A single base mutation in COL5A2 causes Ehlers-Danlos syndrome type II

Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis

BACKGROUND

SMAD2 is a coregulator that binds a variety of transcription factors in human development. Heterozygous SMAD2 loss-of-function and missense variants are identified in patients with congenital heart disease (CHD) or arterial aneurysms. Mechanisms that cause distinct cardiovascular phenotypes remain unknown. We aimed to define transcriptional and epigenetic effects of SMAD2 variants and their role in CHD. We also assessed the function of SMAD2 missense variants of uncertain significance.

METHODS AND RESULTS

Rare SMAD2 variants (minor allele frequency ≤10-5) were identified in exome sequencing of 11 336 participants with CHD. We constructed isogenic induced pluripotent stem cells with heterozygous or homozygous loss-of-function and missense SMAD2 variants identified in CHD probands. Wild-type and mutant induced pluripotent stem cells were analyzed using bulk RNA sequencing, chromatin accessibility (Assay for Transposase-Accessible Chromatin With Sequencing), and integrated with published SMAD2/3 chromatin immunoprecipitation data. Cardiomyocyte differentiation and contractility were evaluated. Thirty participants with CHD had heterozygous loss-of-function or missense SMAD2 variants. SMAD2 haploinsufficiency altered chromatin accessibility at promoters and dysregulated expression of 385 SMAD regulated genes, including 10 CHD-associated genes. Motifs enriched in differential Assay for Transposase-Accessible Chromatin peaks predicted that SMAD2 haploinsufficiency disrupts interactions with transcription factors NANOG (homeobox protein NANOG), ETS, TEAD3/4 (transcriptional enhanced associate domain 3/4), CREB1 (cAMP response element binding protein 1), and AP1 (activator protein 1). Compared with SMAD2-haploinsufficient cells, induced pluripotent stem cells with R114C or W274C variants exhibited distinct and shared chromatin accessibility and transcription factor binding changes.

CONCLUSIONS

SMAD2 haploinsufficiency disrupts transcription factor binding and chromatin interactions critical for cardiovascular development. Differences between the molecular consequences of loss-of-function and missense variants likely contribute to phenotypic heterogeneity. These findings indicate opportunities for molecular analyses to improve reclassification of SMAD2 variants of uncertain clinical significance.

Molecular Basis of Pathogenic Variants in the Fibrillar Collagens

The fibrillar collagen family is comprised of the quantitatively major types I, II and III collagens and the quantitatively minor types V and XI. These form heterotypic collagen fibrils (composed of more than a single collagen type) where the minor collagens have a regulatory role in controlling fibril formation and diameter. The structural pre-requisites for normal collagen biosynthesis and fibrillogenesis result in many places where this process can be disrupted, and consequently a wide variety of phenotypes result when pathogenic changes occur in these fibrillar collagen genes. Another contributing factor is alternative splicing, both naturally occurring and as the result of pathogenic DNA alterations. This article will discuss how these factors should be taken into account when assessing DNA sequencing results from a patient.

Independent COL5A1 Variants in Cats with Ehlers-Danlos Syndrome

We investigated four cats with similar clinical skin-related signs strongly suggestive of Ehlers-Danlos syndrome (EDS). Cases no. 1 and 4 were unrelated and the remaining two cases, no. 2 and 3, were reportedly siblings. Histopathological changes were characterized by severely altered dermal collagen fibers. Transmission electron microscopy in one case demonstrated abnormalities in the collagen fibril organization and structure. The genomes of the two unrelated affected cats and one of the affected siblings were sequenced and individually compared to 54 feline control genomes. We searched for private protein changing variants in known human EDS candidate genes and identified three independent heterozygous COL5A1 variants. COL5A1 is a well-characterized candidate gene for classical EDS. It encodes the proα1 chain of type V collagen, which is needed for correct collagen fibril formation and the integrity of the skin. The identified variants in COL5A1 are c.112_118+15del or r.spl?, c.3514A>T or p.(Lys1172*), and c.3066del or p.(Gly1023Valfs*50) for cases no. 1, 2&3, and 4, respectively. They presumably all lead to nonsense-mediated mRNA decay, which results in haploinsufficiency of COL5A1 and causes the alterations of the connective tissue. The whole genome sequencing approach used in this study enables a refinement of the diagnosis for the affected cats as classical EDS. It further illustrates the potential of such experiments as a precision medicine approach in animals with inherited diseases.

Profiling and targeting connective tissue remodeling in autoimmunity - A novel paradigm for diagnosing and treating chronic diseases

Connective tissue (ConT) remodeling is an essential process in tissue regeneration, where a balanced replacement of old tissue by new tissue occurs. This balance is disturbed in chronic diseases, often autoimmune diseases, usually resulting in the buld up of fibrosis and a gradual loss of organ function. During progression of liver, lung, skin, heart, joint, skeletal and kidney diseasesboth ConT formation and degradation are elevated, which is tightly linked to immune cell activation and a loss of specific cell types and extracellular matrix (ECM) structures that are required for normal organ function. Here, we address the balance of key general and organ specific components of the ECM during homeostasis and in disease, with a focus on collagens, which are emerging as both structural and signaling molecules harbouring neoepitopes and autoantigens that are released during ConT remodeling. Specific collagen molecular signatures of ConT remodeling are linked to disease activity and stage, and to prognosis across different organs. These signatures accompany and further drive disease progression, and often become detectable before clinical disease manifestation (illness). Recent advances allow to quantify and define the nature of ConT remodeling via blood-based assays that measure the levels of well-defined collagen fragments, reflecting different facets of ConT formation and degradation, and associated immunological processes. These novel serum assays are becoming important tools of precision medicine, to detect various chronic and autoimmune diseases before their clinical manifestation, and to non-invasively monitor the efficacy of a broad range of pharmacological interventions.

A Heterozygous Missense Variant in the COL5A2 in Holstein Cattle Resembling the Classical Ehlers-Danlos Syndrome

Simple Summary

Genodermatoses represent inherited disorders of the skin that mostly follow a monogenic mode of inheritance. Heritable connective tissue disorders such as classical Ehlers–Danlos syndrome (cEDS) belong to this group of human rare diseases that sporadically occur in other species. Herein, affected cattle are reported showing skin lesions including cutis laxa clinically and pathologically resembling cEDS in humans. Microscopic findings in the deeper dermis were consistent with collagen dysplasia. Whole-genome sequencing (WGS) identified a most likely disease-causing mutation in the COL5A2 gene. The COL5A2 gene is known to be associated with dominant inherited cEDS forms in mice and humans, but so far, it was not shown to cause a similar phenotype in domestic animals. The disease phenotype examined herein showed co-segregation with the identified missense variant within the maternal line across two generations and is most likely due to a spontaneous mutation event. Rare non-lethal disorders such as cEDS in livestock are mostly not diagnosed, but might affect animal welfare and thus lower the value of affected animals. WGS-based precision diagnostics allows understanding rare disorders and supports the value of surveillance of cattle breeding populations for harmful genetic disorders.

Abstract

Classical Ehlers–Danlos syndrome (cEDS) is a heritable connective tissue disorder characterized by variable degrees of skin hyperextensibility and fragility, atrophic scarring, and generalized joint hypermobility. The purpose of this study was to characterize the clinicopathological phenotype of a cEDS-affected Holstein calf and to identify the causative genetic variant associated with the disorder by whole-genome sequencing (WGS). A 3-day-old female Holstein calf was referred because of easily induced skin detachment and hyperextensibility in the neck. A complete clinical investigation was performed in the calf, dam, and maternal-grandmother. The calf and dam showed hyperextensibility of the neck skin and atrophic scarring; additionally, the calf presented skin fragility. Moreover, the histopathology of biopsies from the calf and its dam showed that the collagen bundles in affected skin areas were wavy, short, thin, and surrounded by edema and moderate to severe acute hemorrhages. Genetic analysis revealed a private heterozygous missense variant in COL5A2 (c.2366G>T; p.Gly789Val) that was present only in the calf and dam. This confirmed the diagnosis of cEDS and represents the first report of a causal variant for cEDS in cattle and the first COL5A2-related large animal model.

Col11a1a Expression Is Required for Zebrafish Development

The autosomal dominant chondrodystrophies, the Stickler type 2 and Marshall syndromes, are characterized by facial abnormalities, vision deficits, hearing loss, and articular joint issues resulting from mutations in COL11A1. Zebrafish carry two copies of the Col11a1 gene, designated Col11a1a and Col11a1b. Col11a1a is located on zebrafish chromosome 24 and Col11a1b is located on zebrafish chromosome 2. Expression patterns are distinct for Col11a1a and Col11a1b and Col11a1a is most similar to COL11A1 that is responsible for human autosomal chondrodystrophies and the gene responsible for changes in the chondrodystrophic mouse model cho/cho. We investigated the function of Col11a1a in craniofacial and axial skeletal development in zebrafish using a knockdown approach. Knockdown revealed abnormalities in Meckel's cartilage, the otoliths, and overall body length. Similar phenotypes were observed using a CRISPR/Cas9 gene-editing approach, although the CRISPR/Cas9 effect was more severe compared to the transient effect of the antisense morpholino oligonucleotide treatment. The results of this study provide evidence that the zebrafish gene for Col11a1a is required for normal development and has similar functions to the mammalian COL11A1 gene. Due to its transparency, external fertilization, the Col11a1a knockdown, and knockout zebrafish model systems can, therefore, contribute to filling the gap in knowledge about early events during vertebrate skeletal development that are not as tenable in mammalian model systems and help us understand Col11a1-related early developmental events.

Identification of Two Independent COL5A1 Variants in Dogs with Ehlers-Danlos Syndrome

The Ehlers–Danlos syndromes (EDS) are a heterogeneous group of heritable disorders affecting connective tissues. The mutations causing the various forms of EDS in humans are well characterized, but the genetic mutations causing EDS-like clinical pathology in dogs are not known, thus hampering accurate clinical diagnosis. Clinical analysis of two independent cases of skin hyperextensibility and fragility, one with pronounced joint hypermobility was suggestive of EDS. Whole-genome sequencing revealed de novo mutations of COL5A1 in both cases, confirming the diagnosis of the classical form of EDS. The heterozygous COL5A1 p.Gly1013ValfsTer260 mutation characterized in case 1 introduced a premature termination codon and would be expected to result in α1(V) mRNA nonsense-mediated mRNA decay and collagen V haploinsufficiency. While mRNA was not available from this dog, ultrastructural analysis of the dermis demonstrated variability in collagen fibril diameter and the presence of collagen aggregates, termed ‘collagen cauliflowers’, consistent with COL5A1 mutations underlying classical EDS. In the second case, DNA sequencing demonstrated a p.Gly1571Arg missense variant in the COL5A1 gene. While samples were not available for further analysis, such a glycine substitution would be expected to destabilize the strict molecular structure of the collagen V triple helix and thus affect protein stability and/or integration of the mutant collagen into the collagen V/collagen I heterotypic dermal fibrils. This is the first report of genetic variants in the COL5A1 gene causing the clinical presentation of EDS in dogs. These data provided further evidence of the important role of collagen V in dermal collagen fibrillogenesis. Importantly, from the clinical perspective, we showed the utility of DNA sequencing, combined with the established clinical criteria, in the accurate diagnosis of EDS in dogs.

Mapping the Tooth Enamel Proteome and Amelogenin Phosphorylation Onto Mineralizing Porcine Tooth Crowns

Tooth enamel forms in an ephemeral protein matrix where changes in protein abundance, composition and posttranslational modifications are critical to achieve healthy enamel properties. Amelogenin (AMELX) with its splice variants is the most abundant enamel matrix protein, with only one known phosphorylation site at serine 16 shown in vitro to be critical for regulating mineralization. The phosphorylated form of AMELX stabilizes amorphous calcium phosphate, while crystalline hydroxyapatite forms in the presence of the unphosphorylated protein. While AMELX regulates mineral transitions over space and time, it is unknown whether and when un-phosphorylated amelogenin occurs during enamel mineralization. This study aims to reveal the spatiotemporal distribution of the cleavage products of the most abundant AMLEX splice variants including the full length P173, the shorter leucine-rich amelogenin protein (LRAP), and the exon 4-containing P190 in forming enamel, all within the context of the changing enamel matrix proteome during mineralization. We microsampled permanent pig molars, capturing known stages of enamel formation from both crown surface and inner enamel. Nano-LC-MS/MS proteomic analyses after tryptic digestion rendered more than 500 unique protein identifications in enamel, dentin, and bone. We mapped collagens, keratins, and proteolytic enzymes (CTSL, MMP2, MMP10) and determined distributions of P173, LRAP, and P190 products, the enamel proteins enamelin (ENAM) and ameloblastin (AMBN), and matrix-metalloprotease-20 (MMP20) and kallikrein-4 (KLK4). All enamel proteins and KLK4 were near-exclusive to enamel and in excellent agreement with published abundance levels. Phosphorylated P173 and LRAP products decreased in abundance from recently deposited matrix toward older enamel, mirrored by increasing abundances of testicular acid phosphatase (ACPT). Our results showed that hierarchical clustering analysis of secretory enamel links closely matching distributions of unphosphorylated P173 and LRAP products with ACPT and non-traditional amelogenesis proteins, many associated with enamel defects. We report higher protein diversity than previously published and Gene Ontology (GO)-defined protein functions related to the regulation of mineral formation in secretory enamel (e.g., casein α-S1, CSN1S1), immune response in erupted enamel (e.g., peptidoglycan recognition protein, PGRP), and phosphorylation. This study presents a novel approach to characterize and study functional relationships through spatiotemporal mapping of the ephemeral extracellular matrix proteome.

The triple helix of collagens - an ancient protein structure that enabled animal multicellularity and tissue evolution

The cellular microenvironment, characterized by an extracellular matrix (ECM), played an essential role in the transition from unicellularity to multicellularity in animals (metazoans), and in the subsequent evolution of diverse animal tissues and organs. A major ECM component are members of the collagen superfamily -comprising 28 types in vertebrates - that exist in diverse supramolecular assemblies ranging from networks to fibrils. Each assembly is characterized by a hallmark feature, a protein structure called a triple helix. A current gap in knowledge is understanding the mechanisms of how the triple helix encodes and utilizes information in building scaffolds on the outside of cells. Type IV collagen, recently revealed as the evolutionarily most ancient member of the collagen superfamily, serves as an archetype for a fresh view of fundamental structural features of a triple helix that underlie the diversity of biological activities of collagens. In this Opinion, we argue that the triple helix is a protein structure of fundamental importance in building the extracellular matrix, which enabled animal multicellularity and tissue evolution.

The good and the bad collagens of fibrosis - Their role in signaling and organ function

Usually the dense extracellular structure in fibrotic tissues is described as extracellular matrix (ECM) or simply as collagen. However, fibrosis is not just fibrosis, which is already exemplified by the variant morphological characteristics of fibrosis due to viral versus cholestatic, autoimmune or toxic liver injury, with reticular, chicken wire and bridging fibrosis. Importantly, the overall composition of the ECM, especially the relative amounts of the many types of collagens, which represent the most abundant ECM molecules and which centrally modulate cellular functions and physiological processes, changes dramatically during fibrosis progression. We hypothesize that there are good and bad collagens in fibrosis and that a change of location alone may change the function from good to bad. Whereas basement membrane collagen type IV anchors epithelial and other cells in a polarized manner, the interstitial fibroblast collagens type I and III do not provide directional information. In addition, feedback loops from biologically active degradation products of some collagens are examples of the importance of having the right collagen at the right place and at the right time controlling cell function, proliferation, matrix production and fate. Examples are the interstitial collagen type VI and basement membrane collagen type XVIII. Their carboxyterminal propeptides serve as an adipose tissue hormone, endotrophin, and as a regulator of angiogenesis, endostatin, respectively. We provide an overview of the 28 known collagen types and propose that the molecular composition of the ECM in fibrosis needs careful attention to assess its impact on organ function and its potential to progress or reverse. Consequently, to adequately assess fibrosis and to design optimal antifibrotic therapies, we need to dissect the molecular entity of fibrosis for the molecular composition and spatial distribution of collagens and the associated ECM.

α3 Chains of type V collagen regulate breast tumour growth via glypican-1

Pericellular α3(V) collagen can affect the functioning of cells, such as adipocytes and pancreatic β cells. Here we show that α3(V) chains are an abundant product of normal mammary gland basal cells, and that α3(V) ablation in a mouse mammary tumour model inhibits mammary tumour progression by reducing the proliferative potential of tumour cells. These effects are shown to be primarily cell autonomous, from loss of α3(V) chains normally produced by tumour cells, in which they affect growth by enhancing the ability of cell surface proteoglycan glypican-1 to act as a co-receptor for FGF2. Thus, a mechanism is presented for microenvironmental influence on tumour growth. α3(V) chains are produced in both basal-like and luminal human breast tumours, and its expression levels are tightly coupled with those of glypican-1 across breast cancer types. Evidence indicates α3(V) chains as potential targets for inhibiting tumour growth and as markers of oncogenic transformation.

Collagen has a role in cancer and is particularly important for breast cancer. Here the authors show that the expression of α3 type V collagen and one of its receptors- glipican-1- in the same cell, contributes to a deregulated growth of breast cancer cells.

A novel missense mutation of COL5A2 in a patient with Ehlers-Danlos syndrome

Ehlers–Danlos syndrome (EDS) is a group of inherited connective tissue disorders characterized by hyperextensible skin, joint hypermobility and soft tissue fragility. For molecular diagnosis, targeted exome sequencing was performed on a 9-year-old male patient who was clinically suspected to have EDS. The patient presented with progressive kyphoscoliosis, joint hypermobility and hyperextensible skin without scars. Ultimately, classical EDS was diagnosed by identifying a novel, mono-allelic mutation in COL5A2 [NM_000393.3(COL5A2_v001):c.682G>A, p.Gly228Arg].

Craniofacial and Dental Defects in the Col1a1Jrt/+ Mouse Model of Osteogenesis Imperfecta

Certain mutations in the COL1A1 and COL1A2 genes produce clinical symptoms of both osteogenesis imperfecta (OI) and Ehlers-Danlos syndrome (EDS) that include abnormal craniofacial growth, dental malocclusion, and dentinogenesis imperfecta. A mouse model (Col1a1(Jrt)/+) was recently developed that had a skeletal phenotype and other features consistent with moderate-to-severe OI and also with EDS. The craniofacial phenotype of 4- and 20-wk-old Col1a1(Jrt)/+ mice and wild-type littermates was assessed by micro-computed tomography (µCT) and morphometry. Teeth and the periodontal ligament compartment were analyzed by µCT, light microscopy/histomorphometry, and electron microscopy. Over time, at 20 wk, Col1a1(Jrt)/+ mice developed smaller heads, a shortened anterior cranial base, class III occlusion, and a mandibular side shift with shorter morphology in the masticatory region (maxilla and mandible). Col1a1(Jrt)/+ mice also had changes in the periodontal compartment and abnormalities in the dentin matrix and mineralization. These findings validate Col1a1(Jrt)/+ mice as a model for OI and EDS in humans.

Homozygosity and Heterozygosity for Null Col5a2 Alleles Produce Embryonic Lethality and a Novel Classic Ehlers-Danlos Syndrome-Related Phenotype

Null alleles for the COL5A1 gene and missense mutations for COL5A1 or the COL5A2 gene underlie cases of classic Ehlers-Danlos syndrome, characterized by fragile, hyperextensible skin and hypermobile joints. However, no classic Ehlers-Danlos syndrome case has yet been associated with COL5A2 null alleles, and phenotypes that might result from such alleles are unknown. We describe mice with null alleles for the Col5a2. Col5a2(-/-) homozygosity is embryonic lethal at approximately 12 days post conception. Unlike previously described mice null for Col5a1, which die at 10.5 days post conception and virtually lack collagen fibrils, Col5a2(-/-) embryos have readily detectable collagen fibrils, thicker than in wild-type controls. Differences in Col5a2(-/-) and Col5a1(-/-) fibril formation and embryonic survival suggest that α1(V)3 homotrimers, a rare collagen V isoform that occurs in the absence of sufficient levels of α2(V) chains, serve functional roles that partially compensate for loss of the most common collagen V isoform. Col5a2(+/-) adults have skin with marked hyperextensibility and reduced tensile strength at high strain but not at low strain. Col5a2(+/-) adults also have aortas with increased compliance and reduced tensile strength. Results thus suggest that COL5A2(+/-) humans, although unlikely to present with frank classic Ehlers-Danlos syndrome, are likely to have fragile connective tissues with increased susceptibility to trauma and certain chronic pathologic conditions.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

First mouse model for combined osteogenesis imperfecta and Ehlers-Danlos syndrome

By using a genome-wide N-ethyl-N-nitrosourea (ENU)-induced dominant mutagenesis screen in mice, a founder with low bone mineral density (BMD) was identified. Mapping and sequencing revealed a T to C transition in a splice donor of the collagen alpha1 type I (Col1a1) gene, resulting in the skipping of exon 9 and a predicted 18-amino acid deletion within the N-terminal region of the triple helical domain of Col1a1. Col1a1(Jrt) /+ mice were smaller in size, had lower BMD associated with decreased bone volume/tissue volume (BV/TV) and reduced trabecular number, and furthermore exhibited mechanically weak, brittle, fracture-prone bones, a hallmark of osteogenesis imperfecta (OI). Several markers of osteoblast differentiation were upregulated in mutant bone, and histomorphometry showed that the proportion of trabecular bone surfaces covered by activated osteoblasts (Ob.S/BS and N.Ob/BS) was elevated, but bone surfaces undergoing resorption (Oc.S/BS and N.Oc/BS) were not. The number of bone marrow stromal osteoprogenitors (CFU-ALP) was unaffected, but mineralization was decreased in cultures from young Col1a1(Jrt) /+ versus +/+ mice. Total collagen and type I collagen content of matrices deposited by Col1a1(Jrt) /+ dermal fibroblasts in culture was ∼40% and 30%, respectively, that of +/+ cells, suggesting that mutant collagen chains exerted a dominant negative effect on type I collagen biosynthesis. Mutant collagen fibrils were also markedly smaller in diameter than +/+ fibrils in bone, tendon, and extracellular matrices deposited by dermal fibroblasts in vitro. Col1a1(Jrt) /+ mice also exhibited traits associated with Ehlers-Danlos syndrome (EDS): Their skin had reduced tensile properties, tail tendon appeared more frayed, and a third of the young adult mice had noticeable curvature of the spine. Col1a1(Jrt) /+ is the first reported model of combined OI/EDS and will be useful for exploring aspects of OI and EDS pathophysiology and treatment.

Using transmission electron microscopy and 3View to determine collagen fibril size and three-dimensional organization

Collagen fibrils are the major tensile element in vertebrate tissues, in which they occur as ordered bundles in the extracellular matrix. Abnormal fibril assembly and organization results in scarring, fibrosis, poor wound healing and connective tissue diseases. Transmission electron microscopy (TEM) is used to assess the formation of the fibrils, predominantly by measuring fibril diameter. Here we describe a protocol for measuring fibril diameter as well as fibril volume fraction, mean fibril length, fibril cross-sectional shape and fibril 3D organization, all of which are major determinants of tissue function. Serial-section TEM (ssTEM) has been used to visualize fibril 3D organization in vivo. However, serial block face-scanning electron microscopy (SBF-SEM) has emerged as a time-efficient alternative to ssTEM. The protocol described below is suitable for preparing tissues for TEM and SBF-SEM (by 3View). We describe how to use 3View for studying collagen fibril organization in vivo and show how to find and track individual fibrils. The overall time scale is ~8 d from isolating the tissue to having a 3D image stack.

Clinical and molecular characterization of 40 patients with classic Ehlers-Danlos syndrome: identification of 18 COL5A1 and 2 COL5A2 novel mutations

BACKGROUND

Classic Ehlers-Danlos syndrome (cEDS) is a rare autosomal dominant connective tissue disorder that is primarily characterized by skin hyperextensibility, abnormal wound healing/atrophic scars, and joint hypermobility. A recent study demonstrated that more than 90% of patients who satisfy all of these major criteria harbor a type V collagen (COLLV) defect.

METHODS

This cohort included 40 patients with cEDS who were clinically diagnosed according to the Villefranche nosology. The flowchart that was adopted for mutation detection consisted of sequencing the COL5A1 gene and, if no mutation was detected, COL5A2 analysis. In the negative patients the presence of large genomic rearrangements in COL5A1 was investigated using MLPA, and positive results were confirmed via SNP-array analysis.

RESULTS

We report the clinical and molecular characterization of 40 patients from 28 families, consisting of 14 pediatric patients and 26 adults. A family history of cEDS was present in 9 patients. The majority of the patients fulfilled all the major diagnostic criteria for cEDS; atrophic scars were absent in 2 females, skin hyperextensibility was not detected in a male and joint hypermobility was negative in 8 patients (20% of the entire cohort). Wide inter- and intra-familial phenotypic heterogeneity was observed. We identified causal mutations with a detection rate of approximately 93%. In 25/28 probands, COL5A1 or COL5A2 mutations were detected. Twenty-one mutations were in the COL5A1 gene, 18 of which were novel (2 recurrent). Of these, 16 mutations led to nonsense-mediated mRNA decay (NMD) and to COLLV haploinsufficiency and 5 mutations were structural. Two novel COL5A2 splice mutations were detected in patients with the most severe phenotypes. The known p. (Arg312Cys) mutation in the COL1A1 gene was identified in one patient with vascular-like cEDS.

CONCLUSIONS

Our findings highlight that the three major criteria for cEDS are useful and sufficient for cEDS clinical diagnosis in the large majority of the patients. The borderline patients for whom these criteria fail can be diagnosed when minor signs of connective tissue diseases and family history are present and when genetic testing reveals a defect in COLLV. Our data also confirm that COL5A1 and COL5A2 are the major, if not the only, genes involved in cEDS.

Molecular diagnosis of genodermatoses

The progress of molecular genetics helps clinicians to prove or exclude a suspected diagnosis for a vast and yet increasing number of genodermatoses. This leads to precise genetic counselling, prenatal diagnosis and preimplantation genetic haplotyping for many inherited skin conditions. It is also helpful in such occasions as phenocopy, late onset and incomplete penetrance, uniparental disomy, mitochondrial inheritance and pigmentary mosaicism. Molecular methods of two genodermatoses are explained in detail, i.e. genodermatoses with skin fragility and neurofibromatosis type 1.

Comprehensive mass spectrometric mapping of the hydroxylated amino acid residues of the α1(V) collagen chain

BACKGROUND

α1(V) is an extensively modified collagen chain important in disease.

RESULTS

Comprehensive mapping of α1(V) post-translational modifications reveals unexpectedly large numbers of X-position hydroxyprolines in Gly-X-Y amino acid triplets.

CONCLUSION

The unexpected abundance of X-position hydroxyprolines suggests a mechanism for differential modification of collagen properties.

SIGNIFICANCE

Positions, numbers, and occupancy of modified sites can provide insights into α1(V) biological properties. Aberrant expression of the type V collagen α1(V) chain can underlie the connective tissue disorder classic Ehlers-Danlos syndrome, and autoimmune responses against the α1(V) chain are linked to lung transplant rejection and atherosclerosis. The α1(V) collagenous COL1 domain is thought to contain greater numbers of post-translational modifications (PTMs) than do similar domains of other fibrillar collagen chains, PTMs consisting of hydroxylated prolines and lysines, the latter of which can be glycosylated. These types of PTMs can contribute to epitopes that underlie immune responses against collagens, and the high level of PTMs may contribute to the unique biological properties of the α1(V) chain. Here we use high resolution mass spectrometry to map such PTMs in bovine placental α1(V) and human recombinant pro-α1(V) procollagen chains. Findings include the locations of those PTMs that vary and those PTMs that are invariant between these α1(V) chains from widely divergent sources. Notably, an unexpectedly large number of hydroxyproline residues were mapped to the X-positions of Gly-X-Y triplets, contrary to expectations based on previous amino acid analyses of hydrolyzed α1(V) chains from various tissues. We attribute this difference to the ability of tandem mass spectrometry coupled to nanoflow chromatographic separations to detect lower-level PTM combinations with superior sensitivity and specificity. The data are consistent with the presence of a relatively large number of 3-hydroxyproline sites with less than 100% occupancy, suggesting a previously unknown mechanism for the differential modification of α1(V) chain and type V collagen properties.

Extracellular matrix remodeling: the common denominator in connective tissue diseases. Possibilities for evaluation and current understanding of the matrix as more than a passive architecture, but a key player in tissue failure

Increased attention is paid to the structural components of tissues. These components are mostly collagens and various proteoglycans. Emerging evidence suggests that altered components and noncoded modifications of the matrix may be both initiators and drivers of disease, exemplified by excessive tissue remodeling leading to tissue stiffness, as well as by changes in the signaling potential of both intact matrix and fragments thereof. Although tissue structure until recently was viewed as a simple architecture anchoring cells and proteins, this complex grid may contain essential information enabling the maintenance of the structure and normal functioning of tissue. The aims of this review are to (1) discuss the structural components of the matrix and the relevance of their mutations to the pathology of diseases such as fibrosis and cancer, (2) introduce the possibility that post-translational modifications (PTMs), such as protease cleavage, citrullination, cross-linking, nitrosylation, glycosylation, and isomerization, generated during pathology, may be unique, disease-specific biochemical markers, (3) list and review the range of simple enzyme-linked immunosorbent assays (ELISAs) that have been developed for assessing the extracellular matrix (ECM) and detecting abnormal ECM remodeling, and (4) discuss whether some PTMs are the cause or consequence of disease. New evidence clearly suggests that the ECM at some point in the pathogenesis becomes a driver of disease. These pathological modified ECM proteins may allow insights into complicated pathologies in which the end stage is excessive tissue remodeling, and provide unique and more pathology-specific biochemical markers.

Comprehensive molecular analysis demonstrates type V collagen mutations in over 90% of patients with classic EDS and allows to refine diagnostic criteria

Type V collagen mutations are associated with classic Ehlers-Danlos Syndrome (EDS), but it is unknown for which proportion they account and to what extent other genes are involved. We analyzed COL5A1 and COL5A2 in 126 patients with a diagnosis or suspicion of classic EDS. In 93 patients, a type V collagen defect was found, of which 73 were COL5A1 mutations, 13 were COL5A2 mutations and seven were COL5A1 null-alleles with mutation unknown. The majority of the 73 COL5A1 mutations generated a COL5A1 null-allele, whereas one-third were structural mutations, scattered throughout COL5A1. All COL5A2 mutations were structural mutations. Reduced availability of type V collagen appeared to be the major disease-causing mechanism, besides other intra- and extracellular contributing factors. All type V collagen defects were identified within a group of 102 patients fulfilling all major clinical Villefranche criteria, that is, skin hyperextensibility, dystrophic scarring and joint hypermobility. No COL5A1/COL5A2 mutation was detected in 24 patients who displayed skin and joint hyperextensibility but lacked dystrophic scarring. Overall, over 90% of patients fulfilling all major Villefranche criteria for classic EDS were shown to harbor a type V collagen defect, which indicates that this is the major--if not only--cause of classic EDS.

Minor fibrillar collagens, variable regions alternative splicing, intrinsic disorder, and tyrosine sulfation

Minor fibrillar collagen types V and XI, are those less abundant than the fibrillar collagen types I, II and III. The alpha chains share a high degree of similarity with respect to protein sequence in all domains except the variable region. Genomic variation and, in some cases, extensive alternative splicing contribute to the unique sequence characteristics of the variable region. While unique expression patterns in tissues exist, the functions and biological relevance of the variable regions have not been elucidated. In this review, we summarize the existing knowledge about expression patterns and biological functions of the collagen types V and XI alpha chains. Analysis of biochemical similarities among the peptides encoded by each exon of the variable region suggests the potential for a shared function. The alternative splicing, conservation of biochemical characteristics in light of low sequence conservation, and evidence for intrinsic disorder, suggest modulation of binding events between the surface of collagen fibrils and surrounding extracellular molecules as a shared function.

Regulation of collagen fibril nucleation and initial fibril assembly involves coordinate interactions with collagens V and XI in developing tendon

Collagens V and XI comprise a single regulatory type of fibril-forming collagen with multiple isoforms. Both co-assemble with collagen I or II to form heterotypic fibrils and have been implicated in regulation of fibril assembly. The objective of this study was to determine the roles of collagens V and XI in the regulation of tendon fibrillogenesis. Flexor digitorum longus tendons from a haplo-insufficient collagen V mouse model of classic Ehlers Danlos syndrome (EDS) had decreased biomechanical stiffness compared with controls consistent with joint laxity in EDS patients. However, fibril structure was relatively normal, an unexpected finding given the altered fibrils observed in dermis and cornea from this model. This suggested roles for other related molecules, i.e. collagen XI, and compound Col5a1(+/-),Col11a1(+/-) tendons had altered fibril structures, supporting a role for collagen XI. To further evaluate this, transcript expression was analyzed in wild type tendons. During development (E18-P10) both collagen V and XI were comparably expressed; however, collagen V predominated in mature (P30) tendons. The collagens had a similar expression pattern. Tendons with altered collagen V and/or XI expression (Col5a1(+/-); Col11a1(+/-); Col5a1(+/-),Col11a1(+/-); Col11a1(-/-); Col5a1(+/-),Col11a1(-/-)) were analyzed at E18. All genotypes demonstrated a reduced fibril number and altered structure. This phenotype was more severe with a reduction in collagen XI. However, the absence of collagen XI with a reduction in collagen V was associated with the most severe fibril phenotype. The data demonstrate coordinate roles for collagens V and XI in the regulation of fibril nucleation and assembly during tendon development.

α3(V) collagen is critical for glucose homeostasis in mice due to effects in pancreatic islets and peripheral tissues

Collagen V, broadly expressed as α1(V)2 α2(V) heterotrimers that regulate collagen fibril geometry and strength, also occurs in some tissues, such as white adipose tissue (WAT), pancreatic islets, and skeletal muscle, as the poorly characterized α1(V) α2(V) α3(V) heterotrimer. Here, we investigate the role of α3(V) collagen chains by generating mice with a null allele of the α3(V) gene Col5a3 (Col5a3–/– mice). Female Col5a3–/– mice had reduced dermal fat and were resistant to high-fat diet–induced weight gain. Male and female mutant mice were glucose intolerant, insulin-resistant, and hyperglycemic, and these metabolic defects worsened with age. Col5a3–/– mice demonstrated decreased numbers of pancreatic islets, which were more susceptible to streptozotocin-induced apoptosis, and islets isolated from mutant mice displayed blunted glucose-stimulated insulin secretion. Moreover, Col5a3–/– WAT and skeletal muscle were defective in glucose uptake and mobilization of intracellular GLUT4 glucose transporter to the plasma membrane in response to insulin. Our results underscore the emerging view of the importance of ECM to the microenvironments that inform proper development/functioning of specialized cells, such as adipocytes, β cells, and skeletal muscle.

The expression patterns of minor fibrillar collagens during development in zebrafish

Minor fibrillar collagens are recognized as the organizers and nucleators during collagen fibrillogenesis but likely serve additional functions. The minor fibrillar collagens include collagens type V and XI. Mutations of collagens type V and XI can cause Ehlers-Danlos, Stickler's, and Marshall's syndromes in human. We have characterized the spatiotemporal expression patterns of Col11a1, Col11a2, Col5a1 as well as Col5a3 in zebrafish embryos by in situ hybridization. Col5a1 is expressed in developing somites, neural crest, the head mesenchyme, developing cranial cartilage, pharyngeal arches and vertebrae. Col5a3 is detected in the notochord, mesenchyme cells in the eyes and lens. Both Col11a1 and Col11a2 have similar expression patterns, including notochord, otic vesicle, and developing cranial cartilages. Zebrafish may therefore serve as a valuable vertebrate model system for the study of diseases associated with collagens type V and XI mutations.

Characterization of the six zebrafish clade B fibrillar procollagen genes, with evidence for evolutionarily conserved alternative splicing within the pro-alpha1(V) C-propeptide

Genes for tetrapod fibrillar procollagen chains can be divided into two clades, A and B, based on sequence homologies and differences in protein domain and gene structures. Although the major fibrillar collagen types I-III comprise only clade A chains, the minor fibrillar collagen types V and XI comprise both clade A chains and the clade B chains pro-alpha1(V), pro-alpha3(V), pro-alpha1(XI) and pro-alpha2(XI), in which defects can underlie various genetic connective tissue disorders. Here we characterize the clade B procollagen chains of zebrafish. We demonstrate that in contrast to the four tetrapod clade B chains, zebrafish have six clade B chains, designated here as pro-alpha1(V), pro-alpha3(V)a and b, pro-alpha1(XI)a and b, and pro-alpha2(XI), based on synteny, sequence homologies, and features of protein domain and gene structures. Spatiotemporal expression patterns are described, as are conserved and non-conserved features that provide insights into the function and evolution of the clade B chain types. Such features include differential alternative splicing of NH(2)-terminal globular sequences and the first case of a non-triple helical imperfection in the COL1 domain of a clade B, or clade A, fibrillar procollagen chain. Evidence is also provided for previously unknown and evolutionarily conserved alternative splicing within the pro-alpha1(V) C-propeptide, which may affect selectivity of collagen type V/XI chain associations in species ranging from zebrafish to human. Data presented herein provide insights into the nature of clade B procollagen chains and should facilitate their study in the zebrafish model system.

Extracellular matrix molecules: potential targets in pharmacotherapy

The extracellular matrix (ECM) consists of numerous macromolecules classified traditionally into collagens, elastin, and microfibrillar proteins, proteoglycans including hyaluronan, and noncollagenous glycoproteins. In addition to being necessary structural components, ECM molecules exhibit important functional roles in the control of key cellular events such as adhesion, migration, proliferation, differentiation, and survival. Any structural inherited or acquired defect and/or metabolic disturbance in the ECM may cause cellular and tissue alterations that can lead to the development or progression of disease. Consequently, ECM molecules are important targets for pharmacotherapy. Specific agents that prevent the excess accumulation of ECM molecules in the vascular system, liver, kidney, skin, and lung; alternatively, agents that inhibit the degradation of the ECM in degenerative diseases such as osteoarthritis would be clinically beneficial. Unfortunately, until recently, the ECM in drug discovery has been largely ignored. However, several of today's drugs that act on various primary targets affect the ECM as a byproduct of the drugs' actions, and this activity may in part be beneficial to the drugs' disease-modifying properties. In the future, agents and compounds targeting directly the ECM will significantly advance the treatment of various human diseases, even those for which efficient therapies are not yet available.

Molecular mechanisms of classical Ehlers-Danlos syndrome (EDS)

Classical Ehlers-Danlos syndrome (EDS) is a heritable disorder characterized by joint hypermobility, skin hyperextensibility, and abnormal wound healing. The majority of affected individuals have alterations in 1 of the 2 type V collagen genes, COL5A1 and COL5A2. The most common mechanism is COL5A1 haploinsufficiency due to instability of the transcript of one allele. In dermal fibroblasts from our population of 76 individuals with clinical features of classical EDS, there were 21 (29.5%) with decreased expression of one COL5A1 allele, consistent with published estimates of the frequency of null alleles. We identified the causative mutation in nine of these cell strains (mutations for seven others had been previously described), and found two nonsense mutations, five splice mutations, and two insertion/deletions. The same type of genomic change at splice sites can have different effects at the RNA level and the outcome could not be predicted from the primary genomic DNA alteration.

Molecular genetics in classic Ehlers-Danlos syndrome

Classic Ehlers-Danlos syndrome is a heritable disorder of connective tissue that is characterized by skin hyperextensibility, fragile and soft skin, delayed wound healing with formation of atrophic scars, easy bruising, and generalized joint hypermobility. Mutations in the COL5A1 and the COL5A2 gene, encoding the alpha1 and the alpha2-chain of type V collagen respectively, are identified in approximately 50% of patients with a clinical diagnosis of classic EDS. In approximately one third of patients, the disease is caused by a mutation leading to a non-functional COL5A1 allele, and resulting in haplo-insufficiency of type V collagen. In a smaller proportion of patients, a structural mutation in COL5A1 or COL5A2, resulting in the production of a functionally defective type V collagen protein, is responsible for the phenotype. Inter- and intrafamilial phenotypic variability is observed, but no genotype-phenotype correlations can be made so far. The relatively low mutation detection rate in the COL5A1/A2 genes suggests genetic heterogeneity. Indeed rarely mutations in type I collagen have been identified in patients with classic EDS. Mutations in the gene for tenascin-X have been implicated in an autosomal recessive condition phenotypically overlapping with classic EDS. Several other candidate genes, such as decorin, have emerged from the study of transgenic mouse models with clinical and ultrastructural features reminiscent of classic EDS. However, to date, no human examples have been reported for these mouse models.

Murine model of the Ehlers-Danlos syndrome. col5a1 haploinsufficiency disrupts collagen fibril assembly at multiple stages

The most commonly identified mutations causing Ehlers-Danlos syndrome (EDS) classic type result in haploinsufficiency of proalpha1(V) chains of type V collagen, a quantitatively minor collagen that co-assembles with type I collagen as heterotypic fibrils. To determine the role(s) of type I/V collagen interactions in fibrillogenesis and elucidate the mechanism whereby half-reduction of type V collagen causes abnormal connective tissue biogenesis observed in EDS, we analyzed mice heterozygous for a targeted inactivating mutation in col5a1 that caused 50% reduction in col5a1 mRNA and collagen V. Comparable with EDS patients, they had decreased aortic stiffness and tensile strength and hyperextensible skin with decreased tensile strength of both normal and wounded skin. In dermis, 50% fewer fibrils were assembled with two subpopulations: relatively normal fibrils with periodic immunoreactivity for collagen V where type I/V interactions regulate nucleation of fibril assembly and abnormal fibrils, lacking collagen V, generated by unregulated sequestration of type I collagen. The presence of the aberrant fibril subpopulation disrupts the normal linear and lateral growth mediated by fibril fusion. Therefore, abnormal fibril nucleation and dysfunctional fibril growth with potential disruption of cell-directed fibril organization leads to the connective tissue dysfunction associated with EDS.

Collagen, type V, alpha1 (COL5A1) is regulated by TGF-beta in osteoblasts

Bone matrix contains high concentrations of growth factors that are known to play important regulatory roles during osteogenesis, particularly transforming growth factor-beta (TGF-beta). Divergent effects of TGF-beta on bone formation have been reported both in vitro and in vivo depending upon experimental conditions, cells employed and their stage of maturation. In this study, we have used a clonal osteoblastic cell line MC3T3-E1, derived from newborn mouse calvaria, as an in vitro model of bone development. These cells undergo an ordered, time-dependent developmental sequence characterized by three stages (proliferation, differentiation and mineralization), over a 30-35-day period. In this study, cDNA microarray technology was used to study the expression profile of 8470 genes, in the presence of TGF-beta1 during osteoblast development. Microarray analysis revealed 120 cDNAs to be differentially expressed in MC3T3-E1 osteoblasts that had been treated with TGF-beta1. From the 120 differentially expressed genes, we selected Collagen, type V, alpha1 (COL5A1) {differential expression=+4.9} for further studies since it represents a previously uncharacterized component of the bone matrix. Using Northern blotting, we found that, when MC3T3-E1 cells were treated with TGF-beta1, COL5A1 was up-regulated during the proliferation and differentiation phases of osteogenesis. Furthermore, by a combination of RNA in situ hybridization and Northern blotting, we found COL5A1 mRNA to be expressed in the calvaria and developing bone of the E17.5 mouse embryos. Lastly, significant COL5A1 protein expression was observed by immunohistochemistry in the developing bone of the E17.5 mouse embryos. In conclusion, by the use of in vitro and in vivo approaches, we have discovered that the COL5A1 gene is a target of TGF-beta during osteogenesis.

Rare autosomal recessive cardiac valvular form of Ehlers-Danlos syndrome results from mutations in the COL1A2 gene that activate the nonsense-mediated RNA decay pathway

Splice site mutations in the COL1A2 gene of type I collagen can give rise to forms of Ehlers-Danlos syndrome (EDS) because of partial or complete skipping of exon 6, as well as to mild, moderate, or lethal forms of osteogenesis imperfecta as a consequence of skipping of other exons. We identified three unrelated individuals with a rare recessively inherited form of EDS (characterized by joint hypermobility, skin hyperextensibility, and cardiac valvular defects); in two of them, COL1A2 messenger RNA (mRNA) instability results from compound heterozygosity for splice site mutations in the COL1A2 gene, and, in the third, it results from homozygosity for a nonsense codon. The splice site mutations led to use of cryptic splice donor sites, creation of a downstream premature termination codon, and extremely unstable mRNA. In the wild-type allele, the two introns (IVS11 and IVS24) in which these mutations occurred were usually spliced slowly in relation to their respective immediate upstream introns. In the mutant alleles, the upstream intron was removed, so that exon skipping could not occur. In the context of the mutation in IVS24, computer-generated folding of a short stretch of mRNA surrounding the mutation site demonstrated realignment of the relationships between the donor and acceptor sites that could facilitate use of a cryptic donor site. These findings suggest that the order of intron removal is an important variable in prediction of mutation outcome at splice sites and that folding of the nascent mRNA could be one element that contributes to determination of order of splicing. The complete absence of pro alpha 2(I) chains has the surprising effect of producing cardiac valvular disease without bone involvement.

Reduced type I collagen utilization: A pathogenic mechanism in COL5A1 haplo-insufficient Ehlers-Danlos syndrome

To examine mechanisms by which reduced type V collagen causes weakened connective tissues in the Ehlers-Danlos syndrome (EDS), we examined matrix deposition and collagen fibril morphology in long-term dermal fibroblast cultures. EDS cells with COL5A1 haplo-insufficiency deposited less than one-half of hydroxyproline as collagen compared to control fibroblasts, though total collagen synthesis rates are near-normal because type V collagen represents a small fraction of collagen synthesized. Cells from patients with osteogenesis imperfecta (OI) and haplo-insufficiency for proalpha1(I) chains of type I collagen also incorporated about one-half the collagen as controls, but this amount was proportional to their reduced rates of total collagen synthesis. Collagen fibril diameter was inversely proportional to type V/type I collagen ratios (EDS > control > OI). However, a reduction of type V collagen, in the EDS derived cells, was associated with the assembly of significantly fewer fibrils compared to control and OI cells. These data indicate that in cell culture, the quantity of collagen fibrils deposited in matrix is highly sensitive to reduction in type V collagen, far out of proportion to type V collagen's contribution to collagen mass.

The molecular basis of classic Ehlers-Danlos syndrome: A comprehensive study of biochemical and molecular findings in 48 unrelated patients

Classic Ehlers-Danlos syndrome (EDS) is characterized by fragile and hyperextensible skin, atrophic scarring, and joint hypermobility. Mutations in the COL5A1 and the COL5A2 gene encoding the alpha1(V) and the alpha2(V) chains, respectively, of type V collagen have been shown to cause the disorder, but it is unknown what proportion of classic EDS patients carries a mutation in these genes. We studied fibroblast cultures from 48 patients with classic EDS by SDS-PAGE for the presence of type V collagen defects. An abnormal collagen pattern was detected in only 2 out of 48 cell lines, making this a poor method for routine diagnostic evaluation. A total of 42 out of 48 (88%) patients were heterozygous for an expressed polymorphic variant in COL5A1. cDNA from 18 (43%) of them expressed only one COL5A1 allele. In 37 patients, the COL5A1/A2 genes were then analyzed by SSCP and conformation sensitive gel electrophoresis (CSGE). A total of 26 patients that were mutation-negative after SSCP/CSGE screening were reanalyzed by dHPLC. In addition, 11 other patients were analyzed by dHPLC only. In total, 17 mutations leading to a premature stop codon and five structural mutations were identified in the COL5A1 and the COL5A2 genes. In three patients with a positive COL5A1 null-allele test, no causal mutation was found. Overall, in 25 out of 48 patients (52%) with classic EDS, an abnormality in type V collagen was confirmed. Variability in severity of the phenotype was observed, but no significant genotype-phenotype correlations emerged. The relatively low mutation detection rate suggests that other genes are involved in classic EDS. We excluded the COL1A1, COL1A2, and DCN gene as major candidate genes for classic EDS, since no causal mutation in these genes was found in a number of patients who tested negative for COL5A1 and COL5A2.

Connective Tissue Disorders with Spontaneous Spinal Cerebrospinal Fluid Leaks and Intracranial Hypotension: A Prospective Study

OBJECTIVE

Intracranial hypotension attributable to a spontaneous spinal cerebrospinal fluid (CSF) leak is an increasingly recognized cause of postural headaches. The cause of these leaks is poorly understood, but it is likely multifactorial and may involve a primary connective tissue disorder. We undertook a study to estimate the contribution of systemic connective tissue disorders to the development of spontaneous spinal CSF leaks.

METHODS

We examined a group of 18 consecutive patients with spontaneous spinal CSF leaks for features of a connective tissue disorder.

RESULTS

The mean age of the 15 female patients and 3 male patients was 38 years (range, 22-55 yr). Seven patients (38%) demonstrated stigmata of a systemic connective tissue disorder, and three distinct types of disorders could be identified, as follows. 1) The association of spontaneous spinal CSF leaks and minor skeletal features of Marfan syndrome was noted for three patients. 2) Ehlers-Danlos syndrome Type II was noted for two patients. 3) Joint hypermobility associated with marked attenuation of the dorsal muscular fascia, precluding proper wound closure, was noted for two patients. In addition, isolated small-joint hypermobility was observed for five patients (28%). Slit-lamp ocular examinations, echocardiographic evaluations, histopathological examinations of skin biopsy specimens, and renal scanning did not reveal any other features of a systemic connective tissue disorder.

CONCLUSION

Findings suggesting connective tissue disorders are common among patients with spontaneous spinal CSF leaks, and manifestations may be subtle. A variety of disorders can be identified, probably reflecting genetic heterogeneity. Problems with wound healing may occur as a result of the systemic nature of the underlying connective tissue disorder.

[The Ehlers-Danlos syndrome: the extracellular matrix scaffold in question]

Ehlers-Danlos syndrome (EDS) is a heterogeneous heritable connective tissue disorder characterized by hyper-extensible skin, hypermobile joints and fragile vessels. The molecular causes of this disorder are often, although not strictly, related to collagens and to the enzymes that process these proteins. The classical form of the syndrome, which will be principally discussed in this review, can be due to mutations on collagen V, a fibrillar collagen present in small amounts in affected tissues. However, collagen I and tenascin have also been demonstrated to be involved in the same type of EDS. Moreover gene disruption of several other matrix molecules (thrombospondin, SPARC, small leucine rich proteoglycans...) in mice, lead to phenotypes that mimic EDS and these molecules have thus emerged as new players. As collagen V remains the prime candidate, we discuss, based on fundamental and clinical observations, its physiological role. We also explore its potential interactions with other matrix molecules to determine tissue properties.

Homozygous Gly530Ser substitution in COL5A1 causes mild classical Ehlers-Danlos syndrome

Skin hyperelasticity, tissue fragility with atrophic scars, and joint hypermobility are characteristic for the classical type of Ehlers-Danlos syndrome (EDS). The disease is usually inherited as an autosomal dominant trait; however, recessive mode of inheritance has been documented in tenascin-X-deficient EDS patients. Mutations in the genes coding for collagen alpha1(V) chain (COL5A1), collagen alpha2(V) chain (COL5A2), tenascin-X (TNX), and collagen alpha1(I) chain (COL1A1) have been characterized in patients with classical EDS, thus confirming the suspected genetic heterogeneity. Recently, we described a patient with severe classical EDS due to a Gly1489Glu substitution in the alpha1(V) triple-helical domain who was, in addition, heterozygous for a disease-modifying Gly530Ser substitution in the alpha1(V) NH(2)-terminal domain [Giunta and Steinmann, 2000: Am. J. Med. Genet. 90:72-79; Steinmann and Giunta, 2000: Am. J. Med. Genet. 93:342]. Here, we report on a 4-year-old boy with mild classical EDS, born to healthy consanguineous Turkish parents; the mother presented a soft skin, while the father had a normal thick skin. Ultrastructural analysis of the dermis revealed in the patient the typical "cauliflower" collagen fibrils, while in both parents variable moderate aberrations were seen. Mutation revealed the presence of a homozygous Gly530Ser substitution in the alpha1(V) collagen chains in the patient, while both parents were heterozygous for the same substitution. An additional mutation in either the COL5A1 and COL5A2 genes was excluded. Furthermore, haplotype analysis with polymorphic microsatellite markers excluded linkage to the genes coding for alpha3(V) collagen (COL5A3), tenascin-X (TNX), thrombospondin-2 (THBS2), and decorin (DCN). These new findings support further our previous hypothesis that the heterozygous Gly530Ser substitution is disease modifying and now suggest that in the homozygous state it is disease causing.

Prevalence of aortic root dilation in the Ehlers-Danlos syndrome

PURPOSE

To determine the prevalence of proximal aortic abnormalities in patients with Ehlers-Danlos syndrome (EDS).

METHODS

In a prospective cohort study, aortic measurements by two-dimensional echocardiography were performed on consecutive EDS patients.

RESULTS

Twenty-eight percent (20 of 71) had aortic root dilation (ARD) (> +2 SD above population based norms). Fourteen of 42 individuals with the classical form of EDS (types I/II) and 6 of 29 individuals with the hypermobile form (type III) had ARD, with no gender differences.

CONCLUSION

ARD is a common finding in EDS. Longitudinal studies are indicated to determine progression of ARD and its clinical significance.

Gerodermia osteodysplastica and wrinkly skin syndrome: are they the same?

Gerodermia osteodysplastica (GO) is a connective tissue disorder characterized by premature aging, wrinkled, and lax skin with reduced elasticity which is more marked on the dorsum of the hands and feet associated with hyperextensible joints and osteoporosis. The wrinkly skin syndrome (WSS) is characterized by wrinkled skin over the dorsum of the hands, feet, and abdomen; hyperextensible joints, particularly of the hands; intrauterine growth retardation; postnatal failure to thrive; and mental and developmental delay. We report on five children from two consanguineous Arab families with features overlapping both GO and WSS. All five children had similar dysmorphic facial features consisting of broad and prominent forehead, hypotelorism with epicanthal folds, prominent bulbous nose, flat malar region, and large protruding ears. All had wrinkling of the skin more marked on the dorsum of the hands, feet, and abdomen; hyperextensibility of the joints, particularly of the hands; and aged appearance. Intrauterine growth retardation, subsequent failure to thrive, developmental delay, and variable degree of osteoporosis was also present in all of them. The older three children developed progressive prognathism. We suggest that GO and WSS could represent variable manifestation of the same disorder.

COL5A1 haploinsufficiency is a common molecular mechanism underlying the classical form of EDS

We have identified haploinsufficiency of the COL5A1 gene that encodes the proalpha1(V) chain of type V collagen in the classical form of the Ehlers-Danlos syndrome (EDS), a heritable connective-tissue disorder that severely alters the collagen-fibrillar structure of the dermis, joints, eyes, and blood vessels. Eight of 28 probands with classical EDS who were heterozygous for expressed polymorphisms in COL5A1 showed complete or nearly complete loss of expression of one COL5A1 allele. Reduced levels of proalpha1(V) mRNA relative to the levels of another type V collagen mRNA, proalpha2(V), were also observed in the cultured fibroblasts from EDS probands. Products of the two COL5A1 alleles were approximately equal after the addition of cycloheximide to the fibroblast cultures. After harvesting of mRNAs from cycloheximide-treated cultured fibroblasts, heteroduplex analysis of overlapping reverse transcriptase-PCR segments spanning the complete proalpha1(V) cDNA showed anomalies in four of the eight probands that led to identification of causative mutations, and, in the remaining four probands, targeting of CGA-->TGA mutations in genomic DNA revealed a premature stop at codon in one of them. We estimate that approximately one-third of individuals with classical EDS have mutations of COL5A1 that result in haploinsufficiency. These findings indicate that the normal formation of the heterotypic collagen fibrils that contain types I, III, and V collagen requires the expression of both COL5A1 alleles.

Null alleles of the COL5A1 gene of type V collagen are a cause of the classical forms of Ehlers-Danlos syndrome (types I and II)

Ehlers-Danlos syndrome (EDS) types I and II, which comprise the classical variety, are well characterized from the clinical perspective, but it has been difficult to identify the molecular basis of the disorder in the majority of affected individuals. Several explanations for this failure to detect mutations have been proposed, including genetic heterogeneity, failure of allele expression, and technical difficulties. Genetic heterogeneity has been confirmed as an explanation for such failure, since causative mutations have been identified in the COL5A1, COL5A2, and tenascin X genes and since they have been inferred in the COL1A2 gene. Nonetheless, in the majority of families with autosomal dominant inheritance of EDS, there appears to be linkage to loci that contain the COL5A1 or COL5A2 genes. To determine whether allele-product instability could explain failure to identify some mutations, we analyzed polymorphic variants in the COL5A1 gene in 16 individuals, and we examined mRNA for the expression of both alleles and for alterations in splicing. We found a splice-site mutation in a single individual, and we determined that, in six individuals, the mRNA from one COL5A1 allele either was not expressed or was very unstable. We identified small insertions or deletions in five of these cell strains, but we could not identify the mutation in the sixth individual. Thus, although as many as one-half of the mutations that give rise to EDS types I and II are likely to lie in the COL5A1 gene, a significant portion of them result in very low levels of mRNA from the mutant allele, as a consequence of nonsense-mediated mRNA decay.

Classical Ehlers-Danlos syndrome caused by a mutation in type I collagen

Classical Ehlers-Danlos syndrome (EDS) is characterized by skin hyperelasticity, joint hypermobility, increased tendency to bruise, and abnormal scarring. Mutations in type V collagen, a regulator of type I collagen fibrillogenesis, have been shown to underlie this type of EDS. However, to date, mutations have been found in only a limited number of patients, which suggests genetic heterogeneity. In this article, we report two unrelated patients with typical features of classical EDS, including excessive skin fragility, in whom we found an identical arginine-->cysteine substitution in type I collagen, localized at position 134 of the alpha1(I) collagen chain. The arginine residue is highly conserved and localized in the X position of the Gly-X-Y triplet. As a consequence, intermolecular disulfide bridges are formed, resulting in type I collagen aggregates, which are retained in the cells. Whereas substitutions of glycine residues in type I collagen invariably result in osteogenesis imperfecta, substitutions of nonglycine residues in type I collagen have not yet been associated with a human disease. In contrast, arginine-->cysteine substitutions in type II collagen have been identified in a variety of chondrodysplasias. Our findings show that mutations in other fibrillar collagens can be causally involved in classical EDS and point to genetic heterogeneity of this disorder.