Lens subluxation and retinal dysfunction in a girl with homozygous VSX2 mutation

Clinical and Genetic Landscape of Ectopia Lentis Based on a Cohort of Patients From 156 Families

Purpose

To extend the mutation spectrum and explore the characteristics of genotypes and ocular phenotypes in ectopia lentis (EL).

Methods

Variants in all 14 reported EL-associated genes were selected from in-house data sets as well as literature review, and available clinical data were analyzed.

Results

Likely pathogenic variants in three genes were identified in 156 unrelated families with EL from the in-house cohort, of which 97.4% resulted from variants in FBN1, whereas the remaining were caused by variants in ADAMTSL4 (1.3%) and LTBP2 (1.3%). A comparative analysis of the in-house data and literature review suggested several characteristics: (1) a higher proportion of cysteine involvement variants in FBN1, either variants introducing or eliminating cysteine, and an earlier diagnosis age were presented in our cohort than in published literature; (2) the axial length (AL) and refractive error increased more rapidly with age in preschool EL children than normal children, and the increased rate of AL was slower in patients with surgery than those without surgery; (3) aberrant astigmatism was common in EL; and (4) worse vision and earlier onset age were observed in patients with non-FBN1 variants (all P < 0.05).

Conclusions

Variants in FBN1 are the predominant cause of EL, with the most common cysteine involvement variants. Early-stage EL manifests refractive error but gradually converts to axial myopia through defocus introduced by lens dislocation. Aberrant astigmatism is a suggestive sign of EL. Non-FBN1 variants cause early-onset and severe phenotypes. These results provide evidence for early diagnosis as well as timely treatment for EL.

Combined Single Gene Testing and Genome Sequencing as an Effective Diagnostic Approach for Anophthalmia and Microphthalmia Patients

Anophthalmia and microphthalmia (A/M) are among the most severe congenital developmental eye disorders. Despite the advancements in genome screening technologies, more than half of A/M patients do not receive a molecular diagnosis. We included seven consanguineous families affected with A/M from Pakistani cohort and an unknown molecular basis. Single gene testing of FOXE3 was performed, followed by genome sequencing for unsolved probands in order to establish a genetic diagnosis for these families. All seven families were provided with a genetic diagnosis. The identified variants were all homozygous, classified as (likely) pathogenic and present in an A/M-associated gene. Targeted FOXE3 sequencing revealed two previously reported pathogenic FOXE3 variants in four families. In the remaining families, genome sequencing revealed a known pathogenic PXDN variant, a novel 13bp deletion in VSX2, and one novel deep intronic splice variant in PXDN. An in vitro splice assay was performed for the PXDN splice variant which revealed a severe splicing defect. Our study confirmed the utility of genome sequencing as a diagnostic tool for A/M-affected individuals. Furthermore, the identification of a novel deep intronic pathogenic variant in PXDN highlights the role of non-coding variants in A/M-disorders and the value of genome sequencing for the identification of this type of variants.

Association of Missense Variants in VSX2 With a Peculiar Form of Congenital Stationary Night Blindness Affecting All Bipolar Cells

Importance

Congenital stationary night blindness (CSNB) is an inherited stationary retinal disorder that is clinically and genetically heterogeneous. To date, the genetic association between some cases with CSNB and an unusual complex clinical picture is unclear.

Objective

To describe an unreported CSNB phenotype and the associated gene defect in 3 patients from 2 unrelated families.

Design, Setting, and Participants

This retrospective case series was conducted in 2021 and 2022 at a national referral center for rare ocular diseases. Data for 3 patients from a cohort of 140 genetically unsolved CSNB cases were analyzed clinically and genetically.

Exposures

Complete ocular examination including full-field electroretinography and multimodal fundus imaging (spectral-domain optical coherence tomography, color, infrared reflectance, and short-wavelength autofluorescence photographs) were performed. The gene defect was identified by exome sequencing and confirmed by Sanger sequencing and co-segregation analysis in 1 family. Screening was performed for genetically unsolved CSNB cases for VSX2 variants by direct Sanger sequencing.

Main Outcomes and Measures

Ocular and molecular biology findings.

Results

The series included 3 patients whose clinical investigations occurred at ages in the early 30s, younger than 12 years, and in the mid 40s. They had nystagmus, low stable visual acuity, and myopia from birth and experienced night blindness. Two older patients had bilateral lens luxation and underwent lens extraction. Full-field electroretinography revealed an electronegative Schubert-Bornschein appearance, combining characteristics of incomplete and complete CSNB, affecting the function of rod and cone ON- and OFF-bipolar cells. Exome sequencing and co-segregation analysis in a consanguineous family with 2 affected members identified a homozygous variant in VSX2. Subsequently, screening of the CSNB cohort identified another unrelated patient harboring a distinct VSX2 variant.

Conclusions and Relevance

This case series revealed a peculiar pan-bipolar cell retinopathy with lens luxation associated with variants in VSX2. Clinicians should be aware of this association and VSX2 added to CSNB diagnostic gene panels.

Next-generation sequencing panel analysis in 24 Chinese patients with congenital ectopia lentis

BACKGROUND

Congenital ectopia lentis (CEL) is a rare but serious disease. We use next-generation sequencing to detect genes associated with lens abnormalities in 24 patients with bilateral CEL and search for pathogenic genes and mutation sites.

MATERIALS AND METHODS

A total of 24 patients diagnosed with CEL from January 2019 to November 2019 were enrolled in this study, and their clinical data were collected and genome-wide deoxyribonucleic acid was extracted from peripheral venous blood. Targeted gene capture technology was used to obtain 188 exons of lens abnormality-related genes, which were sequenced using a high-throughput method. The mutation sites were determined through data analysis and verified by the Sanger method. According to the data from previous studies, the association between the genotype and clinical phenotype was analysed.

RESULT

Of the 24 patients, 23 had mutations in the fibrillin-1 (FBN1) gene, and 20 were diagnosed with Marfan syndrome. The 23 cases of FBN1 mutations were all heterozygous mutations, including 17 missense mutations, 3 splicing variants, 2 exon deletion mutations, 1 codon mutation, and 9 new mutations. A total of 17 mutations were located in the calcium-binding epidermal growth factor domain, including 16 mutations that contained missense mutations of cysteine. In addition, a heterozygous mutation of the gap junction protein alpha 8 (GJA8) gene was detected in one patient.

CONCLUSION

In this study, we identified 23 FBN1 gene mutations and 1 GJA8 gene mutation in 24 patients with CEL. Of these, 9 new FBN1 mutations and 14 known mutations were found. The results expanded the mutation spectrum of the FBN1 gene, suggesting that FBN1 mutation may be the main cause of CEL in Chinese patients.

Mechanism of Disease: Recessive ADAMTSL4 Mutations and Craniosynostosis with Ectopia Lentis

Craniosynostosis, the premature fusion of the calvarial bones, has numerous etiologies. Among them, several involve mutations in genes related to the TGFb signaling pathway, a critical molecular mediator of human development. These TGFb pathway-associated craniosynostosis syndromes include Loeys–Dietz syndrome (LDS) and Shprintzen–Goldberg syndrome (SGS). LDS and SGS have many similarities common to fibrillinopathies, specifically Marfan syndrome (MFS), which is caused by mutations in FBN1. Historically discriminating features of MFS from LDS and SGS are (1) the presence of ectopia lentis (the subluxation/dislocation of the ocular lens) and (2) the absence of craniosynostosis. Curiously, several instances of a seemingly novel syndrome involving only craniosynostosis and ectopia lentis have recently been reported to be caused by recessive mutations in ADAMTSL4, a poorly characterized gene as of yet. Here, we report on two new cases of craniosynostosis with ectopia lentis, each harboring recessive mutations in ADAMTSL4. We also discuss a proposed mechanism for the relationship between ADAMTSL4, FBN1, and TGFb pathway-related syndromes.

Marfan syndrome and the eye clinic: from diagnosis to management

Marfan syndrome (MFS) is an autosomal dominantly inherited disorder affecting the cardiovascular, ocular and musculoskeletal systems. Frequently, clinical suspicion and subsequent diagnosis begins in the ophthalmology clinic. Importantly, the ophthalmologist has a responsibility to cater not only to the eye, but also to be involved in a holistic approach for these patients. In this review, we discuss how MFS may present to an eye clinic, including clinical features, ocular morbidity, genetic diagnosis and management. Although this condition is ideally managed by a multidisciplinary team, our focus will be on MFS and the eye, including other conditions which may present with similar phenotypes. The ophthalmologist's role as the potential first contact for a patient with suspected MFS is crucial in making the proper investigations and referral, with the knowledge that not all ectopia lentis cases are MFS and vice versa. Management of ocular conditions in MFS may range from simple observation to surgical intervention; current options will be discussed.

Analysis of transcript-deleterious variants in Mendelian disorders: implications for RNA-based diagnostics

Background

At least 50% of patients with suspected Mendelian disorders remain undiagnosed after whole-exome sequencing (WES), and the extent to which non-coding variants that are not captured by WES contribute to this fraction is unclear. Whole transcriptome sequencing is a promising supplement to WES, although empirical data on the contribution of RNA analysis to the diagnosis of Mendelian diseases on a large scale are scarce.

Results

Here, we describe our experience with transcript-deleterious variants (TDVs) based on a cohort of 5647 families with suspected Mendelian diseases. We first interrogate all families for which the respective Mendelian phenotype could be mapped to a single locus to obtain an unbiased estimate of the contribution of TDVs at 18.9%. We examine the entire cohort and find that TDVs account for 15% of all “solved” cases. We compare the results of RT-PCR to in silico prediction. Definitive results from RT-PCR are obtained from blood-derived RNA for the overwhelming majority of variants (84.1%), and only a small minority (2.6%) fail analysis on all available RNA sources (blood-, skin fibroblast-, and urine renal epithelial cells-derived), which has important implications for the clinical application of RNA-seq. We also show that RNA analysis can establish the diagnosis in 13.5% of 155 patients who had received “negative” clinical WES reports. Finally, our data suggest a role for TDVs in modulating penetrance even in otherwise highly penetrant Mendelian disorders.

Conclusions

Our results provide much needed empirical data for the impending implementation of diagnostic RNA-seq in conjunction with genome sequencing.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

NGS panel analysis in 24 ectopia lentis patients; a clinically relevant test with a high diagnostic yield

BACKGROUND

Several genetic causes of ectopia lentis (EL), with or without systemic features, are known. The differentiation between syndromic and isolated EL is crucial for further treatment, surveillance and counseling of patients and their relatives. Next generation sequencing (NGS) is a powerful tool enabling the simultaneous, highly-sensitive analysis of multiple target genes.

OBJECTIVE

The aim of this study was to evaluate the diagnostic yield of our NGS panel in EL patients. Furthermore, we provide an overview of currently described mutations in ADAMTSL4, the main gene involved in isolated EL.

METHODS

A NGS gene panel was analysed in 24 patients with EL.

RESULTS

A genetic diagnosis was confirmed in 16 patients (67%). Of these, four (25%) had a heterozygous FBN1 mutation, 12 (75%) were homozygous or compound heterozygous for ADAMTSL4 mutations. The known European ADAMTSL4 founder mutation c.767_786del was most frequently detected.

CONCLUSION

The diagnostic yield of our NGS panel was high. Causative mutations were exclusively identified in ADAMTSL4 and FBN1. With this approach the risk of misdiagnosis or delayed diagnosis can be reduced. The value and clinical implications of establishing a genetic diagnosis in patients with EL is corroborated by the description of two patients with an unexpected underlying genetic condition.

Axial Length of the Eyeball Is Important in Secondary Dislocation of the Intraocular Lens, Capsular Bag, and Capsular Tension Ring Complex

Purpose. To analyze the patients with secondary dislocation of CTR and IOL within 5 years from cataract surgery, to determine predisposing factors. Methods. 16 eyes of 15 patients aged 66.2 ± 6.7 (from 49 to 82) with CTR/IOL complex dislocation within 5 years from cataract surgery were compared with 26 patients aged 67.1 ± 7.2 (from 53 to 85), implanted with CTR during cataract surgery to manage zonule dehiscence and did not dislocate for at least 5 years, in respect of cause, axial length and IOL power, refraction, coexistent pathology, and trauma. Results. Axial length of the eyeball was 23.8 ± 1.3 (from 21 to 29) in the group of patients with CTR/IOL dislocation and 20.7 ± 1.2 (from 19 to 24) in patients with no dislocation present (p = 0.008). Crystalline lens dislocation was diagnosed before surgery in 13 of 16 patients with CTR/IOL complex dislocation as opposed to 7 of 26 eyes in the control group (p = 0.01). Pseudoexfoliation was present in 50% and 58% in both groups, respectively. Traumatic dislocation was present in 8 patients, none of them with CTR/IOL dislocation (p = 0.04). Conclusion. Longer axial length may contribute to the failure of the CTR to prevent in-the-bag IOL dislocation. Traumatic dislocation appears to be well fixed with the CTR.

Comorbidity in the Tunisian population

Genetic diseases in the Tunisian population represent a real problem of public health as their spectrum encompasses more than 400 disorders. Their frequency and distribution in the country have been influenced by demographic, economic and social features especially consanguinity. In this article, we report on genetic disease association referred to as comorbidity and discuss factors influencing their expressivity. Seventy-five disease associations have been reported among Tunisian families. This comorbidity could be individual or familial. In 39 comorbid associations, consanguinity was noted. Twenty-one founder and 11 private mutations are the cause of 34 primary diseases and 13 of associated diseases. As the information dealing with this phenomenon is fragmented, we proposed to centralize it in this report in order to draw both clinicians' and researcher's attention on the occurrence of such disease associations in inbred populations as it makes genetic counseling and prenatal diagnosis challenging even when mutations are known.

Conserved genetic pathways associated with microphthalmia, anophthalmia, and coloboma

The human eye is a complex organ whose development requires extraordinary coordination of developmental processes. The conservation of ocular developmental steps in vertebrates suggests possible common genetic mechanisms. Genetic diseases involving the eye represent a leading cause of blindness in children and adults. During the last decades, there has been an exponential increase in genetic studies of ocular disorders. In this review, we summarize current success in identification of genes responsible for microphthalmia, anophthalmia, and coloboma (MAC) phenotypes, which are associated with early defects in embryonic eye development. Studies in animal models for the orthologous genes identified overlapping phenotypes for most factors, confirming the conservation of their function in vertebrate development. These animal models allow for further investigation of the mechanisms of MAC, integration of various identified genes into common developmental pathways and finally, provide an avenue for the development and testing of therapeutic interventions.

Genetic chimeras reveal the autonomy requirements for Vsx2 in embryonic retinal progenitor cells

BACKGROUND

Vertebrate retinal development is a complex process, requiring the specification and maintenance of retinal identity, proliferative expansion of retinal progenitor cells (RPCs), and their differentiation into retinal neurons and glia. The homeobox gene Vsx2 is expressed in RPCs and required for the proper execution of this retinal program. However, our understanding of the mechanisms by which Vsx2 does this is still rudimentary. To define the autonomy requirements for Vsx2 in the regulation of RPC properties, we generated chimeric mouse embryos comprised of wild-type and Vsx2-deficient cells.

RESULTS

We show that Vsx2 maintains retinal identity in part through the cell-autonomous repression of the retinal pigment epithelium determinant Mitf, and that Lhx2 is required cell autonomously for the ectopic Mitf expression in Vsx2-deficient cells. We also found significant cell-nonautonomous contributions to Vsx2-mediated regulation of RPC proliferation, pointing to an important role for Vsx2 in establishing a growth-promoting extracellular environment. Additionally, we report a cell-autonomous requirement for Vsx2 in controlling when neurogenesis is initiated, indicating that Vsx2 is an important mediator of neurogenic competence. Finally, the distribution of wild-type cells shifted away from RPCs and toward retinal ganglion cell precursors in patches of high Vsx2-deficient cell density to potentially compensate for the lack of fated precursors in these areas.

CONCLUSIONS

Through the generation and analysis of genetic chimeras, we demonstrate that Vsx2 utilizes both cell-autonomous and cell-nonautonomous mechanisms to regulate progenitor properties in the embryonic retina. Importantly, Vsx2's role in regulating Mitf is in part separable from its role in promoting proliferation, and proliferation is excluded as the intrinsic timer that determines when neurogenesis is initiated. These findings highlight the complexity of Vsx2 function during retinal development and provide a framework for identifying the molecular mechanisms mediating these functions.

Molecular pathogenesis and management strategies of ectopia lentis

Ectopia lentis (EL) is a condition that can either herald underlying systemic conditions, or be isolated. The recent expansion in the genetics of these conditions has furthered the understanding of the underlying molecular aetiology. It is becoming apparent that novel genes, and in particular the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family, are important in ocular development. The common link in these genes seems to be EL. The clinical management of EL is challenging. In particular, the options for addressing surgically induced aphakia in the context of an ectopic capsule are varied. Little evidence exists to direct management of these issues. This review summarises the molecular pathogenesis of EL and conditions associated with it, using the genetic aetiology as a framework. Furthermore, it summarises some of the issues involved in its clinical management.