outcome measures. Retinal examination of the novel ush2au507 zebrafish mutant revealed a slowly progressive degeneration of predominantly rods, accompanied by rhodopsin and blue cone opsin mislocalization from 6 to 12 months of age with lysosome-like structures observed in the photoreceptors. This was further evaluated in the ush2armc zebrafish model, which revealed similar changes in photopigment mislocalization with elevated autophagy levels at 6 days post fertilization, indicating a more severe genotype-phenotype correlation and providing evidence of new insights into the pathophysiology underlying USH2A-retinal disease.

Foveal structure and visual function in nanophthalmos and posterior microphthalmos

BACKGROUND/AIMS

The reason for visual impairment in patients with nanophthalmos and posterior microphthalmos is not completely understood. Therefore, this study aims to investigate foveal structure, and the impact of demographic, clinical and imaging parameters on best-corrected visual acuity (BCVA) in these conditions.

METHODS

Sixty-two eyes of 33 patients with nanophthalmos (n=40) or posterior microphthalmos (n=22), and 114 eyes of healthy controls with high-resolution retinal imaging including spectral-domain or swept-source optical coherence tomography images were included in this cross-sectional case-control study. Foveal retinal layer thickness was determined by two independent readers. A mixed-effect model was used to perform structure-function correlations and predict the BCVA based on subject-specific variables.

RESULTS

Most patients (28/33) had altered foveal structure associated with loss of foveal avascular zone and impaired BCVA. However, widening of outer nuclear layer, lengthening of photoreceptor outer segments, normal distribution of macular pigment and presence of Henle fibres were consistently found. Apart from the presence of choroidal effusion, which had significant impact on BCVA, the features age, refractive error, axial length and retinal layer thickness at the foveal centre explained 61.7% of the variability of BCVA.

CONCLUSION

This study demonstrates that choroidal effusion, age, refractive error, axial length and retinal layer thickness are responsible for the majority of interindividual variability of BCVA as well as the morphological foveal heterogeneity in patients with nanophthalmos or posterior microphthalmos. This might give further insights into the physiology of foveal development and the process of emmetropisation, and support clinicians in the assessment of these disease entities.

Pathogenic NR2F1 variants cause a developmental ocular phenotype recapitulated in a mutant mouse model

Pathogenic NR2F1 variants cause a rare autosomal dominant neurodevelopmental disorder referred to as the Bosch-Boonstra-Schaaf Optic Atrophy Syndrome. Although visual loss is a prominent feature seen in affected individuals, the molecular and cellular mechanisms contributing to visual impairment are still poorly characterized. We conducted a deep phenotyping study on a cohort of 22 individuals carrying pathogenic NR2F1 variants to document the neurodevelopmental and ophthalmological manifestations, in particular the structural and functional changes within the retina and the optic nerve, which have not been detailed previously. The visual impairment became apparent in early childhood with small and/or tilted hypoplastic optic nerves observed in 10 cases. High-resolution optical coherence tomography imaging confirmed significant loss of retinal ganglion cells with thinning of the ganglion cell layer, consistent with electrophysiological evidence of retinal ganglion cells dysfunction. Interestingly, for those individuals with available longitudinal ophthalmological data, there was no significant deterioration in visual function during the period of follow-up. Diffusion tensor imaging tractography studies showed defective connections and disorganization of the extracortical visual pathways. To further investigate how pathogenic NR2F1 variants impact on retinal and optic nerve development, we took advantage of an Nr2f1 mutant mouse disease model. Abnormal retinogenesis in early stages of development was observed in Nr2f1 mutant mice with decreased retinal ganglion cell density and disruption of retinal ganglion cell axonal guidance from the neural retina into the optic stalk, accounting for the development of optic nerve hypoplasia. The mutant mice showed significantly reduced visual acuity based on electrophysiological parameters with marked conduction delay and decreased amplitude of the recordings in the superficial layers of the visual cortex. The clinical observations in our study cohort, supported by the mouse data, suggest an early neurodevelopmental origin for the retinal and optic nerve head defects caused by NR2F1 pathogenic variants, resulting in congenital vision loss that seems to be non-progressive. We propose NR2F1 as a major gene that orchestrates early retinal and optic nerve head development, playing a key role in the maturation of the visual system.

Prevalence of electronegative electroretinograms in a healthy adult cohort

Objective

An electronegative electroretinogram (ERG) can indicate important ocular or systemic disease. This study explored the prevalence of electronegative responses to dark-adapted stimuli in a largely healthy cohort.

Methods and Analysis

211 participants recruited from the TwinsUK cohort underwent ERG testing incorporating international standard (International Society for Clinical Electrophysiology of Vision (ISCEV)) protocols and additional stimuli. Responses were recorded using conductive fibre electrodes, following pupil dilation and 20 min dark adaptation. Responses analysed were to the ISCEV standard and strong flashes (3.0 and 10 cd/m² s), and to additional white flashes (0.67–67 cd/m² s). A-wave and b-wave amplitudes were extracted; b:a ratios were calculated and proportions of eyes with ratios<1 were noted.

Results

Mean (SD) age was 62.4 (11.4) years (median, 64.3; range 23–86 years). 93% were female. Mean (SD) b:a ratios for right and left eyes, respectively, were 1.86 (0.33) and 1.81 (0.29) for the standard flash, and 1.62 (0.25) and 1.58 (0.23) for the stronger flash; average b:a ratio was lower for the stronger flash (p<0.0001). No waveforms were electronegative. For additional flashes, b:a ratio decreased with increasing flash strength. No electronegative waveforms were seen except in three eyes (0.7%) for the strongest flash; in some cases, drift in the waveform may have artefactually reduced the b:a ratio.

Conclusion

For standard dark-adapted stimuli, no participants had electronegative waveforms. The findings support the notion that electronegative waveforms (in response to standard flash strengths) are unusual, and should prompt further investigation.

A Novel Pathogenic NOD2 Variant in a Mother and Daughter with Blau Syndrome

BACKGROUND

Blau syndrome (BS) is a rare dominantly-inherited autoinflammatory disorder characterized by the triad of arthritis, uveitis and dermatitis that is consequence of gain-of-function NOD2 mutations. We describe the clinical features and genetic basis of a family with two affected members in consecutive generations affected with childhood onset arthritis and uveitis.

MATERIALS AND METHODS

Clinical features were retrospectively collected from clinical records. Genetic studies were performed using the Sanger method of DNA sequencing.

RESULTS

The proband is a 44 years-old female, who was diagnosed with juvenile onset arthritis at the age of 9 years. She subsequently developed uveitis at age 12 and since then she was managed between the uveitis and rheumatology services. The proband's daughter developed episcleritis at the age of 7 years, and arthritis with bilateral intermediate uveitis two years later. NOD2 analyses revealed in both patients the heterozygous c.1494A>C transversion, predicted to lead the novel, missense p.E498D variant in the NOD2 protein. Additional studies including databases searches and in silico bioinformatic predictions strongly support the "likely pathogenic" classification for this novel variant.

CONCLUSIONS

We report a novel pathogenic NOD2 variant in a multiplex family with clinical features compatible with the BS diagnosis. This condition is inherited as a dominant trait in its familial form and should be considered in patients with granulomatous uveitis in association with arthritis and/or dermatitis. Further insight into NOD2 variants and their downstream effects may have implications in the treatment of BS and other inflammatory granulomatous diseases.

CNGB1-related rod-cone dystrophy: A mutation review and update

Cyclic nucleotide-gated channel β1 (CNGB1) encodes the 240-kDa β subunit of the rod photoreceptor cyclic nucleotide-gated ion channel. Disease-causing sequence variants in CNGB1 lead to autosomal recessive rod-cone dystrophy/retinitis pigmentosa (RP). We herein present a comprehensive review and analysis of all previously reported CNGB1 sequence variants, and add 22 novel variants, thereby enlarging the spectrum to 84 variants in total, including 24 missense variants (two of which may also affect splicing), 21 nonsense, 19 splicing defects (7 at noncanonical positions), 10 small deletions, 1 small insertion, 1 small insertion-deletion, 7 small duplications, and 1 gross deletion. According to the American College of Medical Genetics and Genomics classification criteria, 59 variants were considered pathogenic or likely pathogenic and 25 were variants of uncertain significance. In addition, we provide further phenotypic data from 34 CNGB1-related RP cases, which, overall, are in line with previous findings suggesting that this form of RP has long-term retention of useful central vision despite the early onset of night blindness, which is valuable for patient counseling, but also has implications for it being considered a priority target for gene therapy trials.

Expanding the FDXR-Associated Disease Phenotype: Retinal Dystrophy Is a Recurrent Ocular Feature

Purpose

The purpose of this study was to report retinal dystrophy as a novel clinical feature and expand the ocular phenotype in patients harboring biallelic candidate FDXR variants.

Methods

Patients carrying biallelic candidate FDXR variants were identified by whole genome sequencing (WGS) as part of the National Institute for Health Research BioResource rare-disease and the UK's 100,000 Genomes Project (100KGP) with an additional case identified by exome sequencing. Retrospective clinical data were collected from the medical records. Haplotype reconstruction was performed in families harboring the same missense variant.

Results

Ten individuals from 8 unrelated families with biallelic candidate variants in FDXR were identified. In addition to bilateral optic atrophy and variable extra-ocular findings, 7 of 10 individuals manifested retinal dystrophy comprising dysfunction and degeneration of both rod and cone photoreceptors. Five of 10 subjects had sensorineural hearing loss. The previously unreported missense variant (c.1115C > A, p.(Pro372His)) was found in 5 of 8 (62.5%) study families. Haplotype reconstruction using WGS data demonstrated a likely ancestral haplotype.

Conclusions

FDXR-associated disease is a phenotypically heterogeneous disorder with retinal dystrophy being a major clinical feature observed in this cohort. In addition, we hypothesize that a number of factors are likely to drive the pathogenesis of optic atrophy, retinal degeneration, and perhaps the associated systemic manifestations.

KCNV2-Associated Retinopathy: Genetics, Electrophysiology, and Clinical Course-KCNV2 Study Group Report 1

PURPOSE

To investigate genetics, electrophysiology, and clinical course of KCNV2-associated retinopathy in a cohort of children and adults.

STUDY DESIGN

This was a multicenter international clinical cohort study.

METHODS

Review of clinical notes and molecular genetic testing. Full-field electroretinography (ERG) recordings, incorporating the international standards, were reviewed and quantified and compared with age and recordings from control subjects.

RESULTS

In total, 230 disease-associated alleles were identified from 117 patients, corresponding to 75 different KCNV2 variants, with 28 being novel. The mean age of onset was 3.9 years old. All patients were symptomatic before 12 years of age (range, 0-11 years). Decreased visual acuity was present in all patients, and 4 other symptoms were common: reduced color vision (78.6%), photophobia (53.5%), nyctalopia (43.6%), and nystagmus (38.6%). After a mean follow-up of 8.4 years, the mean best-corrected visual acuity (BCVA ± SD) decreased from 0.81 ± 0.27 to 0.90 ± 0.31 logarithm of minimal angle of resolution. Full-field ERGs showed pathognomonic waveform features. Quantitative assessment revealed a wide range of ERG amplitudes and peak times, with a mean rate of age-associated reduction indistinguishable from the control group. Mean amplitude reductions for the dark-adapted 0.01 ERG, dark-adapted 10 ERG a-wave, and LA 3.0 30 Hz and LA3 ERG b-waves were 55%, 21%, 48%, and 74%, respectively compared with control values. Peak times showed stability across 6 decades.

CONCLUSION

In KCNV2-associated retinopathy, full-field ERGs are diagnostic and consistent with largely stable peripheral retinal dysfunction. Report 1 highlights the severity of the clinical phenotype and established a large cohort of patients, emphasizing the unmet need for trials of novel therapeutics.

Panel-based genetic testing for inherited retinal disease screening 176 genes

Background

This case series reports the performance of a next‐generation sequencing (NGS) panel of 176 retinal genes (NGS 176) in patients with inherited retinal disease (IRD).

Methods

Subjects are patients who underwent genetic testing between 1 August 2016 and 1 January 2018 at Moorfields Eye Hospital, London, UK. Panel‐based genetic testing was performed unless a specific gene (e.g., RS1) or small group of genes (e.g., ABCA4, PRPH2) were suspected. If a novel variant was identified, a further comment on their predicted pathogenicity and evolutionary conservation was offered and segregation studies performed. The main outcome measure is the likelihood of obtaining a genetic diagnosis using NGS 176.

Results

488 patients were included. A molecular diagnosis was obtained for 59.4% of patients. Younger patients were more likely to receive a molecular diagnosis; with 92% of children under the age of 6 years receiving a conclusive result. There was a change in their initially assigned inheritance pattern in 8.4% of patients following genetic testing. Selected IRD diagnoses (e.g., achromatopsia, congenital stationary night blindness) were associated with high diagnostic yields.

Conclusion

This study confirms that NGS 176 is a useful first‐tier genetic test for most IRD patients. Age and initial clinical diagnosis were strongly associated with diagnostic yield.

Prospective deep phenotyping of choroideremia patients using multimodal structure-function approaches

OBJECTIVE

To investigate the retinal changes in choroideremia (CHM) patients to determine correlations between age, structure and function.

SUBJECTS/METHODS

Twenty-six eyes from 13 male CHM patients were included in this prospective longitudinal study. Participants were divided into <50-year (n = 8) and ≥50-year (n = 5) old groups. Patients were seen at baseline, 6-month, and 1-year visits. Optical coherence tomography (OCT), OCT angiography, and fundus autofluorescence were performed to measure central foveal (CFT) and subfoveal choroidal thickness (SCT), as well as areas of preserved choriocapillaris (CC), ellipsoid zone (EZ), and autofluorescence (PAF). Patients also underwent functional investigations including visual acuity (VA), contrast sensitivity (CS), colour testing, microperimetry, dark adaptometry, and handheld electroretinogram (ERG). Vision-related quality-of-life was assessed by using the NEI-VFQ-25 questionnaire.

RESULTS

Over the 1-year follow-up period, progressive loss was detected in SCT, EZ, CC, PAF, and CFT. Those ≥50-years exhibited more structural and functional defects with SCT, EZ, CC, and PAF showing strong correlation with patient age (rho ≤ -0.47, p ≤ 0.02). CS and VA did not change over the year, but CS was significantly correlated with age (rho = -0.63, p = 0.001). Delayed to unmeasurable dark adaptation, decreased colour discrimination and no detectable ERG activity were observed in all patients. Minimal functional deterioration was observed over one year with a general trend of slower progression in the ≥50-years group.

CONCLUSIONS

Quantitative structural parameters including SCT, CC, EZ, and PAF are most useful for disease monitoring in CHM. Extended follow-up studies are required to determine longitudinal functional changes.

New variants and in silico analyses in GRK1 associated Oguchi disease

Biallelic mutations in G-Protein coupled receptor kinase 1 (GRK1) cause Oguchi disease, a rare subtype of congenital stationary night blindness (CSNB). The purpose of this study was to identify disease causing GRK1 variants and use in-depth bioinformatic analyses to evaluate how their impact on protein structure could lead to pathogenicity. Patients' genomic DNA was sequenced by whole genome, whole exome or focused exome sequencing. Disease associated variants, published and novel, were compared to nondisease associated missense variants. The impact of GRK1 missense variants at the protein level were then predicted using a series of computational tools. We identified twelve previously unpublished cases with biallelic disease associated GRK1 variants, including eight novel variants, and reviewed all GRK1 disease associated variants. Further structure-based scoring revealed a hotspot for missense variants in the kinase domain. In addition, to aid future clinical interpretation, we identified the bioinformatics tools best able to differentiate disease associated from nondisease associated variants. We identified GRK1 variants in Oguchi disease patients and investigated how disease-causing variants may impede protein function in-silico.

Novel Biallelic Variants and Phenotypic Features in Patients with SLC38A8-Related Foveal Hypoplasia

Biallelic pathogenic variants in solute carrier family 38 member 8, SLC38A8, cause a pan-ocular autosomal recessive condition known as foveal hypoplasia 2, FVH2, characterised by foveal hypoplasia, nystagmus and optic nerve chiasmal misrouting. Patients are often clinically diagnosed with ocular albinism, but foveal hypoplasia can occur in several other ocular disorders. Here we describe nine patients from seven families who had molecularly confirmed biallelic recessive variants in SLC38A8 identified through whole genome sequencing or targeted gene panel testing. We identified four novel sequence variants (p.(Tyr88*), p.(Trp145*), p.(Glu233Gly) and c.632+1G>A). All patients presented with foveal hypoplasia, nystagmus and reduced visual acuity; however, one patient did not exhibit any signs of chiasmal misrouting, and three patients had features of anterior segment dysgenesis. We highlight these findings in the context of 30 other families reported to date. This study reinforces the importance of obtaining a molecular diagnosis in patients whose phenotype overlap with other inherited ocular conditions, in order to support genetic counselling, clinical prognosis and family planning. We expand the spectrum of SLC38A8 mutations which will be relevant for treatment through future genetic-based therapies.

Sector Retinitis Pigmentosa: Extending the Molecular Genetics Basis and Elucidating the Natural History

Purpose

To determine the genetic background of sector retinitis pigmentosa (RP) natural history to better inform patient counseling.

Design

Retrospective case series.

Methods

Review of clinical notes, retinal imaging including color fundus photography (CFP), fundus autofluorescence (FAF), optical coherence tomography (OCT), electrophysiological assessment (ERG), and molecular genetic testing were performed in patients with sector RP from a single tertiary referral center. Main outcomes measured were demographic data, signs and symptoms, visual acuity, molecular genetics; and ERG, FAF, and OCT findings.

Results

Twenty-six molecularly confirmed patients from 23 different families were identified harboring likely disease-causing variants in 9 genes. The modes of inheritance were autosomal recessive (AR, n=6: USH1C, n=2; MYO7A, n=2; CDH3, n=1; EYS, n=1), X-linked (XL, n=4: PRPS1, n=1; RPGR, n=3), and autosomal dominant (AD, n=16: IMPDH1, n=3; RP1, n=3; RHO, n=10), with a mean age of disease onset of 38.5, 30.5, and 39.0 years old, respectively. Five of these genes have not previously been reported to cause sector RP (PRPS1, MYO7A, EYS, IMPDH1, and RP1). Inferior and nasal predilection was common across the different genotypes, and patients tended to maintain good central vision. Progression on serial FAF was observed in RPGR, MYO7A, CDH23, EYS, IMPDH1, RP1, and RHO-associated sector RP.

Conclusions

The genotypic spectrum of the disease is broader than previously reported. The longitudinal data provided will help to make accurate patient prognoses and counseling as well as inform patients' potential participation in the increasing numbers of trials of novel therapeutics and access to future treatments.

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This is the largest series and longitudinal study in sector retinitis pigmentosa.

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The genotypic spectrum of the disease is broader than previously reported.

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The longitudinal data provided more accurate patient prognosis and counseling.

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The study informed patients' potential participation in the increasing numbers of trials of novel therapeutics and access to future treatments.

Reanalysis of Association of Pro50Leu Substitution in Guanylate Cyclase Activating Protein-1 With Dominant Retinal Dystrophy

Question

Is there evidence that the Pro50Leu substitution in guanylate cyclase activating protein-1 (encoded by the gene GUCA1A) is associated with a dominant retinal dystrophy?

Findings

In this cross-sectional study reevaluating the original published study of a family after examination of another family member and further genetic testing, a pathogenic variant in the X chromosome–linked RPGR gene was found. Also, publicly available genomic data show that the variant in GUCA1A is too common to cause a dominant retinal dystrophy.

Meaning

The p.(Pro50Leu) variant in GUCA1A should not be considered a pathogenic variant.

Importance

As genetic and genomic screening is becoming more widely accessed, correctly distinguishing pathogenic from nonpathogenic variants is of increasing relevance.

Objective

To reevaluate a previously reported family in whom the p.(Pro50Leu) variant in the gene GUCA1A was associated with a dominant retinal dystrophy, in light of new examination findings in the proband’s daughter.

Design, Setting, and Participants

A genetic study relating to a family with an inherited retinal dystrophy was performed at the retinal genetics service of Moorfields Eye Hospital from October 27, 2009, to May 23, 2019, after the proband’s daughter underwent fundus examination.

Main Outcomes and Measures

Results of sequencing of X chromosome–linked retinitis pigmentosa genes in the proband and specific analysis of the repetitive ORF15 region of the RPGR gene.

Results

A frame-shifting single-nucleotide deletion was found in the ORF15 exon of RPGR (GRCh37 [hg19] x:38145160delT; NM_001034853.1: c.3092delA p.[Glu1031Glyfs*58]), which may be associated with the loss of 121 amino acid residues at the carboxyl terminus of the protein. The p.(Pro50Leu) variant in GUCA1A was also found to be too common in a publicly available genome database to be a fully penetrant cause of a dominant retinal dystrophy.

Conclusions and Relevance

The phenotype in the family is now associated with the variant in RPGR. The findings suggest that the p.(Pro50Leu) variant in GUCA1A should not be regarded as pathogenic. This report also highlights the relevance of examining relatives, of reevaluating diagnoses in light of new data, and of considering X chromosome–linked inheritance in apparently autosomal dominant pedigrees unless there is clear male-to-male transmission.

Structural Variants Create New Topological-Associated Domains and Ectopic Retinal Enhancer-Gene Contact in Dominant Retinitis Pigmentosa

The cause of autosomal-dominant retinitis pigmentosa (adRP), which leads to loss of vision and blindness, was investigated in families lacking a molecular diagnosis. A refined locus for adRP on Chr17q22 (RP17) was delineated through genotyping and genome sequencing, leading to the identification of structural variants (SVs) that segregate with disease. Eight different complex SVs were characterized in 22 adRP-affected families with >300 affected individuals. All RP17 SVs had breakpoints within a genomic region spanning YPEL2 to LINC01476. To investigate the mechanism of disease, we reprogrammed fibroblasts from affected individuals and controls into induced pluripotent stem cells (iPSCs) and differentiated them into photoreceptor precursor cells (PPCs) or retinal organoids (ROs). Hi-C was performed on ROs, and differential expression of regional genes and a retinal enhancer RNA at this locus was assessed by qPCR. The epigenetic landscape of the region, and Hi-C RO data, showed that YPEL2 sits within its own topologically associating domain (TAD), rich in enhancers with binding sites for retinal transcription factors. The Hi-C map of RP17 ROs revealed creation of a neo-TAD with ectopic contacts between GDPD1 and retinal enhancers, and modeling of all RP17 SVs was consistent with neo-TADs leading to ectopic retinal-specific enhancer-GDPD1 accessibility. qPCR confirmed increased expression of GDPD1 and increased expression of the retinal enhancer that enters the neo-TAD. Altered TAD structure resulting in increased retinal expression of GDPD1 is the likely convergent mechanism of disease, consistent with a dominant gain of function. Our study highlights the importance of SVs as a genomic mechanism in unsolved Mendelian diseases.

Autosomal Recessive Bestrophinopathy: Clinical Features, Natural History, and Genetic Findings in Preparation for Clinical Trials

Purpose

To investigate the clinical course, genetic findings, and phenotypic spectrum of autosomal recessive bestrophinopathy (ARB) in a large cohort of children and adults.

Design

Retrospective case series.

Participants

Patients with a detailed clinical phenotype consistent with ARB, biallelic likely disease-causing sequence variants in the BEST1 gene, or both identified at a single tertiary referral center.

Methods

Review of case notes, retinal imaging (color fundus photography, fundus autofluorescence, OCT), electrophysiologic assessment, and molecular genetic testing.

Main Outcome Measures

Visual acuity (VA), retinal imaging, and electrophysiologic changes over time.

Results

Fifty-six eyes of 28 unrelated patients were included. Compound heterozygous variants were detected in most patients (19/27), with 6 alleles recurring in apparently unrelated individuals, the most common of which was c.422G→A, p.(Arg141His; n = 4 patients). Mean presenting VA was 0.52 ± 0.36 logarithm of the minimum angle of resolution (logMAR), and final VA was 0.81 ± 0.75 logMAR (P = 0.06). The mean rate of change in VA was 0.05 ± 0.13 logMAR/year. A significant change in VA was detected in patients with a follow-up of 5 years or more (n = 18) compared with patients with a follow-up of 5 years or less (n = 10; P = 0.001). Presence of subretinal fluid and vitelliform material were early findings in most patients, and this did not change substantially over time. A reduction in central retinal thickness was detected in most eyes (80.4%) over the course of follow-up. Many patients (10/26) showed evidence of generalized rod and cone system dysfunction. These patients were older (P < 0.001) and had worse VA (P = 0.02) than those with normal full-field electroretinography results.

Conclusions

Although patients with ARB are presumed to have no functioning bestrophin channels, significant phenotypic heterogeneity is evident. The clinical course is characterized by a progressive loss of vision with a slow rate of decline, providing a wide therapeutic window for anticipated future treatment strategies.