Absence of Collagen Flowers on Electron Microscopy and Identification of (Likely) Pathogenic COL5A1 Variants in Two Patients

Novel COL5A1 variants and associated disease phenotypes in dogs with classical Ehlers-Danlos syndrome

BACKGROUND

Human patients with Ehlers-Danlos syndrome (EDS) are categorized into subtypes based on causative genetic variants and phenotypes. The classical form of EDS, primarily caused by variants in COL5A1 or COL5A2, is a very common subtype in people but is poorly characterized in dogs.

OBJECTIVE

Describe likely causal COL5A1 variants in dogs with classical EDS, summarize clinical histories, discuss potential disease mechanisms, and draw conclusions about disease prognosis.

ANIMALS

Seven client-owned dogs that exhibited clinical signs of classical EDS.

METHODS

Clinical information was recorded from medical records and communication with attending veterinarians and dog owners. To identify potential causal gene sequence variants whole-genome sequence analyses (n = 6) or Sanger sequencing (n = 1) were performed on DNA isolated from the probands. Pathological abnormalities in skin biopsy samples were assessed using histology and electron microscopy in 3 dogs.

RESULTS

Six distinct heterozygous COL5A1 sequence variants were identified. The most common clinical signs included fragile skin (n = 7), hyperextensible skin (n = 7), joint hypermobility (n = 6), and atrophic scars (n = 5). The median age at last follow-up or death was 12 years (range, 6.5-14 years). Ultrastructural abnormalities in dermal collagen differed among dogs with different COL5A1 variants.

CONCLUSION AND CLINICAL IMPORTANCE

We describe the genotypic and phenotypic spectrum of the classical subtype of EDS by identifying 6 novel COL5A1 variants in conjunction with detailed clinical histories that included long-term follow-up information in 7 dogs.

Genetic complexity of diagnostically unresolved Ehlers-Danlos syndrome

BACKGROUND

The Ehlers-Danlos syndromes (EDS) are heritable disorders of connective tissue (HDCT), reclassified in the 2017 nosology into 13 subtypes. The genetic basis for hypermobile Ehlers-Danlos syndrome (hEDS) remains unknown.

METHODS

Whole exome sequencing (WES) was undertaken on 174 EDS patients recruited from a national diagnostic service for complex EDS and a specialist clinic for hEDS. Patients had already undergone expert phenotyping, laboratory investigation and gene sequencing, but were without a genetic diagnosis. Filtered WES data were reviewed for genes underlying Mendelian disorders and loci reported in EDS linkage, transcriptome and genome-wide association studies (GWAS). A genetic burden analysis (Minor Allele Frequency (MAF) <0.05) incorporating 248 Avon Longitudinal Study of Parents and Children (ALSPAC) controls sequenced as part of the UK10K study was undertaken using TASER methodology.

RESULTS

Heterozygous pathogenic (P) or likely pathogenic (LP) variants were identified in known EDS and Loeys-Dietz (LDS) genes. Multiple variants of uncertain significance where segregation and functional analysis may enable reclassification were found in genes associated with EDS, LDS, heritable thoracic aortic disease (HTAD), Mendelian disorders with EDS symptomatology and syndromes with EDS-like features. Genetic burden analysis revealed a number of novel loci, although none reached the threshold for genome-wide significance. Variants with biological plausibility were found in genes and pathways not currently associated with EDS or HTAD.

CONCLUSIONS

We demonstrate the clinical utility of large panel-based sequencing and WES for patients with complex EDS in distinguishing rare EDS subtypes, LDS and related syndromes. Although many of the P and LP variants reported in this cohort would be identified with current panel testing, they were not at the time of this study, highlighting the use of extended panels and WES as a clinical tool for complex EDS. Our results are consistent with the complex genetic architecture of EDS and suggest a number of novel hEDS and HTAD candidate genes and pathways.

Dermatologic manifestations and diagnostic assessments of the Ehlers-Danlos syndromes: A clinical review

BACKGROUND

The Ehlers-Danlos syndromes (EDSs) comprise a group of connective tissue disorders that manifest with skin hyperextensibility, easy bruising, joint hypermobility and fragility of skin, soft tissues, and some organs. A correct assessment of cutaneous features along with the use of adjunct technologies can improve diagnostic accuracy.

OBJECTIVES

To systematically review the cutaneous features and adjunct investigations of EDS.

METHODS

A search of PubMed and Web of Science for EDS-related cutaneous features and additional investigations was undertaken from publication of the 2017 International Classification of EDS until January 15, 2022.

RESULTS

One-hundred-and-forty studies involved 839 patients with EDS. The EDS female-to-male ratio was 1.36:1 (P < .001). A high prevalence of skin hyperextensibility, bruising, and soft skin were noted. Most patients with vascular Ehlers-Danlos syndrome showed venous visibility, skin fragility, and acrogeria. Classical EDS showed subcutaneous spheroids and molluscoid pseudotumours. In patients that underwent skin biopsies, only 30.3% and 71.4% showed features suggestive of EDS using light microscopy and transmission electron microscopy, respectively.

LIMITATIONS

Retrospective study and small cases numbers for some EDS-subtypes.

CONCLUSIONS

An accurate clinical diagnosis increases the chances of a molecular diagnosis, particularly for rarer EDS subtypes, whilst decreasing the need for genetic testing where there is a low clinical suspicion for a monogenic EDS-subtype.

The role of cutaneous manifestations in the diagnosis of the Ehlers-Danlos syndromes

The Ehlers-Danlos syndromes (EDS) comprise a group of inherited connective tissue disorders presenting with features of skin hyperextensibility, joint hypermobility, abnormal scarring and fragility of skin, blood vessels and some organs. The disease is generally diagnosed through the cluster of clinical features, though the addition of genetic analysis is the gold standard for diagnosis of most subtypes. All subtypes display skin manifestations, which are essential to the accurate clinical diagnosis of the condition. Furthermore, cutaneous features can be the first and/or only presenting feature in some cases of EDS and thus understanding these signs is vital for diagnosis. This review focuses on particular cutaneous features of each EDS subtype and their clinical importance. Provision of a specific diagnosis is important for management, prognosis and genetic counselling, often for family members beyond the individual.

A patient with a novel pathogenic variant in COL5A1 exhibiting prominent vascular and cardiac features

The Ehlers-Danlos Syndromes (EDS) are a group of inherited connective tissue disorders with a worldwide prevalence of 1 in 2500 to 1 in 5000 births irrespective of sex or ethnicity. Fourteen subtypes of Ehlers-Danlos Syndrome (EDS) have been described, each with characteristic phenotypes and associated genes. Pathogenic variants in COL5A1 and COL5A2 cause the classical EDS subtypes. Pathogenic variants in COL3A1 cause vascular EDS. In this case report, we describe a patient with a phenotype resembling that of vascular EDS, caused by a novel pathogenic variant in COL5A1.

Mechanobiology in the Comorbidities of Ehlers Danlos Syndrome

Ehlers-Danlos Syndromes (EDSs) are a group of connective tissue disorders, characterized by skin stretchability, joint hypermobility and instability. Mechanically, various tissues from EDS patients exhibit lowered elastic modulus and lowered ultimate strength. This change in mechanics has been associated with EDS symptoms. However, recent evidence points toward a possibility that the comorbidities of EDS could be also associated with reduced tissue stiffness. In this review, we focus on mast cell activation syndrome and impaired wound healing, comorbidities associated with the classical type (cEDS) and the hypermobile type (hEDS), respectively, and discuss potential mechanobiological pathways involved in the comorbidities.

The Role of Cell Adhesion and Cytoskeleton Dynamics in the Pathogenesis of the Ehlers-Danlos Syndromes and Hypermobility Spectrum Disorders

The Ehlers-Danlos syndromes (EDS) are a group of 13 disorders, clinically defined through features of joint hypermobility, skin hyperextensibility, and tissue fragility. Most subtypes are caused by mutations in genes affecting the structure or processing of the extracellular matrix (ECM) protein collagen. The Hypermobility Spectrum Disorders (HSDs) are clinically indistinguishable disorders, but are considered to lack a genetic basis. The pathogenesis of all these disorders, however, remains poorly understood. Genotype-phenotype correlations are limited, and findings of aberrant collagen fibrils are inconsistent and associate poorly with the subtype and severity of the disorder. The defective ECM, however, also has consequences for cellular processes. EDS/HSD fibroblasts exhibit a dysfunctional phenotype including impairments in cell adhesion and cytoskeleton organization, though the pathological significance of this has remained unclear. Recent advances in our understanding of fibroblast mechanobiology suggest these changes may actually reflect features of a pathomechanism we herein define. This review departs from the traditional view of EDS/HSD, where pathogenesis is mediated by the structurally defective ECM. Instead, we propose EDS/HSD may be a disorder of membrane-bound collagen, and consider how aberrations in cell adhesion and cytoskeleton dynamics could drive the abnormal properties of the connective tissue, and be responsible for the pathogenesis of EDS/HSD.

Low penetrance COL5A1 variants in a young patient with intracranial aneurysm and very mild signs of Ehlers-Danlos syndrome

Spontaneous cervical artery dissection (CeAD) is a major cause of ischemic stroke in young adults, whose genetic susceptibility factors are still largely unknown. Nevertheless, subtle ultrastructural connective tissue alterations (especially in the collagen fibril morphology) are recognized in a large proportion of CeAD patients, in which recent genetic investigations reported an enrichment of variants in genes associated with known connective tissue disorders. In this regard, COL5A1 variants have been reported in a small subset of CeAD patients, with or without classical Ehlers-Danlos syndrome (cEDS) features. We investigated a 22-year-old patient with intracranial aneurysm and mild connective tissue manifestations reminiscent of EDS. Whole-exome sequencing identified two COL5A1 missense variants in trans configuration: NM_000093.5:c.[1588G>A];[4135C>T], NP_000084.3:p.[(Gly530Ser)];[(Pro1379Ser)]. Functional assays demonstrated a significant decrease of collagen α1(V) chain expression in both heterozygous parents compared to control cells, and an additive effect of these two variants in the proband. Interestingly, both parents manifested very subtle EDS signs, such as atrophic scars, recurrent bone fractures, colonic diverticulosis, varicose veins, and osteoarthritis. Our findings emphasize the involvement of COL5A1 in the predisposition to vascular phenotypes and provide novel insights on the c.1588G>A variant, whose functional significance has not been definitely established. In fact, it was previously reported as both "disease modifying", and as a biallelic causative mutation (with heterozygous individuals showing subtle clinical signs of cEDS). We speculated that the c.1588G>A variant might lead to overt phenotype in combination with additional genetic "hits" lowering the collagen α1(V) chain expression below a hypothetical disease threshold.

3d phase-contrast nanotomography of unstained human skin biopsies may identify morphological differences in the dermis and epidermis between subjects

BACKGROUND

Enteric neuropathy is described in most patients with gastrointestinal dysmotility and may be found together with reduced intraepidermal nerve fiber density (IENFD). The aim of this pilot study was to assess whether three-dimensional (3d) imaging of skin biopsies could be used to examine various tissue components in patients with gastrointestinal dysmotility.

MATERIAL AND METHODS

Four dysmotility patients of different etiology and two healthy volunteers were included. From each subject, two 3-mm punch skin biopsies were stained with antibodies against protein gene product 9.5 or evaluated as a whole with two X-ray phase-contrast computed tomography (CT) setups, a laboratory µCT setup and a dedicated synchrotron radiation nanoCT end-station.

RESULTS

Two patients had reduced IENFD, and two normal IENFD, compared with controls. µCT and X-ray phase-contrast holographic nanotomography scanned whole tissue specimens, with optional high-resolution scans revealing delicate structures, without differentiation of various fibers and cells. Irregular architecture of dermal fibers was observed in the patient with Ehlers-Danlos syndrome and the patient with idiopathic dysmotility showed an abundance of mesenchymal ground substance.

CONCLUSIONS

3d phase-contrast tomographic imaging may be useful to illustrate traits of connective tissue dysfunction in various organs and to demonstrate whether disorganized dermal fibers could explain organ dysfunction.

Arterial complications in classical Ehlers-Danlos syndrome: a case series

BACKGROUND

The Ehlers-Danlos syndromes (EDS) are a group of connective tissue disorders with several recognised types. Patients with a type of EDS have connective tissue abnormalities resulting in a varying degree of joint hypermobility, skin and vascular fragility and generalised tissue friability. Classical EDS (cEDS) typically occurs as a result of dominant pathogenic variants in COL5A1 or COL5A2. The cardinal features of cEDS are hyperextensible skin, atrophic scarring and joint hypermobility. Arterial complications are more characteristically a feature of vascular EDS although individual cases of arterial events in cEDS have been reported.

METHODS

A cohort of 154 patients with a clinical diagnosis of cEDS from the UK was analysed.

RESULTS

Seven patients (4.5%) with a diagnosis of cEDS (four pathogenic, one likely pathogenic and two variants of uncertain significance in COL5A1) who had experienced arterial complications were identified. Arterial complications mostly involved medium-sized vessels and also two abdominal aortic aneurysms. No unique clinical features were identified in this group of patients.

CONCLUSION

There is a possible increased risk of arterial complications in patients with cEDS, although not well-defined. Clinicians need to be aware of this possibility when presented with a patient with an arterial complication and features of cEDS. Long-term management in families with cEDS and a vascular complication should be individually tailored to the patient's history and their family's history of vascular events.

Molecular Genetics and Pathogenesis of Ehlers-Danlos Syndrome and Related Connective Tissue Disorders

Ehlers–Danlos syndromes (EDS) are a group of heritable connective tissue disorders (HCTDs) characterized by a variable degree of skin hyperextensibility, joint hypermobility and tissue fragility. The current EDS classification distinguishes 13 subtypes and 19 different causal genes mainly involved in collagen and extracellular matrix synthesis and maintenance. EDS need to be differentiated from other HCTDs with a variable clinical overlap including Marfan syndrome and related disorders, some types of skeletal dysplasia and cutis laxa. Clinical recognition of EDS is not always straightforward and for a definite diagnosis, molecular testing can be of great assistance, especially in patients with an uncertain phenotype. Currently, the major challenging task in EDS is to unravel the molecular basis of the hypermobile EDS that is the most frequent form, and for which the diagnosis is only clinical in the absence of any definite laboratory test. This EDS subtype, as well as other EDS-reminiscent phenotypes, are currently investigated worldwide to unravel the primary genetic defect and related pathomechanisms. The research articles, case report, and reviews published in this Special Issue focus on different clinical, genetic and molecular aspects of several EDS subtypes and some related disorders, offering novel findings and future research and nosological perspectives.