Mutations in the Genes for Interphotoreceptor Matrix Proteoglycans, IMPG1 and IMPG2, in Patients with Vitelliform Macular Lesions

Novel IMPG2 variant causing adult macular vitelliform dystrophy: A case report

INTRODUCTION

Adult-onset vitelliform macular dystrophy (AVMD) is an inherited maculopathy characterized by metamorphopsias and decrease in visual acuity occurring between the fourth and the sixth decade. It is characterized by an 'egg yolk' macular lesion eventually evolving towards foveal atrophy and fibrosis. It is usually an autosomal dominant inherited disorder with variable penetrance, mainly related to variants in BEST1, PRPH2, IMPG1, and IMPG2 genes.

CASE DESCRIPTION

A 47-year-old woman complaining of "wavy" vision was referred to our clinic. Her past medical history and reported family history did not reveal any ocular disease. Complete ophthalmological evaluation was performed. Funduscopic examination and multimodal imaging revealed a round vitelliform lesion in both eyes, leading to a diagnosis of AVMD. Genetic analysis revealed a novel, likely pathogenetic, heterozygous c.478G > T (p.Glu160Ter), (NM_016247) variant in the IMPG2 gene.

DISCUSSION

Our patient exhibits a novel pathogenetic variant in a gene associated with AVMD. Heterozygous variants in the IMPG2 gene have been reported in multiple individuals with vitelliform macular dystrophy, with an autosomal dominant mode of inheritance. Genetic screening is essential to characterize patients, to predict vision loss in patients with a positive family history and to characterize eligible patients for new potential emerging therapies. Genotype-phenotype correlation studies are needed to have a clearer picture of pathogenetic mechanisms. Our study characterizes the phenotype related to a novel IMPG2 pathogenic variant through multimodal imaging.

Heterogeneity in the progression of retinal pathologies in mice harboring patient mimicking Impg2 mutations

Biallelic mutations in interphotoreceptor matrix proteoglycan 2 (IMPG2) in humans cause retinitis pigmentosa (RP) with early macular involvement, albeit the disease progression varies widely due to genetic heterogeneity and IMPG2 mutation type. There are currently no treatments for IMPG2-RP. To aid preclinical studies toward eventual treatments, there is a need to better understand the progression of disease pathology in appropriate animal models. Toward this goal, we developed mouse models with patient mimicking homozygous frameshift (T807Ter) or missense (Y250C) Impg2 mutations, as well as mice with a homozygous frameshift mutation (Q244Ter) designed to completely prevent IMPG2 protein expression, and characterized the trajectory of their retinal pathologies across postnatal development until late adulthood. We found that the Impg2T807Ter/T807Ter and Impg2Q244Ter/Q244Ter mice exhibited early onset gliosis, impaired photoreceptor outer segment maintenance, appearance of subretinal deposits near the optic disc, disruption of the outer retina, and neurosensorial detachment, whereas the Impg2Y250C/Y250C mice exhibited minimal retinal pathology. These results demonstrate the importance of mutation type in disease progression in IMPG2-RP and provide a toolkit and preclinical data for advancing therapeutic approaches.

Best Disease: Global Mutations Review, Genotype-Phenotype Correlation, and Prevalence Analysis in the Israeli Population

Purpose

To review all reported disease-causing mutations in BEST1, perform genotype-phenotype correlation, and estimate disease prevalence in the Israeli population.

Methods

Medical records of patients diagnosed with Best disease and allied diseases from nine Israeli medical centers over the past 20 years were collected, as were clinical data including ocular findings, electrophysiology results, and retina imaging. Mutation detection involved mainly whole exome sequencing and candidate gene analysis. Demographic data were obtained from the Israeli Bureau of Statistics (January 2023). A bibliometric study was also conducted to gather mutation data from online sources.

Results

A total of 134 patients were clinically diagnosed with Best disease and related conditions. The estimated prevalence of Best disease was calculated to be 1 in 127,000, with higher rates among Arab Muslims (1 in 76,000) than Jews (1 in 145,000). Genetic causes were identified in 76 individuals (57%), primarily showing autosomal-dominant inheritance due to BEST1 mutations (58 patients). Critical conserved domains were identified consisting of a high percentage of dominant missense mutations, primarily in transmembrane domains and the intracellular region (Ca2+ binding domain) of the BEST1 protein.

Conclusions

This study represents the largest cohort of patients with Best disease reported in Israel and globally. The prevalence in Israel is akin to that in Denmark but is lower than that in the United States. Critical conserved domains within the BEST1 protein are pivotal for normal functioning, and even minor missense alterations in these areas lead to a dominant disease manifestation. Genetic testing is indispensable as the gold standard for Best disease diagnosis due to the variable clinical presentation of the disease.

IMPG2-Related Maculopathy

PURPOSE

To investigate the phenotype, variability, and penetrance of IMPG2-related maculopathy.

DESIGN

Retrospective observational case series.

METHODS

Clinical evaluation, multimodal retinal imaging, genetic testing, and molecular modeling.

RESULTS

A total of 25 individuals with a mono-allelic IMPG2 variant were included, 5 of whom were relatives of patients with IMPG2-associated retinitis pigmentosa. A distinct maculopathy was present in 17 individuals (median age, 52 years; range, 20-72 years), and included foveal elevation with or without subretinal vitelliform material or focal atrophy of the retinal pigment epithelium. Best-corrected visual acuity (BCVA) was ≥20/50 in the better eye (n = 15), and 5 patients were asymptomatic. Longitudinal observation (n = 8, up to 19 years) demonstrated stable maculopathy (n = 3), partial/complete resorption (n = 4) or increase (n = 1) of the subretinal material, with overall stable vision (n = 6). No manifest maculopathy was observed in 8 individuals (median age, 58 years; range, 43-83 years; BCVA ≥20/25), all were identified through segregation analysis. All 8 individuals were asymptomatic, with minimal foveal changes observed on optical coherence tomography in 3 cases. A total of 18 different variants were detected, 11 of them truncating. Molecular modeling of 5 missense variants [c.727G>C, c.1124C>A, c.2816T>A, c.3047T>C, and c.3193G>A] supported the hypothesis that these have a loss-of-function effect.

CONCLUSIONS

Mono-allelic IMPG2 variants may result in haploinsufficiency manifesting as a maculopathy with variable penetrance and expressivity. Family members of patients with IMPG2-related retinitis pigmentosa may present with vitelliform lesions. The maculopathy often remains limited to the fovea and is usually associated with moderate visual impairment.

Identification of the zebrafish homologues of IMPG2, a retinal proteoglycan

Photoreceptor outer segments are surrounded by a carbohydrate-rich matrix, the interphotoreceptor matrix, necessary for physiological retinal function. Few roles for molecules characterizing the interphotoreceptor matrix have been clearly defined. Recent studies have found the presence of nonsense mutations in the interphotoreceptor matrix proteoglycan 2 (IMPG2) gene in patients affected by retinal dystrophies. IMPG2 encodes for a proteoglycan synthesized by photoreceptors and secreted in the interphotoreceptor matrix. Little is known about the structure and function of this protein, we thus decided to characterize zebrafish impg2. In zebrafish there are two Impg2 proteins, Impg2a and Impg2b. We generated a phylogenetic tree based on IMPG2 protein sequence similarity among vertebrates, showing a significant similarity between humans and teleosts. The human and zebrafish proteins share conserved domains, as also shown by homology models. Expression analyses of impg2a and impg2b show a continued expression in the photoreceptor layer starting from developmental stages and continuing through adulthood. Between 1 and 6 months post-fertilization, there is a significant shift of Impg2 expression toward the outer segment region, suggesting an increase in secretion. This raises intriguing hypotheses about its possible role(s) during retinal maturation, laying the groundwork for the generation of most needed models for the study of IMPG2-related inherited retinal dystrophies.

The morphological and functional diversity of apical microvilli

Sensory neurons use specialized apical processes to perceive external stimuli and monitor internal body conditions. The apical apparatus can include cilia, microvilli, or both, and is adapted for the functions of the particular cell type. Photoreceptors detect light through a large, modified cilium (outer segment), that is supported by a surrounding ring of microvilli-like calyceal processes (CPs). Although first reported 150 years ago, CPs remain poorly understood. As a basis for future study, we therefore conducted a review of existing literature about sensory cell microvilli, which can act either as the primary sensory detector or as support for a cilia-based detector. While all microvilli are finger-like cellular protrusions with an actin core, the processes vary across cell types in size, number, arrangement, dynamics, and function. We summarize the current state of knowledge about CPs and the characteristics of the microvilli found on inner ear hair cells (stereocilia) and cerebral spinal fluid-contacting neurons, with comparisons to the brush border of the intestinal and renal epithelia. The structure, stability, and dynamics of the actin core are regulated by a complement of actin-binding proteins, which includes both common components and unique features when compared across cell types. Further, microvilli are often supported by lateral links, a glycocalyx, and a defined extracellular matrix, each adapted to the function and environment of the cell. Our comparison of microvillar features will inform further research into how CPs support photoreceptor function, and also provide a general basis for investigations into the structure and functions of apical microvilli found on sensory neurons.

Photoreceptor function and structure in retinal degenerations caused by biallelic BEST1 mutations

The only approved retinal gene therapy is for biallelic RPE65 mutations which cause a recessive retinopathy with a primary molecular defect located at the retinal pigment epithelium (RPE). For a distinct recessive RPE disease caused by biallelic BEST1 mutations, a pre-clinical proof-of-concept for gene therapy has been demonstrated in canine eyes. The current study was undertaken to consider potential outcome measures for a BEST1 clinical trial in patients demonstrating a classic autosomal recessive bestrophinopathy (ARB) phenotype. Spatial distribution of retinal structure showed a wide expanse of abnormalities including large intraretinal cysts, shallow serous retinal detachments, abnormalities of inner and outer segments, and an unusual prominence of the external limiting membrane. Surrounding the central macula extending from 7 to 30 deg eccentricity, outer nuclear layer was thicker than expected from a cone only retina and implied survival of many rod photoreceptors. Co-localized however, were large losses of rod sensitivity despite preserved cone sensitivities. The dissociation of rod function from rod structure observed, supports a large treatment potential in the paramacular region for biallelic bestrophinopathies.

Human retinal organoids harboring IMPG2 mutations exhibit a photoreceptor outer segment phenotype that models advanced retinitis pigmentosa

Interphotoreceptor matrix proteoglycan 2 (IMPG2) mutations cause a severe form of early-onset retinitis pigmentosa (RP) with macular involvement. IMPG2 is expressed by photoreceptors and incorporated into the matrix that surrounds the inner and outer segments (OS) of rods and cones, but the mechanism of IMPG2-RP remains unclear. Loss of Impg2 function in mice produces a mild, late-onset photoreceptor phenotype without the characteristic OS loss that occurs in human patients. We generated retinal organoids (ROs) from patient-derived induced pluripotent stem (iPS) cells and gene-edited embryonic stem cells to model human IMPG2-RP in vitro. All ROs harboring IMPG2 mutations lacked an OS layer, in contrast to isogenic controls. Subsequent protein analyses revealed that this phenotype arises due to a loss of IMPG2 expression or its inability to undergo normal post-translational modifications. We hypothesized that loss of IMPG2 function destabilizes the interphotoreceptor matrix and renders the OS vulnerable to physical stressors, which is accentuated in the tissue culture environment. In support of this mechanism, transplantation of IMPG2 mutant ROs into the protected subretinal space of immunocompromised rodents restored OS production. Beyond providing a robust platform to study IMPG2-RP, this human RO model system may serve a broader role in honing strategies to treat advanced photoreceptor-based diseases.

Interphotoreceptor matrix proteoglycans IMPG1 and IMPG2 proteolyze in the SEA domain and reveal localization mutual dependency

The interphotoreceptor matrix (IPM) is a specialized extracellular mesh of molecules surrounding the inner and outer segments of photoreceptor neurons. Interphotoreceptor matrix proteoglycan 1 and 2 (IMPG1 and IMPG2) are major components of the IPM. Both proteoglycans possess SEA (sperm protein, enterokinase and agrin) domains, which may support proteolysis. Interestingly, mutations in the SEA domains of IMPG1 and IMPG2 are associated with vision disease in humans. However, if SEA domains in IMPG molecules undergo proteolysis, and how this contributes to vision pathology is unknown. Therefore, we investigated SEA-mediated proteolysis of IMPG1 and IMPG2 and its significance to IPM physiology. Immunoblot analysis confirmed proteolysis of IMPG1 and IMPG2 in the retinas of wildtype mice. Point mutations mimicking human mutations in the SEA domain of IMPG1 that are associated with vision disease inhibited proteolysis. These findings demonstrate that proteolysis is part of the maturation of IMPG1 and IMPG2, in which deficits are associated with vision diseases. Further, immunohistochemical assays showed that proteolysis of IMPG2 generated two subunits, a membrane-attached peptide and an extracellular peptide. Notably, the extracellular portion of IMPG2 trafficked from the IPM around the inner segment toward the outer segment IPM by an IMPG1-dependent mechanism. This result provides the first evidence of a trafficking system that shuttles IMPG1 and IMPG2 from the inner to outer IPM in a co-dependent manner. In addition, these results suggest an interaction between IMPG1-IMPG2 and propose that mutations affecting one IMPG could affect the localization of the normal IMPG partner, contributing to the disease mechanism of vision diseases associated with defective IMPG molecules.

Identification of a Complex Allele in IMPG2 as a Cause of Adult-Onset Vitelliform Macular Dystrophy

Purpose

Inherited retinal diseases are a group of clinically and genetically heterogeneous disorders with approximately 270 genes involved. IMPG2 is associated with adult-onset vitelliform macular dystrophy. Here, we investigated two unrelated patients with vitelliform macular dystrophy to identify the underlying genetic cause.

Methods

Whole-exome sequencing identified a putative causal complex allele consisting of c.3023-15T>A and c.3023G>A (p.(Gly1008Asp)) in IMPG2 in both individuals. To assess its effect, in vitro splice assays in HEK293T and further characterization in patient-derived photoreceptor precursor cells (PPCs) were conducted.

Results

The results of the midigene splice assays in HEK293T showed that the complex allele causes a variety of splicing defects ranging from a small deletion to (multiple-)exon skipping. This finding was further validated using patient-derived PPCs that showed a significant increase of out-of-frame transcripts lacking one or multiple exons compared to control-derived PPCs. Overall, control PPCs consistently showed low levels of aberrantly spliced IMPG2 transcripts that were highly elevated in patient-derived PPCs. These differences were even more obvious upon inhibition of nonsense-mediated decay with cycloheximide.

Conclusions

We report a heterozygous complex allele in IMPG2 causative for adult-onset vitelliform macular dystrophy in two unrelated individuals with mild visual loss and bilateral vitelliform lesions. The predicted causal missense mutation c.3023G>A, located in the consensus splice acceptor site, enhances the splicing effect of the upstream variant c.3023-15T>A, leading to the generation of aberrant transcripts that decrease the full-length IMPG2 levels. These results suggest a haploinsufficiency mechanism of action and highlight the complementarity of using different models to functionally assesses splicing defects.

Whole exome sequencing identifies a novel splice-site mutation in IMPG2 gene causing Stargardt-like juvenile macular dystrophy in a north Indian family

We report on the genetic analysis of a north Indian family affected with Stargardt-like juvenile macular dystrophy. Considering an autosomal recessive inheritance of macular dystrophy in the recruited family, whole exome sequencing was employed in two affected siblings and their mother. We have identified a novel splice-site variant NC_000003.11(NM_016247.3):c.1239 + 1G > T, co-segregating in the affected siblings, in the Interphotoreceptor Matrix Proteoglycan 2 (IMPG2) gene. The identified variant is present immediately after exon 11, and is predicted to disrupt the wild-type donor splice-site of IMPG2 transcripts. We confirmed the splice-site changes in the IMPG2 transcripts using minigene functional assay. Although a number of studies on IMPG2 have demonstrated its involvement in retinitis pigmentosa and vitelliform macular dystrophy, this is the first report of a splice-site variant in IMPG2 that is responsible for Stargardt-like juvenile macular dystrophy.

ADULT-ONSET VITELLIFORM MACULAR DYSTROPHY SECONDARY TO A NOVEL IMPG2 GENE VARIANT

PURPOSE

To report a case of adult-onset vitelliform macular dystrophy in a patient who was found to have a previously unreported variant of the IMPG2 gene.

METHODS

Case report.

RESULTS

A 65-year-old white woman with no significant medical or ocular history presented with a complaint of persistent wavy vision for 10 months. On funduscopic examination, bilateral vitelliform lesions of approximately 1 mm in the right eye and 0.5 mm in the left eye were evident, with no choroidal neovascularization in either eye. The patient was diagnosed with adult-onset vitelliform macular dystrophy. Genetic testing revealed a single likely pathogenic variant of the IMPG2 gene that may explain the examination findings.

CONCLUSION

Adult-onset vitelliform macular dystrophy is a common and relatively benign condition occurring in approximately 1 in 8,000 individuals. Although vitelliform lesions can be a manifestation of systemic diseases or be idiopathic, in a minority of patients, genetic predisposition may play a role. Mutations in four particular genes BEST1, PRPH2, IMPG1, and IMPG2 have been associated with some cases of adult-onset vitelliform macular dystrophy, with this particular gene variant of IMPG2 being previously unreported.

Diagnosis of Inherited Retinal Diseases

Inherited retinal diseases are a frequent cause of severe visual impairment or blindness in children and adults of working age. Across this group of diseases, there is great variability in the degree of visual impairment, the impact on everyday life, disease progression, and the suitability to therapeutic intervention. Therefore, an early and precise diagnosis is crucial for patients and their families. Characterizing inherited retinal diseases involves a detailed medical history, clinical examination with testing of visual function, multimodal retinal imaging as well as molecular genetic testing. This may facilitate a distinction between different inherited retinal diseases, as well as a differentiation from monogenic systemic diseases with retinal involvement, and from mimicking diseases.

Different Phenotypes in Pseudodominant Inherited Retinal Dystrophies

Retinal dystrophies (RD) are a group of Mendelian disorders caused by rare genetic variations leading to blindness. A pathogenic variant may manifest in both dominant or recessive mode and clinical and genetic heterogeneity makes it difficult to establish a precise diagnosis. In this study, families with autosomal dominant RD in successive generations were identified, and we aimed to determine the disease's molecular origin in these consanguineous families. Whole exome sequencing was performed in the index patient of each family. The aim was to determine whether these cases truly represented examples of dominantly inherited RD, or whether another mode of inheritance might be applicable. Six potentially pathogenic variants in four genes were identified in four families. In index patient with enhanced S-cone syndrome in F1, we identified a new digenetic combination: a heterozygous variant p.[G51A];[=] in RHO and a homozygous pathogenic variant p.[R311Q];[R311Q] in NR2E3. Helicoid subretinal fibrosis associated with recessive NR2E3 variant p.[R311Q];[R311Q] was identified in F2. A new frameshift variant c.[105delG];[105delG] in RDH12 was found in F3 with cone-rod dystrophy. In F4, the compound heterozygous variants p.[R964^*];[W758^*] were observed in IMPG2 with a retinitis pigmentosa (RP) phenotype. We showed that both affected parents and the offspring, were homozygous for the same variants in all four families. Our results provide evidence that in consanguineous families, autosomal recessive can be transmitted as pseudodominant inheritance in RD patients, and further extend our knowledge of pathogenic variants in RD genes.

A LINE-1 insertion situated in the promoter of IMPG2 is associated with autosomal recessive progressive retinal atrophy in Lhasa Apso dogs

Background

Canine progressive retinal atrophies are a group of hereditary retinal degenerations in dogs characterised by depletion of photoreceptor cells in the retina, which ultimately leads to blindness. PRA in the Lhasa Apso (LA) dog has not previously been clinically characterised or described in the literature, but owners in the UK are advised to have their dog examined through the British Veterinary Association/ Kennel Club/ International Sheep Dog Society (BVA/KC/ISDS) eye scheme annually, and similar schemes that are in operation in other countries. After the exclusion of 25 previously reported canine retinal mutations in LA PRA-affected dogs, we sought to identify the genetic cause of PRA in this breed.

Results

Analysis of whole-exome sequencing data of three PRA-affected LA and three LA without signs of PRA did not identify any exonic or splice site variants, suggesting the causal variant was non-exonic. We subsequently undertook a genome-wide association study (GWAS), which identified a 1.3 Mb disease-associated region on canine chromosome 33, followed by whole-genome sequencing analysis that revealed a long interspersed element-1 (LINE-1) insertion upstream of the IMPG2 gene. IMPG2 has previously been implicated in human retinal disease; however, until now no canine PRAs have been associated with this gene. The identification of this PRA-associated variant has enabled the development of a DNA test for this form of PRA in the breed, here termed PRA4 to distinguish it from other forms of PRA described in other breeds. This test has been used to determine the genotypes of over 900 LA dogs. A large cohort of genotyped dogs was used to estimate the allele frequency as between 0.07–0.1 in the UK LA population.

Conclusions

Through the use of GWAS and subsequent sequencing of a PRA case, we have identified a LINE-1 insertion in the retinal candidate gene IMPG2 that is associated with a form of PRA in the LA dog. Validation of this variant in 447 dogs of 123 breeds determined it was private to LA dogs. We envisage that, over time, the developed DNA test will offer breeders the opportunity to avoid producing dogs affected with this form of PRA.

Proteoglycan IMPG2 Shapes the Interphotoreceptor Matrix and Modulates Vision

Photoreceptor neurons are surrounded by an extracellular matrix, called the interphotoreceptor matrix (IPM). Activities crucial to vision occur within the IPM, including trafficking of nutrients and metabolites, retinal attachment, and interactions needed for normal outer segment phagocytosis. The IPM includes the following two unique proteoglycans: IPM proteoglycan 1 (IMPG1) and IMPG2. Patients with mutations in IMPG1/IMPG2 develop visual deficits with subretinal material accumulation, highlighting the critical role of the IPM in vision. To determine the role of these proteoglycans in retinal physiology and the pathologic mechanisms that lead to vision loss, we generated mouse models lacking IMPG1/IMPG2. In normal retina, IMPG1 and IMPG2 occupy distinct IPM compartments, represent the main source of chondroitin sulfate and are fundamental for the constitution of the cone-specific glycocalyx stained by the PNA (peanut agglutinin) lectin marker. No evident morphologic or functional deficits were found in mice lacking IMPG1. In the absence of IMPG2, IMPG1 abnormally accumulated at the subretinal space need, likely leading to the formation of subretinal lesions and reduced visual function. Interestingly, mice lacking both IMPG1 and IMPG2, regardless of sex, showed normal retinal structure and function, demonstrating that the aberrant IMPG1 distribution is the main cause of the visual alterations observed in the absence of IMPG2. In conclusion, our results show the dependence of secreted proteoglycans such as IMPG1 on the extracellular environment to properly integrate into the matrix, demonstrate the role of IMPG2 in shaping the IPM, and shed light on the potential mechanisms leading to the development of subretinal lesions and vision loss.SIGNIFICANCE STATEMENT The photoreceptors are specialized neurons that drive phototransduction in the mammalian retina. These cells are organized and surrounded by an extracellular matrix, the interphotoreceptor matrix (IPM). Mutations in IPM proteoglycans are associated with blindness in humans. Our studies show that two specific proteoglycans of the IPM, IPM proteoglycan 1 (IMPG1) and IMPG2, form a dynamic structure with distinct localization and dependency. When IMPG2 is absent, IMPG1 cannot integrate into the IPM, leading to abnormal proteoglycan accumulation and visual deficits. This work adds a new layer of understanding to IPM physiology and describes the pathologic events following deficits in proteoglycans, providing novel possibilities for visual restoration in patients with IMPG-related pathologies.

Phenotypic Spectrum of Pentosan Polysulfate Sodium-Associated Maculopathy: A Multicenter Study

Importance

A unique pigmentary maculopathy was recently described in 6 patients with long-term exposure to pentosan polysulfate sodium (PPS), a long-standing oral therapy for interstitial cystitis.

Objective

To characterize the exposure characteristics and clinical manifestations of PPS-associated maculopathy.

Design, Setting, and Participants

In this multi-institutional case series, medical records of patients who exhibited the characteristic maculopathy in the setting of prior PPS exposure were retrospectively reviewed. Data were collected from August 1, 2012, to October 1, 2018, and data were analyzed from October 2018 to January 2019.

Main Outcomes and Measures

Drug exposure, visual acuity, and retinal imaging characteristics.

Results

Of the 35 included patients (70 eyes), 34 (97%) were female, and the median (range) age was 60 (37-79) years. The median (range) duration of PPS intake was 15 (3-22) years, and the median (range) cumulative exposure was 1.61 (0.44-4.31) kg. The leading visual symptoms were metamorphopsia, blurred vision, and prolonged dark adaptation. Median (range) logMAR visual acuity of all eyes was 0.10 (-0.12 to 1.18). Fundus examination often revealed hyperpigmented macular spots (34 of 64 eyes [53%]) with interspersed pale-yellow deposits, although less commonly in eyes that exhibited retinal pigment epithelial atrophy (6 of 26 eyes [23%]; P < .001). Optical coherence tomography showed foci of retinal pigment epithelium elevation or thickening associated with hyperreflectance on near-infrared reflectance imaging. Fundus autofluorescence imaging typically revealed a symmetric, confluent pattern of hyperautofluorescent and hypoautofluorescent spots that involved the fovea in all eyes and extended to the retinal periphery in 24 eyes (36%). Longitudinal evaluation demonstrated dynamic changes in pigmentary abnormalities.

Conclusions and Relevance

These findings suggest that PPS-associated maculopathy is a vision-threatening condition that can manifest in the setting of long-term exposure to the drug. Multimodal imaging posits a distinctive clinical phenotype, characterized in this cohort by dynamic alterations within the retinal pigment epithelium and at the retinal pigment epithelium-photoreceptor interface. Ongoing work might explore causality and direct screening guidelines.

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.

Special Issue Introduction: Inherited Retinal Disease: Novel Candidate Genes, Genotype-Phenotype Correlations, and Inheritance Models

Inherited retinal diseases (IRDs) are genetically and clinically heterogeneous disorders.[...].