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

<p><b>Objective</b>: This study was undertaken with the objective to investigate the potential involvement of VAX2 in retinal degeneration.</p> <p><b>Methods</b>: A cohort of macular and cone dystrophy patients (<i>n</i> = 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 <i>VAX2</i> mutants were generated using the GeneArt® Site-Directed Mutagenesis kit. <i>In vitro</i> 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.</p> <p><b>Results</b>: 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 <i>in vitro</i> 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 <i>VAX2</i> 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.</p> <p><b>Conclusions</b>: This study raises the interesting possibility for evaluating <i>VAX2</i> as a candidate gene for cone dystrophy.</p

The treatment of refractory angle-closure glaucoma in a patient with X-linked juvenile retinoschisis

<p>X-Linked Retinoschisis (XLRS) is a common genetically determined form of macular degeneration affecting young males. XLRS is due to mutations in the RS1 gene located on chromosome Xp22 which codes for retinoschisin and is estimated to affect between 1:5000 to 1:20000 individuals worldwide.</p> <p>We report a case of refractory angle-closure glaucoma in a thirty-nine-year-old Caucasian man with atypical XLRS. The patient presented with a two-day history of left eye pain, acutely reduced vision and a nine-month history of hemicranial pain. Examination identified left intraocular pressure (IOP) of 52mmHg. Gonioscopy confirmed complete angle closure.</p> <p>Following failure of medical management and persistently raised left IOP (43-46mmHg), the patient underwent left phacoemulsification and intraocular lens insertion without complication. After surgery, his IOP reduced to 10-14mmHg on all follow up examinations without the need for glaucoma drops. His iridocorneal angle remained open and vision improved to 20/100.</p> <p>Our case demonstrates the additional role of lens surgery in the treatment of secondary angle-closure glaucoma in the presence of an inherited retinal dystrophy. All patients with inherited retinopathy presenting with a headache or eye pain should undergo gonioscopic examination to exclude angle-closure glaucoma.</p

Schematic and representative images of measurements in fundus autofluorescence imaging and spectral-domain optical coherence tomography.

<p>Patient 9: area of questionably decreased autofluorescence (QDAF, blue), 1.37 mm²; area of definitely decreased autofluorescence (black), 0.33 mm²; transverse loss of external limiting membrane (ELM-loss, red), 1.75 mm, transverse loss of ellipsoid zone (EZ-loss, blue), 2.24 mm; best-corrected visual acuity, 20/100; <i>ABCA4</i> variants, c.1622T>C;3113C>T:p.[Leu541Pro;Ala1038Val] and c.6316C>T:p.(Arg2106Cys).</p

<i>ABCA4</i> variants in early-onset Stargardt patients from Radboud university medical center (Radboudumc) and Moorfields Eye Hospital (MEH).

<p><i>ABCA4</i> variants in early-onset Stargardt patients from Radboud university medical center (Radboudumc) and Moorfields Eye Hospital (MEH).</p

Characteristics of early-onset Stargardt cohorts from Radboud university medical center (Radboudumc) and Moorfields Eye Hospital (MEH).

<p>Characteristics of early-onset Stargardt cohorts from Radboud university medical center (Radboudumc) and Moorfields Eye Hospital (MEH).</p

Highest potential mean-to-standard deviation ratio (MSDR) for each single outcome measure at different weightings with all possible weight combinations of the other metrics.

<p>MSDRs for best-corrected visual acuity (grey) decrease at increasing weight. MSDRs for transition zones of questionably decreased autofluorescence (blue) increase until 25% weight, but gradually decrease at higher weights. MSDRs for transition zones of definitely decreased autofluorescence decrease at weights higher than 5%. MSDRs for loss of the ellipsoid zone (green) are constant, but decrease substantially at weights higher than approximately 70%. MSDRs for loss of the external limiting membrane (black) decrease at weights higher than approximately 80%.</p

Weighted composite score and predicted outcome.

<p>Matching colors represent the right and left eye of the same patient. (A) Results from six early-onset Stargardt patients. (B) The predicted outcome in the replication cohort showed comparable results.</p

Visual acuity as a function of degrees of retinal eccentricity.

<p>Visual acuity as a function of degrees of retinal eccentricity.</p

Yearly progression rate of changes in retinal eccentricity (<i>ε</i>) by visual function, fundus autofluorescence and optical coherence tomography.

<p>Yearly progression rate of changes in retinal eccentricity (<i>ε</i>) by visual function, fundus autofluorescence and optical coherence tomography.</p

Genome-wide linkage and haplotype sharing analysis implicates the <i>MCDR3</i> locus as a candidate region for a developmental macular disorder in association with digit abnormalities

<p><i>Background</i>: Developmental macular disorders are a heterogeneous group of rare retinal conditions that can cause significant visual impairment from childhood. Among these disorders, autosomal dominant North Carolina macular dystrophy (NCMD) has been mapped to 6q16 (<i>MCDR1</i>) with recent support for a non-coding disease mechanism of <i>PRDM13</i>. A second locus on 5p15-5p13 (<i>MCDR3</i>) has been implicated in a similar phenotype, but the disease-causing mechanism still remains unknown.</p> <p><i>Methods</i>: Two families affected by a dominant developmental macular disorder that closely resembles NCMD in association with digit abnormalities were included in the study. Family members with available DNA were genotyped using the Affymetrix GeneChip Human Mapping 250K Sty array. A parametric multipoint linkage analysis assuming a fully penetrant dominant model was performed using MERLIN. Haplotype sharing analysis was carried out using the non-parametric Homozygosity Haplotype method. Whole-exome sequencing was conducted on selected affected individuals.</p> <p><i>Results</i>: Linkage analysis excluded <i>MCDR1</i> from the candidate regions (LOD < –2). There was suggestive linkage (LOD = 2.7) at two loci, including 9p24.1 and 5p15.32 that overlapped with <i>MCDR3</i>. The haplotype sharing analysis in one of the families revealed a 5 cM shared IBD segment at 5p15.32 (<i>p</i> value = 0.004). Whole-exome sequencing did not provide conclusive evidence for disease-causing alleles.</p> <p><i>Conclusions</i>: These findings do not exclude that this phenotype may be allelic with NCMD <i>MCDR3</i> at 5p15 and leave the possibility of a non-coding disease mechanism, in keeping with recent findings on 6q16. Further studies, including whole-genome sequencing, may help elucidate the underlying genetic cause of this phenotype and shed light on macular development and function.</p