More than meets the eye: Expanding and reviewing the clinical and mutational spectrum of brittle cornea syndrome

Brittle cornea syndrome: A novel mutation

Purpose

To report the clinical, tomographic, histopathological and genetic findings of a patient with brittle cornea syndrome and a novel mutation in the ZNF469 gene likely implicated in the development of this disorder.

Methods

A 64-year-old man presented with a two-year history of worsening vision in both eyes. The patient and his son were examined by imaging and genetic analysis.

Results

The patient exhibited persistent ocular irritation, decreased vision, corneal epithelial defects and corneal stromal opacity. Confocal microscopy revealed that the anterior corneal stroma had a large amount of highly reflective and striated tissue. However, his son had no symptoms. Genetic analysis identified a heterozygous c.1781C > T:p.P594L variation in the ZNF469 gene.

Conclusions

We reported a novel mutation in the ZNF469 gene (c.1781C > T:p.P594L) in a patient with brittle cornea syndrome from China, which enriched the spectrum of ZNF469 variants implicated in brittle cornea syndrome.

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.

An Eye into the Aorta: The Role of Extracellular Matrix Regulatory Genes ZNF469 and PRDM5, from Their Previous Association with Brittle Cornea Syndrome to Their Novel Association with Aortic and Arterial Aneurysmal Diseases

The extracellular matrix is a complex network of proteins and other molecules that are essential for the support, integrity, and structure of cells and tissues within the human body. The genes ZNF469 and PRDM5 each produce extracellular-matrix-related proteins that, when mutated, have been shown to result in the development of brittle cornea syndrome. This dysfunction results from aberrant protein function resulting in extracellular matrix disruption. Our group recently identified and published the first known associations between variants in these genes and aortic/arterial aneurysms and dissection diseases. This paper delineates the proposed effects of mutated ZNF469 and PRDM5 on various essential extracellular matrix components, including various collagens, TGF-B, clusterin, thrombospondin, and HAPLN-1, and reviews our recent reports associating single-nucleotide variants to these genes' development of aneurysmal and dissection diseases.

Clinical-Genomic Analysis of 1261 Patients with Ehlers-Danlos Syndrome Outlines an Articulo-Autonomic Gene Network (Entome)

Systematic evaluation of 80 history and 40 history findings diagnosed 1261 patients with Ehlers-Danlos syndrome (EDS) by direct or online interaction, and 60 key findings were selected for their relation to clinical mechanisms and/or management. Genomic testing results in 566 of these patients supported EDS relevance by their differences from those in 82 developmental disability patients and by their association with general rather than type-specific EDS findings. The 437 nuclear and 79 mitochondrial DNA changes included 71 impacting joint matrix (49 COL5), 39 bone (30 COL1/2/9/11), 22 vessel (12 COL3/8VWF), 43 vessel-heart (17FBN1/11TGFB/BR), 59 muscle (28 COL6/12), 56 neural (16 SCN9A/10A/11A), and 74 autonomic (13 POLG/25porphyria related). These genes were distributed over all chromosomes but the Y, a network analogized to an 'entome' where DNA change disrupts truncal mechanisms (skin constraint, neuromuscular support, joint vessel flexibility) and produces a mirroring cascade of articular and autonomic symptoms. The implied sequences of genes from nodal proteins to hypermobility to branching tissue laxity or dysautonomia symptoms would be ideal for large language/artificial intelligence analyses.

Variants in the ZNF469 gene in families with Brittle cornea syndrome and keratoconus

Background

Brittle cornea syndrome 1 (BCS1) is a rare autosomal recessive disorder characterized by corneal and sclera thinning and fragility that is caused by zinc finger protein 469 (ZNF469) gene mutation. Keratoconus is another disease related to corneal thinning. Several reports have linked ZNF469 variants and keratoconus. We recruited a four-generation BCS1 family and two keratoconus families to explore pathogenic ZNF469 variants.

Methods

This study included 11 members from a family with BCS1, 2 families with keratoconus, 368 sporadic keratoconus patients and 325 unrelated healthy controls. Whole exome sequencing of DNA from peripheral blood and cross species conservation analysis was used to investigate and verify ZNF469 variants.

Results

A new homozygous frameshift mutation c. 6727del (p.Asp2243Thr fs*8) in ZNF469 was detected in the BSC1 family. Two ZNF469 heterozygous variants g.88494671G > A (c.793G > A, p.G265S, rs754776767) were detected in keratoconus family 1 and a heterozygous missense variant g.88498262G > A (c.4384G > A, p.D1462 N, rs577890057) was found in keratoconus family 2. Based on the American College of Medical Genetics and Genomics guidelines, rs577890057 and rs754776767 were predicted to be variants of uncertain significance. c. 6727del (p. Asp2243Thr fs*8) in ZNF469 was identified to be pathogenic.

Conclusions

We identified a new homozygous frameshift mutation and two heterozygous missense variations in ZNF469 in the three families. Our findings extend the spectrum of ZNF469 variants associated with keratoconus.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

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.

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.

The Association of Novel Single-Nucleotide Variants in the Collagen Matrix-Encoding Gene PRDM5 with Aortic Aneurysmal Disease

Thoracic aortic aneurysms are clinical conditions that are associated with severe clinical endpoints including dissection and rupture, potentially leading to sudden death. Contrary to their abdominal counterparts, thoracic aortic aneurysms are well-recognized to have a genetic basis underlying their development. Among all patients with aneurysmal disease who underwent clinical genetic screening in our program (N = 145), two patients were found to have variants of uncertain significance (VUS) in the PRDM5 gene. This gene is responsible for multiple regulatory functions in extracellular matrix development, and this is the first report, to our knowledge, to associate this gene with aortopathy.

New ZNF469 Mutations in Spanish Siblings With Brittle Cornea Syndrome

PURPOSE

The aim of this study was to describe the clinical, tomographic, and genetic findings of 2 Spanish siblings with brittle cornea syndrome and report a new mutation of gene ZNF469 implicated in the development of this disorder.

METHODS

In this study, 2 male siblings who had been diagnosed with brittle cornea syndrome underwent ophthalmologic and genetic assessment.

RESULTS

A novel homozygous deletion c.2972del, p.(Pro991Hisfs62) in the ZNF469 gene was identified in a Spanish family.

CONCLUSIONS

This is the first report of a ZNF469 mutation in a Spanish family causing brittle cornea syndrome. The discovery of this new mutation amplifies the spectrum of ZNF469 variants implicated in this syndrome.

NRF2 Shortage in Human Skin Fibroblasts Dysregulates Matrisome Gene Expression and Affects Collagen Fibrillogenesis

NRF2 is a master regulator of the antioxidative response that was recently proposed as a potential regulator of extracellular matrix (ECM) gene expression. Fibroblasts are major ECM producers in all connective tissues, including the dermis. A better understanding of NRF2-mediated ECM regulation in skin fibroblasts is thus of great interest for skin homeostasis maintenance and aging protection. In this study, we investigate the impact of NRF2 downregulation on matrisome gene expression and ECM deposits in human primary dermal fibroblasts. RNA-sequencing‒based transcriptome analysis of NRF2 silenced dermal fibroblasts shows that ECM genes are the most regulated gene sets, highlighting the relevance of the NRF2-mediated matrisome program in these cells. Using complementary light and electron microscopy methods, we show that NRF2 deprivation in dermal fibroblasts results in reduced collagen I biosynthesis and impacts collagen fibril deposition. Moreover, we identify ZNF469, a putative transcriptional regulator of collagen biosynthesis, as a target of NRF2. Both ZNF469 silenced fibroblasts and fibroblasts derived from Brittle Corneal Syndrome patients carrying variants in ZNF469 gene show reduced collagen I gene expression. Our study shows that NRF2 orchestrates matrisome expression in human skin fibroblasts through direct or indirect transcriptional mechanisms that could be prioritized to target dermal ECM homeostasis in health and disease.

A novel homozygous ZNF469 variant causing brittle cornea syndrome is associated with corneal ectasias in heterozygous carriers

AIM

To describe a family segregating a novel truncating ZNF469 homozygous mutation causing brittle cornea syndrome type 1 in a male patient and associated with corneal ectasia in his two heterozygous young children.

METHODS

A 49-year-old affected male and his 12- and 8-year-old, apparently healthy, siblings underwent phenotypic and genetic assessment. An Oculus Pentacam Scheimpflug topographer system was employed for keratometries and central corneal thickness measurements. Exome sequencing was performed in DNA from the index case with subsequent Sanger sequencing confirmation of the ZNF469 gene causal variant in his relatives.

RESULTS

The index case had a history of bilateral keratoglobus, corneal perforations, bilateral hypoacusia, and skeletal anomalies. His two children exhibited topographic anomalies compatible with keratoconus suspects as well as mild skeletal anomalies. Genetic analysis identified a novel homozygous c.2340delC variant in the ZNF469 gene, which predicts a p.(Arg781Glufs*19) truncated protein. Sanger sequencing identified heterozygosity for the c.2340delC variant in DNA from both siblings.

CONCLUSION

Our results expand the mutational spectrum associated with brittle cornea syndrome and provide the first demonstration of early corneal anomalies in subjects carrying monoallelic ZNF469 variants.

The Ehlers–Danlos Syndromes against the Backdrop of Inborn Errors of Metabolism

The Ehlers–Danlos syndromes are a group of multisystemic heritable connective tissue disorders with clinical presentations that range from multiple congenital malformations, over adolescent-onset debilitating or even life-threatening complications of connective tissue fragility, to mild conditions that remain undiagnosed in adulthood. To date, thirteen different EDS types have been recognized, stemming from genetic defects in 20 different genes. While initial biochemical and molecular analyses mainly discovered defects in genes coding for the fibrillar collagens type I, III and V or their modifying enzymes, recent discoveries have linked EDS to defects in non-collagenous matrix glycoproteins, in proteoglycan biosynthesis and in the complement pathway. This genetic heterogeneity explains the important clinical heterogeneity among and within the different EDS types. Generalized joint hypermobility and skin hyperextensibility with cutaneous fragility, atrophic scarring and easy bruising are defining manifestations of EDS; however, other signs and symptoms of connective tissue fragility, such as complications of vascular and internal organ fragility, orocraniofacial abnormalities, neuromuscular involvement and ophthalmological complications are variably present in the different types of EDS. These features may help to differentiate between the different EDS types but also evoke a wide differential diagnosis, including different inborn errors of metabolism. In this narrative review, we will discuss the clinical presentation of EDS within the context of inborn errors of metabolism, give a brief overview of their underlying genetic defects and pathophysiological mechanisms and provide a guide for the diagnostic approach.

Value of second opinion subspecialty radiology consultation in suspected abdominal medium vessel vasculitis

PURPOSE

To perform a descriptive analysis of individuals with suspected Polyarteritis nodosa (PAN) referred for second opinion imaging consultation.

METHODS

A retrospective observational cohort study was performed at a single institution. A consecutive sample was performed of individuals who underwent a second opinion CT or MR angiography subspecialty radiologist consultation between January 2008 and September 2019 for suspected abdominal medium vessel vasculitis. Demographic, clinical, and imaging data were collected. Clinical and imaging findings were reported for PAN, small vessel vasculitis, and "non-vasculitis" groups. Agreement and diagnostic accuracy between final clinical and second opinion imaging diagnoses for PAN were determined. Two-tailed t-tests with a significant p-value < 0.05 were utilized.

RESULTS

Of the 58 participants, 9 were clinically diagnosed with PAN, 11 with small vessel vasculitis (including lupus, IgA, and ANCA-associated vasculitis), and 38 with non-vasculitis diagnoses. The non-vasculitis group included 15 SAM, 3 FMD, and 1 SAM-FMD spectrum diagnoses. Higher C-reactive protein level (51 vs 17, p = 0.04) and superior mesenteric artery involvement (56% vs 21%, p = 0.04) were more common in PAN than non-vasculitis diagnoses, while arterial dissection (40% vs 0%, p = 0.02) and celiac vasculature involvement (53% vs 0%, p = 0.003) were more common in the non-vasculitis group. There was 88% agreement (51/58; Cohen's kappa 0.56); sensitivity was 67% [95%-confidence interval (CI) 30-93%] and specificity was 92% (95%-CI 80-98%).

CONCLUSION

Isolated celiac artery involvement and arterial dissection were more common in non-inflammatory vasculopathies than PAN. Our findings highlight the need for multidisciplinary collaboration and awareness of the diverse findings of abdominal vasculopathies.

Does brittle cornea syndrome have a bone fragility phenotype?

Brittle cornea syndrome is a rare recessively inherited disorder (a sub-type of Ehlers-Danlos syndrome) with a clinical presentation dominated by corneal fragility and deafness. There have been suggestions that it may also have a bone fragility phenotype, but there has been little detailed description. We describe two siblings with brittle cornea syndrome due to compound heterozygous mutations in ZNF469 who had sustained ten or more fractures, the majority before the age of 15. When investigated as adults they had osteopenia, with lower z-scores than their parents who each carried one mutation. A bone biopsy from one sibling showed reduced cortical porosity. Both parents, who were heterozygous mutation carriers, had also suffered fractures but had normal bone density. This data supports the view that brittle cornea syndrome may have a bone fragility phenotype.

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.