Natural history and biomarkers of KCNV2-associated retinopathy.

BACKGROUND: KCNV2-associated retinopathy is an autosomal recessive inherited retinal disease classically named cone dystrophy with supernormal rod response (CDSRR). This study aims to identify the best biomarker for evaluating the condition. METHODS: A retrospective review of eight patients from seven families with genetically confirmed KCNV2-associated retinopathy was performed. The best corrected visual acuity (BCVA), full-field electroretinogram (ffERG), pattern ERG (pERG), fundus imaging: retinal photograph and fundus autofluorescence (FAF), and optical coherence tomography (OCT) were analysed. RESULTS: There was a disproportionate increase in b-wave amplitude with a relatively small light intensity increase, especially between the two dimmest stimuli of DA 0.002 and 0.01 (-2.7 and -2.0 log cd.s/m2). The a-wave amplitude was normal. The a-wave peak time was delayed in all stimuli. The b-wave peak time was delayed compared to normal, but the gap tightened as intensity increased. The b:a wave ratio was above or at the upper limit for the reference values. FAF bull's eye maculopathy pattern was prominent and variable foveal disruption on OCT was apparent in all patients. Legal blindness was reached before the age of 25. CONCLUSIONS: We identified three potential electrophysiology biomarkers to assist in evaluating future therapies: the disproportionate b-wave amplitude jump, delayed a-wave and b-wave peak time, and the higher than normal b:a wave ratio. Any of these biomarkers found with photoreceptor ellipsoid zone foveal-perifoveal disruption should prompt consideration for KCNV2 retinopathy. The BCVA natural history data suggests the probable optimum therapeutic window in the first three decades of life.

Impaired Ca2+ Sensitivity of a Novel GCAP1 Variant Causes Cone Dystrophy and Leads to Abnormal Synaptic Transmission Between Photoreceptors and Bipolar Cells.

Guanylate cyclase-activating protein 1 (GCAP1) is involved in the shutdown of the phototransduction cascade by regulating the enzymatic activity of retinal guanylate cyclase via a Ca2+/cGMP negative feedback. While the phototransduction-associated role of GCAP1 in the photoreceptor outer segment is widely established, its implication in synaptic transmission to downstream neurons remains to be clarified. Here, we present clinical and biochemical data on a novel isolate GCAP1 variant leading to a double amino acid substitution (p.N104K and p.G105R) and associated with cone dystrophy (COD) with an unusual phenotype. Severe alterations of the electroretinogram were observed under both scotopic and photopic conditions, with a negative pattern and abnormally attenuated b-wave component. The biochemical and biophysical analysis of the heterologously expressed N104K-G105R variant corroborated by molecular dynamics simulations highlighted a severely compromised Ca2+-sensitivity, accompanied by minor structural and stability alterations. Such differences reflected on the dysregulation of both guanylate cyclase isoforms (RetGC1 and RetGC2), resulting in the constitutive activation of both enzymes at physiological levels of Ca2+. As observed with other GCAP1-associated COD, perturbation of the homeostasis of Ca2+ and cGMP may lead to the toxic accumulation of second messengers, ultimately triggering cell death. However, the abnormal electroretinogram recorded in this patient also suggested that the dysregulation of the GCAP1-cyclase complex further propagates to the synaptic terminal, thereby altering the ON-pathway related to the b-wave generation. In conclusion, the pathological phenotype may rise from a combination of second messengers' accumulation and dysfunctional synaptic communication with bipolar cells, whose molecular mechanisms remain to be clarified.

PDE6C: Novel Mutations, Atypical Phenotype, and Differences Among Children and Adults.

Purpose: Genetic variation in PDE6C is associated with achromatopsia and cone dystrophy, with only a few reports of cone-rod dystrophy in the literature. We describe two pediatric and two adult patients with PDE6C related cone and cone-rod dystrophy and the first longitudinal data of a pediatric patient with PDE6C-related cone dystrophy. Methods: This cohort of four patients underwent comprehensive ophthalmologic evaluation at the National Eye Institute's Ophthalmic Genetics clinic, including visual field testing, retinal imaging and electroretinogram (ERG). Next-generation sequencing-based genetic testing was performed and subsequent analysis of the variants was done through three-dimensional protein models generated by Phyre2 and Chimera. Results: All cases shared decreased best-corrected visual acuity and poor color discrimination. Three of the four patients had a cone-rod dystrophy, presenting with an ERG showing decreased amplitude on both photopic and scotopic waveforms and a mild to moderately constricted visual field. One of the children was diagnosed with cone dystrophy, having a preserved peripheral field. The children had none to minor structural retinal changes, whereas the adults had clear macular dystrophy. Conclusions: PDE6C-related cone-rod dystrophy consists of a severe phenotype characterized by early-onset nystagmus, decreased best-corrected visual acuity, poor color discrimination, progressive constriction of the visual field, and night blindness. Our work contributes with valuable information toward understanding the visual prognosis and allelic heterogeneity of PDE6C-related cone and cone-rod dystrophy.

Phenotypical Characteristics of POC1B-Associated Retinopathy in Japanese Cohort: Cone Dystrophy With Normal Funduscopic Appearance.

Purpose: Cone/cone-rod dystrophy is a large group of retinal disorders with both phonotypic and genetic heterogeneity. The purpose of this study was to characterize the phenotype of eight patients from seven families harboring POC1B mutations in a cohort of the Japan Eye Genetics Consortium (JEGC). Methods: Whole-exome sequencing with targeted analyses identified homozygous or compound heterozygous mutations of the POC1B gene in 7 of 548 families in the JEGC database. Ophthalmologic examinations including the best-corrected visual acuity, perimetry, fundus photography, fundus autofluorescence imaging, optical coherence tomography, and full-field and multifocal electroretinography (ERGs) were performed. Results: There were four men and four women whose median age at the onset of symptoms was 15.6 years (range, 6-23 years) and that at the time of examination was 40.3 years (range, 22-67 years). The best-corrected visual acuity ranged from -0.08 to 1.52 logMAR units. The funduscopic appearance was normal in all the cases except in one case with faint mottling in the fovea. Optical coherence tomography revealed an absence of the interdigitation zone and blurred ellipsoid zone in the posterior pole, but the foveal structures were preserved in three cases. The full-field photopic ERGs were reduced or extinguished with normal scotopic responses. The central responses of the multifocal ERGs were preserved in two cases. The diagnosis was either generalized cone dystrophy in five cases or cone dystrophy with foveal sparing in three cases. Conclusions: Generalized or peripheral cone dystrophy with normal funduscopic appearance is the representative phenotype of POC1B-associated retinopathy in our cohort.

Progressive Cone Dystrophy and Cone-Rod Dystrophy (XL, AD, and AR).

A heterogenous group of diseases, progressive cone dystrophy usually begins in the mid-teenage years or later in life. The estimated prevalence is 1 in 30,000-40,000 individuals. Patients usually present with decreased central vision and a color vision deficit; the visual loss is progressive and often accompanied by day blindness (hemeralopia) and light intolerance (photophobia). Over time, affected individuals develop night blindness and loss of peripheral field. Visual acuity deteriorates to 20/200 or even counting fingers. There is some association between X-linked cone-rod dystrophy (CORD) and high myopia.

Identification and characterization of the VAX2 p.Leu139Arg variant: possible involvement of VAX2 in cone dystrophy.

OBJECTIVE: This study was undertaken with the objective to investigate the potential involvement of VAX2 in retinal degeneration. METHODS: A cohort of macular and cone dystrophy patients (n = 70) was screened for variant identification. Polymerase chain reaction (PCR) products were purified using ExoSAP-IT. Direct sequencing of PCR products was performed using BigDye 3.1 on the ABI 3730 DNA Analyzer and analyzed using DNASTAR software tool. Search for known variant was performed using the following platforms: 1000 Genomes Project, Ensembl, UCSC, ExAc, and dbSNP. The VAX2 mutants were generated using the GeneArt® Site-Directed Mutagenesis kit. In vitro analysis was performed in hTERTRPE-1 (RPE-1) cell line. Cells were photographed using a Zeiss AXIOVERT S100 microscope. Images were analyzed using Photoshop CS4 software. RESULTS: Here, we report the identification of a heterozygous non-synonymous variant (c.416T>G; p.Leu139Arg) in one cone dystrophy proband. Functional characterization of this variant in vitro revealed an aberrant phenotype seen as protein mislocalization to cytoplasm/nucleus and aggregates undergoing degradation or forming aggresomes. The cellular phenotype suggests protein loss-of-function. Analysis of the VAX2 p.Leu139Met, a variant present in the normal population, showed a phenotype similar to the wild-type, further supporting the hypothesis for the Leucine 139 to Arginine change to be damaging. CONCLUSIONS: This study raises the interesting possibility for evaluating VAX2 as a candidate gene for cone dystrophy.