Clinical and Molecular Characterization of Achromatopsia Patients: A Longitudinal Study

Clinical and genetic features of CNGA3 achromatopsia in preschool children: novel insights into retinal architecture and therapeutic window for clinical trials

Purpose

Achromatopsia (ACHM) is a rare genetic disorder with an infantile onset that affects cone photoreceptors. This study aims to provide a comprehensive phenotyping of the retinal structure and identify novel genetic variants in a preschool cohort with ACHM in China.

Methods

We recruited patients with pathogenic genes (CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, and ATF6) known to cause ACHM, all of whom had an age of symptom onset before 6 years of age. Whole exome sequencing, Sanger sequencing, and comprehensive ocular examinations, including optical coherence tomography (OCT), were conducted. Furthermore, retinal outer layer damage was evaluated using a novel modified classification system.

Results

Nystagmus (46.13%) and photophobia (46.13%) were the most common initial complaints/reports from parents of our patients. These symptoms are easily noticed early (mean age 0.88 ± 1.07 years at onset of initial symptom). OCT revealed a wide range of degeneration in the outer retina of the fovea, exactly in the interdigitation zone (IZ) and ellipsoid zone (EZ). Retinal outer layer damage was observed in 18 eyes (9 patients), with the modified classification distribution: grade 1 in 1 eye (5.6%), grade 2 in 9 eyes (50.0%), and grade 3 in 8 eyes (44.4%). Eleven novel variants of CNAG3 were identified. The higher grade of outer retinal layer damage was shown in patients with genetic variants, potentially leading to structural changes in the cyclic guanosine monophosphate (cGMP) binding site of the synthesized protein (p = 0.046).

Conclusion

ACHM can manifest at very early stages of life. Mild damage to the outer layers of the retina is a typical change in early-stage ACHM. Patients with genetic variants potentially leading to structural changes in the cGMP binding site of the synthesized protein tend to exhibit more severe retinal phenotypes. Ultimately, our research may aid in formulating guidelines for selecting patients and determining the optimal timing for interventions in upcoming gene replacement therapies.

Rescue of the disease-associated phenotype in CRISPR-corrected hiPSCs as a therapeutic approach for inherited retinal dystrophies

Inherited retinal dystrophies (IRDs), such as retinitis pigmentosa and Stargardt disease, are a group of rare diseases caused by mutations in more than 300 genes that currently have no treatment in most cases. They commonly trigger blindness and other ocular affectations due to retinal cell degeneration. Gene editing has emerged as a promising and powerful strategy for the development of IRD therapies, allowing the permanent correction of pathogenic variants. Using clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 and transcription activator-like effector nucleases (TALEN) gene-editing tools, we precisely corrected seven hiPS cell lines derived from IRD patients carrying mutations in ABCA4, BEST1, PDE6A, PDE6C, RHO, or USH2A. Homozygous mutations and point insertions/deletions resulted in the highest homology-directed repair efficiencies, with at least half of the clones repaired properly without off-target effects. Strikingly, correction of a heterozygous pathogenic variant was achieved using the wild-type allele of the patient as the template for DNA repair. These results suggest the unexpected potential application of CRISPR as a donor template-free strategy for single-nucleotide modifications. Additionally, the corrected clones exhibited a reversion of the disease-associated phenotype in retinal cellular models. These data strengthen the study and application of gene editing-based approaches for IRD treatment.

Looking to the Future of Viral Vectors in Ocular Gene Therapy: Clinical Review

Eye diseases can significantly affect the quality of life of patients due to decreased visual acuity. Although modern ophthalmological diagnostic methods exist, some diseases of the visual system are asymptomatic in the early stages. Most patients seek advice from an ophthalmologist as a result of rapidly progressive manifestation of symptoms. A number of inherited and acquired eye diseases have only supportive treatment without eliminating the etiologic factor. A promising solution to this problem may be gene therapy, which has proven efficacy and safety shown in a number of clinical studies. By directly altering or replacing defective genes, this therapeutic approach will stop as well as reverse the progression of eye diseases. This review examines the concept of gene therapy and its application in the field of ocular pathologies, emphasizing the most recent scientific advances and their potential impacts on visual function status.

Onset and Progression of Disease in Nonhuman Primates With PDE6C Cone Disorder

Purpose

The California National Primate Research Center contains a colony of rhesus macaques with a homozygous missense mutation in PDE6C (R565Q) which causes a cone disorder similar to PDE6C achromatopsia in humans. The purposes of this study are to characterize the phenotype in PDE6C macaques in detail to determine the onset of the cone phenotype, the degree to which the phenotype progresses, if heterozygote animals have an intermediate phenotype, and if rod photoreceptor function declines over time.

Methods

We analyzed spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF), and electroretinography (ERG) data from 102 eyes of 51 macaques (aged 0.25 to 16 years). Measurements of retinal layers as well as cone and rod function over time were quantitatively compared.

Results

Homozygotes as young as 3 months postnatal showed absent cone responses on electroretinogram. Infant homozygotes had reduced foveal outer nuclear layer (ONL) thickness compared with wildtype infants (P < 0.0001). Over 4 years of study, no consistent changes in retinal layer thicknesses were found within 5 adult homozygotes. However, comparisons between infants and adults revealed reductions in foveal ONL thickness suggesting that cone cells slowly degenerate as homozygotes age. The oldest homozygote (11 years) had reduced rod responses. Heterozygotes could not be distinguished from wildtypes in any parameters.

Conclusions

These data suggest that, like humans, macaque PDE6C heterozygotes are normal, and homozygote primates have absent cone function and reduced foveal ONL thickness from infancy. Cone photoreceptors probably degenerate over time and macular atrophy can occur. Rod photoreceptor function may wane in late stages.

Microperimetry Sensitivity Correlates to Structural Macular Changes in Adolescents with Achromatopsia Unlike Other Visual Function Tests

Objectives: Achromatopsia (ACHM) is a rare autosomal, recessively inherited disease that is characterized by cone dysfunction, for which several gene therapies are currently on trial. The aim of this study was to find correlations between the morphological macular changes identified using optical coherence tomography (OCT) and some visual functional parameters. Visual acuity (VA), contrast sensitivity (CS), and macular sensitivity obtained by means of microperimetry were assessed. Methods: Adolescents with ACHM underwent macular microperimetry (S-MAIA device) in mesopic condition, macular OCT, best corrected visual acuity (BCVA), low luminance visual acuity (LLVA), near vision acuity (NVA), and CS measurement. Results: Eight patients (15 eyes) with ACHM were analyzed. The mean age was 17 ± 2.7 years, and genetic variants involved the CNGA3 gene (37.5%) and CNGB3 gene (62.5%). OCT staging significantly correlated with microperimetry sensitivity parameters, namely the sensitivity of the central foveal point (p = 0.0286) and of the first and second perifoveal rings (p = 0.0008 and p = 0.0014, respectively). No correlations were found between OCT staging and VA measurements, nor with CS value. Conclusions: Among the extensive evaluated visual function tests, only microperimetry sensitivity showed a correlation with morphological macular changes identified at OCT. Microperimetry sensitivity may thus represent a useful visual function tool in natural ACHM history studies considering the upcoming research on gene therapies for the treatment of ACHM.

Phenotypic characteristics of Danish patients with achromatopsia

PURPOSE

To describe the phenotype of Danish patients with genetically verified achromatopsia (ACHM) with special focus on signs of progression on structural or functional parameters, and possible genotype-phenotype correlations.

METHODS

Forty-eight patients were identified, with disease-causing variants in five different genes: CNGA3, CNGB3, GNAT2, PDE6C and PDE6H. Longitudinal evaluation was possible for 11 patients and 27 patients participated in a renewed in-depth phenotyping consisting of visual acuity assessment, optical coherence tomography (OCT), fundus autofluorescence, colour vision evaluation, contrast sensitivity, mesopic microperimetry and full-field electroretinography. Foveal morphology was evaluated based on OCT images for all 48 patients using a grading system based on the integrity of the hyperreflective photoreceptor band, the inner segment ellipsoid zone (ISe). Signs of progression were evaluated based on longitudinal data and correlation with age.

RESULTS

We found a statistically significant positive correlation between OCT grade and age (Spearman ρ = 0.62, p < 0.0001) and we observed changes in the foveal morphology in 2 of 11 patients with ≥5 years of follow-up. We did not find any convincing correlation between age and functional parameters (visual acuity, retinal sensitivity and contrast sensitivity) nor did we find correlation between structural and functional parameters, or any clear genotype-phenotype correlation.

CONCLUSIONS

Some patients with ACHM demonstrate signs of progressive foveal changes in OCT characteristics with increasing age. This is relevant in terms of possible new treatments. However, functional characteristics, such as visual acuity, remained stable despite changing foveal structure. Thus, seen from a patient perspective, ACHM can still be considered a non-progressive condition.

Achromatopsia: Long term visual performance and clinical characteristics

BACKGROUND

Achromatopsia is an autosomal recessive cone dysfunction syndrome, characterized by absence of color discrimination, low visual acuity, photophobia, and nystagmus. Achromatopsia constitutes a common cause of visual impairment in children, with a prevalence of 1:30,000 worldwide.

OBJECTIVE

To characterize the clinical characteristics of achromatopsia, the main genes causing the disease in our population and the clinical course of the disease, with an emphasis on visual function stability with increasing age.

METHODS

Retrospective study based on medical charts of patients with achromatopsia. Patients were divided into two groups according to their age at last follow-up: older and younger than 10 years. A subset of patients with long term follow-up were analyzed separately, with patients being described in both age groups.

RESULTS

Seventy-six patients were included in the study. The mean age was 14.28 years. Variants in the CNGA3 gene were the most common (73.6%). Clinical characteristics included photophobia (96.2%), nystagmus (93.6%), hypermetropia (72.3%) and strabismus (51.1%). In the large cohort there was no correlation of age with visual acuity (p = 0.129). In the separate subset cohort with long follow-up there was a relative improvement in visual acuity with age (p < 0.001).

CONCLUSIONS

CNGA3 is the main gene associated with achromatopsia in our population (around ∼ 73%), which is in contrast to the distribution worldwide (∼ 25%). Most achromats suffer from photophobia and nystagmus, and the main refractive error is hypermetropia. Achromatopsia's natural course seems to be stationary, and there may even be a slight improvement in visual acuity with time.

Longitudinal Assessment of OCT-Based Measures of Foveal Cone Structure in Achromatopsia

Purpose

Achromatopsia (ACHM) is an autosomal recessive retinal disease associated with reduced or absent cone function. There is debate regarding the extent to which cone structure shows progressive degeneration in patients with ACHM. Here, we used optical coherence tomography (OCT) images to evaluate outer nuclear layer (ONL) thickness and ellipsoid zone (EZ) integrity over time in individuals with ACHM.

Methods

Sixty-three individuals with genetically confirmed ACHM with follow-up ranging from about 6 months to 10 years were imaged using either Bioptigen or Cirrus OCT. Foveal cone structure was evaluated by assessing EZ integrity and ONL thickness.

Results

A total of 470 OCT images were graded, 243 OD and 227 OS. The baseline distribution of EZ grades was highly symmetrical between eyes (P = 0.99) and there was no significant interocular difference in baseline ONL thickness (P = 0.12). The EZ grade remained unchanged over the follow-up period for 60 of 63 individuals. Foveal ONL thickness showed a clinically significant change in only 1 of the 61 individuals analyzed, although detailed adaptive optics imaging revealed no changes in cone density in this individual.

Conclusions

ACHM appears to be a generally stable condition, at least over the follow-up period assessed here. As cones are the cellular targets for emerging gene therapies, stable EZ and ONL thickness demonstrate therapeutic potential for ACHM, although other aspects of the visual system need to be considered when determining the best timing for therapeutic intervention.

Dyschromatopsia: a comprehensive analysis of mechanisms and cutting-edge treatments for color vision deficiency

Color blindness is a retinal disease that mainly manifests as a color vision disorder, characterized by achromatopsia, red-green color blindness, and blue-yellow color blindness. With the development of technology and progress in theory, extensive research has been conducted on the genetic basis of color blindness, and various approaches have been explored for its treatment. This article aims to provide a comprehensive review of recent advances in understanding the pathological mechanism, clinical symptoms, and treatment options for color blindness. Additionally, we discuss the various treatment approaches that have been developed to address color blindness, including gene therapy, pharmacological interventions, and visual aids. Furthermore, we highlight the promising results from clinical trials of these treatments, as well as the ongoing challenges that must be addressed to achieve effective and long-lasting therapeutic outcomes. Overall, this review provides valuable insights into the current state of research on color blindness, with the intention of informing further investigation and development of effective treatments for this disease.

Functional evaluation allows ACMG/AMP-based re-classification of CNGA3 variants associated with achromatopsia

PURPOSE

CNGA3 encoding the main subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors is one of the major disease-associated genes for achromatopsia. Most CNGA3 variants are missense variants with the majority being functionally uncharacterized and therefore hampering genetic diagnosis. In light of potential gene therapy, objective variant pathogenicity assessment is essential.

METHODS

We established a medium-throughput aequorin-based luminescence bioassay allowing mutant CNGA3 channel function assessment via quantification of CNGA3 channel-mediated calcium influx in a cell culture system, thereby enabling American College of Medical Genetics and Genomics/Association for Molecular Pathology-based variant re-classification.

RESULTS

We provide functional read-out obtained for 150 yet uncharacterized CNGA3 missense substitutions of which 55 were previously categorized as variants of uncertain significance (VUS) identifying 25 as functionally normal and 125 as functionally abnormal. These data enabled the American College of Medical Genetics and Genomics/ Association for Molecular Pathology-based variant re-classification of 52/55 VUS as either benign, likely benign, or likely pathogenic reaching a VUS re-classification rate of 94.5%.

CONCLUSION

Our aequorin-based bioassay allows functionally ensured clinical variant interpretation for 150 CNGA3 missense variants enabling and supporting VUS re-classification and assuring molecular diagnosis to patients affected by CNGA3-associated achromatopsia, hereby identifying patients eligible for future gene therapy trials on this disease.

Phenotype and genotype of 15 Saudi patients with achromatopsia: A case series

PURPOSE

Achromatopsia is a rare stationary retinal disorder that primarily affects the cone photoreceptors. Individuals with achromatopsia present with photophobia, nystagmus, reduced visual acuity (VA), and color blindness. Multiple genes responsible for achromatopsia have been identified (e.g. cyclic nucleotide-gated channel subunit alpha 3 [CNGA3] and activating transcription factor 6). Studies have assessed the role of gene therapy in achromatopsia. Therefore, for treatment and prevention, the identification of phenotypes and genotypes is crucial. Here, we described the clinical manifestations and genetic mutations associated with achromatopsia in patients from Saudi Arabia.

METHODS

This case series study included 15 patients with clinical presentations, suggestive of achromatopsia, who underwent ophthalmological and systemic evaluations. Patients with typical achromatopsia phenotype underwent genetic evaluation using whole-exome testing.

RESULTS

All patients had nystagmus (n = 15) and 93.3% had photophobia (n = 14). In addition, all patients (n = 15) had poor VA. Hyperopia with astigmatism was observed in 93.3% (n = 14) and complete color blindness in 93.3% of the patients (n = 14). In the context of family history, both parents of all patients (n = 15) were genetic carriers, with a high consanguinity rate (82%, n = 9 families). Electroretinography showed cone dysfunction with normal rods in 66.7% (n = 10) and both cone-rod dysfunction in 33.3% (n = 5) patients. Regarding the genotypic features, 93% of patients had variants in CNGA3 (n = 14) categorized as pathogenic Class 1 (86.7%, n = 13). Further, 66.7% (n = 10) of patients also harbored the c.661C>T DNA variant. Further, the patients were homozygous for these mutations. Three other variants were also identified: c.1768G>A (13.3%, n = 2), c.830G>A (6.6%, n = 1), and c. 822G >T (6.6%, n = 1).

CONCLUSION

Consanguinity and belonging to the same tribe are major risk factors for disease inheritance. The most common genotype was CNGA3 with the c.661C>T DNA variant. We recommend raising awareness among families and providing genetic counseling for this highly debilitating disease.

Prenylation is essential for the enrichment of cone phosphodiesterase-6 (PDE6) in outer segments and efficient cone phototransduction

Phosphodiesterase-6 (PDE6) is the key phototransduction effector enzyme residing in the outer segment (OS) of photoreceptors. Cone PDE6 is a tetrameric protein consisting of two inhibitory subunits (γ') and two catalytic subunits (α'). The catalytic subunit of cone PDE6 contains a C-terminus prenylation motif. Deletion of PDE6α' C-terminal prenylation motif is linked to achromatopsia (ACHM), a type of color blindness in humans. However, mechanisms behind the disease and roles for lipidation of cone PDE6 in vision are unknown. In this study, we generated two knock-in mouse models expressing mutant variants of cone PDE6α' lacking the prenylation motif (PDE6α'∆C). We find that the C-terminal prenylation motif is the primary determinant for the association of cone PDE6 protein with membranes. Cones from PDE6α'∆C homozygous mice are less sensitive to light, and their response to light is delayed, whereas cone function in heterozygous PDE6α'∆C/+ mice is unaffected. Surprisingly, the expression level and assembly of cone PDE6 protein were unaltered in the absence of prenylation. Unprenylated assembled cone PDE6 in PDE6α'∆C homozygous animals is mislocalized and enriched in the cone inner segment and synaptic terminal. Interestingly, the disk density and the overall length of cone OS in PDE6α'∆C homozygous mutants are altered, highlighting a novel structural role for PDE6 in maintaining cone OS length and morphology. The survival of cones in the ACHM model generated in this study bodes well for gene therapy as a treatment option for restoring vision in patients with similar mutations in the PDE6C gene.

Morphological and Functional Aspects and Quality of Life in Patients with Achromatopsia

(1) Background: Achromatopsia is a rare disease of which the natural course and impact on life are still unknown to this date. We aimed to assess the morphological, functional characteristics, and quality of life in a large sample size of patients with achromatopsia. (2) A total of 94 achromats were included in this retrospective cohort study. Sixty-four were patients of the Department of Ophthalmology, Saarland University Medical Centre in Homburg/Saar, Germany, between 2008 and 2021. Thirty further participants with achromatopsia from the national support group were included using an online questionnaire, which is available under 'Supplementary data'. Statistical analysis was performed using SPSS Version 25; (3) The 94 patients (37 males (39.4%) and 57 females (60.6%)) showed a mean age of 24.23 ± 18.53 years. Visual acuity was stable (SD ± 0.22 logMAR at 1.0 logMAR) over a time of observation from 2008 to 2021. Edge filter glasses were the most used optical aids, while enlarged reading glasses were the most used low vision aids. (4) Conclusions: Our findings give an insight into describing the natural process and the quality of life of achromatopsia. The results demonstrate that achromatopsia is a predominantly stationary disease. The individual prescription of edge filters and low-vision aids is essential following a personalised fitting.

Molecular and Clinical Characterization of CNGA3 and CNGB3 Genes in Brazilian Patients Affected with Achromatopsia

Achromatopsia (ACHM) is a congenital cone photoreceptor disorder characterized by reduced visual acuity, nystagmus, photophobia, and very poor or absent color vision. Pathogenic variants in six genes encoding proteins composing the cone phototransduction cascade (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2) and of the unfolded protein response (ATF6) have been related to ACHM cases, while CNGA3 and CNGB3 alone are responsible for most cases. Herein, we provide a clinical and molecular overview of 42 Brazilian patients from 38 families affected with ACHM related to biallelic pathogenic variants in the CNGA3 and CNGB3 genes. Patients' genotype and phenotype were retrospectively evaluated. The majority of CNGA3 variants were missense, and the most prevalent CNGB3 variant was c.1148delC (p.Thr383Ilefs*13), resulting in a frameshift and premature stop codon, which is compatible with previous publications in the literature. A novel variant c.1893T>A (p.Tyr631*) in the CNGB3 gene is reported for the first time in this study. A great variability in morphologic findings was observed in our patients, although no consistent correlation with age and disease stage in OCT foveal morphology was found. The better understanding of the genetic variants landscape in the Brazilian population will help in the diagnosis of this disease.

Genetic and Clinical Characterization of Danish Achromatopsia Patients

Achromatopsia is a rare congenital condition with cone photoreceptor dysfunction causing color blindness, reduced vision, nystagmus and photophobia. New treatments are being developed, but the current evidence is still conflicting regarding possible progression over time, and there is no clear genotype-phenotype correlation. This natural history study aimed to further explore the course of disease and potential clinical differences between various genotypes. The retrospective design allowed for the study of a large cohort with a long follow-up. Patients were identified from the Danish national registries. If not already available, genetic analysis was offered to the patient. Clinical data from 1945–2022 were retrieved from medical records and included best-corrected visual acuity (BCVA), color vision, refractive error, nystagmus, visual fields and fundoscopic findings. We identified variants believed to be disease causing in five of the known achromatopsia genes: CNGA3; CNGB3; GNAT2; PDE6C and PDE6H; and novel variants were identified in CNGB3 and PDE6C. Progressive deterioration of BCVA only attributable to achromatopsia was found in three of 58 patients. Progressive phenotype was seen with variants in CNGB3 and PDE6C. The results indicate that myopia could be more frequently occurring with variants in GNAT2, PDE6C and PDE6H and support the evidence that achromatopsia is a predominantly stationary condition with respect to BCVA. Although a clear genotype-phenotype correlation can still not be concluded, there may be differences in phenotypical characteristics with variants in different genes.

Clinical and Genetic Features of Korean Patients with Achromatopsia

This multicenter study aimed to characterize Korean patients with achromatopsia. The patients' genotypes and phenotypes were retrospectively evaluated. Twenty-one patients (with a mean age at the baseline of 10.9 years) were enrolled and followed up for a mean of 7.3 years. A targeted gene panel or exome sequencing was performed. The pathogenic variants of the four genes and their frequencies were identified. CNGA3 and PDE6C were equally the most prevalent genes: CNGA3 (N = 8, 38.1%), PDE6C (N = 8, 38.1%), CNGB3 (N = 3, 14.3%), and GNAT2 (N = 2, 9.5%). The degree of functional and structural defects varied among the patients. The patients' age exhibited no significant correlation with structural defects. During the follow-up, the visual acuity and retinal thickness did not change significantly. In CNGA3-achromatopsia patients, a proportion of patients with a normal foveal ellipsoid zone on the OCT was significantly higher than that of patients with other causative genes (62.5% vs. 16.7%; p = 0.023). In PDE6C-achromatopsia patients, the same proportion was significantly lower than that of patients with other causative genes (0% vs. 58.3%; p = 0.003). Korean patients with achromatopsia showed similar clinical features but a higher prevalence of PDE6C variants than those of other ethnic groups. The retinal phenotypes of the PDE6C variants were more likely to be worse than those of other genes.

High-Efficiency CRISPR/Cas9-Mediated Correction of a Homozygous Mutation in Achromatopsia-Patient-Derived iPSCs

Achromatopsia is an autosomal recessive disorder, in which cone photoreceptors undergo progressive degeneration, causing color blindness and poor visual acuity, among other significant eye affectations. It belongs to a group of inherited retinal dystrophies that currently have no treatment. Although functional improvements have been reported in several ongoing gene therapy studies, more efforts and research should be carried out to enhance their clinical application. In recent years, genome editing has arisen as one of the most promising tools for personalized medicine. In this study, we aimed to correct a homozygous PDE6C pathogenic variant in hiPSCs derived from a patient affected by achromatopsia through CRISPR/Cas9 and TALENs technologies. Here, we demonstrate high efficiency in gene editing by CRISPR/Cas9 but not with TALENs approximation. Despite a few of the edited clones displaying heterozygous on-target defects, the proportion of corrected clones with a potentially restored wild-type PDE6C protein was more than half of the total clones analyzed. In addition, none of them presented off-target aberrations. These results significantly contribute to advances in single-nucleotide gene editing and the development of future strategies for the treatment of achromatopsia.

Biology, Pathobiology and Gene Therapy of CNG Channel-Related Retinopathies

The visual process begins with the absorption of photons by photopigments of cone and rod photoreceptors in the retina. In this process, the signal is first amplified by a cyclic guanosine monophosphate (cGMP)-based signaling cascade and then converted into an electrical signal by cyclic nucleotide-gated (CNG) channels. CNG channels are purely ligand-gated channels whose activity can be controlled by cGMP, which induces a depolarizing Na⁺/Ca²⁺ current upon binding to the channel. Structurally, CNG channels belong to the superfamily of pore-loop cation channels and share structural similarities with hyperpolarization-activated cyclic nucleotide (HCN) and voltage-gated potassium (KCN) channels. Cone and rod photoreceptors express distinct CNG channels encoded by homologous genes. Mutations in the genes encoding the rod CNG channel (CNGA1 and CNGB1) result in retinitis-pigmentosa-type blindness. Mutations in the genes encoding the cone CNG channel (CNGA3 and CNGB3) lead to achromatopsia. Here, we review the molecular properties of CNG channels and describe their physiological and pathophysiological roles in the retina. Moreover, we summarize recent activities in the field of gene therapy aimed at developing the first gene therapies for CNG channelopathies.

The Diagnostic Yield of Next Generation Sequencing in Inherited Retinal Diseases: A Systematic Review and Meta-analysis

PURPOSE

Accurate genotyping of individuals with inherited retinal diseases (IRD) is essential for patient management and identifying suitable candidates for gene therapies. This study evaluated the diagnostic yield of next generation sequencing (NGS) in IRDs.

DESIGN

Systematic review and meta-analysis.

METHODS

This systematic review was prospectively registered (CRD42021293619). Ovid MEDLINE and Ovid Embase were searched on 6 June 2022. Clinical studies evaluating the diagnostic yield of NGS in individuals with IRDs were eligible for inclusion. Risk of bias assessment was performed. Studies were pooled using a random...effects inverse variance model. Sources of heterogeneity were explored using stratified analysis, meta-regression, and sensitivity analysis.

RESULTS

This study included 105 publications from 28 countries. Most studies (90 studies) used targeted gene panels. The diagnostic yield of NGS was 61.3% (95% confidence interval: 57.8-64.7%; 51 studies) in mixed IRD phenotypes, 58.2% (51.6-64.6%; 41 studies) in rod-cone dystrophies, 57.7% (46.8-68.3%; eight studies) in macular and cone/cone-rod dystrophies, and 47.6% (95% CI: 41.0-54.3%; four studies) in familial exudative vitreoretinopathy. For mixed IRD phenotypes, a higher diagnostic yield was achieved pooling studies published between 2018-2022 (64.2% [59.5-68.7%]), studies using exome sequencing (73.5% [58.9-86.1%]), and studies using the American College of Medical Genetics variant interpretation standards (65.6% [60.8-70.4%]).

CONCLUSION

The current diagnostic yield of NGS in IRDs is between 52-74%. The certainty of the evidence was judged as low or very low. A key limitation of the current evidence is the significant heterogeneity between studies. Adoption of standardized reporting guidelines could improve confidence in future meta-analyses.

Genetic epidemiology of inherited retinal diseases in a large patient cohort followed at a single center in Italy

Inherited retinal diseases (IRDs) are the leading cause of vision loss in the working-age population. We performed a retrospective epidemiological study to determine the genetic basis of IRDs in a large Italian cohort (n = 2790) followed at a single referral center. We provided, mainly by next generation sequencing, potentially conclusive molecular diagnosis for 2036 patients (from 1683 unrelated families). We identified a total of 1319 causative sequence variations in 132 genes, including 353 novel variants, and 866 possibly actionable genotypes for therapeutic approaches. ABCA4 was the most frequently mutated gene (n = 535; 26.3% of solved cases), followed by USH2A (n = 228; 11.2%) and RPGR (n = 102; 5.01%). The other 129 genes had a lower contribution to IRD pathogenesis (e.g. CHM 3.5%, RHO 3.5%; MYO7A 3.4%; CRB1 2.7%; RPE65 2%, RP1 1.8%; GUCY2D 1.7%). Seventy-eight genes were mutated in five patients or less. Mitochondrial DNA variants were responsible for 2.1% of cases. Our analysis confirms the complex genetic etiology of IRDs and reveals the high prevalence of ABCA4 and USH2A mutations. This study also uncovers genetic associations with a spectrum of clinical subgroups and highlights a valuable number of cases potentially eligible for clinical trials and, ultimately, for molecular therapies.

Longitudinal Evaluation of Changes in Retinal Architecture Using Optical Coherence Tomography in Achromatopsia

Purpose

This prospective study investigates longitudinal changes in retinal structure in patients with achromatopsia (ACHM) using optical coherence tomography (OCT).

Methods

Seventeen patients (five adults, 12 children) with genetically confirmed CNGA3- or CNGB3-associated ACHM underwent ocular examination and OCT over a follow-up period of between 2 and 9.33 years (mean = 5.7 years). Foveal tomograms were qualitatively graded and were segmented for quantitative analysis: central macular thickness (CMt), outer nuclear layer thickness (ONLt), and size of the foveal hyporeflective zone (vertical HRZ thickness: HRZt and horizontal HRZ width: HRZw) were measured. Data were analyzed using linear mixed regression models. Both age and visit were included into the models, to explore the possibility that the rate of disease progression depends on patient age.

Results

Fifteen of 17 patients (88%) showed longitudinal changes in retinal structure over the follow-up period. The most common patterns of progression was development of ellipsoid zone (EZ) disruption and HRZ. There was a significant increase in HRZt (P = 0.01) and HRZw (P = 0.001) between visits and no significant change in CMt and ONLt. Retinal parameters showed no difference in changes by genetic mutation (CNGA3 (n = 11), CNGB3 (n = 6)).

Conclusions

This study demonstrates clear longitudinal changes in foveal structure mainly in children, but also in adults with ACHM, over a long follow-up period. The longitudinal foveal changes suggest that treatment at an earlier age should be favored.

Disease Progression in CNGA3 and CNGB3 Retinopathy; Characteristics of Slovenian Cohort and Proposed OCT Staging Based on Pooled Data from 126 Patients from 7 Studies

Achromatopsia has been proposed to be a morphologically predominately stable retinopathy with rare reports of progression of structural changes in the macula. A five-grade system of optical coherence tomography (OCT) features has been used for the classification of structural macular changes. However, their association with age remains questionable. We characterized the Slovenian cohort of 12 patients with pathogenic variants in CNGA3 or CNGB3 who had been followed up with OCT for up to 9 years. Based on observed structural changes in association with age, the following four-stage classification of retinal morphological changes was proposed: (I) preserved inner segment ellipsoid band (Ise), (II) disrupted ISe, (III) ISe loss and (IV) ISe and RPE loss. Data from six previously published studies reporting OCT morphology in CNGA3 and CNGB3 patients were additionally collected, forming the largest CNGA3/CNGB3 cohort to date, comprising 126 patients aged 1–71 years. Multiple regression analysis showed a significant correlation of OCT stage with age (p < 0.001) and no correlation with gene (p > 0.05). The median ages of patients with stages I–IV were 12 years, 23 years, 27 years and 48 years, respectively, and no patient older than 50 years had continuous ISe. Our findings suggest that achromatopsia presents with slowly but steadily progressive structural changes of the macular outer retinal layers. However, whether morphological changes in time follow the proposed four-stage linear pattern needs to be confirmed in a long-term study.

Blue Cone Monochromatism with Foveal Hypoplasia Caused by the Concomitant Effect of Variants in OPN1LW/OPN1MW and GPR143 Genes

Blue cone monochromatism (BCM) is an X-linked recessive cone dysfunction disorder caused by mutations in the OPN1LW/OPN1MW gene cluster, encoding long (L)- and middle (M)-wavelength-sensitive cone opsins. Here, we report on the unusual clinical presentation of BCM caused by a novel mutation in the OPN1LW gene in a young man. We describe in detail the phenotype of the proband, and the subclinical morpho-functional anomalies shown by his carrier mother. At a clinical level, the extensive functional evaluation demonstrated in the proband the M/L cone affection and the sparing of S-cone function, distinctive findings of BCM. Interestingly, spectral-domain optical coherence tomography showed the presence of foveal hypoplasia with focal irregularities of the ellipsoid layer in the foveal area, reported to be associated with some cases of cone-rod dystrophy and achromatopsia. At a molecular level, we identified the novel mutation c.427T > C p.(Ser143Pro) in the OPN1LW gene and the common missense mutation c.607T > C (p.Cys203Arg) in the OPN1MW gene. In addition, we discovered the c.768-2_769delAGTT splicing variant in the GPR143 gene. To our knowledge, this is the first case of foveal hypoplasia in a BCM patient and of mild clinical affection in a female carrier caused by the concomitant effect of variants in OPN1LW/OPN1MW and GPR143 genes, thus as the result of the simultaneous action of two independent genetic defects.