Phenotype–genotype correlations and emerging pathways in ocular anterior segment dysgenesis

The Red Reflex Test and Leukocoria in Childhood

The red reflex test, performed using a direct ophthalmoscope, serves as a critical diagnostic tool in identifying various ocular conditions. These conditions encompass retinal anomalies (such as retinoblastoma, Coats disease, retinopathy of prematurity, familial exudative vitreoretinopathy, myelinated nerve fibers, ocular toxocariasis, ocular toxoplasmosis, retinochoroidal coloboma, astrocytic, and combined hamartoma), vitreous abnormalities (including persistent fetal vasculature), lens issues (like cataract), anterior chamber and corneal conditions (comprising dysgenesis of the anterior segment, congenital glaucoma, birth trauma), and tear film disturbances. During this examination, the presence of leukocoria, characterized by a white pupillary reflex, can suggest the presence of underlying conditions. Any suspicion of an abnormal red reflex test warrants immediate evaluation by a qualified ophthalmologist. This article primarily underscores the paramount importance of the red reflex examination, not only to identify potential sight-threateningbut also life-threatening conditions. It delves into the most common causes of leukocoria in childhood and offers insights into a comprehensive diagnostic approach. The target audience for this article includes pediatricians, primary care clinicians, and ophthalmologists, all of whom play a pivotal role in the early detection and intervention of these critical eye disorders.

Early Diagnosis of Syndromic Congenital Cataracts in a Large Cohort of Congenital Cataracts

PURPOSE

To explore the factors related to the diagnosis yield of syndromic congenital cataracts and describe the phenotype-genotype correlation in congenital cataract patients.

DESIGN

Prospective cohort study.

METHODS

Setting: the participants from underwent clinical examinations between 2021 and 2022. Facial and anterior eye segment photographs, pre- and postoperative ocular parameters, and medical and family histories were recorded. Bioinformatics analysis was performed using whole-exome sequencing data. Statistical and correlation analyses were performed using the basic characteristics, deep phenotype, and genotype data.

PARTICIPANTS

115 patients with unrelated congenital cataract.

INTERVENTIONS

performing clinical examinations, whole-exome sequencing, and bioinformatics analysis for all participants.

MAIN OUTCOMES AND MEASURES

factors related to the genetic diagnosis yield of syndromic congenital cataracts.

RESULTS

Bilaterally asymmetrical cataracts were identified to be associated with syndromic congenital cataracts. The overall genetic diagnostic yield in the cohort was 72.2%. In total, 34.8% of the probands were early diagnosed with various syndromes with the help of genetic information. A phenotype-genotype correlation was detected for some genes and deep phenotypes.

CONCLUSIONS

We highlight the importance of screening syndromic diseases in the patients with asymmetrical congenital cataracts. Application of whole-exome sequencing helps provide early diagnosis and treatment for the patients with syndromic congenital cataracts. This study also achieved a high genetic diagnostic yield, expanded the genotypic spectrum, and found phenotype-genotype correlations. A comprehensive analysis of cataract symmetricity, family history, and deep phenotypes makes the genotype prediction of some congenital cataract patients possible.

Managing the apparently blind child presenting in the first year of life: A review

Severe vision impairment and blindness in childhood have a significant health burden on the child, family and society. This review article seeks to provide a structured framework for managing the apparently blind child presenting in the first year of life, starting from a comprehensive history and examination. Different investigation modalities and the increasingly important role of genetics will also be described, in addition to common causes of severe vision impairment. Crucially, a systematic approach to the blind infant is key to correct diagnoses and timely management. Incorrect diagnoses can be costly to all involved, however it is important to note that diagnoses can change with ongoing follow-up and investigations. Furthermore, the modern age of ophthalmology requires a multi-disciplinary approach and close collaboration with specialists including paediatricians, neurologists and geneticists, in addition to rehabilitation and low vision services, to ensure the best care for these vulnerable infants.

Classifications of anterior segment structure of congenital corneal opacity in infants and toddlers by ultrasound biomicroscopy and slit-lamp microscopic photographs: an observational study

BACKGROUND

The structural features have an impact on the surgical prognosis for congenital corneal opacity (CCO). The structural classification system of CCO, however, is lacking. Based on data from ultrasound biomicroscopy (UBM) findings in infants and toddlers with CCO, this research proposed a classification system for the anterior segment structure severity.

METHODS

Medical records, preoperative UBM images and slit-lamp photographs of infants and toddlers diagnosed with CCO at University Third Hospital between December 2018 and June 2022 were reviewed. According to the anterior segment structural features observed in UBM images, eyes were classified as follows: U1, opaque cornea only; U2, central anterior synechia; U3, peripheral anterior synechia combined with angle closure; and U4, aniridia or lens anomaly. The opacity appearance and corneal vascularization density observed in slit-lamp photographs were assigned grades according to previous studies. The extent of vascularization was also recorded. The corresponding intraocular anomaly classifications and ocular surface lesion severity were analysed.

RESULTS

Among 81 eyes (65 patients), 41 (50.6%) were right eyes, and 40 (49.4%) were left eyes. The median age at examination was 6.91 months (n = 81, 1.00, 34.00). Two (2.5%) of the 81 eyes were classified as U1, 20 (24.7%) as U2, 22 (27.2%) as U3a, 11 (13.6%) as U3b and 26 (32.1%) as U4. Bilateral CCO eyes had more severe UBM classifications (P = 0.019), more severe dysgenesis (P = 0.012) and a larger angle closure (P = 0.009). Eyes with more severe UBM classifications had higher opacity grades (P = 0.003) and vascularization grades (P = 0.014) and a larger vascularization extent (P = 0.001). Eyes with dysgenesis had higher haze grades (P = 0.012) and more severe vascularization (P = 0.003 for density; P = 0.008 for extent), while the angle closure range was related to haze grade (P = 0.013) and vascularization extent (P = 0.003).

CONCLUSIONS

This classification method based on UBM and slit-lamp photography findings in the eyes of CCO infants and toddlers can truly reflect the degree of abnormality of the ocular surface and anterior segment and is correlated with the severity of ocular surface anomalies. This method might provide meaningful guidance for surgical procedure design and prognostic determinations for keratoplasty in CCO eyes.

Clinical and diagnostic imaging profile of three anterior segment dysgenesis disorders presenting with infantile corneal opacities

PURPOSE

To describe three anterior segment dysgenesis disorders with infantile corneal opacities, namely, congenital hereditary endothelial dystrophy (CHED), primary congenital glaucoma (PCG), and Peters anomaly (PA) in terms of clinical characteristics, histopathology, genetic association, and diagnostic imaging profiles using imaging modalities such as ultrasound biomicroscopy (UBM) and microscope-integrated intraoperative optical coherence tomography (i-OCT).

MATERIALS AND METHODS

Seventy-four eyes with 22 eyes of CHED, 28 eyes of PA, and 24 eyes of PCG were clinically evaluated and underwent imaging using UBM and i-OCT. Corneal buttons of 16 operated patients underwent histopathological analysis, while genetic analysis was done in 23 patients using whole-exome sequencing.

RESULTS

Corneal diameters (CD) and UBM parameters like anterior chamber depth (ACD), iris thickness (IT), and ciliary body (CB) thickness revealed a statistically significant difference between the three categories. In PA, 9 eyes had a third rare phenotype with only a posterior corneal defect with no iris adhesions. Genetic mutations were seen in all tested patients with CHED, in 83.3% of patients with PCG, and in 80% of patients with the third type of PA. i-OCT helped in the characterization of corneal opacity, identification of posterior corneal defects, iridocorneal adhesions, and contour of Descemet's membrane.

CONCLUSION

Overlapping phenotypes of the above disorders cause a diagnostic dilemma and parameters like CDs, UBM ACD, IT, and CB thickness help differentiate between them. i-OCT can help in classifying the diseases in a high resolution, non-contact manner, and can better delineate corneal characteristics. The rare third type of PA phenotype may have a genetic association.

Peters anomaly: An overview

Peters anomaly (PA) is a rare, often bilateral, congenital corneal opacity, usually with a sporadic inheritance pattern, characterized by corneal opacities and irido-corneal or lenticular-corneal adhesions with a defect in the Descemet's membrane, occurring due to anterior segment dysgenesis during fetal development. Due to other ocular and systemic comorbidities, a team comprising pediatric cornea, glaucoma, and strabismus specialists in addition to a pediatrician and geneticist is necessary for the appropriate management of these children. Since the outcome of pediatric penetrating keratoplasty is variable and has a higher chance of failure when accompanied by additional procedures, such as lensectomy and vitrectomy, minimally invasive alternatives are increasingly being offered to these patients. Of note is the recently reported novel procedure: selective endothelialectomy for PA, which avoids the need for a corneal transplant and results in gradual clearing of the corneal opacity over time. In this overview, we aimed to describe the etiology, classification, pathophysiology, histopathology, clinical features, and management of PA.

Commercial Gene Panels for Congenital Anterior Segment Anomalies: Are They All the Same?

PURPOSE

We compared next generation sequencing multigene panels (NGS-MGP) from 5 commercial laboratories to inform ophthalmologists' decision making in diagnostic genetic testing for congenital anterior segment anomalies (CASAs).

DESIGN

Comparison of commercial genetic testing panels.

METHODS

This observational study gathered publicly available information on NGS-MGP from 5 commercial laboratories for the following: cataracts, glaucoma, anterior segment dysgenesis (ASD), microphthalmia-anophthalmia-coloboma (MAC), corneal dystrophies, and Axenfeld-Rieger syndrome (ARS). We compared gene panel composition, consensus rate (genes covered by all the panels per condition, "concurrent"), dissensus rate (genes covered by only 1 panel per condition, "standalone"), and intronic variant coverage. For individual genes, we compared publication history and association with systemic conditions.

RESULTS

Altogether, cataract, glaucoma, corneal dystrophies, MAC, ASD, and ARS panels tested 239, 60, 36, 292, and 10 discrete genes, respectively. The consensus rate varied between 16% and 50%, and the dissensus rate varied between 14% and 74%. After pooling concurrent genes from all conditions, 20% of these genes were concurrent in 2 or more conditions. For both cataract and glaucoma, concurrent genes had significantly stronger correlation with the condition than standalone genes.

CONCLUSIONS

The genetic testing of CASAs using NGS-MGPs is complicated, owing to their number, variety, and phenotypic and genetic overlap. Although the inclusion of additional genes, such as the standalone ones, might increase diagnostic yield, these genes are also less well studied, indicating uncertainty over their role in CASA pathogenesis. Rigorous prospective diagnostic yield studies of NGS-MGPs will aid in making decisions of panel selection for the diagnosis of CASAs.

[Glaucoma in infancy and childhood]

Glaucoma in infancy and childhood is a rare disease. An immediate diagnosis and treatment are absolutely necessary to prevent blindness of affected children. Childhood glaucoma is characterized by a heterogeneous phenotype: besides primary congenital glaucoma, secondary types often exist and the individualized treatment requires an experienced interdisciplinary team. The pathogenesis is not always discernible and genetic alterations sometimes cause the disease. A surgical procedure is usually necessary to lower the intraocular pressure. Refractive and orthoptic care are equally important to avoid amblyopia. This article gives an overview of childhood glaucoma and outlines the most important diagnostic and therapeutic aspects.

Genotype-phenotype association of PITX2 and FOXC1 in Axenfeld-Rieger syndrome

PITX2 and FOXC1 are the most common pathogenic genes associated with Axenfeld-Rieger syndrome (ARS). In this study, we aimed to explore the variation spectrum of PITX2 and FOXC1 and their associated phenotype based on data from our study and previously reported literatures. Whole exome sequencing was performed on eight probands in our study. Multistep bioinformatic and co-segregation analyses were performed to detect pathogenic variants. Genotype-phenotype correlations of PITX2 and FOXC1 and the differences between them were determined. We detected three variants of FOXC1 and two variants of PITX2 in five unrelated families with ARS. Macular retinoschisis had been observed in AR1 with variant in PITX2 and it is not reported before. Additionally, a review of published literature and our study led to the identification of 593 families with variants of PITX2 or FOXC1, including 316 families with heterozygous variants in FOXC1, 251 families with heterozygous variants in PITX2, 13 families with variants in double genes, seven families with homozygous or compound heterozygous variants in FOXC1, and six families with variants in ADAMTS17, PRDM5, COL4A1 or CYP1B1. Significant differences were observed between the prevalence of missense and in-frame, truncation, and large deletion variants in PITX2 (32.00%, 42.67%, and 25.33%, respectively) and FOXC1 (34.49%, 35.13%, 30.38%, respectively) (p = 1.16E-43). Enrichment and frequency analyses revealed that missense variants were concentrated in the forkhead domain of FOXC1 (76.14%) and homeodomain of PITX2 (87.50%). The percentage of Caucasians with variants in FOXC1 was significantly higher than that of PITX2 (p = 2.00E-2). Significant differences between PITX2 and FOXC1 were observed in glaucoma (p = 3.00E-2), corectopia (p = 3.050E-6), and polycoria (p = 5.21E-08). Additionally, we observed a significant difference in best-corrected visual acuity (BCVA) between FOXC1 and PITX2 (p = 3.80E-2). Among all the family members with PITX2 or FOXC1 variants, the prevalence of systemic abnormalities was significantly higher in PITX2 than in FOXC1 (89.16% vs. 58.77%, p = 5.44E-17). In conclusion, macular retinoschisis as a novel phenotype had been observed in patient with variant in PITX2. Significant differences were detected in phenotypes and genotypes between PITX2 and FOXC1.

Axenfeld-Rieger syndrome: a novel histopathologic finding associated with corneal abnormalities

BACKGROUND

Axenfeld-Rieger syndrome (ARS) is a rare kind of anterior segment dysgenesis (ASD). The most common ocular features of ARS are posterior embryotoxon and iris hypoplasia, while some patients may manifest as corneal opacity and edema. However, the current understanding of how ARS affects the cornea is still incomplete. This study reports a novel histopathological finding of ARS, complicating corneal abnormalities, including congenital corneal opacity and irreversible endothelial decompensation.

METHODS

This retrospective study included 6 eyes of 3 ARS patients, 5 of which underwent keratoplasty for irreversible endothelial decompensation from May 2016 to January 2019. No eye had a history of surgery. We reviewed the data of epidemiology, clinical manifestations and histopathologic examinations.

RESULTS

Five eyes developed irreversible endothelial decompensation, among which 4 were born with corneal opacity. One eye exhibited transparent cornea but showed a continuous loss of endothelial cells in the absence of surgery and elevated intraocular pressure thereafter. Anterior segment optical coherence tomography photographs showed that anterior synechia existed in the area with corneal opacities, where we found the interlayer splitting of the Descemet membrane inserted by hypoplastic iris and a basement membrane-like structure under a light microscope.

CONCLUSION

Anterior synechia might be associated with corneal abnormalities in ARS patients. The novel histopathologic finding revealed the internal relation between anterior segment dysgenesis and would help explore the inner mechanism of corneal abnormalities in ARS.

Outcomes following tacrolimus systemic immunosuppression for penetrating keratoplasty in infants and young children

OBJECTIVE

To report outcomes of tacrolimus immunosuppression after penetrating keratoplasty (PK) in very young children.

METHODS

Retrospective, consecutive, cohort study of children undergoing PK at a tertiary children's hospital between 2005 and 2016. Oral tacrolimus immunosuppression was given for 2 years, followed by topical tacrolimus.

RESULTS

Fourteen children (20 eyes) had 24 PKs; nineteen eyes had primary PKs, five eyes had repeat PKs. Mean age at primary graft was 95 days (3.1 months) for anterior segment dysgenesis (ASD), 430 days (14.3 months) for non-ASD children. Eleven children (15 eyes) had ASD. Three children (five eyes) had non-ASD: two children (three eyes) had glaucoma-related corneal opacity and one child (two eyes) had congenital hereditary endothelial dystrophy (CHED). One-year rejection-free survival rates following primary PK was 80% for ASD (n = 15) and 100% for non-ASD (n = 4). At final review, 5/15 of primary grafts for ASD were clear. 10/15 failed after a mean of 19 months, specifically attributable to infection (n = 2), rejection (n = 2) and glaucoma (n = 2). 4/4 primary non-ASD grafts are clear at final review (mean follow-up = 77 months). All repeat grafts (n = 5), failed after a mean of 38.25 months. Considering all grafts, 15/24 (62.5%) failed: 5/15 due to infection, 2/15 due to rejection, 8/15 due to glaucoma, phthisis, perforation or vascularised with no rejection. At last review (mean = 58.1 months, range 28-84), overall cohort survival is 37.5%. Final visual acuities range between 0.86 and 2.4 LogMAR.

CONCLUSION

We compare our results to published literature: 1-year graft survival was higher than previously reported, with lower failure due to rejection. Overall infection rates did not increase, however, proportionally, severe infections were higher. Overall graft survival is at least comparable to reported literature.

Biallelic variants in CPAMD8 are associated with primary open-angle glaucoma and primary angle-closure glaucoma

BACKGROUND/AIMS

This study aims to assess the contribution of biallelic CPAMD8 variants in patients with different forms of glaucoma, especially primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG), based on a systematic analysis of exome sequencing (ES).

METHODS

Potentially pathogenic CPAMD8 variants were selected from the ES data of 5307 subjects with various eye conditions through multiple bioinformatics analyses. Of the 5307 subjects, 1221 probands had different forms of primary glaucoma. The genotype-phenotype correlation was assessed by a systematic review of biallelic CPAMD8 variants that including our data and data from the literature. The expression profile of CPAMD8 in human tissues was determined at the mRNA and protein levels.

RESULTS

Biallelic CPAMD8 variants, including one frameshift and six missense variants, were exclusively present and significantly enriched in patients with glaucoma (one with juvenile open-angle glaucoma (JOAG), two with POAG and two with PACG) compared with none of the 4086 probands with other eye conditions in this cohort (p=4.1E-07). The effect of variants in these patients is relatively mild compared with that reported in patients with anterior segment dysgenesis or primary congenital glaucoma. CPAMD8 mRNA was highly expressed in the optic nerve, ciliary body, retina and iris, whereas the CPAMD8 protein was mainly detected in the nonpigmented epithelium of the iris and ciliary process, determined by immunohistochemistry.

CONCLUSIONS

The data from this study not only provide further evidence to support the association of biallelic CPAMD8 variants with JOAG but also suggest that biallelic CPAMD8 variants might be associated with POAG and PACG.

Snail Track Lesion with Flat Keratometry in Anterior Segment Dysgenesis Caused by a Novel FOXC1 Variant

We report the phenotype of a 15-year-old female patient with anterior segment dysgenesis (ASD) caused by a novel heterozygous loss-of-function FOXC1 variant. The proband underwent an ophthalmic examination as well as a molecular genetic investigation comprising exome sequencing, a single nucleotide polymorphism array to access copy number and Sanger sequencing to exclude non-coding causal variants. There was bilateral mild iris hypoplasia with pupil deformation and iridocorneal adhesions. In addition to these features of ASD, the corneas were flat, with mean keratometry readings of 38.8 diopters in the right eye and 39.5 diopters in the left eye. There was a snail track lesion of the left cornea at the level of the Descemet membrane. The central corneal endothelial cell density was reduced bilaterally at 1964 and 1373 cells/mm² in the right and left eyes, respectively. Molecular genetic analysis revealed that the proband was a carrier of a novel heterozygous frameshifting variant in FOXC1, c.605del p.(Pro202Argfs*113). Neither parent had this change, suggesting a de novo origin which was supported by paternity testing. We found no possibly pathogenic variants in the other genes associated with posterior corneal dystrophies or ASD. Further studies are warranted to verify whether there is a true association between snail track lesions, corneal flattening, and pathogenic variants in FOXC1.

Cell atlas of the human ocular anterior segment: Tissue-specific and shared cell types

The anterior segment of the eye consists of the cornea, iris, ciliary body, crystalline lens, and aqueous humor outflow pathways. Together, these tissues are essential for the proper functioning of the eye. Disorders of vision have been ascribed to defects in all of them; some disorders, including glaucoma and cataract, are among the most prevalent causes of blindness in the world. To characterize the cell types that compose these tissues, we generated an anterior segment cell atlas of the human eye using high-throughput single-nucleus RNA sequencing (snRNAseq). We profiled 195,248 nuclei from nondiseased anterior segment tissues of six human donors, identifying >60 cell types. Many of these cell types were discrete, whereas others, especially in the lens and cornea, formed continua corresponding to known developmental transitions that persist in adulthood. Having profiled each tissue separately, we performed an integrated analysis of the entire anterior segment, revealing that some cell types are unique to a single structure, whereas others are shared across tissues. The integrated cell atlas was then used to investigate cell type-specific expression patterns of more than 900 human ocular disease genes identified through either Mendelian inheritance patterns or genome-wide association studies.

Elevated TGFβ signaling contributes to ocular anterior segment dysgenesis in Col4a1 mutant mice

Ocular anterior segment dysgenesis (ASD) refers to a collection of developmental disorders affecting the anterior structures of the eye. Although a number of genes have been implicated in the etiology of ASD, the underlying pathogenetic mechanisms remain unclear. Mutations in genes encoding collagen type IV alpha 1 (COL4A1) and alpha 2 (COL4A2) cause Gould syndrome, a multi-system disorder that often includes ocular manifestations such as ASD and glaucoma. COL4A1 and COL4A2 are abundant basement membrane proteins that provide structural support to tissues and modulate signaling through interactions with other extracellular matrix proteins, growth factors, and cell surface receptors. In this study, we used a combination of histological, molecular, genetic and pharmacological approaches to demonstrate that altered TGFβ signaling contributes to ASD in mouse models of Gould syndrome. We show that TGFβ signaling was elevated in anterior segments from Col4a1 mutant mice and that genetically reducing TGFβ signaling partially prevented ASD. Notably, we identified distinct roles for TGFβ1 and TGFβ2 in ocular defects observed in Col4a1 mutant mice. Importantly, we show that pharmacologically promoting type IV collagen secretion or reducing TGFβ signaling ameliorated ocular pathology in Col4a1 mutant mice. Overall, our findings demonstrate that altered TGFβ signaling contributes to COL4A1-related ocular dysgenesis and implicate this pathway as a potential therapeutic target for the treatment of Gould syndrome.

Animal Model Contributions to Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is an ocular disease characterized by congenital anterior segmental maldevelopment with progressive optic nerve degeneration. Certain genes, such as cytochrome P450 family 1 subfamily B member 1 and latent TGF-β-binding protein 2, are involved in the pathogenesis of PCG, but the exact pathogenic mechanism has not yet been fully elucidated. There is an urgent need to determine the etiology and pathophysiology of PCG and develop new therapeutic methods to stop disease progression. Animal models can simulate PCG and are essential to study the pathogenesis and treatment of PCG. Various animal species have been used in the study of PCG, including rabbits, rats, mice, cats, zebrafish, and quails. These models are formed spontaneously or by combining with genetic engineering technology. The focus of the present study is to review the characteristics and potential applications of animal models in PCG and provide new approaches to understand the mechanism and develop new treatment strategies for patients with PCG.

Kindliche Glaukomerkrankungen

Glaukomerkrankungen im Kindesalter sind selten. Da ohne Behandlung in der Regel die Erblindung eintritt, ist eine umgehende Diagnosestellung und Therapie von höchster Bedeutung. Die Heterogenität der Erkrankung erfordert eine genaue Kenntnis der möglichen Ursachen und deren individuelle Behandlung. Dieser Artikel soll einen Überblick über die kindlichen Glaukome vermitteln und die wichtigsten Aspekte der Therapie aufzeigen.

[Childhood Glaucoma]

Childhood glaucoma is a rare disease. Since a lacking therapy normally leads to blindness an immediate diagnosis and appropriate treatment are crucial. The heterogeneity of childhood glaucoma requires a comprehensive knowledge of possible underlying pathomechanisms of primary and secondary childhood glaucoma types. Several types of childhood glaucoma are accompanied with ocular or systemic syndromes and hereditary causes are frequent. Thus, an interdisciplinary team of ophthalmologists, orthoptists, pediatricians, human geneticists, and anesthesiologists is vital for a successful supply. Most cases rely on a dysgenesis of trabecular meshwork with impaired outflow. Thus, usually a surgical approach is indicated. To handle a surgery in a buphthalmic eye an experienced hand is required. Special attention should be paid on the correct prescription of topical antiglaucomatous therapy in children since they are more prone to develop side effects. This article aims to provide an overview about the different childhood glaucoma types and to point out the most important aspects of their individual treatment strategies.

Approach to childhood glaucoma: A review

Childhood glaucoma represents a heterogenous group of rare ocular conditions that may result in significant sight threatening complications related to elevated intraocular pressure (IOP). It can be classified as either primary or secondary and the latter may have systemic associations. This review will be based on the work of the childhood glaucoma research network (CGRN) and will focus on the diagnosis and management of the most common types of childhood glaucoma. These include primary congenital glaucoma (PCG) and juvenile open angle glaucoma (JOAG) as well as secondary causes of glaucoma associated with non-acquired ocular anomalies (Axenfeld-Rieger anomaly; Peters anomaly and Aniridia), glaucoma associated with systemic disease (Sturge Weber syndrome and Neurofibromatosis), those due to acquired conditions (Uveitic glaucoma, trauma and tumours) and importantly glaucoma following cataract surgery.

First evidence of SOX2 mutations in Peters' anomaly: lessons from molecular screening of 95 patients

Peters' anomaly (PA) is a rare anterior segment dysgenesis characterized by central corneal opacity and irido-lenticulo-corneal adhesions. Several genes are involved in syndromic or isolated PA (B3GLCT, PAX6, PITX3, FOXE3, CYP1B1). Some Copy Number Variations (CNVs) have also been occasionally reported. Despite this genetic heterogeneity, most of patients remain without genetic diagnosis. We retrieved a cohort of 95 individuals with PA and performed genotyping using a combination of Comparative genomic hybridization, whole genome, exome and targeted sequencing of 119 genes associated with ocular development anomalies. Causative genetic defects involving 12 genes and CNVs were identified for 1/3 of patients. Unsurprisingly, B3GLCT and PAX6 were the most frequently implicated genes, respectively in syndromic and isolated PA. Unexpectedly, the third gene involved in our cohort was SOX2, the major gene of micro-anophthalmia. Four unrelated patients with PA (isolated or with microphthalmia) were carrying pathogenic variants in this gene that was never associated with PA before. Here we described the largest cohort of PA patients ever reported. The genetic bases of PA are still to be explored as genetic diagnosis was unavailable for 2/3 of patients. Nevertheless, we showed here for the first time the involvement of SOX2 in PA, offering new evidence for its role in corneal transparency and anterior segment development. This article is protected by copyright. All rights reserved.

First Results from the Prospective German Registry for Childhood Glaucoma: Phenotype-Genotype Association

Childhood glaucoma is a heterogeneous disease and can be associated with various genetic alterations. The aim of this study was to report first results of the phenotype–genotype relationship in a German childhood glaucoma cohort. Forty-nine eyes of 29 children diagnosed with childhood glaucoma were prospectively included in the registry. Besides medical history, non-genetic risk factor anamnesis and examination results, genetic examination report was obtained (23 cases). DNA from peripheral blood or buccal swab was used for molecular genetic analysis using a specific glaucoma gene panel. Primary endpoint was the distribution of causative genetic mutations and associated disorders. Median age was 1.8 (IQR 0.6; 3.8) years, 64% participants were female. Secondary childhood glaucoma (55%) was more common than primary childhood glaucoma (41%). In 14%, parental consanguinity was indicated. A mutation was found in all these cases, which makes consanguinity an important risk factor for genetic causes in childhood glaucoma. CYP1B1 (30%) and TEK (10%) mutations were found in primary childhood glaucoma patients. In secondary childhood glaucoma cases, alterations in CYP1B1 (25%), SOX11 (13%), FOXC1 (13%), GJA8 (13%) and LTBP2 (13%) were detected. Congenital cataract was associated with variants in FYCO1 and CRYBB3 (25% each), and one case of primary megalocornea with a CHRDL1 aberration. Novel variants of causative genetic mutations were found. Distribution of childhood glaucoma types and causative genes was comparable to previous investigated cohorts. This is the first prospective study using standardized forms to determine phenotypes and non-genetic factors in childhood glaucoma with the aim to evaluate their association with genotypes in childhood glaucoma.

Novel CHRDL1 mutation causing X-linked megalocornea in a family with mild anterior segment manifestations in carrier females

PURPOSE

X-linked megalocornea (XMC) is a rare anterior segment malformation characterized by a nonprogressive enlargement of the cornea to 13 mm or greater in the setting of normal intraocular pressure. XMC is caused by mutations in the CHRDL1 gene and it is inherited as an X-linked recessive trait affecting only males. Here, we describe the results of phenotypic and genetic assessment in a novel XMC pedigree.

METHODS

Three subjects (a father and his two daughters) underwent a complete clinical and imaging ocular examination including biomicroscopy, fundoscopy, tonometry, visual acuity, Pentacam Scheimpflug imaging, anterior segment Swept Source OCT, and ultrabiomicroscopy. Genetic analysis was performed through whole exome sequencing in 3 family members. Candidate variants were validated by sanger sequencing.

RESULTS

The affected father exhibited megalocornea, very deep anterior chambers, retrocorneal pigmentation, iris atrophy, queer iris configuration, extremely open iridocorneal angles, and cataracts. Notably, both daughters showed queer iris configuration and abnormally widely open iridocorneal angles in both eyes. Genetic analysis identified a novel hemizygous c.207+1G>A splicing variant in CHRDL1 in the affected father. Both mildly affected daughters were heterozygous for the pathogenic variant.

CONCLUSIONS

Here, we report an additional XMC family due to a novel mutation in the CHRDL1 gene. Mild anterior segment anomalies were observed in two heterozygous carriers demonstrating for the first time a CHRDL1-linked phenotype in females. A detailed comparison of the clinical and genetic features of this pedigree with those observed in previously published XMC cases is also presented.

Genetics and epidemiology of aniridia: Updated guidelines for genetic study

Aniridia is a panocular disease characterized by iris hypoplasia, accompanied by other ocular manifestations, with a high clinical variability and overlapping with different abnormalities of the anterior and posterior segment. This review focuses on the genetic features of this autosomal dominant pathology, which is caused by the haploinsufficiency of the PAX6 gene. Mutations causing premature stop codons are the most frequent among the wider mutational spectrum of PAX6, with more than 600 different mutations identified so far. Recent advances in next-generation sequencing (NGS) have increased the diagnostic yield in aniridia and contributed to elucidate new etiopathogenic mechanisms leading to PAX6 haploinsufficiency. Here, we also update good practices and recommendations to improve genetic testing and clinical management of aniridia using more cost-effective NGS analysis. Those new approaches also allow studying simultaneously both structural variants and point-mutations in PAX6 as well as other genes for differential diagnosis, simultaneously. Some patients with atypical phenotypes might present mutations in FOXC1 and PITX2, both genes causing a wide spectrum of anterior segment dysgenesis, or in ITPR1, which is responsible for a distinctive form of circumpupillary iris aplasia present in Gillespie syndrome, or other mutations in minor genes. Since aniridia can also associate extraocular anomalies, as it occurs in carriers of PAX6 and WT1 microdeletions leading to WAGR syndrome, genetic studies are crucial to assure a correct diagnosis and clinical management, besides allowing prenatal and preimplantational genetic testing in families.

Glaucoma Syndromes: Insights into Glaucoma Genetics and Pathogenesis from Monogenic Syndromic Disorders

Monogenic syndromic disorders frequently feature ocular manifestations, one of which is glaucoma. In many cases, glaucoma in children may go undetected, especially in those that have other severe systemic conditions that affect other parts of the eye and the body. Similarly, glaucoma may be the first presenting sign of a systemic syndrome. Awareness of syndromes associated with glaucoma is thus critical both for medical geneticists and ophthalmologists. In this review, we highlight six categories of disorders that feature glaucoma and other ocular or systemic manifestations: anterior segment dysgenesis syndromes, aniridia, metabolic disorders, collagen/vascular disorders, immunogenetic disorders, and nanophthalmos. The genetics, ocular and systemic features, and current and future treatment strategies are discussed. Findings from rare diseases also uncover important genes and pathways that may be involved in more common forms of glaucoma, and potential novel therapeutic strategies to target these pathways.

Genetics and epidemiology of aniridia: Updated guidelines for genetic study

Aniridia is a panocular disease characterized by iris hypoplasia, accompanied by other ocular manifestations, with a high clinical variability and overlapping with different abnormalities of the anterior and posterior segment. This review focuses on the genetic features of this autosomal dominant pathology, which is caused by the haploinsufficiency of the PAX6 gene. Mutations causing premature stop codons are the most frequent among the wider mutational spectrum of PAX6, with more than 600 different mutations identified so far. Recent advances in next-generation sequencing (NGS) have increased the diagnostic yield in aniridia and contributed to elucidate new etiopathogenic mechanisms leading to PAX6 haploinsufficiency. Here, we also update good practices and recommendations to improve genetic testing and clinical management of aniridia using more cost-effective NGS analysis. Those new approaches also allow studying simultaneously both structural variants and point-mutations in PAX6 as well as other genes for differential diagnosis, simultaneously. Some patients with atypical phenotypes might present mutations in FOXC1 and PITX2, both genes causing a wide spectrum of anterior segment dysgenesis, or in ITPR1, which is responsible for a distinctive form of circumpupillary iris aplasia present in Gillespie syndrome, or other mutations in minor genes. Since aniridia can also associate extraocular anomalies, as it occurs in carriers of PAX6 and WT1 microdeletions leading to WAGR syndrome, genetic studies are crucial to assure a correct diagnosis and clinical management, besides allowing prenatal and preimplantational genetic testing in families.

Novel Mutations in COL6A3 That Associated With Peters' Anomaly Caused Abnormal Intracellular Protein Retention and Decreased Cellular Resistance to Oxidative Stress

Peters' anomaly (PA) is a rare form of anterior segment dysgenesis characterized by central corneal opacity accompanied by iridocorneal or lenticulo-corneal adhesions. Although genetic mutations, particularly those affecting transcription factors that function in eye development, are known to cause PA, the etiology of this disease remains poorly understood. In this study, 23 patients with PA were recruited for panel sequencing. Four out of 23 patients were found to carry variants in known PA causal genes, PITX2 and PITX3. More importantly, two homozygous mutations (NM_057164: p.Val86Ala and p.Arg689Cys) in the COL6A3 gene (collagen type VI alpha-3 chain) that correlated with the phenotype of type I PA were identified, and then validated by following whole-exome sequencing. The expression profile of the COL6A3 gene in the cornea and the impact of the mutations on protein physiological processing and cellular function were further explored. It was shown that COL6A3 presented relatively high expression in the cornea. The mutant COL6A3 protein was relatively retained intracellularly, and its expression reduced cellular resistance to oxidative stress through an enhanced endoplasmic reticulum stress response. Taken together, our findings expanded the known genetic spectrum of PA, and provided evidence for the involvement of COL6A3 or collagen VI in ocular anterior segment development, thereby offering new insight for future investigations targeting PA.

Long-Term Visual Outcomes and Clinical Course of Patients With Peters Anomaly

PURPOSE

To present long-term clinical and visual outcomes of patients with Peters anomaly.

METHODS

The charts of all patients diagnosed with Peters anomaly from January 2000 to December 2012 were reviewed retrospectively. Peters anomaly was classified as type I (with no lens involvement) or type II (presence of keratolenticular adhesions or cataract), with further severity grading to mild, moderate, and severe disease depending on corneal opacity location and size. Mild cases were observed. Moderate cases were managed with pupillary dilation either pharmacologically or surgically. Penetrating keratoplasty (PKP) was reserved for more severe opacity. The main outcome measures were final best spectacle-corrected visual acuity (BSCVA), incidence of glaucoma, graft survival, and nystagmus rates.

RESULTS

Sixty eyes of 40 patients were included in the study. The median age of patients at presentation was 0.5 ± 20.7 months (range, 0.0-111.0 months), with a mean follow-up time of 75.8 ± 52.9 months (range, 12.1-225.3 months). Overall, final best spectacle-corrected visual acuity ranged from 0.1 logMAR to no light perception with 33 eyes (55.9%) achieving vision of 1.0 logMAR or better. Clear grafts at the last follow-up were obtained in 67.6% (25/37) of transplanted eyes, 76.0% (19/25) in Peters type I, and 50.0% (6/12) in Peters type II (P = 0.11). The probability of a clear graft at 10 years was 74.2% and 38.9% for type I and type II, respectively. Glaucoma was diagnosed in 33.3% eyes, 90.0% of which occurred after PKP. Nystagmus was highly associated with PKP intervention, occurring in 81.1% (30/37) of eyes undergoing PKP compared with 34.8% (8/23) of eyes with no PKP (P = 0.0003).

CONCLUSIONS

Visual rehabilitation in Peters anomaly remains a challenge, but outcomes can be optimized using a comprehensive clinical management algorithm according to disease severity.

The Use of Induced Pluripotent Stem Cells as a Model for Developmental Eye Disorders

Approximately one-third of childhood blindness is attributed to developmental eye disorders, of which 80% have a genetic cause. Eye morphogenesis is tightly regulated by a highly conserved network of transcription factors when disrupted by genetic mutations can result in severe ocular malformation. Human-induced pluripotent stem cells (hiPSCs) are an attractive tool to study early eye development as they are more physiologically relevant than animal models, can be patient-specific and their use does not elicit the ethical concerns associated with human embryonic stem cells. The generation of self-organizing hiPSC-derived optic cups is a major advancement to understanding mechanisms of ocular development and disease. Their development in vitro has been found to mirror that of the human eye and these early organoids have been used to effectively model microphthalmia caused by a VSX2 variant. hiPSC-derived optic cups, retina, and cornea organoids are powerful tools for future modeling of disease phenotypes and will enable a greater understanding of the pathophysiology of many other developmental eye disorders. These models will also provide an effective platform for identifying molecular therapeutic targets and for future clinical applications.

Updates on the molecular genetics of primary congenital glaucoma (Review)

Primary congenital glaucoma (PCG) is one of the primary causes of blindness in children and is characterized by congenital trabecular meshwork and anterior chamber angle dysplasia. While being a rare condition, PCG severely impairs the quality of life of affected patients. However, the pathogenesis of PCG remains to be fully elucidated. It has previously been indicated that genetic factors serve a critical role in the pathogenesis of PCG, although patients with PCG exhibit significant genetic heterogeneity. Mutations in the cytochrome P450 family 1 subfamily B member 1 gene have been implicated in PCG and further genes that have been reported to be involved in PCG are myocilin, forkhead box C1, collagen type I α1 chain and latent transforming growth factor β binding protein 2. The present review aims to provide an up to date understanding of the genes associated with PCG and the use of molecular technologies in the identification of such genes and mutations. This may pave the way for the development of preventative methods, early diagnosis and improved therapeutic strategies in PCG.

Exome Sequencing in a Swiss Childhood Glaucoma Cohort Reveals CYP1B1 and FOXC1 Variants as Most Frequent Causes

Purpose

The aim of this study was to investigate the molecular basis of childhood glaucoma in Switzerland to recommend future targeted genetic analysis in the Swiss population.

Methods

Whole-exome sequencing and copy number variation (CNV) analysis was performed in a Swiss cohort of 18 patients from 14 unrelated families. Identified variants were validated by Sanger sequencing and multiplex ligation-dependent probe amplification. Breakpoints of structural variants were determined by a microarray. A minigene assay was conducted for functional analysis of a splice site variant.

Results

A diagnosis of primary congenital glaucoma was made in 14 patients, of which six (43%) harbored pathogenic variants in CYP1B1, one (7%) a frameshift variant in FOXC1, and seven (50%) remained without a genetic diagnosis. Three patients were diagnosed with glaucoma associated with nonacquired ocular anomalies, of which two patients with mild ocular features of Axenfeld-Rieger syndrome harbored a FOXC1 duplication plus an additional FOXC1 missense variant, and one patient with a Barkan membrane remained without genetic diagnosis. A diagnosis of juvenile open-angle glaucoma was made in one patient, and genetic analysis revealed a FOXC1 duplication.

Conclusions

Sequencing of CYP1B1 and FOXC1, as well as analysis of CNVs in FOXC1, should be performed before extended gene panel sequencing.

Translational Relevance

The identification of the molecular cause of childhood glaucoma is a prerequisite for genetic counseling and personalized care for patients and families.

Revealing hidden genetic diagnoses in the ocular anterior segment disorders

Purpose

Ocular anterior segment disorders (ASDs) are clinically and genetically heterogeneous, and genetic diagnosis often remains elusive. In this study, we demonstrate the value of a combined analysis protocol using phenotypic, genomic, and pedigree structure data to achieve a genetic conclusion.

Methods

We utilized a combination of chromosome microarray, exome sequencing, and genome sequencing with structural variant and trio analysis to investigate a cohort of 41 predominantly sporadic cases.

Results

We identified likely causative variants in 54% (22/41) of cases, including 51% (19/37) of sporadic cases and 75% (3/4) of cases initially referred as familial ASD. Two-thirds of sporadic cases were found to have heterozygous variants, which in most cases were de novo. Approximately one-third (7/22) of genetic diagnoses were found in rarely reported or recently identified ASD genes including PXDN, GJA8, COL4A1, ITPR1, CPAMD8, as well as the new phenotypic association of Axenfeld–Rieger anomaly with a homozygous ADAMTS17 variant. The remainder of the variants were in key ASD genes including FOXC1, PITX2, CYP1B1, FOXE3, and PAX6.

Conclusions

We demonstrate the benefit of detailed phenotypic, genomic, variant, and segregation analysis to uncover some of the previously “hidden” heritable answers in several rarely reported and newly identified ocular ASD-related disease genes.

Phenotype expansion of heterozygous FOXC1 pathogenic variants toward involvement of congenital anomalies of the kidneys and urinary tract (CAKUT)

PURPOSE

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of chronic kidney disease in childhood and adolescence. We aim to identify novel monogenic causes of CAKUT.

METHODS

Exome sequencing was performed in 550 CAKUT-affected families.

RESULTS

We discovered seven FOXC1 heterozygous likely pathogenic variants within eight CAKUT families. These variants are either never reported, or present in <5 alleles in the gnomAD database with ~141,456 controls. FOXC1 is a causal gene for Axenfeld-Rieger syndrome type 3 and anterior segment dysgenesis 3. Pathogenic variants in FOXC1 have not been detected in patients with CAKUT yet. Interestingly, mouse models for Foxc1 show severe CAKUT phenotypes with incomplete penetrance and variable expressivity. The FOXC1 variants are enriched in the CAKUT cohort compared with the control. Genotype-phenotype correlations showed that Axenfeld-Rieger syndrome or anterior segment dysgenesis can be caused by both truncating and missense pathogenic variants, and the missense variants are located at the forkhead domain. In contrast, for CAKUT, there is no truncating pathogenic variant, and all variants except one are located outside the forkhead domain.

CONCLUSION

We thereby expanded the phenotype of FOXC1 pathogenic variants toward involvement of CAKUT, which can potentially be explained by allelism.

Primary congenital glaucoma in Denmark, 1977-2016

PURPOSE

To perform an epidemiological survey of all patients in Denmark diagnosed with primary congenital glaucoma (PCG) from 1977 to 2016.

METHODS

A retrospective, nationwide study based on a review of medical files of all children with PCG born in Denmark from 1977 to 2016. PCG was defined as glaucoma due to isolated angle dysgenesis affecting children from birth and including late onset/late recognized PCG, excluding glaucoma associated with other congenital abnormalities. Incidence and risk factors of PCG including gender, consanguinity, family history, ethnicity, comorbidity and prematurity were evaluated and stratified by decade (1977-1986, 1987-1996, 1997-2006 and 2007-2016). Age at first symptoms, age at diagnosis, age at time of first surgery and possible diagnostic delay were assessed.

RESULTS

Of 118 patients were identified, annual incidence of PCG was 4.8 per 100 000 live born. 62.3% of cases were bilateral. The relative risk (RR) of PCG was significantly higher in boys (62.7% of patients, RR 1.60 (95% CI 1.10-2.32)). 13.6% had comorbidity. Median age at time of first symptoms was 75 days, median age at time of diagnosis was 150 days and median diagnostic delay was 75 days with no significant difference throughout the decades. Unilateral cases presented symptoms and were diagnosed significantly later than bilateral cases.

CONCLUSION

We provide unique nation-based information on the incidence of PCG from a single country covering 40 years. Male gender was a risk factor. Diagnostic delay was unchanged throughout the 4 decades and a high percentage of comorbidity was revealed. Introducing a standardized paediatric screening of all PCG children should be considered.

Clinical utility of genetic testing in 201 preschool children with inherited eye disorders

Purpose

A key property to consider in all genetic tests is clinical utility, the ability of the test to influence patient management and health outcomes. Here we assess the current clinical utility of genetic testing in diverse pediatric inherited eye disorders (IEDs).

Methods

Two hundred one unrelated children (0–5 years old) with IEDs were ascertained through the database of the North West Genomic Laboratory Hub, Manchester, UK. The cohort was collected over a 7-year period (2011–2018) and included 74 children with bilateral cataracts, 8 with bilateral ectopia lentis, 28 with bilateral anterior segment dysgenesis, 32 with albinism, and 59 with inherited retinal disorders. All participants underwent panel-based genetic testing.

Results

The diagnostic yield of genetic testing for the cohort was 64% (ranging from 39% to 91% depending on the condition). The test result led to altered management (including preventing additional investigations or resulting in the introduction of personalized surveillance measures) in 33% of probands (75% for ectopia lentis, 50% for cataracts, 33% for inherited retinal disorders, 7% for anterior segment dysgenesis, 3% for albinism).

Conclusion

Genetic testing helped identify an etiological diagnosis in the majority of preschool children with IEDs. This prevented additional unnecessary testing and provided the opportunity for anticipatory guidance in significant subsets of patients.

Primary cilia deficiency in neural crest cells models anterior segment dysgenesis in mouse

Defects affecting tissues of the anterior segment (AS) of the eye lead to a group of highly debilitating disorders called Anterior Segment Dysgenesis (ASD). Despite the identification of some causative genes, the pathogenesis of ASD remains unclear. Interestingly, several ciliopathies display conditions of the AS. Using conditional targeting of Ift88 with Wnt1-Cre, we show that primary cilia of neural crest cells (NCC), precursors of most AS structures, are indispensable for normal AS development and their ablation leads to ASD conditions including abnormal corneal dimensions, defective iridocorneal angle, reduced anterior chamber volume and corneal neovascularization. Mechanistically, NCC cilia ablation abolishes hedgehog (Hh) signaling in the periocular mesenchyme (POM) canonically activated by choroid-secreted Indian Hh, reduces proliferation of POM cells surrounding the retinal pigment epithelium and decreases the expression of Foxc1 and Pitx2, two transcription factors identified as major ASD causative genes. Thus, we uncovered a signaling axis linking cilia and ASD.