A homozygous stop codon in the lysyl hydroxylase gene in two siblings with Ehlers-Danlos syndrome type VI

Spontaneous celiac artery aneurysms in 13-year-old and 10-year-old brothers with PLOD1-related kyphoscoliotic Ehlers-Danlos syndrome

PLOD1-related kyphoscoliotic Ehlers-Danlos syndrome is a rare, autosomal recessive connective tissue disorder characterized by congenital hypotonia, early-onset, progressive kyphoscoliosis, and generalized joint hypermobility. PLOD1-kyphoscoliotic Ehlers-Danlos syndrome is also associated with heightened vascular fragility, resulting in an elevated susceptibility to recurrent vascular complications such as arterial aneurysms, dissection, and spontaneous arterial rupture. We report the cases of two affected brothers: a 13-year-old boy presenting with spontaneous rupture of a celiac artery aneurysm and a 10-year-old boy presenting with a rapidly enlarging celiac artery aneurysm requiring urgent repair.

Heterozygous THBS2 pathogenic variant causes Ehlers-Danlos syndrome with prominent vascular features in humans and mice

Ehlers-Danlos syndromes (EDS) are a group of connective tissue disorders caused by mutations in collagen and collagen-interacting genes. We delineate a novel form of EDS with vascular features through clinical and histopathological phenotyping and genetic studies of a three-generation pedigree, displaying an apparently autosomal dominant phenotype of joint hypermobility and frequent joint dislocations, atrophic scarring, prolonged bleeding time and age-related aortic dilatation and rupture. Coagulation tests as well as platelet counts and function were normal. Reticular dermis displayed highly disorganized collagen fibers and transmission electron microscopy (TEM) revealed abnormally shaped fibroblasts and endothelial cells, with high amount and irregular shape of extracellular matrix (ECM) substance, especially near blood vessels. Genetic analysis unraveled a heterozygous mutation in THBS2 (NM_003247.5:c.2686T>C, p.Cys896Arg). We generated CRISPR/Cas9 knock-in (KI) mice, bearing the heterozygous human mutation in the mouse ortholog. The KI mice demonstrated phenotypic traits correlating with those observed in the human subjects, as evidenced by morphologic, histologic, and TEM analyses, in conjunction with bleeding time assays. Our findings delineate a novel form of human EDS with classical-like elements combined with vascular features, caused by a heterozygous THBS2 missense mutation. We further demonstrate a similar phenotype in heterozygous THBS2Cys896Arg KI mice, in line with previous studies in Thbs2 homozygous null-mutant mice. Notably, THBS2 encodes Thrombospondin-2, a secreted homotrimeric matricellular protein that directly binds the ECM-shaping Matrix Metalloproteinase 2 (MMP2), mediating its clearance. THBS2 loss-of-function attenuates MMP2 clearance, enhancing MMP2-mediated proteoglycan cleavage, causing ECM abnormalities similar to those seen in the human and mouse disease we describe.

Unleashing the Potential of 1,3-Diketone Analogues as Selective LH2 Inhibitors

Lysyl hydroxylase 2 (LH2) catalyzes the formation of highly stable hydroxylysine aldehyde-derived collagen cross-links (HLCCs), thus promoting lung cancer metastasis through its capacity to modulate specific types of collagen cross-links within the tumor stroma. Using 1 and 2 from our previous high-throughput screening (HTS) as lead probes, we prepared a series of 1,3-diketone analogues, 1-18, and identified 12 and 13 that inhibit LH2 with IC50's of approximately 300 and 500 nM, respectively. Compounds 12 and 13 demonstrate selectivity for LH2 over LH1 and LH3. Quantum mechanics/molecular mechanics (QM/MM) modeling indicates that the selectivity of 12 and 13 may stem from noncovalent interactions like hydrogen bonding between the morpholine/piperazine rings with the LH2-specific Arg661. Treatment of 344SQ WT cells with 13 resulted in a dose-dependent reduction in their migration potential, whereas the compound did not impede the migration of the same cell line with an LH2 knockout (LH2KO).

A severe case of PLOD1-related kyphoscoliotic Ehlers-Danlos syndrome associated with several arterial and venous complications: A case report

Kyphoscoliotic Ehlers-Danlos syndrome (kEDS) is a rare genetic disorder combining congenital hypotonia, congenital/early onset and progressive kyphoscoliosis, and generalized joint hypermobility. Vascular fragility is another characteristic of the disease rarely described. We report a severe case of kEDS-PLOD1 with several vascular complications leading to difficulties in disease management.

Comparative genomic and biochemical analyses identify a collagen galactosylhydroxylysyl glucosyltransferase from Acanthamoeba polyphaga mimivirus

Humans and Acanthamoeba polyphaga mimivirus share numerous homologous genes, including collagens and collagen-modifying enzymes. To explore this homology, we performed a genome-wide comparison between human and mimivirus using DELTA-BLAST (Domain Enhanced Lookup Time Accelerated BLAST) and identified 52 new putative mimiviral proteins that are homologous with human proteins. To gain functional insights into mimiviral proteins, their human protein homologs were organized into Gene Ontology (GO) and REACTOME pathways to build a functional network. Collagen and collagen-modifying enzymes form the largest subnetwork with most nodes. Further analysis of this subnetwork identified a putative collagen glycosyltransferase R699. Protein expression test suggested that R699 is highly expressed in Escherichia coli, unlike the human collagen-modifying enzymes. Enzymatic activity assay and mass spectrometric analyses showed that R699 catalyzes the glucosylation of galactosylhydroxylysine to glucosylgalactosylhydroxylysine on collagen using uridine diphosphate glucose (UDP-glucose) but no other UDP-sugars as a sugar donor, suggesting R699 is a mimiviral collagen galactosylhydroxylysyl glucosyltransferase (GGT). To facilitate further analysis of human and mimiviral homologous proteins, we presented an interactive and searchable genome-wide comparison website for quickly browsing human and Acanthamoeba polyphaga mimivirus homologs, which is available at RRID Resource ID: SCR_022140 or https://guolab.shinyapps.io/app-mimivirus-publication/ .

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.

Case Report: Identification and Functional Analysis of a Homozygous Synonymous Variant in the PLOD1 Gene in a Chinese Neonatal With the Ehlers-Danlos Syndrome

BACKGROUND

Kyphoscoliotic Ehlers-Danlos syndrome (kEDS; OMIM225400) is a rare autosomal recessive genetic disease caused by variants in the PLOD1 gene. This research was conducted to verify the disease-causing gene in a Chinese neonatal family with the EDS.

METHODS

We recruited a Han Chinese neonate with PLOD1-related kEDS without kyphoscoliosis. Detailed clinical examination and laboratory tests were performed and whole exome sequencing (WES) was used to detect the pathogenic genes of the proband. In vivo experiments (reverse-transcription PCR, quantitative real-time PCR) and in vitro experiments (minigene analysis) were used to verify the function of variants suspected of affecting the splicing process. The effect of the splice site variant on the PLOD1 transcript was analyzed using splice prediction programs NetGene2 and Alternative Splice Site Predictor (ASSP).

RESULTS

A homozygous synonymous variant c.1095C>T (p.Gly365, rs1032781250) in the PLOD1 gene was found and verified in the family with kEDS. This splicing variant resulted in a premature termination codon of exon 10 and affected the expression of the four bases GCGC.

CONCLUSION

Our research showed that the homozygous synonymous variant in PLOD1 was the pathogenic cause in the proband. The combined application of WES and functional studies verified the effect of uncertain gene variants on splicing, upgrading pathogenicity evidence, and determining the cause of disease. This is helpful for the early diagnosis and treatment of kEDS.

A collagen glucosyltransferase drives lung adenocarcinoma progression in mice

Cancer cells are a major source of enzymes that modify collagen to create a stiff, fibrotic tumor stroma. High collagen lysyl hydroxylase 2 (LH2) expression promotes metastasis and is correlated with shorter survival in lung adenocarcinoma (LUAD) and other tumor types. LH2 hydroxylates lysine (Lys) residues on fibrillar collagen's amino- and carboxy-terminal telopeptides to create stable collagen cross-links. Here, we show that electrostatic interactions between the LH domain active site and collagen determine the unique telopeptidyl lysyl hydroxylase (tLH) activity of LH2. However, CRISPR/Cas-9-mediated inactivation of tLH activity does not fully recapitulate the inhibitory effect of LH2 knock out on LUAD growth and metastasis in mice, suggesting that LH2 drives LUAD progression, in part, through a tLH-independent mechanism. Protein homology modeling and biochemical studies identify an LH2 isoform (LH2b) that has previously undetected collagen galactosylhydroxylysyl glucosyltransferase (GGT) activity determined by a loop that enhances UDP-glucose-binding in the GLT active site and is encoded by alternatively spliced exon 13 A. CRISPR/Cas-9-mediated deletion of exon 13 A sharply reduces the growth and metastasis of LH2b-expressing LUADs in mice. These findings identify a previously unrecognized collagen GGT activity that drives LUAD progression.

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

Brittle cornea syndrome (BCS) is a rare autosomal recessive disorder characterized by corneal thinning and fragility, leading to corneal rupture, the main hallmark of this disorder. Non-ocular symptoms include not only hearing loss but also signs of connective tissue fragility, placing it in the Ehlers-Danlos syndrome (EDS) spectrum. It is caused by biallelic pathogenic variants in ZNF469 or PRDM5, which presumably encode transcription factors for extracellular matrix components. We report the clinical and molecular features of nine novel BCS families, four of which harbor variants in ZNF469 and five in PRDM5. We also performed a genotype- and phenotype-oriented literature overview of all (n = 85) reported patients with ZNF469 (n = 53) and PRDM5 (n = 32) variants. Musculoskeletal findings may be the main reason for referral and often raise suspicion of another heritable connective tissue disorder, such as kyphoscoliotic EDS, osteogenesis imperfecta, or Marfan syndrome, especially when a corneal rupture has not yet occurred. Our findings highlight the multisystemic nature of BCS and validate its inclusion in the EDS classification. Importantly, gene panels for heritable connective tissue disorders should include ZNF469 and PRDM5 to allow for timely diagnosis and appropriate preventive measures for this rare condition.

Quality Control of Procollagen in Cells

Collagen is the most abundant protein in mammals. A unique feature of collagen is its triple-helical structure formed by the Gly-Xaa-Yaa repeats. Three single chains of procollagen make a trimer, and the triple-helical structure is then folded in the endoplasmic reticulum (ER). This unique structure is essential for collagen's functions in vivo, including imparting bone strength, allowing signal transduction, and forming basement membranes. The triple-helical structure of procollagen is stabilized by posttranslational modifications and intermolecular interactions, but collagen is labile even at normal body temperature. Heat shock protein 47 (Hsp47) is a collagen-specific molecular chaperone residing in the ER that plays a pivotal role in collagen biosynthesis and quality control of procollagen in the ER. Mutations that affect the triple-helical structure or result in loss of Hsp47 activity cause the destabilization of procollagen, which is then degraded by autophagy. In this review, we present the current state of the field regarding quality control of procollagen.

Hypermobile Ehlers-Danlos syndromes: Complex phenotypes, challenging diagnoses, and poorly understood causes

The Ehlers-Danlos syndromes (EDS) are a group of heritable, connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. There is phenotypic and genetic variation among the 13 subtypes. The initial genetic findings on EDS were related to alterations in fibrillar collagen, but the elucidation of the molecular basis of many of the subtypes revealed several genes not involved in collagen biosynthesis or structure. However, the genetic basis of the hypermobile type of EDS (hEDS) is still unknown. hEDS is the most common type of EDS and involves generalized joint hypermobility, musculoskeletal manifestations, and mild skin involvement along with the presence of several comorbid conditions. Variability in the spectrum and severity of symptoms and progression of patient phenotype likely depend on age, gender, lifestyle, and expression domains of the EDS genes during development and postnatal life. In this review, we summarize the current molecular, genetic, epidemiologic, and pathogenetic findings related to EDS with a focus on the hypermobile type.

The first case report of Kyphoscoliotic Ehlers-Danlos syndrome of chinese origin with a novel PLOD1 gene mutation

Background

Kyphoscoliotic Ehlers-Danlos syndrome (kEDS) is a rare autosomal recessive connective tissue disorder characterized by progressive kyphoscoliosis, congenital muscular hypotonia, marked joint hypermobility, and severe skin hyperextensibility and fragility. Deficiency of lysyl hydroxylase 1 (LH1) due to mutations of PLOD1 (procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1) gene has been identified as the pathogenic cause of kEDS (kEDS-PLOD1). Up to now, kEDS-PLOD1 has not been reported among Chinese population.

Case presentation

A 17-year-old Chinese male patient presenting with hypotonia, joint hypermobility and scoliosis was referred to our hospital. After birth, he was found to have severe hypotonia leading to delayed motor development. Subsequently, joint hypermobility, kyphoscoliosis and amblyopia were found. Inguinal hernia was found at age 5 years and closed by surgery. At the same time, he presented with hyperextensible and bruisable velvety skin with widened atrophic scarring after minor trauma. Dislocation of elbow joint was noted at age of 6 years. Orthopedic surgery for correction of kyphoscoliosis was performed at age 10 years. His family history was unremarkable. Physical examination revealed elevated blood pressure. Slight facial dysmorphologies including high palate, epicanthal folds, and down-slanting palpebral fissures were found. He also had blue sclerae with normal hearing. X-rays revealed severe degree of scoliosis and osteopenia. The Echocardiography findings were normal. Laboratory examination revealed a slightly elevated bone turnover. Based on the clinical manifestations presented by our patient, kEDS was suspected. Genetic analysis revealed a novel homozygous missense mutation of PLOD1 (c.1697 G > A, p.C566Y), confirming the diagnosis of kEDS-PLOD1. The patient was treated with alfacalcidol and nifedipine. Improved physical strength and normal blood pressure were reported after 12-month follow-up.

Conclusions

This is the first case of kEDS-PLOD1 of Chinese origin. We identified one novel mutation of PLOD1, extending the mutation spectrum of PLOD1. Diagnosis of kEDS-PLOD1 should be considered in patients with congenital hypotonia, progressive kyphoscoliosis, joint hypermobility, and skin hyperextensibility and confirmed by mutation analysis of PLOD1.

Human 2-oxoglutarate-dependent oxygenases: nutrient sensors, stress responders, and disease mediators

Fe(II)/2-oxoglutarate (2OG)-dependent oxygenases are a conserved enzyme class that catalyse diverse oxidative reactions across nature. In humans, these enzymes hydroxylate a broad range of biological substrates including DNA, RNA, proteins and some metabolic intermediates. Correspondingly, members of the 2OG-dependent oxygenase superfamily have been linked to fundamental biological processes, and found dysregulated in numerous human diseases. Such findings have stimulated efforts to understand both the biochemical activities and cellular functions of these enzymes, as many have been poorly studied. In this review, we focus on human 2OG-dependent oxygenases catalysing the hydroxylation of protein and polynucleotide substrates. We discuss their modulation by changes in the cellular microenvironment, particularly with respect to oxygen, iron, 2OG and the effects of oncometabolites. We also describe emerging evidence that these enzymes are responsive to cellular stresses including hypoxia and DNA damage. Moreover, we examine how dysregulation of 2OG-dependent oxygenases is associated with human disease, and the apparent paradoxical role for some of these enzymes during cancer development. Finally, we discuss some of the challenges associated with assigning biochemical activities and cellular functions to 2OG-dependent oxygenases.

Rare Cases of PLOD1-Related Kyphoscoliotic Ehlers-Danlos Syndrome in a Korean Family Identified by Next Generation Sequencing

Kyphoscoliotic Ehlers-Danlos syndrome (kEDS) is an autosomal recessive connective tissue disorder characterized by muscular hypotonia, hyperextensible skin, skin fragility, joint hypermobility, and progressive kyphoscoliosis. The disorder results from a deficiency of the enzyme collagen lysyl hydroxylase 1 due to mutations in the gene PLOD1. We describe the rare cases of kEDS in Korean siblings with two novel compound heterozygous variants, c.926_934del (p.Leu309_Leu311del) and c.2170_2172del (p.Phe724del) in the PLOD1 gene. They had congenital hypotonia, joint laxity, skin hyperextensibility, Marfanoid habitus, high myopia and atrophic scarring. The younger sibling had an early-onset progressive kyphoscoliosis, while the older sibling showed mild scoliosis during childhood. Intrafamilial variability of the clinical severity and age of kyphoscoliosis onset observed in our cases.

SiMPLOD, a Structure-Integrated Database of Collagen Lysyl Hydroxylase (LH/PLOD) Enzyme Variants

PLOD genes encode for procollagen lysyl hydroxylase enzymes (LH/PLOD), a family of proteins essential for collagen biosynthesis. Several mutations affect these genes, causing severe disorders, such as Ehlers-Danlos and Bruck syndrome, as well a connective tissue disease with phenotype resembling osteogenesis imperfecta caused by lack of LH3 functions. The recently determined three-dimensional (3D) structures of the full-length human LH3/PLOD3 isoform, together with the structure of a fragment of a viral LH/PLOD homolog, are now allowing molecular mapping of the numerous disease-causing mutations, providing insights often suitable for the interpretation of the resulting disease phenotypes. However, the added value of molecular structure interpretation is affected by the limited accessibility of complex molecular data to scientific communities lacking direct expertise in structural biology. In this work, we present a Structurally-integrated database for Mutations of PLOD genes (SiMPLOD), a publicly-available manually-curated online database with an embedded molecular viewer interface for the visualization and interpretation of LH/PLOD mutations on available molecular models. Each SiMPLOD entry is accompanied by manual annotations extrapolated from literature references and comments about the localization of the amino acid variants on the molecular structure. Additional links to the appropriate online resources for clinically-relevant as well as biochemical data are also provided in a standardized format. The web application is available at http://fornerislab.unipv.it/SiMPLOD. © 2019 American Society for Bone and Mineral Research.

Anterior cervical corpectomy decompression and fusion for cervical kyphosis in a girl with Ehlers-Danlos syndrome: A case report

BACKGROUND

Spinal deformities in Ehlers-Danlos syndrome (EDS; type VI) are generally progressive and severe. Surgical treatment has been described for kyphoscoliosis in the thoracolumbar spine. However, there are few studies describing the consequences of an anterior approach in cervical kyphosis. An anterior approach may not be able to fully decompress the spinal canal and restore the normal curvature of the cervical spine. Therefore, the anterior approach for cervical kyphosis in young children is hard. We describe the first case in an EDS girl with cervical kyphosis who received satisfactory anterior cervical corpectomy decompression and fusion.

CASE SUMMARY

The chief complaints of a 16-year-old girl with EDS were double upper limb weakness for 7 years and double lower limb walking instability for 2 years. Moreover, the imaging results revealed that the degree of kyphosis from cervical vertebra 2 to 4 accompanying with spinal cord compression was 30°. An anterior cervical corpectomy involving cervical vertebra 3 and a titanium mesh implant were performed with internal fixation. The results at 3 mo after surgery demonstrated that the anterior fusion was solid, and the kyphosis of the cervical spine was corrected. Additionally, the power of all four extremities was significantly improved.

CONCLUSION

The incidence rate of cervical kyphosis in EDS is rare. The surgical treatment for these patients, especially an anterior approach, is challenging. Therefore, to develop safer and more effective strategies to treat cervical kyphosis in EDS, there is still much work to do.

Collagen glycosylation

Despite the ubiquity of collagens in the animal kingdom, little is known about the biology of the disaccharide Glc(α1-2)Gal(β1-O) bound to hydroxylysine across collagens from sponges to mammals. The extent of collagen glycosylation varies by the types of collagen, with basement membrane collagen type IV being more glycosylated than fibrillar collagens. Beyond true collagens, proteins including collagen domains such as the complement protein 1Q and the hormone adiponectin also feature glycosylated hydroxylysine. Collagen glycosylation is initiated in the endoplasmic reticulum by the galactosyltransferases COLGALT1 and COLGALT2. Mutations in the COLGALT1 gene cause cerebral small vessel abnormality and porencephaly, which are common in collagen type IV deficiency. Beyond the strongly conserved Glc(α1-2)Gal(β1-O) glycan, additional forms of collagen glycosylation have been described in the deep-sea worm Riftia pachyptila and in the giant virus Mimivirus, thereby suggesting that further forms of collagen glycosylation are likely to be identified in the future.

Recent examples of α-ketoglutarate-dependent mononuclear non-haem iron enzymes in natural product biosyntheses

Covering: up to 2018 α-Ketoglutarate (αKG, also known as 2-oxoglutarate)-dependent mononuclear non-haem iron (αKG-NHFe) enzymes catalyze a wide range of biochemical reactions, including hydroxylation, ring fragmentation, C-C bond cleavage, epimerization, desaturation, endoperoxidation and heterocycle formation. These enzymes utilize iron(ii) as the metallo-cofactor and αKG as the co-substrate. Herein, we summarize several novel αKG-NHFe enzymes involved in natural product biosyntheses discovered in recent years, including halogenation reactions, amino acid modifications and tailoring reactions in the biosynthesis of terpenes, lipids, fatty acids and phosphonates. We also conducted a survey of the currently available structures of αKG-NHFe enzymes, in which αKG binds to the metallo-centre bidentately through either a proximal- or distal-type binding mode. Future structure-function and structure-reactivity relationship investigations will provide crucial information regarding how activities in this large class of enzymes have been fine-tuned in nature.

Vascular aspects of the Ehlers-Danlos Syndromes

The Ehlers-Danlos Syndromes comprise a heterogeneous group of rare monogenic conditions that are characterized by joint hypermobility, skin and vascular fragility and generalized connective tissue friability. The latest classification recognizes 13 clinical subtypes, with mutations identified in 19 different genes. Besides defects in fibrillar collagens (collagen types I, III and V), their modifying enzymes (ADAMTS-2, lysylhydroxylase 1 (LH1)), and molecules involved in collagen folding (FKBP22), defects have recently been identified in other constituents of the extracellular matrix (e.g. Tenascin-X, collagen type XII), enzymes involved in glycosaminoglycan biosynthesis (β4GalT7 and β3GalT6), dermatan 4-O-sulfotransferase-1 (D4ST1), dermatan sulfate epimerase (DSE)), (putative) transcription factors (ZNF469, PRDM5), components of the complement pathway (C1r, C1s) and an intracellular Zinc transporter (ZIP13). Easy bruising is, to a variable degree, present in all subtypes of EDS. A variable bleeding tendency, manifesting e.g. as gum bleeding, menometrorraghia, postnatal or peri-operative hemorrhage is observed in many EDS-patients of varying EDS subtypes. Life-threatening arterial aneurysms, dissections and ruptures of medium-sized and large arteries are a hallmark of the vascular subtype of EDS, caused by a molecular defect in collagen type III, an important constituent of blood vessel walls and hollow organs. They may however also occur in other EDS subtypes, especially in classical EDS, caused by defects in type V collagen or, rarely, type I collagen, and in kyphoscoliotic EDS, caused by defects in LH1 or FKBP22. These manifestations of vascular fragility and bleeding are usually attributed to fragility of the blood vessel walls and the perivascular connective tissues, but the molecular pathomechanisms underlying these complications are poorly studied. This review summarizes current knowledge on manifestations of vascular fragility in the different EDS subtypes.

The Ehlers-Danlos syndromes, rare types

The Ehlers-Danlos syndromes comprise a clinically and genetically heterogeneous group of heritable connective tissue disorders, which are characterized by joint hypermobility, skin hyperextensibility, and tissue friability. In the Villefranche Nosology, six subtypes were recognized: The classical, hypermobile, vascular, kyphoscoliotic, arthrochalasis, and dermatosparaxis subtypes of EDS. Except for the hypermobile subtype, defects had been identified in fibrillar collagens or in collagen-modifying enzymes. Since 1997, a whole spectrum of novel, clinically overlapping, rare EDS-variants have been delineated and genetic defects have been identified in an array of other extracellular matrix genes. Advances in molecular testing have made it possible to now identify the causative mutation for many patients presenting these phenotypes. The aim of this literature review is to summarize the current knowledge on the rare EDS subtypes and highlight areas for future research. © 2017 Wiley Periodicals, Inc.

Molecular insights into prolyl and lysyl hydroxylation of fibrillar collagens in health and disease

Collagen is a macromolecule that has versatile roles in physiology, ranging from structural support to mediating cell signaling. Formation of mature collagen fibrils out of procollagen α-chains requires a variety of enzymes and chaperones in a complex process spanning both intracellular and extracellular post-translational modifications. These processes include modifications of amino acids, folding of procollagen α-chains into a triple-helical configuration and subsequent stabilization, facilitation of transportation out of the cell, cleavage of propeptides, aggregation, cross-link formation, and finally the formation of mature fibrils. Disruption of any of the proteins involved in these biosynthesis steps potentially result in a variety of connective tissue diseases because of a destabilized extracellular matrix. In this review, we give a revised overview of the enzymes and chaperones currently known to be relevant to the conversion of lysine and proline into hydroxyproline and hydroxylysine, respectively, and the O-glycosylation of hydroxylysine and give insights into the consequences when these steps are disrupted.

OH, the Places You'll Go! Hydroxylation, Gene Expression, and Cancer

Hydroxylation is an emerging modification generally catalyzed by a family of ∼70 enzymes that are dependent on oxygen, Fe(II), ascorbate, and the Kreb's cycle intermediate 2-oxoglutarate (2OG). These "2OG oxygenases" sit at the intersection of nutrient availability and metabolism where they have the potential to regulate gene expression and growth in response to changes in co-factor abundance. Characterized 2OG oxygenases regulate fundamental cellular processes by catalyzing the hydroxylation or demethylation (via hydroxylation) of DNA, RNA, or protein. As such they have been implicated in various syndromes and diseases, but particularly cancer. In this review we discuss the emerging role of 2OG oxygenases in gene expression control, examine the regulation of these unique enzymes by nutrient availability and metabolic intermediates, and describe these properties in relation to the expanding role of these enzymes in cancer.

Kyphoscoliotic type of Ehlers-Danlos Syndrome (EDS VIA) in six Egyptian patients presenting with a homogeneous clinical phenotype

The kyphoscoliotic type of the Ehlers-Danlos syndrome (EDS VIA) is a rare recessively inherited connective tissue disorder characterized by bruisable, hyperextensible skin, generalized joint laxity, severe muscular hypotonia at birth and progressive congenital scoliosis or kyphosis. Deficiency of the enzyme lysyl hydroxylase 1 (LH1) due to mutations in PLOD1 results in underhydroxylation of collagen lysyl residues and, hence, in the abnormal formation of collagen cross-links. Here, we report on the clinical, biochemical, and molecular findings in six Egyptian patients from four unrelated families severely affected with EDS VIA. In addition to the frequently reported p.Glu326_Lys585dup, we identified two novel sequence variants p.Gln208* and p.Tyr675*, which lead either to loss of function of LH1 or to its deficiency. All affected children presented with similar clinical features of the disorder, and in addition, several dysmorphic craniofacial features, not yet described in EDS VIA. These were specific for the affected individuals of each family, but absent in their parents and their unaffected siblings.

CONCLUSION

Our description of six patients presenting with a homogeneous clinical phenotype and dysmorphic craniofacial features will help pediatricians in the diagnosis of this rare disorder.

Identification of domains and amino acids essential to the collagen galactosyltransferase activity of GLT25D1

Collagen is modified by hydroxylation and glycosylation of hydroxylysine residues. This glycosylation is initiated by the β1,O galactosyltransferases GLT25D1 and GLT25D2. The structurally similar protein cerebral endothelial cell adhesion molecule CEECAM1 was previously reported to be inactive when assayed for collagen glycosyltransferase activity. To address the cause of the absent galactosyltransferase activity, we have generated several chimeric constructs between the active human GLT25D1 and inactive human CEECAM1 proteins. The assay of these chimeric constructs pointed to a short central region and a large C-terminal region of CEECAM1 leading to the loss of collagen galactosyltransferase activity. Examination of the three DXD motifs of the active GLT25D1 by site-directed mutagenesis confirmed the importance of the first (amino acids 166–168) and second motif (amino acids 461–463) for enzymatic activity, whereas the third one was dispensable. Since the second DXD motif is incomplete in CEECAM1, we have restored the motif by introducing the substitution S461D. This change did not restore the activity of the C-terminal region, thereby showing that additional amino acids were required in this C-terminal region to confer enzymatic activity. Finally, we have introduced the substitution Q471R-V472M-N473Q-P474V in the CEECAM1-C-terminal construct, which is found in most animal GLT25D1 and GLT25D2 isoforms but not in CEECAM1. This substitution was shown to partially restore collagen galactosyltransferase activity, underlining its importance for catalytic activity in the C-terminal domain. Because multiple mutations in different regions of CEECAM1 contribute to the lack of galactosyltransferase activity, we deduced that CEECAM1 is functionally different from the related GLT25D1 protein.

Mimivirus collagen is modified by bifunctional lysyl hydroxylase and glycosyltransferase enzyme

Collagens, the most abundant proteins in animals, are modified by hydroxylation of proline and lysine residues and by glycosylation of hydroxylysine. Dedicated prolyl hydroxylase, lysyl hydroxylase, and collagen glycosyltransferase enzymes localized in the endoplasmic reticulum mediate these modifications prior to the formation of the collagen triple helix. Whereas collagen-like proteins have been described in some fungi, bacteria, and viruses, the post-translational machinery modifying collagens has never been described outside of animals. We demonstrate that the L230 open reading frame of the giant virus Acanthamoeba polyphaga mimivirus encodes an enzyme that has distinct lysyl hydroxylase and collagen glycosyltransferase domains. We show that mimivirus L230 is capable of hydroxylating lysine and glycosylating the resulting hydroxylysine residues in a native mimivirus collagen acceptor substrate. Whereas in animals from sponges to humans the transfer of galactose to hydroxylysine in collagen is conserved, the mimivirus L230 enzyme transfers glucose to hydroxylysine, thereby defining a novel type of collagen glycosylation in nature. The presence of hydroxylysine in mimivirus proteins was confirmed by amino acid analysis of mimivirus recovered from A. polyphaga cultures. This work shows for the first time that collagen post-translational modifications are not confined to the domains of life. The utilization of glucose instead of the galactose found throughout animals as well as a bifunctional enzyme rather than two separate enzymes may represent a parallel evolutionary track in collagen biology. These results suggest that giant viruses may have contributed to the evolution of collagen biology.

Digenic inheritance of mutations in FOXC1 and PITX2 : correlating transcription factor function and Axenfeld-Rieger disease severity

Disease-causing mutations affecting either one of the transcription factor genes, PITX2 or FOXC1, have been previously identified in patients with Axenfeld-Rieger syndrome (AR). We identified a family who segregate novel mutations in both PITX2 (p.Ser233Leu) and FOXC1 (c.609delC). The most severely affected individual, who presented with an atypical phenotype of corneal opacification, lens extrusion, persistent hyperplastic primary vitreous (PHPV), and subsequent bilateral retinal detachment, inherited mutations in both genes, whereas the single heterozygous mutations caused mild AR phenotypes. This is the first report of such digenic inheritance. By analyzing cognate targets of each gene, we showed that FOXC1 and PITX2 can independently regulate their own and each other's target gene promoters and do not show synergistic action in vitro. Mutation in either gene caused reduced transcriptional activation to different extents on the FOXO1 and PLOD1 promoters, whereas both mutations in combination showed the lowest level of activation. These data show how the compensatory activity of one factor, when the other is impaired, may lessen the phenotypic impact of developmental anomalies, yet reduced activity of both transcription factors increased disease severity. This suggests an under-reported mechanism for phenotypic variability whereby single mutations cause mild AR phenotypes, whereas digenic inheritance increases phenotypic severity.

Phenotypic variability of the kyphoscoliotic type of Ehlers-Danlos syndrome (EDS VIA): clinical, molecular and biochemical delineation

BACKGROUND

The kyphoscoliotic type of Ehlers-Danlos syndrome (EDS VIA) (OMIM 225400) is a rare inheritable connective tissue disorder characterized by a deficiency of collagen lysyl hydroxylase 1 (LH1; EC 1.14.11.4) due to mutations in PLOD1. Biochemically this results in underhydroxylation of collagen lysyl residues and, hence, an abnormal pattern of lysyl pyridinoline (LP) and hydroxylysyl pyridinoline (HP) crosslinks excreted in the urine. Clinically the disorder is characterized by hypotonia and kyphoscoliosis at birth, joint hypermobility, and skin hyperelasticity and fragility. Severe hypotonia usually leads to delay in gross motor development, whereas cognitive development is reported to be normal.

METHODS

We describe the clinical, biochemical and molecular characterisation, as well as electron microscopy findings of skin, in 15 patients newly diagnosed with this rare type of Ehlers-Danlos syndrome.

RESULTS

Age at diagnosis ranged from 5 months to 27 years, with only 1/3 of the patients been diagnosed correctly in the first year of life. A similar disease frequency was found in females and males, however a broad disease severity spectrum (intra- and interfamilial), independent of molecular background or biochemical phenotype, was observed. Kyphoscoliosis, one of the main clinical features was not present at birth in 4 patients. Importantly we also noted the occurrence of vascular rupture antenatally and postnatally, as well as developmental delay in 5 patients.

CONCLUSION

In view of these findings we propose that EDS VIA is a highly variable clinical entity, presenting with a broad clinical spectrum, which may also be associated with cognitive delay and an increased risk for vascular events. Genotype/phenotype association studies and additional molecular investigations in more extended EDS VIA populations will be necessary to further elucidate the cause of the variability of the disease severity.

Physiological and biochemical aspects of hydroxylations and demethylations catalyzed by human 2-oxoglutarate oxygenases

Pioneering work in the 1960s defined prolyl and lysyl hydroxylations as physiologically important oxygenase-catalyzed modifications in collagen biosynthesis; subsequent studies demonstrated that extracellular epidermal growth factor-like domains were hydroxylated at aspartyl and asparaginyl residues. More recent work on the hypoxia-sensing mechanism in animals has shown that prolyl and asparaginyl hydroxylation of the hypoxia-inducible transcription factor play central roles in sensing hypoxia, by regulating protein-protein interactions in an oxygen-dependent manner. The collective results imply that protein hydroxylation is more common than previously perceived. Most protein hydroxylases employ Fe(II) as a cofactor, and 2-oxoglutarate and oxygen as co-substrates. Related enzymes catalyze the demethylation of N(ɛ)-methyl lysine residues in histones and of N-methylated nucleic acids, as well as hydroxylation of 5-methyl cytosine in DNA and 5-methoxycarbonylmethyluridine at the wobble position of tRNA. The combination of new molecular biological and analytical techniques is likely to reveal further roles for oxygenase-mediated modifications to biomacromolecules.

RIN2 deficiency results in macrocephaly, alopecia, cutis laxa, and scoliosis: MACS syndrome

Inherited disorders of elastic tissue represent a complex and heterogeneous group of diseases, characterized often by sagging skin and occasionally by life-threatening visceral complications. In the present study, we report on an autosomal-recessive disorder that we have termed MACS syndrome (macrocephaly, alopecia, cutis laxa, and scoliosis). The disorder was mapped to chromosome 20p11.21-p11.23, and a homozygous frameshift mutation in RIN2 was found to segregate with the disease phenotype in a large consanguineous kindred. The mutation identified results in decreased expression of RIN2, a ubiquitously expressed protein that interacts with Rab5 and is involved in the regulation of endocytic trafficking. RIN2 deficiency was found to be associated with paucity of dermal microfibrils and deficiency of fibulin-5, which may underlie the abnormal skin phenotype displayed by the patients.

Spondylocheiro dysplastic form of the Ehlers-Danlos syndrome--an autosomal-recessive entity caused by mutations in the zinc transporter gene SLC39A13

We present clinical, radiological, biochemical, and genetic findings on six patients from two consanguineous families that show EDS-like features and radiological findings of a mild skeletal dysplasia. The EDS-like findings comprise hyperelastic, thin, and bruisable skin, hypermobility of the small joints with a tendency to contractures, protuberant eyes with bluish sclerae, hands with finely wrinkled palms, atrophy of the thenar muscles, and tapering fingers. The skeletal dysplasia comprises platyspondyly with moderate short stature, osteopenia, and widened metaphyses. Patients have an increased ratio of total urinary pyridinolines, lysyl pyridinoline/hydroxylysyl pyridinoline (LP/HP), of approximately 1 as opposed to approximately 6 in EDS VI or approximately 0.2 in controls. Lysyl and prolyl residues of collagens were underhydroxylated despite normal lysyl hydroxylase and prolyl 4-hydroxylase activities; underhydroxylation was a generalized process as shown by mass spectrometry of the alpha1(I)- and alpha2(I)-chain-derived peptides of collagen type I and involved at least collagen types I and II. A genome-wide SNP scan and sequence analyses identified in all patients a homozygous c.483_491 del9 SLC39A13 mutation that encodes for a membrane-bound zinc transporter SLC39A13. We hypothesize that an increased Zn(2+) content inside the endoplasmic reticulum competes with Fe(2+), a cofactor that is necessary for hydroxylation of lysyl and prolyl residues, and thus explains the biochemical findings. These data suggest an entity that we have designated "spondylocheiro dysplastic form of EDS (SCD-EDS)" to indicate a generalized skeletal dysplasia involving mainly the spine (spondylo) and striking clinical abnormalities of the hands (cheiro) in addition to the EDS-like features.

CRTAP Is Required for Prolyl 3- Hydroxylation and Mutations Cause Recessive Osteogenesis Imperfecta

Prolyl hydroxylation is a critical posttranslational modification that affects structure, function, and turnover of target proteins. Prolyl 3-hydroxylation occurs at only one position in the triple-helical domain of fibrillar collagen chains, and its biological significance is unknown. CRTAP shares homology with a family of putative prolyl 3-hydroxylases (P3Hs), but it does not contain their common dioxygenase domain. Loss of Crtap in mice causes an osteochondrodysplasia characterized by severe osteoporosis and decreased osteoid production. CRTAP can form a complex with P3H1 and cyclophilin B (CYPB), and Crtap-/- bone and cartilage collagens show decreased prolyl 3-hydroxylation. Moreover, mutant collagen shows evidence of overmodification, and collagen fibrils in mutant skin have increased diameter consistent with altered fibrillogenesis. In humans, CRTAP mutations are associated with the clinical spectrum of recessive osteogenesis imperfecta, including the type II and VII forms. Hence, dysregulation of prolyl 3-hydroxylation is a mechanism for connective tissue disease.

Ehlers-Danlos syndrome: classifications, oral manifestations, and dental considerations

Ehlers-Danlos syndrome (EDS) is the name given for 6 types of connective tissue disorders. While the prevalence of this disease is small, it is seen on every continent and affects both sexes and all races. The various types of EDS are reviewed with reference given to both the older Berlin nosology and the newer Villefranche nosology. Phenotypes of EDS vary depending upon which type of collagen is altered, leading the practitioner to the diagnosis before biochemical confirmation is obtained. In this regard, because collagen is present throughout the head and neck, oral and maxillofacial manifestations of the disease are discussed and are readily noticeable to the astute dentist. Specialists in several fields of dentistry are made aware of the complications EDS can pose on treatment, healing, and follow-up care.

The myotomal diwanka (lh3) glycosyltransferase and type XVIII collagen are critical for motor growth cone migration

The initial migration of motor growth cones from the spinal cord into the periphery requires extrinsic cues, yet their identities are largely unknown. In zebrafish diwanka mutants, motor growth cones are motile but fail to pioneer into the periphery. Here, we report on the positional cloning of diwanka and show that it encodes LH3, a myotomally expressed multifunctional enzyme with lysyl hydroxylase and glycosyltransferase domains. Cloning, expression analysis, and ubiquitous overexpression of other LH family members reveals that only diwanka (lh3) possesses a critical role in growth cone migration. We show that this unique role depends critically on the LH3 glycosyltransferase domain, and provide compelling evidence that diwanka (lh3) acts through myotomal type XVIII collagen, a ligand for neural-receptor protein tyrosine phosphatases that guide motor axons. Together, our results provide the first genetic evidence that glycosyltransferase modifications of the ECM play a critical role during vertebrate motor axon migration.

Mechanisms in protein O-glycan biosynthesis and clinical and molecular aspects of protein O-glycan biosynthesis defects: a review

BACKGROUND

Genetic diseases that affect the biosynthesis of protein O-glycans are a rapidly growing group of disorders. Because this group of disorders does not have a collective name, it is difficult to get an overview of O-glycosylation in relation to human health and disease. Many patients with an unsolved defect in N-glycosylation are found to have an abnormal O-glycosylation as well. It is becoming increasingly evident that the primary defect of these disorders is not necessarily localized in one of the glycan-specific transferases, but can likewise be found in the biosynthesis of nucleotide sugars, their transport to the endoplasmic reticulum (ER)/Golgi, and in Golgi trafficking. Already, disorders in O-glycan biosynthesis form a substantial group of genetic diseases. In view of the number of genes involved in O-glycosylation processes and the increasing scientific interest in congenital disorders of glycosylation, it is expected that the number of identified diseases in this group will grow rapidly over the coming years.

CONTENT

We first discuss the biosynthesis of protein O-glycans from their building blocks to their secretion from the Golgi. Subsequently, we review 24 different genetic disorders in O-glycosylation and 10 different genetic disorders that affect both N- and O-glycosylation. The key clinical, metabolic, chemical, diagnostic, and genetic features are described. Additionally, we describe methods that can be used in clinical laboratory screening for protein O-glycosylation biosynthesis defects and their pitfalls. Finally, we introduce existing methods that might be useful for unraveling O-glycosylation defects in the future.

Tendon and ligament: development, repair and disease

Tendons and ligaments (T/L) are very similar fibrous tissues that respectively connect muscle to bone and bone to bone. They are comprised of fibroblasts that produce large amounts of extra-cellular matrix, resulting in a dense and hypocellular structure. The complex molecular organization of T/L, together with high water content, are responsible for their viscoelastic properties, hence insuring their mechanical function. We will first review recent work on tendon embryology and discuss ligament formation, which has been less documented. We will next summarize our current knowledge of T/L molecular architecture, alterations of which are a major cause for disease. We will finally focus on T/L repair after injury and on genetic diseases responsible for T/L defects.

Nevo syndrome is allelic to the kyphoscoliotic type of the Ehlers-Danlos syndrome (EDS VIA)

We report on seven patients affected with Nevo syndrome, a rare, autosomal recessive disorder characterized by increased perinatal length, kyphosis, muscular hypotonia, and joint laxity. Since its first description by Nevo et al. [1974], only a few cases have been reported. Because some of these patients present clinical features similar to those of the kyphoscoliotic type of Ehlers-Danlos syndrome (EDS VIA), an inherited connective tissue disorder characterized by a deficiency of lysyl hydroxylase due to mutations in PLOD1, we studied seven patients with Nevo syndrome, three of whom have previously been reported, and four of whom are new. In the five patients from whom urine was available, the ratio of total urinary lysyl pyridinoline (LP) to hydroxylysyl pyridinoline (HP) was elevated (8.2, 7.8, 8.6, 3.5, and 4.8, respectively) compared with that in controls (0.20 +/- 0.05, range 0.10-0.38), and similar to that observed in patients with EDS VIA (5.97 +/- 0.99, range 4.3-8.1). Six patients were homozygous for a point mutation in exon 9 of PLOD1 causing a p.R319X nonsense mutation, while one patient was homozygous for a large deletion comprising exon 17 of PLOD1. We conclude that the Nevo syndrome is allelic to and clinically indistinguishable from EDS VIA, and present evidence that increased length at birth and wristdrop, in addition to muscular hypotonia and kyphoscoliosis, should prompt the physician to consider EDS VIA earlier than heretofore.

Spontaneous Multiple Arterial Dissections Presenting With Renal Infarction and Subarachnoid Hemorrhage in a Patient Under Treatment for Infertility

A 36-year-old woman developed multiple spontaneous arterial dissections in both renal arteries, the carotid artery, superior mesenteric artery, and vertebral artery, but not the aorta, and she suffered a renal infarction and subarachnoid hemorrhage within a short period of time. She had been undergoing frequent injections of human chorionic gonadotropin and human menopausal gonadotropin, together with oral estrogen therapy, during a 5-year infertility treatment regimen. As she had no other history of any disorder affecting the arterial walls, this therapy is suspected to have caused the multiple arterial deformities. Although cases of isolated arterial dissection are occasionally reported, it is rare for multiple dissections and serious symptoms to occur simultaneously.

Identification, expression, and tissue distribution of the three rat lysyl hydroxylase isoforms

Lysyl hydroxylases (LH) (procollagen-lysine 2-oxoglutarate 5-dioxygenase; PLOD) catalyse the hydroxylation of lysine residues during the post-translational modification of collagenous proteins. In this paper, we describe the first identification and cloning of LH isoforms 2 and 3 from the rat, including both LH2 splice variants (LH2a and LH2b). The rat LHs are expressed in almost all tissue and cell types examined, indicating a probable lack of tissue specificity for LH function. All LH isoforms were stably transfected into CHO-K1 cells and this represents the first example of recombinant LH production in a eukaryotic cell line. Expression and production of all LH isoforms led to an increase in total collagen synthesis. LH1 and LH2a expression and production led to an increase in total pyridinium cross-link production. Evidence that LH2a possesses telopeptide lysyl hydroxylase activity, previously thought to be a novel enzyme, is presented.

PITX2 isoform-specific regulation of atrial natriuretic factor expression: synergism and repression with Nkx2.5

PITX2 and Nkx2.5 are two of the earliest known transcriptional markers of vertebrate heart development. Pitx2-/- mice present with severe cardiac malformations and embryonic lethality, demonstrating a role for PITX2 in heart development. However, little is known about the downstream targets of PITX2 in cardiogenesis. We report here that the atrial natriuretic factor (ANF) promoter is a target of PITX2. PITX2A, PITX2B, and PITX2C isoforms differentially activate the ANF promoter. However, only PITX2C can synergistically activate the ANF promoter in the presence of Nkx2.5. We further demonstrate that the procollagen lysyl hydroxylase (PLOD1) promoter is regulated by Nkx2.5. Mechanistically, PITX2C and Nkx2.5 synergistically regulate ANF and PLOD1 expression through binding to their respective DNA elements. Surprisingly, PITX2A activation of the ANF and PLOD1 promoters is repressed by co-transfection of Nkx2.5 in the C3H10T1/2 embryonic fibroblast cell line. Pitx2a and Pitx2c are endogenously expressed in C3H10T1/2 cells, and these cells express factors that differentially regulate PITX2 isoform activities. We provide a new mechanism for the regulation of heart development by PITX2 isoforms through the regulation of ANF and PLOD1 gene expression and Nkx2.5 transcriptional activity.

The kyphoscoliotic type of Ehlers-Danlos syndrome (type VI): differential effects on the hydroxylation of lysine in collagens I and II revealed by analysis of cross-linked telopeptides from urine

The kyphoscoliotic type of Ehlers-Danlos syndrome (EDS type VIA) (OMIM 225400) is an autosomal recessive connective tissue disorder that results from mutations in the lysyl hydroxylase 1 gene (PLOD1) causing underhydroxylation of lysine residues in tissue collagens, particularly of skin. Previous studies have shown that the pool of collagen cross-linking amino acids, hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP) excreted in urine has an abnormally low HP/LP ratio, which is diagnostic of the condition. Here we isolated cross-linked peptides containing these residues from the urine of a child with EDS VIA homozygous for a mutation that results in a stop codon and effective null expression of PLOD1 enzyme activity. Peptides that had originated from bone type I collagen and cartilage type II collagen were identified. A cross-linked N-telopeptide fraction that is derived from bone type I collagen contained only LP, no HP, which means that the helical lysines at residues 930 of alpha 1(I) and 933 of alpha 2(I) of the collagen triple-helix had not been hydroxylated. The equivalent peptide fraction from a normal child's urine gave a ratio of HP to LP of 1.5:1 typical for normal bone collagen. A second cross-linked peptide that is derived from the C-telopeptide domain of cartilage type II collagen showed both HP and LP in a 2:1 ratio, compared with 18:1 for the equivalent peptide from a normal child's urine. The results show that in EDS VIA, bone type I collagen is more markedly underhydroxylated than cartilage type II collagen, at least at those helical sites that form cross-links. The residual fraction of HP found in the urine of EDS VI patients therefore appears to be contributed in significant part by the degradation products of cartilage. Since PLOD1 is null, other PLOD genes must be responsible for the helical hydroxylation activity that results in HP. The presented approach of analyzing urinary cross-linked C-telopeptide fragments of type II collagen may allow the detection of chondrodysplasias due to genetic defects in lysyl hydroxylase isoforms active in cartilage.

Tenascin-X deficiency mimics Ehlers-Danlos syndrome in mice through alteration of collagen deposition

Tenascin-X is a large extracellular matrix protein of unknown function. Tenascin-X deficiency in humans is associated with Ehlers-Danlos syndrome, a generalized connective tissue disorder resulting from altered metabolism of the fibrillar collagens. Because TNXB is the first Ehlers-Danlos syndrome gene that does not encode a fibrillar collagen or collagen-modifying enzyme, we suggested that tenascin-X might regulate collagen synthesis or deposition. To test this hypothesis, we inactivated Tnxb in mice. Tnxb-/- mice showed progressive skin hyperextensibility, similar to individuals with Ehlers-Danlos syndrome. Biomechanical testing confirmed increased deformability and reduced tensile strength of their skin. The skin of Tnxb-/- mice was histologically normal, but its collagen content was significantly reduced. At the ultrastructural level, collagen fibrils of Tnxb-/- mice were of normal size and shape, but the density of fibrils in their skin was reduced, commensurate with the reduction in collagen content. Studies of cultured dermal fibroblasts showed that although synthesis of collagen I by Tnxb-/- and wildtype cells was similar, Tnxb-/- fibroblasts failed to deposit collagen I into cell-associated matrix. This study confirms a causative role for TNXB in human Ehlers-Danlos syndrome and suggests that tenascin-X is an essential regulator of collagen deposition by dermal fibroblasts.

A recessive form of the Ehlers-Danlos syndrome caused by tenascin-X deficiency

BACKGROUND

The Ehlers-Danlos syndrome is a heritable connective-tissue disorder caused by defects in fibrillar-collagen metabolism. Mutations in the type V collagen genes account for up to 50 percent of cases of classic Ehlers-Danlos syndrome, but many other cases are unexplained. We investigated whether the deficiency of the tenascins, extracellular-matrix proteins that are highly expressed in connective tissues, was associated with the Ehlers-Danlos syndrome.

METHODS

We screened serum samples from 151 patients with the classic, hypermobility, or vascular types of the Ehlers-Danlos syndrome; 75 patients with psoriasis; 93 patients with rheumatoid arthritis; and 21 healthy persons for the presence of tenascin-X and tenascin-C by enzyme-linked immunosorbent assay. We examined the expression of tenascins and type V collagen in skin by immunohistochemical methods and sequenced the tenascin-X gene.

RESULTS

Tenascin-X was present in serum from all normal subjects, all patients with psoriasis, all patients with rheumatoid arthritis, and 146 of 151 patients with the Ehlers-Danlos syndrome. Tenascin-X was absent from the serum of the 5 remaining patients with Ehlers-Danlos syndrome, who were unrelated. Tenascin-X deficiency was confirmed in these patients by analysis of skin fibroblasts and by immunostaining of skin. The expression of tenascin-C and type V collagen was normal in these patients. All five of these patients had hypermobile joints, hyperelastic skin, and easy bruising, without atrophic scarring. Tenascin-X mutations were identified in all tenascin-X-deficient patients; one patient had a homozygous tenascin-X gene deletion, one was heterozygous for the deletion, and three others had homozygous truncating point mutations, confirming a causative role for tenascin-X and a recessive pattern of inheritance.

CONCLUSIONS

Tenascin-X deficiency causes a clinically distinct, recessive form of the Ehlers-Danlos syndrome. This finding indicates that factors other than the collagens or collagen-processing enzymes can cause the syndrome and suggests a central role for tenascin-X in maintaining the integrity of collagenous matrix.

Different pattern of collagen cross-links in two sclerotic skin diseases: lipodermatosclerosis and circumscribed scleroderma

Changes in the process of cross-linking of collagen molecules are associated with defects in the biomechanical stability of the extracellular matrix. Fibrosis of skin is characterized by an increase in pyridinolines, which are hydroxylysine aldehyde derived cross-links usually absent in healthy skin. In this study, we analyzed cross-links in lipodermatosclerosis and localized scleroderma to address the question whether all the mature cross-links currently characterized are increased in fibrosis in addition to the increase in pyridinolines. As psoralen plus ultraviolet A treatment leads to clinical improvement of fibrotic plaques in localized scleroderma we analyzed the cross-link content in lesional skin after bath psoralen plus ultraviolet A therapy. In skin from patients with localized scleroderma an increase in the total number of mature cross-links was found to be due to an increase in both pyridinolines and dehydro-histidinohydroxymerodesmosine. The concentration of histidinohydroxylysinonorleucine was unchanged. By contrast, the total number of mature cross-links was decreased in lipodermatosclerosis. This decrease was caused by a decrease of lysine aldehyde derived cross-links (dehydro-histidinohydroxymerodesmosine and histidinohydroxylysinonorleucine), whereas the concentration of pyridinolines increased. A decrease in the content of pyridinolines after bath psoralen plus ultraviolet A treatment was found in six out of nine patients with localized scleroderma, which might reflect a remodeling of the extracellular matrix. Our data provide evidence that sclerosis of skin is associated with either an increase in the number of cross-links per molecule of collagen or a change in the molecular nature of the cross-links formed.

Adenoviral gene transfer restores lysyl hydroxylase activity in type VI Ehlers-Danlos syndrome

Type VI Ehlers-Danlos syndrome is a disease characterized by disturbed lysine hydroxylation of collagen. The disease is caused by mutations in lysyl hydroxylase 1 gene and it affects several organs including the cardiovascular system, the joint and musculoskeletal system, and the skin. The skin of type VI Ehlers-Danlos syndrome patients is hyperelastic, scars easily, and heals slowly and poorly. We hypothesized that providing functional lysyl hydroxylase 1 gene to the fibroblasts in and around wounds in these patients would improve healing. In this study we tested the feasibility of transfer of the lysyl hydroxylase 1 gene into fibroblasts derived from rats and a type VI Ehlers-Danlos syndrome patient (in vitro) and into rat skin (in vivo). We first cloned human lysyl hydroxylase 1 cDNA into a recombinant adenoviral vector (Ad5RSV-LH). Transfection of human type VI Ehlers-Danlos syndrome fibroblasts (about 20% of normal lysyl hydroxylase 1 activity) with the vector increased lysyl hydroxylase 1 activity in these cells to near or greater levels than that of wild type, unaffected fibroblasts. The adenoviral vector successfully transfected rat fibroblasts producing both beta-galactosidase and lysyl hydroxylase 1 gene activity. We next expanded our studies to a rodent model. Intradermal injections of the vector to the abdominal skin of rats produced lysyl hydroxylase 1 mRNA and elevated lysyl hydroxylase 1 activity, in vivo. These data suggest the feasibility of gene replacement therapy to modify skin wound healing in type VI Ehlers-Danlos syndrome patients.

PITX2 regulates procollagen lysyl hydroxylase (PLOD) gene expression: implications for the pathology of Rieger syndrome

The Rieger syndrome is an autosomal dominant disease characterized by ocular, craniofacial, and umbilical defects. Patients have mutations in PITX2, a paired-bicoid homeobox gene, also involved in left/right polarity determination. In this study we have identified a family of genes for enzymes responsible for hydroxylizing lysines in collagens as one group of likely cognate targets of PITX2 transcriptional regulation. The mouse procollagen lysyl hydroxylase (Plod)-2 gene was enriched for by chromatin precipitation using a PITX2/Pitx2-specific antibody. Plod-2, as well as the human PLOD-1 promoters, contains multiple bicoid (PITX2) binding elements. We show these elements to bind PITX2 specifically in vitro. The PLOD-1 promoter induces the expression of a luciferase reporter gene in the presence of PITX2 in cotransfection experiments. The Rieger syndrome causing PITX2 mutant T68P fails to induce PLOD-1-luciferase. Mutations and rearrangements in PLOD-1 are known to be prevalent in patients with Ehlers-Danlos syndrome, kyphoscoliosis type (type VI [EDVI]). Several of the same organ systems are involved in Rieger syndrome and EDVI.

Mutations in the lysyl hydroxylase 1 gene that result in enzyme deficiency and the clinical phenotype of Ehlers-Danlos syndrome type VI

The Ehlers-Danlos syndromes are a heterogeneous group of inherited connective tissue disorders that are characterized by joint hypermobility and skin fragility and hyperextensibility. Patients with the autosomal recessive type VI variant of the Ehlers-Danlos syndromes (EDS VI), also classified as the kyphoscoliotic type, are clinically characterized by neonatal kyphoscoliosis, generalized joint laxity, skin fragility, and severe muscle hypotonia at birth. Biochemically, this has been attributed to a deficiency of lysyl hydroxylase (LH), an important posttranslational modifying enzyme in collagen biosynthesis. This enzyme hydroxylates specific lysine residues in the collagen molecule to form hydroxylysines which have two important functions. The residues serve as attachment sites for galactose and glucosylgalactose and they also act as precursors of the crosslinking process that gives collagen its tensile strength. At least 20 different mutations have been identified in the LH1 gene (the originally described form) that contribute to LH deficiency and the clinical characteristics of EDS VI. Two of these mutations, a large duplication of exons 10-16, arising from a homologous recombination of intronic Alu sequences, and a nonsense mutation, Y511X, in exon 14 of the LH1 gene, have been identified in five or more unrelated patients. Both mutations appear to have originated from a single ancestral gene. Alternative processing pathways involving alternate splicing and mRNA degradation, which reduce the effect of the mutant allele and restore partial activity of the enzyme, have been identified. A second class of EDS VI has been proposed in which patients have the clinical phenotype of EDS VI but their levels of LH activity are normal. The biochemical basis for this form of EDS VI is currently unknown.

A compound heterozygote patient with Ehlers-Danlos syndrome type VI has a deletion in one allele and a splicing defect in the other allele of the lysyl hydroxylase gene

We report the first deletion mutation and the first splicing defect in the lysyl hydroxylase gene in a compound heterozygote patient with Ehlers-Danlos syndrome type VI with markedly reduced lysyl hydroxylase activity. Northern analysis of the RNA isolated from skin fibroblasts of the patient demonstrated the presence of a truncated lysyl hydroxylase mRNA. PCR and sequence analysis confirmed the truncation and indicated that the cells contain two types of shortened mRNAs, one lacking the sequences corresponding to exon 16 and the other lacking that corresponding to exon 17 of the lysyl hydroxylase gene. Analysis of genomic DNA revealed deletion of the penultimate adenosine from the 3' end of intron 15 from one allele. This defect was probably responsible for the skipping of exon 16 sequences from the transcript. The other allele, inherited from the mother, contains an Alu-Alu recombination with a deletion of about 3,000 nucleotides from the gene; this abnormality explains the lack of exon 17 sequences. The identified mutations in exon 16 and exon 17 do not alter the reading frame of the transcripts.

Complete exon-intron organization of the gene for human lysyl hydroxylase 3 (LH3)

Lysyl hydroxylase (LH) catalyzes the formation of hydroxylysine in collagens and related proteins by the hydroxylation of lysine residues in peptide linkages. Three isoenzymes of LH have so far been characterized. We report here that the human LH3 gene is 11.6 kb in size and consists of 19 exons. Transcription is initiated at one major site and several minor sites, the first exon containing 249-335 bp of untranslated sequences and 109 bp of a translated sequence. Exons 2-18 are similar in size to those of the human LH1 gene, whereas the introns are markedly shorter. The LH3 gene contains a total of 15 full length Alu retroposons or partial Alu fragments of more than 100 bp, in introns 5, 6, 12, 15 and 17. These generate a potential for genomic rearrangements, as has been shown for the LH1 gene in Ehlers-Danlos syndrome type VI. The 5'-flanking region of the LH3 gene was found to be entirely different from that of the LH1 gene, suggesting different regulation of these two genes.