Brittle cornea syndrome: current perspectives

Biallelic novel variants in ZNF469 causing Brittle Cornea Syndrome 1: a detailed report of an Indian patient

BACKGROUND

Variations in ZNF469 have been associated with Brittle Cornea Syndrome that presents with bluish sclera, loss of vision after trivial trauma, arachnodactyly, and joint laxity.

MATERIALS AND METHODS

Detailed medical and family history, physical examination, and molecular analysis.

RESULTS

A 21-year-old female presented with bluish discoloration of sclera, diminution of vision following trivial trauma in childhood along with hearing loss and systemic features of arachnodactyly and joint laxity. Clinical diagnosis of brittle cornea syndrome was made which was molecularly proven using next-generation sequencing which identified compound heterozygosity in ZNF469 for pathogenic and likely pathogenic nonsense variants. One variant namely NM_001367624.2:c.5882dup was identified in the exon 3 which was novel and classified as likely pathogenic according to American College of Medical Genetics (ACMG) criteria for variant classification. Another variant NM_001367624.2:c.8992C>T in the exon 2 was classified as pathogenic for Brittle Cornea Syndrome 1.

CONCLUSIONS

The report adds to the allelic heterogeneity in ZNF469 causative of Brittle Cornea Syndrome 1 and shall acquaint the physicians about this potentially vision threatening, underdiagnosed, rare syndrome.

Penetrating keratoplasty in brittle Cornea syndrome: Case series and review of the literature

It concerns three siblings (two 28 year old twin boys and a 25 year old woman) who presented a previous history of rupture of eyeball in one eye and very poor vision in the other. At the first ophthalmoscopic and instrumental evaluation, three patients presented with bluish sclera and keratoglobus in the intact eye. A genetic analysis with whole exome sequencing was then performed on the three siblings, identifying a biallelic variant of the PRDM5 gene that led to the diagnosis of Brittle Cornea Syndrome (BCS), a rare autosomal recessive disorder characterized by corneal thinning and blue sclera. To preserve the only intact eye from possible breakage, the three siblings were trained in using protective measures (polycarbonate goggles etc.) to carry out close monitoring of symptoms and were asked to continue with follow-up visits for ocular and systemic diseases associated with BCS. Given the poor best corrected visual acuity achievable with glasses and contact lenses, penetrating keratoplasty was performed, achieving good visual acuity maintained in the 2-year follow-up in two of the three patients. Knowledge of this pathology and its clinical manifestations is essential for early diagnosis and correct management of this rare but very debilitating pathology. To our knowledge, this is the first case series of BCS reported in an Albanian population.

Identification and Management of a Novel PRDM5 Gene Pathologic Variant in a Family With Brittle Cornea Syndrome

PURPOSE

The aim of this study was to report a novel PRDM5 pathologic variant and ophthalmic findings in a family with 3 children diagnosed with brittle cornea syndrome (BCS). Histopathologic findings and surgical outcome of a child with BCS who underwent full-thickness corneal transplant are described.

METHODS

This is an observational case report of a nonconsanguineous Laotian family with 3 siblings diagnosed with BCS. Data collected included visual acuity, cycloplegic refraction, slit-lamp biomicroscopy, dilated fundus examination, corneal pachymetry, corneal topography, and general medical findings. Targeted testing through PRDM5 gene sequencing with copy number variation detection was conducted.

RESULTS

The 3 siblings included a 12-year-old boy and 8- and 6-year-old sisters, all of whom presented with myopia, blue-tinted sclerae, thin corneas, and variable corneal scarring. All 3 affected children were found to be homozygous for the PRDM5 gene variant c.1117_1123delinsTTTAATGCTTACAAATGTTTG p.Asp373Phefs*57. Coding sequences of PRDM5 and ZNF469 genes were sequenced in their entirety, and this was the only pathologic variant present in this family. The youngest affected sister developed persistent hydrops with severely decreased vision and underwent penetrating keratoplasty. Histopathology revealed severe corneal thinning, diffuse absence of Bowman layer, and ruptured Descemet membrane scrolls.

CONCLUSIONS

Three siblings with clinical signs of BCS, including corneal thinning, myopia, and blue sclerae, were found to have a novel PRDM5 gene pathologic variant. This pathologic variant has not been previously reported, although 1 downstream nonsense pathologic variant has been reported as pathogenic. The similar phenotypes in all affected patients support the pathogenicity of this variant. Surgical management of BCS presents unique challenges due to severe tissue fragility.

Characteristics of brittle cornea syndrome by multimodal imaging modalities: a case report

BACKGROUND

A report of a Brittle cornea syndrome (BCS) case with bluish scleral discoloration, keratoglobus, and myopia based on multimodal imaging modalities including in vivo confocal microscopy (IVCM), high-definition optical coherence tomography (HD-OCT) and scheimpflug corneal densitometry analysis.

CASE PRESENTATION

A 36-year-old Chinese female patient presented with significant bluish discoloration of the sclera in both eyes, extreme corneal thinning with increased corneal curvature, increased central corneal densitometry, and nystagmus. She also had scoliosis, severe osteoporosis, and thyroid disease.

CONCLUSIONS

Timely diagnosis, early detection, and detailed follow-up are essential for BCS. There has been no report of a BCS evaluation performed by IVCM and corneal densitometry methods thus far in the literature. Furthermore, multimodal imaging can offer a more comprehensive view of BCS and contribute to a deeper understanding of the disease. Interestingly, this is a rare case of BCS in an adult with good vision, an intact cornea, and nystagmus.

Biomechanics of keratoconus: Two numerical studies

BACKGROUND

The steep cornea in keratoconus can greatly impair eyesight. The etiology of keratoconus remains unclear but early injury that weakens the corneal stromal architecture has been implicated. To explore keratoconus mechanics, we conducted two numerical simulation studies.

METHODS

A finite-element model describing the five corneal layers and the heterogeneous mechanical behaviors of the ground substance and lamellar collagen-fiber architecture in the anterior and posterior stroma was developed using the Holzapfel-Gasser-Ogden constitutive model. The geometry was from a healthy subject. Its stroma was divided into anterior, middle, and posterior layers to assess the effect of changing regional mechanical parameters on corneal displacement and maximum principal stress under intraocular pressure. Specifically, the effect of softening an inferocentral corneal button, the collagen-based tissues throughout the whole cornea, or specific stromal layers in the button was examined. The effect of simply disorganizing the orthogonally-oriented posterior stromal fibers in the button was also assessed. The healthy cornea was also subjected to eye rubbing-like loading to identify the corneal layer(s) that experienced the most tensional stress.

RESULTS

Conical deformation and corneal thinning emerged when the corneal button or the mid-posterior stroma of the button underwent gradual softening or when the collagen fibers in the mid-posterior stroma of the button were dispersed. Softening the anterior layers of the button or the whole cornea did not evoke conical deformation. Button softening greatly increased and disrupted the stress on Bowman's membrane while mid-posterior stromal softening increased stress in the anterior layers. Eye rubbing profoundly stressed the deep posterior stroma while other layers were negligibly affected.

DISCUSSION

These observations suggest that keratoconus could be initiated, at least partly, by mechanical instability/damage in the mid-posterior stroma that then imposes stress on the anterior layers. This may explain why subclinical keratoconus is marked by posterior but not anterior elevation on videokeratoscopy.

High risk and low prevalence diseases: Open globe injury

INTRODUCTION

Open globe injury (OGI) is a rare but serious condition that carries with it a high rate of morbidity.

OBJECTIVE

This review highlights the pearls and pitfalls of OGI, including presentation, diagnosis, and management in the emergency department (ED) based on current evidence.

DISCUSSION

OGI refers to full-thickness injury to the layers of the eye. OGI can be caused by blunt or sharp trauma, and subtypes include penetration, perforation, intraocular foreign body (IOFB), globe rupture, or mixed types. OGI is more common in males and usually secondary to work-related injury, but in women it is most commonly associated with falls. Emergency clinicians should first assess for and manage other critical, life-threatening injuries. Following this assessment, a thorough eye examination is necessary. Computed tomography (CT) may suggest the disease, but it cannot definitively exclude the diagnosis. While point-of-care ultrasound (POCUS) is highly sensitive and specific for some findings in OGI, its use is controversial due to potential globe content extrusion. Management includes protecting the affected eye from further injury, preventing Valsalva maneuvers that could extrude ocular contents, updating tetanus vaccination status, administering broad-spectrum antibiotics, and ophthalmology consultation for surgical intervention to prevent the sequelae of blindness and endophthalmitis.

CONCLUSION

An understanding of OGI can assist emergency clinicians in diagnosing and managing this sight-threatening traumatic process.

Extracutaneous features and complications of the Ehlers-Danlos syndromes: A systematic review

Introduction

The Ehlers-Danlos syndromes (EDS) comprise a group of inherited connective tissue disorders presenting with variable fragility to skin, soft tissue, and certain internal organs, which can cause significant complications, particularly arterial rupture, bowel perforation and joint difficulties. Currently, there are 14 proposed subtypes of EDS, with all except one subtype (hypermobile EDS) having an identified genetic etiology. An understanding of the extracutaneous features and complications within each subtype is key to maximizing clinical care and reducing the risk of further complications.

Methods

A systematic review of EDS-related extracutaneous features and complications was undertaken.

Results

We identified 839 EDS cases that met the inclusion criteria. We noted a high prevalence of joint hypermobility amongst kyphoscoliotic (39/39, 100%), spondylodysplastic (24/25, 96.0%), and hypermobile (153/160, 95.6%) EDS subtypes. The most common musculoskeletal complications were decreased bone density (39/43, 90.7%), joint pain (217/270, 80.4%), and hypotonia/weakness (79/140, 56.4%). Vascular EDS presented with cerebrovascular events (25/153, 16.3%), aneurysm (77/245, 31.4%), arterial dissection/rupture (89/250, 35.5%), and pneumothorax/hemothorax. Chronic pain was the most common miscellaneous complication, disproportionately affecting hypermobile EDS patients (139/157, 88.5%). Hypermobile EDS cases also presented with chronic fatigue (61/63, 96.8%) and gastrointestinal complications (57/63, 90.5%). Neuropsychiatric complications were noted in almost all subtypes.

Discussion

Understanding the extracutaneous features and complications of each EDS subtype may help diagnose and treat EDS prior to the development of substantial comorbidities and/or additional complications.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022308151, identifier CRD42022308151.

Ehlers-Danlos syndromes and their manifestations in the visual system

Ehlers-Danlos syndrome (EDS) is a rare, genetically variable, heterogenous group of (currently recognized) thirteen connective tissue disorders characterized by skin hyperextensibility, tissue fragility, and generalized joint hypermobility. In addition to these commonly recognized phenotypes, recent studies have notably highlighted variable ophthalmic features in EDS. In this review, we comprehensively gather and discuss the ocular manifestations of EDS and its thirteen subtypes in the clinical setting.

Brittle cornea syndrome: A tale of three brothers

Brittle cornea syndrome (BCS) is a genetic connective tissue disorder with discernible ocular features such as blue scleral and thin cornea that predominantly presents in younger children. We herein describe cases of three siblings with BCS, two of whom presented to us with open globe injuries following trivial trauma. Clinical examination of the other eye in both showed diffusely thin corneas and blue sclera. A systemic evaluation revealed sensorineural hearing loss and hyperextensible joints. The third sibling was screened and found to have features concurrent with BCS. This report highlights the challenges faced in the management of ocular injuries and consecutive complications in these patients.

Spontaneous Rupture of an Infant's Cornea

A 2-year-old boy of consanguineous parents presented with spontaneous globe rupture of the right eye that initially raised suspicions of child abuse. Other ocular and extraocular findings, a similar history of corneal rupture following minor trauma in his sibling, and genetic analysis confirmed the diagnosis of brittle cornea syndrome. [J Pediatr Ophthalmol Strabismus. 2022;59(4):e42-e45.].

Association Between Keratoconus and Shoulder Dislocation: A Cross-Sectional Study

Introduction Few studies have highlighted the correlation between shoulder dislocation and keratoconus (KC). This study aimed to examine the association between KC and shoulder dislocation using patients with KC and matched controls. Methods This cross-sectional study was conducted at Jordan University Hospital. We included patients diagnosed with KC from Jordan University Hospital's Ophthalmology Department between 2015 and 2018. We also included age- and sex-matched controls recruited randomly from fitness centers and shopping malls. All participants had complete ophthalmic and orthopedic assessments. KC was diagnosed by clinical examination followed by Pentacam (Scheimpflug Images, Oculyzer, WaveLight, Alcon, USA) confirmation. Results A total of 238 patients, with a mean age of 29.53 (±11.20) years, were included in this study. They were 144 (60.5%) men and 94 (39.5%) women. Moreover, 120 (50.4%) had KC while 118 (49.6%) did not have KC. Only 11 (4.6%) patients had previous shoulder dislocation. We did not find a significant difference in the frequency of shoulder dislocation between patients with and without KC (p = 0.512). Conclusion This study provides further evidence on the lack of association between shoulder dislocation and KC, an association that was presumed due to shared collagen characteristics.

Surgical technique for the management of corneal perforation in brittle cornea

Brittle cornea syndrome is among the few special scenarios in ophthalmology that are a nightmare not only for the operating surgeon but also for the patient. Here, the thin and fragile corneas are unable to maintain the shape and structural integrity of the globe and are more prone to minor traumatic or spontaneous corneal perforations. Suturing a brittle cornea and closure of the corneal perforation in a brittle cornea are very challenging requiring the utmost care and special precautions. If proper measures are not taken during the surgery, it may be difficult to salvage the eye. Hence, it is imperative to diagnose appropriately, suture effectively, taking necessary preventive measures in salvaging these corneas. This manuscript aims at providing tips for handling brittle corneal perforations. It will also discuss the problems encountered during surgery, highlight the suturing techniques that can be customized, and finally give an insight into postoperative care.

A Mouse Model of Brittle Cornea Syndrome caused by mutation in Zfp469

Brittle cornea syndrome (BCS) is a rare recessive condition characterised by extreme thinning of the cornea and sclera. BCS results from loss-of-function mutations in the poorly understood genes ZNF469 or PRDM5. In order to determine the function of ZNF469 and to elucidate pathogenic mechanisms, we used genome editing to recapitulate a human ZNF469 BCS mutation in the orthologous mouse gene Zfp469. Ophthalmic phenotyping showed that homozygous Zfp469 mutation causes significant central and peripheral corneal thinning arising from reduced stromal thickness. Expression of key components of the corneal stroma in primary keratocytes from Zfp469^BCS/BCS mice is affected, including decreased Col1a1 and Col1a2 expression. This alters the collagen type I/collagen type V ratio and results in collagen fibrils with smaller diameter and increased fibril density in homozygous mutant corneas, correlating with decreased biomechanical strength in the cornea. Cell-derived matrices generated by primary keratocytes show reduced deposition of collagen type I, offering an in vitro model for stromal dysfunction. Work remains to determine whether modulating ZNF469 activity will have therapeutic benefit in BCS or in conditions such as keratoconus in which the cornea thins progressively.

This article has an associated First Person interview with the first author of the paper.

Summary: A mouse model of brittle cornea syndrome was created to elucidate molecular mechanisms underlying the pathology of this rare connective tissue disorder in which extremely thin corneas rupture, causing irreversible blindness.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.

Case report of a PRDM5 linked brittle cornea syndrome type 2 in association with a novel SLC6A5 mutation

A 3-year-old girl presenting with blue sclera, hyperlaxity and developmental dysplasia of hip was found to have bilateral corneal thinning with astigmatism and keratoconus. By clinical exome sequencing, a frameshift mutation c.713_716 del TTTG p.(Val238Alafs*35) in PRDM5 gene causing brittle cornea syndrome 2 and a novel frameshift mutation c.401dup p.(Ser135Glufs*53) in SLC6A5 gene causing Hyperekplexia 3 were identified. No features of hyperekplexia were identified in proband. The novel homozygous mutation of SLC6A5 gene in the proband was presently asymptomatic but they were apprised of the possibility of developing neurological symptoms in the later years.

Whole-Exome Sequencing Identifies Novel Compound Heterozygous ZNF469 Mutations in Two Siblings with Mild Brittle Cornea Syndrome

Connective tissue diseases, including osteogenesis imperfecta (OI) and Ehlers-Danlos syndrome (EDS), exhibit a high degree of clinical and genetic heterogeneity. We report two sisters with blue sclerae, joint hypermobility and hearing loss. Whole-exome sequencing identified two compound heterozygous ZNF469 loss-of-function mutations due to a frameshift. Since these findings indicate the presence of brittle cornea syndrome (BCS), we performed ocular optical coherence tomography (OCT) and pachymetry, which revealed a moderate decrease in corneal thickness. While only one traumatic fracture was observed in each of the patients, a detailed skeletal assessment indicated no specific patterns of bone mass and microstructure reduction as well as normal bone turnover markers. Taken together, our findings point to a mild form of brittle cornea syndrome with a phenotype compatible with the extraskeletal features of OI but also with EDS.