GUCY2D- or GUCA1A-related autosomal dominant cone-rod dystrophy: is there a phenotypic difference?

Comparative analysis of in-silico tools in identifying pathogenic variants in dominant inherited retinal diseases

Inherited retinal diseases (IRDs) are a group of rare genetic eye conditions that cause blindness. Despite progress in identifying genes associated with IRDs, improvements are necessary for classifying rare autosomal dominant (AD) disorders. AD diseases are highly heterogenous, with causal variants being restricted to specific amino acid changes within certain protein domains, making AD conditions difficult to classify. Here, we aim to determine the top-performing in-silico tools for predicting the pathogenicity of AD IRD variants. We annotated variants from ClinVar and benchmarked 39 variant classifier tools on IRD genes, split by inheritance pattern. Using area-under-the-curve (AUC) analysis, we determined the top-performing tools and defined thresholds for variant pathogenicity. Top-performing tools were assessed using genome sequencing on a cohort of participants with IRDs of unknown etiology. MutScore achieved the highest accuracy within AD genes, yielding an AUC of 0.969. When filtering for AD gain-of-function and dominant negative variants, BayesDel had the highest accuracy with an AUC of 0.997. Five participants with variants in NR2E3, RHO, GUCA1A, and GUCY2D were confirmed to have dominantly inherited disease based on pedigree, phenotype, and segregation analysis. We identified two uncharacterized variants in GUCA1A (c.428T>A, p.Ile143Thr) and RHO (c.631C>G, p.His211Asp) in three participants. Our findings support using a multi-classifier approach comprised of new missense classifier tools to identify pathogenic variants in participants with AD IRDs. Our results provide a foundation for improved genetic diagnosis for people with IRDs.

Phenotyping and genotyping inherited retinal diseases: Molecular genetics, clinical and imaging features, and therapeutics of macular dystrophies, cone and cone-rod dystrophies, rod-cone dystrophies, Leber congenital amaurosis, and cone dysfunction syndromes

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.

Occult Macular Dysfunction Syndrome: Identification of Multiple Pathologies in a Clinical Spectrum of Macular Dysfunction with Normal Fundus in East Asian Patients: EAOMD Report No. 5

Occult macular dystrophy (OMD) is the most prevalent form of macular dystrophy in East Asia. Beyond RP1L1, causative genes and mechanisms remain largely uncharacterised. This study aimed to delineate the clinical and genetic characteristics of OMD syndrome (OMDS). Patients clinically diagnosed with OMDS in Japan, South Korea, and China were enrolled. The inclusion criteria were as follows: (1) macular dysfunction and (2) normal fundus appearance. Comprehensive clinical evaluation and genetic assessment were performed to identify the disease-causing variants. Clinical parameters were compared among the genotype groups. Seventy-two patients with OMDS from fifty families were included. The causative genes were RP1L1 in forty-seven patients from thirty families (30/50, 60.0%), CRX in two patients from one family (1/50, 2.0%), GUCY2D in two patients from two families (2/50, 4.0%), and no genes were identified in twenty-one patients from seventeen families (17/50, 34.0%). Different severities were observed in terms of disease onset and the prognosis of visual acuity reduction. This multicentre large cohort study furthers our understanding of the phenotypic and genotypic spectra of patients with macular dystrophy and normal fundus. Evidently, OMDS encompasses multiple Mendelian retinal disorders, each representing unique pathologies that dictate their respective severity and prognostic patterns.

The impact of modifier genes on cone-rod dystrophy heterogeneity: An explorative familial pilot study and a hypothesis on neurotransmission impairment

Cone-rod dystrophies (CORDs) are a heterogeneous group of inherited retinopathies (IRDs) with more than 30 already known disease-causing genes. Uncertain phenotypes and extended range of intra- and interfamilial heterogenicity make still difficult to determine a precise genotype-phenotype correlation. Here, we used a next-generation sequencing approach to study a Sicilian family with a suspected form of CORD. Affected family members underwent ophthalmological examinations and a proband, blind from 50 years, underwent whole genome and exome sequencing. Variant analysis was enriched by pathway analysis and relevant variants were, then, investigated in other family members and in 100 healthy controls from Messina. CORD diagnosis with an intricate pattern of symptoms was confirmed by ophthalmological examinations. A total of about 50,000 variants were identified in both proband's genome and exome. All affected family members presented specific genotypes mainly determined by mutated GUCY2D gene, and different phenotypical traits, mainly related to focus and color perception. Thus, we looked for possible modifier genes. According to relationship with GUCY2D, predicted functional effects, eye localization, and ocular disease affinity, only 9 variants, carried by 6 genes (CACNG8, PAX2, RXRG, CCDC175, PDE4DIP and LTF), survived the filtering. These genes encode key proteins involved in cone development and survival, and retina neurotransmission. Among analyzed variants, CACNG8c.*6819A>T and the new CCDC175 c.76C>T showed extremely low frequency in the control group, suggesting a key role on disease phenotypes. Such discovery could enforce the role of modifier genes into CORD onset/progression, contributing to improve diagnostic test towards a better personalized medicine.

New Insights on the Regulatory Gene Network Disturbed in Central Areolar Choroidal Dystrophy-Beyond Classical Gene Candidates

Central areolar choroidal dystrophy (CACD) is a rare hereditary disease that mainly affects the macula, resulting in progressive and usually profound visual loss. Being part of congenital retinal dystrophies, it may have an autosomal dominant or recessive inheritance and, until now, has no effective treatment. Given the shortage of genotypic information about the disease, this work systematically reviews the literature for CACD-causing genes. Three independent researchers selected 33 articles after carefully searching and filtering the Scielo, Pubmed, Lilacs, Web of Science, Scopus, and Embase databases. Mutations of six genes (PRPH2, GUCA1A, GUCY2D, CDHR1, ABCA4, and TTLL5) are implicated in the monogenic dominant inheritance of CACD. They are functionally related to photoreceptors (either in the phototransduction process, as in the case of GUCY2D, or the recovery of retinal photodegradation in photoreceptors for GUCA1A, or the formation and maintenance of specific structures within photoreceptors for PRPH2). The identified genetic variants do not explain all observed clinical features, calling for further whole-genome and functional studies for this disease. A network analysis with the CACD-related genes identified in the systematic review resulted in the identification of another 20 genes that may influence CACD onset and symptoms. Furthermore, an enrichment analysis allowed the identification of 13 transcription factors and 4 long noncoding RNAs interacting with the products of the previously mentioned genes. If mutated or dysregulated, they may be directly involved in CACD development and related disorders. More than half of the genes identified by bioinformatic tools do not appear in commercial gene panels, calling for more studies about their role in the maintenance of the retina and phototransduction process, as well as for a timely update of these gene panels.

GUCY2D-Related Retinal Dystrophy with Autosomal Dominant Inheritance—A Multicenter Case Series and Review of Reported Data

To report the clinical phenotype and associated genotype of a European patient cohort with GUCY2D-related autosomal-dominant (AD) cone–/cone–rod dystrophy (COD/CORD), we retrospectively analyzed 25 patients (17 female, range 12–68) with GUCY2D-related AD-COD/CORD from three major academic centers in Europe and reviewed the previously published data of 148 patients (visual acuity (VA), foveal thickness, age of first symptoms, and genetic variant). Considering all the patients, the onset of first symptoms was reported at a median age of 7 years (interquartile range 5–19 years, n = 78), and mainly consisted of reduced VA, photophobia and color vision abnormality. The disease showed a high degree of inter-eye symmetry in terms of VA (n = 165, Spearman’s ρ = 0.85, p < 0.0001) and foveal thickness (Spearman’s ρ = 0.96, n = 38, p < 0.0001). Disease progression was assessed by plotting VA as a function of age (n = 170). A linear best-fit analysis suggested a loss of 0.17 logMAR per decade (p < 0.0001). We analyzed the largest cohort described so far (n = 173), and found that the most common mutations were p.(Arg838Cys) and p.(Arg838His). Furthermore, the majority of patients suffered severe vision loss in adulthood, highlighting a window of opportunity for potential intervention. The emerging patterns revealed by this study may aid in designing prospective natural history studies to further define endpoints for future interventional trials.

Characteristic Ocular Features in Cases of Autosomal Recessive PROM1 Cone-Rod Dystrophy

Purpose

To define characteristic ocular features in a group of patients with autosomal recessive (AR) PROM1 cone-rod dystrophy (CRD).

Methods

Three males and one female from three unrelated families were first seen at the ages of 15 to 22 years and diagnosed with CRD. Clinical testing available for review included full-field electroretinogram (ERG) in three patients, as well as near-infrared autofluorescence (NIR-AF), spectral-domain optical coherence tomography (SD-OCT), and color fundus photography in all four patients. Whole exome sequencing (WES) was performed on all cases, and whole genome sequencing (WGS) was performed in two families.

Results

WES found compound heterozygous PROM1 variants in one isolated male, plus heterozygous variants in the remaining patients. WGS uncovered deleterious PROM1 variants in these two families. ERG showed markedly reduced cone-isolated amplitudes and variably reduced rod-isolated amplitudes. The dark-adapted combined rod and cone responses demonstrated notably reduced a-wave amplitudes and moderately reduced b-waves, and the resultant waveform resembled the normal rod-isolated response. On fundus examination, oval-shaped macular lesions were observed, as were several small, circular hypoautofluorescent lesions within the posterior pole on NIR-AF. Three patients showed extramacular circular atrophic lesions.

Conclusions

The autofluorescence changes, peripheral retinal abnormalities, and ERG findings have not been emphasized in previous reports of AR PROM1, but they became a recognizable phenotype in this cohort of patients. A similar constellation of findings may be observed in CRD due to CDHR1, a functionally related gene. The pattern of abnormalities reported herein may help to focus genetic screening in patients with these findings.

Phenotype Analysis of Retinal Dystrophies in Light of the Underlying Genetic Defects: Application to Cone and Cone-Rod Dystrophies

Phenotypes observed in a large cohort of patients with cone and cone-rod dystrophies (COD/CORDs) are described based on multimodal retinal imaging features in order to help in analyzing massive next-generation sequencing data. Structural abnormalities of 58 subjects with molecular diagnosis of COD/CORDs were analyzed through specific retinal imaging including spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (BAF/IRAF). Findings were analyzed with the underlying genetic defects. A ring of increased autofluorescence was mainly observed in patients with CRX and GUCY2D mutations (33% and 22% of cases respectively). “Speckled” autofluorescence was observed with mutations in three different genes (ABCA4 64%; C2Orf71 and PRPH2, 18% each). Peripapillary sparing was only found in association with mutations in ABCA4, although only present in 40% of such genotypes. Regarding SD-OCT, specific outer retinal abnormalities were more commonly observed in particular genotypes: focal retrofoveal interruption and GUCY2D mutations (50%), foveal sparing and CRX mutations (50%), and outer retinal atrophy associated with hyperreflective dots and ABCA4 mutations (69%). This study outlines the phenotypic heterogeneity of COD/CORDs hampering statistical correlations. A larger study correlating retinal imaging with genetic results is necessary to identify specific clinical features that may help in selecting pathogenic variants generated by high-throughput sequencing.

Retinal dystrophies with bull's-eye maculopathy along with negative ERGs

PURPOSE

The aim of this study was to examine the ophthalmological characteristics and genotypes of patients with congenital retinal pathologies, who display a bull's-eye maculopathy in the fundus, along with a negative scotopic electroretinogram.

METHODS

We analysed the results of five patients showing both a bull's-eye maculopathy, as well as a negative scotopic ERG evoked by a bright flash. Their median age was 39 years (range 11-63 years): three males and two females. All underwent a comprehensive examination with determination of distant visual acuity (ETDRS) and recording of the full-field ERG (scotopic and photopic). Fundus, OCT, and FAF images were obtained, the kinetic visual field was determined, and colour vision (D-15) was tested in most patients. Targeted gene panel sequencing was performed on peripheral blood.

RESULTS

One patient carried a homozygous ABCA4 mutation and an additional heterozygous variant in CRX. Two of the five patients were shown to have a heterozygous mutation in the CRX gene, one of whom had an additional heterozygous ABCA4 mutation. Two patients had the common heterozygous mutation c.2413G>A;p.Arg838His in GUCY2D. In all of the patients, there was a reduction in the amplitude of the b-wave with a regular a-wave amplitude in the scotopic bright-flash ERG.

CONCLUSIONS

The five patients with bull's-eye maculopathy along with a negative ERG had differing genotypes. Mutations were found in the CRX gene (2 patients), the ABCA4 gene (1 patient), and the GUCY2D gene (2 patients).

Peripheral Cone Dystrophy: Expanded Clinical Spectrum, Multimodal and Ultrawide-Field Imaging, and Genomic Analysis

PURPOSE

To present new clinical features, multimodal and ultrawide-field imaging characteristics of peripheral cone dystrophy (PCD), and results of laboratory and genetic investigation to decipher the etiology.

METHODS

Retrospective observational case-series.

RESULTS

Three patients with PCD presented with bilateral paracentral scotomas and a mean visual acuity of 20/25. All exhibited confluent macular hyperautofluorescence with a central bull's eye lesion. Spectral-domain optical coherence tomography revealed loss of outer retinal elements, particularly the inner segment ellipsoid band and external limiting membrane, within the area of macular hyperautofluorescence. This area corresponded with a lightened fundus appearance and variable retinal pigment epithelium (RPE) abnormalities. Full field and multifocal electroretinography distinguished PCD from other photoreceptor dystrophies. Ultrawide-field imaging revealed irregular peripheral retinal lesions in a distribution greater nasally than temporally and not contiguous with the macular lesion. Functional and anatomic testing remained stable over a mean follow-up of 3 years. Laboratory investigation for causes of uveitis was negative. Whole exome sequencing identified rare variants in genes associated with macular or cone dystrophy or degeneration.

CONCLUSIONS

In contrast to the original description, the funduscopic and fluorescein angiographic appearance of PCD is abnormal, although the defects are subtle. Peripheral lesions may be observed in some patients. Bilateral, symmetric, macular hyperautofluorescence associated with outer retinal atrophy that spares the fovea is a characteristic of PCD. Pathogenic variants in the same gene were not shared across the cohort, suggesting genetic heterogeneity. Further evaluation is warranted.

Graft versus self (GvS) against T-cell autoantigens is a mechanism of graft-host interaction

Graft-versus-host disease (GVHD) represents the major nonrelapse complication of allogeneic hematopoietic cell transplantation. Although rare, the CNS and the eye can be affected. In this study, manifestation in the retina as part of the CNS and T-cell epitopes recognized by the allogeneic T cells were evaluated. In 2 of 6 patients with posttransplantation retina diseases and 6 of 22 patients without ocular symptoms, antigen-specific T-cell responses against retina-specific epitopes were observed. No genetic differences between donor and recipient could be identified indicating T-cell activation against self-antigens (graft versus self). Transplantation of a preexisting immunity and cross-reactivity with ubiquitous epitopes was excluded in family donors and healthy individuals. In summary, an immunological reaction against retina cells represents a mechanism of graft-versus-host interaction following hematopoietic cell transplantation.

Novel Mutations in Two Saudi Patients with Congenital Retinal Dystrophy

To report novel mutations in two Saudi children with clinical features of Leber congenital amaurosis (LCA) and Alström syndrome.

CASE REPORTS

Case 1 was a child with phenotypic features of LCA including oculodigital sign, bilateral enophthalmos, nystagmus, pale disc, and retinal changes. Direct sequencing of the coding sequence of GUCY2D revealed a missense mutation affecting highly conserved position (c. 743C > T; p.S248 L). Case 2 describes a girl with marked nystagmus, photophobia, and retinal changes in both eyes with short and stubby fingers tapering at the distal phalanges. The electroretinograms were nonrecordable in each eye. She had a hearing aid in the left ear, mid-facial hypoplasia, bilateral enophthalmos, and insulin dependent diabetes. Mutation screening of candidates genes revealed a pathogenic mutation in ALMS1 gene (c. 8441C > A, p.S2814). Two novel mutations causing phenotypic LCA and Alström syndrome in Saudi patients from consanguineous families expand the genotypic spectrum of congenital retinal dystrophies.

Whole exome sequencing reveals GUCY2D as a major gene associated with cone and cone-rod dystrophy in Israel

PURPOSE

The Israeli population has a unique genetic make-up, with a high prevalence of consanguineous marriages and autosomal recessive diseases. In rod-dominated phenotypes, disease-causing genes and mutations that differ from those identified in other populations often are incurred. We used whole exome sequencing (WES) to identify genetic defects in Israeli families with cone-dominated retinal phenotypes.

METHODS

Clinical analysis included family history, detailed ocular examination, visual function testing, and retinal imaging. Whole exome sequencing, followed by segregation analysis, was performed in 6 cone-dominated retinopathy families in which prior mutation analysis did not reveal the causative gene. Based on the WES findings, we screened 106 additional families with cone-dominated phenotypes.

RESULTS

The WES analysis revealed mutations in known retinopathy genes in five of the six families: two pathogenic mutations in the GUCY2D gene in three families, and one each in CDHR1 and C8orf37. Targeted screening of additional cone-dominated families led to identification of GUCY2D mutations in four other families, which included two highly probable novel disease-causing variants.

CONCLUSIONS

Our study suggested that GUCY2D is a major cause of autosomal dominant cone and cone-rod dystrophies in Israel; this is similar to other Caucasian populations and is in contrast with retinitis pigmentosa (primary rod disease), where the genetic make-up of the Israeli population is distinct from other ethnic groups. We also conclude that WES permits more comprehensive and rapid analyses that can be followed by targeted screens of larger samples to delineate the genetic structure of retinal disease in unique population cohorts.