Long-term follow-up of a CRB1-associated maculopathy

Purpose: To report a long-term follow-up of a CRB1-associated maculopathy.

Methods: A case report.

Results: A 47-year-old man was diagnosed with bilateral maculopathy. The clinical picture and the foveoschisis abnormalities present in the right eye were consistent with X-linked retinoschisis. During the follow-up we observed the spontaneous passage from a foveal schitic shape to a cystic profile and then to atrophic maculopathy. Two pathogenic CRB1 mutations were detected and he was subsequently diagnosed with CRB1-associated maculopathy.

Conclusions: Our clinical case allowed us to observe three different stages in the natural history of this particular CRB1-associated macular phenotype: a foveoschisis phenotype, cystoid macular abnormalities involving outer and inner retinal layers and macular atrophy. CRB1 mutations may be a rare cause of foveal schisis which progressively evolves in atrophic maculopathy and the clinician should be aware of this unusual macular phenotype.     

Homozygous and heterozygous retinal phenotypes in families harbouring IMPG2 mutations

Introduction: Biallelic mutations in interphotoreceptor matrix proteoglycan 2 (IMPG2) have been shown to underlie recessive childhood-onset rod-cone dystrophy with early macular involvement in several families. In other families, heterozygous IMPG2 mutations have been associated with dominant vitelliform macular dystrophy. To date, the retinal phenotype of heterozygotes from families with recessive IMPG2-related retinal dystrophy has not been assessed. This study documents the genotypes and phenotypes observed in both homozygotes and available heterozygotes from additional families with IMPG2-related recessive rod-cone dystrophy.

Methods: Retrospective case series (2016–2018).

Results: Four families were identified. All were first-cousin marriages and had no known relation to each other. Individuals with biallelic pathogenic variants (7 individuals) had childhood-onset rod-cone dystrophy. Families 1 and 2 harboured the same novel homozygous mutation c.189dup;p.Gln64Thrfs*9 (5 individuals, 4–17 years old). Family 3 harboured the novel homozygous mutation c.533 + 4_533 + 7del;p.? (1 individual, 17 years old), and Family 4 harboured the previously reported homozygous mutation c.3262C>T;p.Arg1088* (1 individual, 45 years old). The 3 available carriers were genetically confirmed (both parents from Family 1 and the father from Family 3) and had macular focal retinal pigment epithelium thickening by optical coherence tomography (OCT). The father from Family 3 also had unilateral sectoral pigmentary retinopathy.

Conclusions: Childhood-onset recessive rod-cone dystrophy with early macular involvement should prompt examination of the parents for macular focal retinal pigment epithelium thickening on OCT. If present the possibility of biallelic IMPG2 mutations in the proband should be considered. Young affected relatives of the proband can show multimodal imaging abnormalities before they are overtly symptomatic.     

A recurrent arcuate retinopathy in familial cone-rod dystrophy secondary to heterozygous CRX deletion

ABSTRACT

Purpose: To describe an arcuate retinopathy appearance in a familial cone-rod dystrophy and the underlying genetic cause.

Methods: Retrospective case series of an affected three-generation family (eight affected members, eight unaffected members)

Results: The proband, a 47-year-old male, noted significant visual loss since his early thirties. In addition to central macular atrophic changes, retinal examination was notable for peripapillary atrophy and an arcuate of drusenoid deep yellow lesions in the temporal macula. Spectral-domain optical coherence tomography in the area of the lesions showed regional outer neurosensory retina loss with nasal extension (forming a ring around the central retina) but no drusen. Full-field electroretinography revealed cone-rod dysfunction with an electronegative waveform. Fifteen other available family members were examined, and seven (age range 13–71 years old) showed variable expressivity for similar phenotypic findings, most notably the arcuate lesions in all but the oldest individual who had end-stage atrophy. Exome sequencing of the proband’s affected daughter uncovered a heterozygous CRX deletion [NM_000554.4: CRX: c.(100 + 1_101-1)_(c.900 + 1_?)del] that segregated with the disease.

Conclusion: An unusual familial cone-rod dystrophy phenotype was associated with heterozygous CRX deletion, a pathogenic variant that had a presumed mechanism of haploinsufficiency. The consistent finding of arcuate temporal macular lesions among affected family members was striking, particularly given the variable expressivity previously associated with CRX-related retinopathy. Additional phenotypic studies are needed to assess how frequently this temporal arcuate retinopathy appearance occurs in individuals harboring a similar deletion who are not from the current family.     

Familial non-syndromic macular pseudocoloboma secondary to homozygous CLDN19 mutation

Purpose: The purpose of this study is to uncover the genetic cause for non-syndromic macular “coloboma” (pseudocoloboma) in three brothers from a consanguineous family.

Methods: Homozygosity mapping for the three affected brothers and whole-exome sequencing in one affected brother, followed by confirmatory Sanger sequencing and segregation analysis of the candidate gene for all immediate family members; molecular modeling of the candidate mutation; and review of clinical, imaging, and laboratory findings.

Results: Three otherwise-healthy brothers (age 10, 10, and 6 years) had macular pseudocoloboma. Both parents and the fourth brother were not affected. Parents were first cousins. A novel homozygous missense variant in claudin 19 (CLND19: NM_148960.2:c. 263T>A; p.Val88Glu) segregated with the phenotype, and molecular modeling predicts an unfavorable effect to protein function. All prior reported biallelic CLND19 mutations cause symptomatic hypomagnesemia with hypercalciuria and nephrocalcinosis, often with concurrent macular pseudocoloboma. However, general physical assessment, metabolic profile, and renal imaging for the three affected brothers were normal.

Conclusions: A homozygous CLDN19 mutation can cause macular pseudocoloboma without evidence for systemic disease in children. This is the first reported family with CLDN19 mutations to have an ocular phenotype only; however, those identified to harbor biallelic CLDN19 mutations should be considered at risk for the extraocular manifestations that have previously been associated with mutations in the gene.     

Ophthalmic manifestations of Heimler syndrome due to PEX6 mutations

Background/Aims: Pigmentary retinal dystrophy and macular dystrophy have been previously reported in Heimler syndrome due to mutations in PEX1. Here we reported the ocular manifestations in Heimler syndrome due to mutations in PEX6.

Materials and methods: Medical records were reviewed to identify patient demographics, ophthalmic and systemic findings, and results of diagnostic testing including whole genome sequencing.

Results: Patient 1 is 12-year-old boy with a novel mutation c.275T>G (p.Val92Gly) and known mutation c.1802G>A (p.Arg601Gln) in PEX6. Patient 2 is a 7-year-old girl with the same known c.1802G>A (p.Arg601Gln) mutation and another novel missense mutation c.296G>T (p.Arg99Leu). Both patients exhibited a pigmentary retinopathy. Visual acuity in patient 1 was 20/80 and 20/25 following treatment of intraretinal cystoid spaces with carbonic anhydrase inhibitors, while patient 2 had visual acuity of 20/20 in both eyes without intraretinal cysts. Fundus autofluorescence showed a multitude of hyperfluorescent deposits in the paramacular area of both eyes. OCTs revealed significant depletion of photoreceptors in both patients and macular intraretinal cystoid spaces in one patient. Full field electroretinograms showed normal or abnormal photopic but normal scotopic responses. Multifocal electroretinograms were abnormal.

Conclusions: Heimler syndrome due to biallelic PEX6 mutations demonstrates a macular dystrophy with characteristic fundus autofluorescence and may be complicated by intraretinal cystoid spaces.     

Dominant Cone Rod Dystrophy,Previously Assigned to a Missense Variant in RIMS1, Is Fully Explained by Co-Inheritance of a Dominant Allele of PROM1

PurposeAutosomal dominant cone rod dystrophy 7 (CORD7) was initially linked to the gene RIMS1 and reported in a 4-generation British family in 1998. The purpose of this study was to investigate the legitimacy of this association, and to correctly characterize the genetic cause of this condition.MethodsThe allele frequency of RIMS1 c.2459G>A, p.Arg820His, was investigated in the Genomes Aggregation Dataset (gnomAD) datasets and whole genome sequencing (WGS) was performed for 4 members of the CORD7 family with filtering of rare pathogenic variants in a virtual gene panel comprising all genes known to be associated with inherited retinal dystrophy (IRD). Cytogenetic analysis was performed to rule out interchromosomal translocation.Results RIMS1 p.Arg820His has a maximal carrier frequency of >1:5000 in Europeans. A previously well-characterized PROM1 variant: c.1118C>T, p.Arg373Cys, was detected in 9 affected members of the CORD7 family who underwent WGS or direct sequencing. One affected family member is now known to have macular dystrophy in the absence of RIMS1 p.Arg820His. Clinical analysis of affected family members and 27 individuals with retinopathy associated with the same – PROM1 – variant showed consistent phenotypes.ConclusionsThe case for pathogenicity of RIMS1 p.Arg820His is not strong based on its presence on 10 alleles in the gnomAD dataset and absence from additional CORD affected individuals. The finding of a known pathogenic variant in PROM1 correlates well with the phenotypic characteristics of the affected individuals, and is likely to account for the condition. Clear evidence of association between RIMS1 and a retinal dystrophy is yet to be described.     

Characterization of PROM1 p.Arg373Cys Variant in a Cohort of Chinese Patients: Macular Dystrophy Plus Peripheral Bone-Spicule Degeneration

PurposeThe PROM1 p.Arg373Cys variant has been reported to cause dominant Stargardt disease, cone–rod dystrophy, and occasionally retinitis pigmentosa. This study aimed to evaluate the common phenotype associated with this variant in Chinese patients.MethodsVariants in PROM1 were collected from in-house exome data. Potential pathogenic variants were selected, verified, and then confirmed by Sanger sequencing and co-segregation analysis. Ocular phenotypes were reviewed and further clarified by ophthalmologic examinations.ResultsThe heterozygous c.1117C>T (p.Arg373Cys) variant was identified in four unrelated families, and biallelic variants were detected in three families. Of the 10 patients from four families with the p.Arg373Cys variant, six patients from three families who underwent full fundus examination demonstrated various degrees of macular dystrophy, as well as typical bone-spicule pigment deposits in the peripheral retina. The remaining four patients did not undergo a full dilated fundus examination. A relatively preserved zone was observed between the macular and peripheral lesions. Electroretinography results showed cone and rod involvement in three patients.ConclusionsUnlike Stargardt disease alone, which was considered to be the main phenotype of the p.Arg373Cys variant, all patients with full-field fundus examination in our study presented with macular dystrophy plus peripheral retinopathy resembling retinitis pigmentosa. Different phenotypes associated with the p.Arg373Cys variant may actually reflect different stages of the same disease: a predominant central cone phenotype at an early stage and peripheral rod involvement as degeneration progresses. Evaluation of the full fundus, especially the peripheral region in additional patients, is expected to confirm our findings.     

Novel homozygous loss-of-function mutations in RP1 and RP1L1 genes in retinitis pigmentosa patients

ABSTRACT

Background: Retinitis pigmentosa (RP) is a heterogeneous group of ocular dystrophy. It is challenging to identify the underlying genetic defect in individuals with RP due to huge genetic heterogeneity. This study was designed to delineate the genetic defect(s) underlying RP in extended Saudi families and to describe the possible disease mechanism.

Materials and Methods: Fundus photography and a high definition optical coherence tomography (HD-OCT) were performed in order to detect the earlier stages of macular degeneration. Genomic DNA was extracted followed by genome-wide SNP genotyping and whole exome sequencing (WES). Exome data was filtered to identify the genetic variant(s) of interest.

Results: Clinical examination showed that affected individuals manifest key features of RP. The fundus exam shows pale optic disc and bone spicules at the periphery. OCT shows macular degeneration as early as at the age of 4 years. Whole genome scan by SNPs identified multiple homozygous regions. WES identified a 10 bps novel insertion mutation (c.3544_3545insAGAAAAGCTG; p.Ala1182fs) in the RP1 gene in both affected individuals of family A. Affected individual from family B showed a large insertion of 48 nucleotides in the coding part of the RP1L1 gene (c.3955_3956insGGACTAAAGTAATAGAAGGGCTGCAAGAAGAGAGGGTGCAGTTAGAGG; p.Ala1319fs). Sanger sequencing validates the autosomal recessive inheritance of the mutations.

Conclusion: The results strongly suggest that the insertion mutations in the RP1 and RP1L1 genes are responsible for the retinal phenotype in affected individuals from two families. Heterozygous individuals are asymptomatic carriers. We propose that the protective allele in other homozygous regions in heterozygous carriers contribute to the phenotypic variability in asymptomatic individuals.     

CRB1 heterozygotes with regional retinal dysfunction: implications for genetic testing of leber congenital amaurosis

PURPOSE: To test human CRB1 heterozygotes for possible clinical or functional retinal changes and to evaluate whether a patient with Leber congenital amaurosis (LCA) with CRB1 mutations not consistent with previously described CRB1 phenotypes carried a modifier allele in another LCA gene. METHODS: Seven unrelated heterozygous carriers of CRB1 mutations underwent phenotyping by full eye examinations (indirect ophthalmoscopy and slit lamp biomicroscopy) and functional testing (standard full-field electroretinography [ERG] and multifocal ERG). For genotyping of the LCA patients and their parents, denaturing high-performance liquid chromatography (dHPLC) analyses were performed, followed by sequence analysis of CRB1, followed by sequence analysis of the AIPL1 and CRX genes to identify a putative modifier effect in a patient with an atypical CRB1 phenotype. RESULTS: Reduced full-field ERG b-wave amplitudes were observed with scotopic -2 dB flash (140 microV; P < 0.05), normal full-field cone ERGs, and significant regional retinal dysfunction on mfERG in five of seven carriers of CRB1 mutations. A known AIPL1 mutation (p. R302L) was identified as a potential modifier allele in a patient with LCA carrying two CRB1 mutations and with a prominent maculopathy. CONCLUSIONS: In human heterozygotes of CRB1 mutations (parents of offspring with LCA), distinctive regional retinal dysfunctions were found by multifocal ERG measurements that were consistent with the focal histologic abnormalities reported for the two CRB1 knockout mice models. This phenotypic finding may identify CRB1 carriers and point to the causal gene defect in affected LCA offspring, significantly facilitating the molecular diagnostic process. Evidence suggests a modifier allele in AIPL1 in a patient with LCA with prominent atrophic macular lesions and homozygous defects in CRB1.     

Recessive pediatric-onset cone-rod dysfunction or dominant maculopathy in a consanguineous family harboring the peripherin mutation p.Arg220Gln

Purpose: Heterozygous peripherin mutation is associated with a wide range of typically adult-onset retinal phenotypes which can include asymptomatic maculopathy. There are few reports of biallelic peripherin mutations, only one of which detailed the ophthalmic phenotype. This report documents the retinal phenotype associated with homozygosity for a known peripherin mutation (c.659G>A; p.Arg220Gln), highlights its similar appearance to what was described in the one previous report, and shows how examination of family members can be useful in genetic diagnosis.

Methods: Retrospective case series.

Results: A 13-year-old Emirati boy was referred for low vision. The parents felt he was blind at birth but noted improvement with time. Retinal examination was significant for central macula horizontal ovoid discoloration as was documented for young adults with homozygous peripherin mutations in the one previous report. Electroretinography revealed cone-rod dysfunction. Both asymptomatic parents were examined and found to have central macular abnormalities. Sanger sequencing of peripherin based on clinical features uncovered the pathogenic variant c.659G>A; p.Arg22Gln (NM_000322.4) in homozygosity in the child and in heterozygosity in each parent. Exome sequencing in the child excluded pathologic variants in other retinal dystrophy genes.

Conclusions: The experience with this family highlights clinical features suggestive for biallelic peripherin mutations, documents cone-rod dysfunction as associated with homozygosity for the p.Arg220Gln peripherin mutation, and is an example of how examination of family members can help to guide genetic testing.     

Lattice corneal dystrophy associated with the Ala546Asp and Pro551Gln missense changes in the TGFBI gene

PURPOSE: To report a phenotypic variant of lattice corneal dystrophy associated with two missense changes, Ala546Asp and Pro551Gln, in the transforming growth factor-beta-induced gene (TGFBI). DESIGN: Experimental study. METHODS: Genomic DNA was obtained from the proband as well as affected and unaffected family members. Exons 4, 11, 12, and 14 of the TGFBI gene were amplified and sequenced. Additionally, a corneal button excised from the proband was examined by light and transmission electron microscopy. Haplotype analysis was performed on the proband's family and members of a previously identified pedigree with the same TGFBI gene missense changes. RESULTS: Bilateral, symmetric, radially arranged, branching refractile lines within and surrounding an area of central anterior stromal haze were noted in the proband. Multiple polymorphic, refractile deposits were noted in the mid and posterior stroma in both the proband and her daughter. Light and electron microscopic analyses demonstrated amyloid and excluded the presence of deposits characteristic of granular corneal dystrophy. Screening of TGFBI exon 12 in the proband and her affected daughter revealed two missense changes, Ala546Asp and Pro551Gln (both absent in 250 control chromosomes). Haplotype analysis suggested that the mutations in this family and in a previously identified pedigree reflect a founder effect, rather than an independent occurrence. CONCLUSIONS: We present a phenotypic variant of lattice corneal dystrophy associated with the Ala546Asp and Pro551Gln missense changes in exon 12 of the TGFBI gene. A common ancestor appears to account for the missense mutations observed in this pedigree and in a previously reported family.     

Assessment of mutations in the Best macular dystrophy (VMD2) gene in patients with adult-onset foveomacular vitelliform dystrophy, age-related maculopathy, and bull's-eye maculopathy.

PURPOSE: To study the presence of Best macular dystrophy (VMD2) gene mutations in patients diagnosed with maculopathies other than classic Best disease and to describe the clinical characteristics of these subjects. DESIGN: Case-comparison study of phenotype-genotype correlations. METHODS: Patients with either age-related maculopathy (ARM; n = 259) or maculopathies other than classic Best disease (n = 28) were screened for mutations in the Best gene (VMD2; OMIM 153700). These cases were compared with ethnically similar subjects in the same age range without maculopathy (n = 196). All patients underwent a complete dilated ocular examination, and all affected individuals underwent fundus photography. Phenotype-genotype comparisons were made. MAIN OUTCOME MEASURES: Presence of mutations in the Best gene (VMD2; OMIM 153700) and the clinical phenotype. RESULTS: Three of 259 patients (1%) with ARM and 2 of 28 patients (7%) with other maculopathies including 1 of 3 patients with adult-onset foveomacular vitelliform dystrophy and 1 of 5 patients with a bull's eye maculopathy, but none of the controls, were found to possess amino acid-changing variants in the VMD2 gene. These included a man with confluent drusen and retinal pigment epithelial detachments (variant in exon 6; T216I), a man with geographic atrophy and numerous soft drusen (variant in exon 10; L567F), a woman with drusen and retinal pigment epithelial alterations (variant in exon 10; L567F), a woman with drusen and retinal pigment epithelial alterations resembling bull's-eye maculopathy (variant in exon 4; E119Q), and a woman diagnosed with adult-onset foveomacular vitelliform dystrophy (variant in exon 4; A146K). CONCLUSIONS: Novel mutations in the VMD2 gene were found in patients diagnosed with maculopathies other than classic Best disease. Some cases diagnosed as adult-onset vitelliform foveomacular dystrophy may represent a variant of Best disease with delayed onset. The VMD2 gene does not play a major role in the development of ARM.     

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.     

A novel dominant CRX mutation causes adult-onset macular dystrophy

Background: To present the ophthalmological findings of a mother and son initially diagnosed with benign concentric annular macular dystrophy (BCAMD) and later discovered to carry a novel nonsense mutation in the cone-rod homeobox (CRX) gene (19q13.3).

Materials and Methods: Patients received ophthalmic examinations and diagnostic testing. The proband underwent sequencing of 131 retinal dystrophy genes. His mother had targeted testing of the identified sequence variations in CRX and BBS12 (4q27).

Results: The proband (Case I) presented at age 35 years for routine care. He had several male and female relatives with adult-onset retinal degeneration. Over 11 years, visual acuity (VA) dropped from 20/20 OU to 20/25 OD and 20/50 OS. Ophthalmoscopy showed bull’s eye macular lesions OU. The proband’s mother (Case II) presented at age 57 years with unilateral, progressive vision loss. Over 5 years, VA fluctuated 20/80–20/400 OD and remained 20/25 OS. Ophthalmoscopy showed similar findings to Case I. A clinical diagnosis of BCAMD was given because of the characteristic retinal lesion, preserved VA, and presumed autosomal dominant inheritance. Genetic testing identified a novel nonsense mutation in CRX (c.766C>T; p.Gln256Ter) in both patients. The son was also heterozygous for a missense mutation in BBS12 (c.1859A>G; p.Gln620Arg), which was absent in Case II.

Conclusions: CRX mutations are associated with a variety of clinical phenotypes, including an adult-onset macular dystrophy that simulates BCAMD with a bull’s eye macular lesion and fairly well preserved VA.     

CRB1: One Gene,Many Phenotypes

Abstract

Mutations in the CRB1 gene cause severe retinal degenerations, which may present as Leber congenital amaurosis, early onset retinal dystrophy, retinitis pigmentosa, or cone-rod dystrophy. Some clinical features should alert the ophthalmologist to the possibility of CRB1 disease. These features are nummular pigmentation of the retina, atrophic macula, retinal degeneration associated with Coats disease, and a unique form of retinitis pigmentosa named para-arteriolar preservation of the retinal pigment epithelium (PPRPE). Retinal degenerations associated with nanophthalmos and hyperopia, or with keratoconus, can serve as further clinical cues to mutations in CRB1. Despite this, no clear genotype-phenotype relationship has been established in CRB1 disease. In CRB1-disease, as in other inherited retinal degenerations (IRDs), it is essential to diagnose the specific disease-causing gene for the disease as genetic therapy has progressed considerably in the last few years and might be applicable.     

Early-onset retinal dystrophy and chronic dermatitis in a girl with an undiagnosed congenital disorder of glycosylation (SRD5A3-CDG)

Purpose: Early-onset retinal dystrophy is usually isolated but can also be the presenting manifestation of an undiagnosed systemic disease. The purpose of this report is to highlight the initial presentation of a girl with early-onset retinal dystrophy and chronic dermatitis who was found to have an undiagnosed congenital disorder of glycosylation (SRD5A3-CDG).

Methods: Retrospective case report.

Results: A 13-year-old Baluchi girl was referred for evaluation of low vision since soon after birth. Clinical exam confirmed retinal dystrophy. She also had developmental disability and chronic dermatitis. Brain MRI was normal. Whole exome and confirmatory Sanger sequencing uncovered homozygosity for a SRDA3 deletion (p.Gln96delinsX) that was previously reported in two other Baluchi SRDA3-CDG families with ocular coloboma, optic atrophy, atopic dermatitis, cerebellar hypoplasia, and developmental disability. Early-onset retinal dystrophy was not mentioned in those two families but has since been documented in other SRDA3-CDG families harboring different biallelic variants in the gene.

Discussion: Early-onset retinal dystrophy with chronic dermatitis should raise suspicion for biallelic SRDA3 mutations, particularly in the context of developmental disability. Exome sequencing can be a useful analysis in retinal dystrophy patients with multisystem disease. Homozygosity for the SRDA3 deletion p.Gln96delinsX is not always associated with ocular coloboma.     

Clinical characteristics of recessive retinal degeneration due to mutations in the CDHR1 gene and a review of the literature

Background: The clinical phenotype of patients presenting with autosomal recessive CDHR1-related retinopathy has not been well described.

Materials and Methods: This is a retrospective case series of patients presenting to a single institution. Clinical data, including age, visual acuity, dilated fundus exam, fundus photos, fundus autofluorescence (FAF), optical coherence tomography, full-field electroretinograms (ERGs), and results of genetic testing, were collected.

Results: Four patients were identified to have biallelic mutations in the CDHR1 gene. All four patients were found to have at least one c.783G>A (p.Pro261 = ) mutation. A novel splice site mutation, c.152-2A>G, was identified in two patients. Patients became symptomatic between the fourth and sixth decades of life. Three patients presented initially with nyctalopia and peripheral visual field constriction, and one patient presented with simultaneous onset of photophobia and nyctalopia. The fundus appearance was characterized by macular atrophy with or without peripheral retinal pigment epithelium changes and arteriolar attenuation. FAF showed a hyperautofluorescent ring surrounding a central area of speckled hypoautofluorescence. Full-field electroretinography was available on three patients and showed decreased cone-and-rod responses.

Conclusions: CDHR1-related retinal dystrophy should be considered in adult patients with a retinal dystrophy who present with symptoms of cone-and-rod dysfunction and macular atrophy on ophthalmoscopic examination.     

Whole genome sequencing reveals novel mutations causing autosomal dominant inherited macular degeneration

ABSTRACT

Background: Age-related macular degeneration (AMD) is a common sight threatening condition. However, there are a number of monogenic macular dystrophies that are clinically similar to AMD, which can potentially provide pathogenetic insights.

Methods: Three siblings from a non-consanguineous Greek-Cypriot family reported central visual disturbance and nyctalopia. The patients had full ophthalmic examinations and color fundus photography, spectral-domain ocular coherence tomography and scanning laser ophthalmoscopy. Targeted polymerase chain reaction (PCR) was performed as a first step to attempt to identify suspected mutations in C1QTNF5 and TIMP3 followed by whole genome sequencing.

Results: The three patients were noted to have symptoms of nyctalopia, early paracentral visual field loss and, in older patients, central vision loss. Imaging identified pseudodrusen, retinal atrophy and RPE-Bruch’s membrane separation. Whole genome sequencing of the proband revealed two novel heterozygous variants in C1QTNF5, c.556C>T, and c.569C>G. The mutation segregated with disease in this family, occurred in cis, and resulted in missense amino acid changes P186S and S190W in C1QTNF5. In silico modeling of the variants revealed that the S190W mutations was likely to have the greatest pathologic effect and that the combination of the mutations was likely to have an additive effect.

Conclusions: The novel mutations in C1QTNF5 identified here expand the genotypic spectrum of mutations causing late-onset retinal dystrophy.     

Modification of the PROM1 disease phenotype by a mutation in ABCA4

ABSTRACT

Background: The extensive phenotypic heterogeneity of monogenic diseases can be largely traced to intragenic variation; however, recent advances in clinical detection and gene sequencing have uncovered the emerging role of non-allelic variation (i.e. genetic trans-modifiers) in shaping disease phenotypes. Identifying these associations are not only of significant diagnostic value, but also provides scientific insight into the expanded molecular etiology of rare diseases. This reports describes the discordant clinical manifestation of a family segregating mutations in ABCA4 and PROM1.

Methods: Three patients across a two generation family underwent multimodal imaging and functional testing of the retina including color photography, fundus autofluorescence (AF), spectral domain-optical coherence tomography (SD-OCT) and full-field electroretinography (ffERG). Genetic characterization was carried out by direct Sanger and whole exome sequencing.

Results: Clinical examination revealed similar retinal degenerative phenotypes in the proband and her mother. Despite being younger, the proband’s phenotype was more advanced and exhibited additional features related to Stargardt disease not found in the mother. Whole exome sequencing identified a pathogenic missense variant in PROM1, c.400C > T, p.(Arg134Cys), as the underlying cause of retinal disease in both the proband and mother. Sequencing of the ABCA4 locus uncovered a single disease-causing variant, c.5714 + 5G > A in the daughter segregating from the father who, surprisingly, also exhibited very subtle disease changes associated with STGD1 despite being a heterozygous carrier.

Conclusions: Harboring an additional heterozygous ABCA4 mutation increases severity and confers STGD1-like features in patients with PROM1 disease which provides supporting evidence for their shared pathophysiology and potential treatment prospects.     

A clinical study of patients with novel CDHR1 genotypes associated with late-onset macular dystrophy

PurposeTo describe the clinical and electrophysiological features of adult-onset macular dystrophy, due to novel combinations of CDHR1 alleles, and compare the associated phenotypes with previous reports.MethodsThe clinical records of patients with macular dystrophy and biallelic variants in CDHR1 were reviewed. Data analysed included best corrected visual acuity (BCVA), fundus images: autofluorescence (AF) and optical coherence tomography (OCT); full field electroretinography (ERG) and pattern ERG (PERG).ResultsSeven patients from six pedigrees were ascertained. One patient was homozygous for a known synonymous variant p.(Pro261=), four were compound heterozygous for the p.(Pro261=) variant and a novel allele of CDHR1: p.(Gly188Ser), p.(Met1?), or p.(Val458Asp); one patient was compound heterozygous for two previously unreported variants: c.297+1G>T in trans with p.(Pro735Thr). The range of BCVA at the last clinic review was (6/5–6/60). Autofluorescence showed macular flecks of increased AF in mild cases and patches of reduced AF in severe cases. The OCT showed attenuation of the ellipsoid zone (EZ) in mild cases and loss of the EZ and the outer nuclear layer in severe cases; one patient had subfoveal hyporeflective region between the EZ and the retinal pigment epithelium. The full field ERG was normal or borderline subnormal in all cases, and the PERG was subnormal in mild cases or undetectable in severe cases.ConclusionsThis report corroborates previous observations that genotypes distinct from those causing pan-retinal dystrophy can cause a milder phenotype, predominantly affecting the macula, and expands the spectrum of these genotypes. The findings in this cohort suggest a potential macular susceptibility to mild perturbations of the photoreceptor cadherin.Subject terms: Hereditary eye disease, Disease genetics