Collagen type VI and related disorders: Bethlem myopathy and Ullrich scleroatonic muscular dystrophy

Genetic architecture of white striping in turkeys (Meleagris gallopavo)

White striping (WS) is a myopathy of growing concern to the turkey industry. It is rising in prevalence and has negative consequences for consumer acceptance and the functional properties of turkey meat. The objective of this study was to conduct a genome-wide association study (GWAS) and functional analysis on WS severity. Phenotypic data consisted of white striping scored on turkey breast fillets (N = 8422) by trained observers on a 0-3 scale (none to severe). Of the phenotyped birds, 4667 genotypic records were available using a proprietary 65 K single nucleotide polymorphism (SNP) chip. The SNP effects were estimated using a linear mixed model with a 30-SNP sliding window approach used to express the percentage genetic variance explained. Positional candidate genes were those located within 50 kb of the top 1% of SNP windows explaining the most genetic variance. Of the 95 positional candidate genes, seven were further classified as functional candidate genes because of their association with both a significant gene ontology and molecular function term. The results of the GWAS emphasize the polygenic nature of the trait with no specific genomic region contributing a large portion to the overall genetic variance. Significant pathways relating to growth, muscle development, collagen formation, circulatory system development, cell response to stimulus, and cytokine production were identified. These results help to support published biological associations between WS and hypoxia and oxidative stress and provide information that may be useful for future-omics studies in understanding the biological associations with WS development in turkeys.

The recurrent deep intronic pseudoexon-inducing variant COL6A1 c.930+189C>T results in a consistently severe phenotype of COL6-related dystrophy: Towards clinical trial readiness for splice-modulating therapy

Collagen VI-related dystrophies (COL6-RDs) manifest with a spectrum of clinical phenotypes, ranging from Ullrich congenital muscular dystrophy (UCMD), presenting with prominent congenital symptoms and characterised by progressive muscle weakness, joint contractures and respiratory insufficiency, to Bethlem muscular dystrophy, with milder symptoms typically recognised later and at times resembling a limb girdle muscular dystrophy, and intermediate phenotypes falling between UCMD and Bethlem muscular dystrophy. Despite clinical and immunohistochemical features highly suggestive of COL6-RD, some patients had remained without an identified causative variant in COL6A1, COL6A2 or COL6A3. With combined muscle RNA-sequencing and whole-genome sequencing we uncovered a recurrent, de novo deep intronic variant in intron 11 of COL6A1 (c.930+189C>T) that leads to a dominantly acting in-frame pseudoexon insertion. We subsequently identified and have characterised an international cohort of forty-four patients with this COL6A1 intron 11 causative variant, one of the most common recurrent causative variants in the collagen VI genes. Patients manifest a consistently severe phenotype characterised by a paucity of early symptoms followed by an accelerated progression to a severe form of UCMD, except for one patient with somatic mosaicism for this COL6A1 intron 11 variant who manifests a milder phenotype consistent with Bethlem muscular dystrophy. Characterisation of this individual provides a robust validation for the development of our pseudoexon skipping therapy. We have previously shown that splice-modulating antisense oligomers applied in vitro effectively decreased the abundance of the mutant pseudoexon-containing COL6A1 transcripts to levels comparable to the in vivo scenario of the somatic mosaicism shown here, indicating that this therapeutic approach carries significant translational promise for ameliorating the severe form of UCMD caused by this common recurrent COL6A1 causative variant to a Bethlem muscular dystrophy phenotype.

Modeling Human Muscular Dystrophies in Zebrafish: Mutant Lines, Transgenic Fluorescent Biosensors, and Phenotyping Assays

Muscular dystrophies (MDs) are a heterogeneous group of myopathies characterized by progressive muscle weakness leading to death from heart or respiratory failure. MDs are caused by mutations in genes involved in both the development and organization of muscle fibers. Several animal models harboring mutations in MD-associated genes have been developed so far. Together with rodents, the zebrafish is one of the most popular animal models used to reproduce MDs because of the high level of sequence homology with the human genome and its genetic manipulability. This review describes the most important zebrafish mutant models of MD and the most advanced tools used to generate and characterize all these valuable transgenic lines. Zebrafish models of MDs have been generated by introducing mutations to muscle-specific genes with different genetic techniques, such as (i) N-ethyl-N-nitrosourea (ENU) treatment, (ii) the injection of specific morpholino, (iii) tol2-based transgenesis, (iv) TALEN, (v) and CRISPR/Cas9 technology. All these models are extensively used either to study muscle development and function or understand the pathogenetic mechanisms of MDs. Several tools have also been developed to characterize these zebrafish models by checking (i) motor behavior, (ii) muscle fiber structure, (iii) oxidative stress, and (iv) mitochondrial function and dynamics. Further, living biosensor models, based on the expression of fluorescent reporter proteins under the control of muscle-specific promoters or responsive elements, have been revealed to be powerful tools to follow molecular dynamics at the level of a single muscle fiber. Thus, zebrafish models of MDs can also be a powerful tool to search for new drugs or gene therapies able to block or slow down disease progression.

Bethlem Myopathy (Collagen VI-Related Dystrophies): A Retrospective Cohort Study on Musculoskeletal Pathologies and Clinical Course

BACKGROUND

Collagen VI-related myopathies with pathologic COL6A1, COL6A2, and COL6A3 variants manifest as a phenotypic continuum of rare disorders, including Bethlem myopathy (BM), characterized by early onset muscle weakness, proximal joint contractures, and distal joint laxity. Herein we discuss the concomitant orthopedic manifestations of BM, potential management strategies, and patient outcomes.

METHODS

An IRB-approved retrospective cohort study (n=23) from 2 pediatric institutions with a confirmed diagnosis of BM. Charts were reviewed for demographic data, age of disease presentation and diagnosis, COL6 genotype, diagnosis method, ambulation status, need for assistance, musculoskeletal abnormalities, other systemic comorbidities, advanced imaging and screening diagnostics, previous surgical interventions, and progression of the disease.

RESULTS

The mean age was 11.65 years (range 3 to 19 y). Mean age at initial presentation with symptoms was 4.18 years old, whereas diagnosis was delayed until 8.22 years old on average. Muscle weakness was the most common presenting symptom (65.2%), and 73.9% of patients required some use of assistive or mobility devices. Overall, 30.4% of patients were diagnosed with scoliosis; 57.1% required operative intervention for their scoliosis; 43.5% of patients had acetabular dysplasia; 10% required open reduction of a dislocated hip; 10% required closed reduction with hip spica application; 10% required bilateral periacetabular osteotomies for instability; 91.3% of patients developed foot and ankle deformities; 33.3% of patients underwent posteromedial-lateral equinovarus releases; 28.6% required an Achilles tendon lengthening, and 86.9% of patients had muscle tendon contractures, the most common locations being the ankle (55%) and elbow (40%).

CONCLUSION

Although often less severe than other more common neuropathies and myopathies like Charcot-Marie-Tooth disease and Duchenne muscular dystrophy, BM does lead to progressive musculoskeletal deformity and disability. Its relative rarity makes it less familiar to providers and likely contributes to delays in diagnosis. Scoliosis, hip dysplasia, and equinus and varus ankle deformities are the most common musculoskeletal deformities. Physicians and surgeons should appropriately counsel patients and families about the clinical course of this disorder and the potential need for mobility assistance or surgical procedures.

LEVEL OF EVIDENCE

III, Prognostic. study.

The Presentation of Two Unrelated Clinical Cases from the Republic of North Ossetia-Alania with the Same Previously Undescribed Variant in the COL6A2 Gene

Here, we described three affected boys from two unrelated families of Ossetian-Digor origin from the Republic of North Ossetia-Alania who were admitted to the Research Centre for Medical Genetics with unspecified muscular dystrophy. High-throughput sequencing was performed and revealed two novel frameshift variants in the COL6A2 gene (NM_001849.3) in a heterozygous state each in both cases: c.508_535delinsCTGTGG and c.1659_1660del (case 1) and c.1689del and c.1659_1660del (case 2). In two cases, the same nucleotide variant in the COL6A2 gene (c.1659_1660del) was observed. We have suggested that the variant c.1659_1660del may be common in the Ossetian-Digor population because two analyzed families have the same ancestry from the same subethnic group of Ossetians). The screening for an asymptomatic carriage of the nucleotide variant c.1659_1660del in 54 healthy donors from Ossetian-Digor population revealed that the estimated carrier frequency is 0.0093 (CI: 0.0002–0.0505), which is high for healthy carriers of the pathogenic variant. Molecular genetic, anamnestic data and clinical examination results allowed us to diagnose Ullrich muscular dystrophy in those affected boys. Genetic heterogeneity and phenotypic diversity of muscular dystrophies complicate diagnosis. It is important to make a differential diagnosis of such conditions and use HTS methods to determine the most accurate diagnosis.

Molecular Pathways and Key Genes Associated With Breast Width and Protein Content in White Striping and Wooden Breast Chicken Pectoral Muscle

Growth-related abnormalities affecting modern chickens, known as White Striping (WS) and Wooden Breast (WB), have been deeply investigated in the last decade. Nevertheless, their precise etiology remains unclear. The present study aimed at providing new insights into the molecular mechanisms involved in their onset by identifying clusters of co-expressed genes (i.e., modules) and key loci associated with phenotypes highly related to the occurrence of these muscular disorders. The data obtained by a Weighted Gene Co-expression Network Analysis (WGCNA) were investigated to identify hub genes associated with the parameters breast width (W) and total crude protein content (PC) of Pectoralis major muscles (PM) previously harvested from 12 fast-growing broilers (6 normal vs. 6 affected by WS/WB). W and PC can be considered markers of the high breast yield of modern broilers and the impaired composition of abnormal fillets, respectively. Among the identified modules, the turquoise (r = -0.90, p < 0.0001) and yellow2 (r = 0.91, p < 0.0001) were those most significantly related to PC and W, and therefore respectively named “protein content” and “width” modules. Functional analysis of the width module evidenced genes involved in the ubiquitin-mediated proteolysis and inflammatory response. GTPase activator activity, PI3K-Akt signaling pathway, collagen catabolic process, and blood vessel development have been detected among the most significant functional categories of the protein content module. The most interconnected hub genes detected for the width module encode for proteins implicated in the adaptive responses to oxidative stress (i.e., THRAP3 and PRPF40A), and a member of the inhibitor of apoptosis family (i.e., BIRC2) involved in contrasting apoptotic events related to the endoplasmic reticulum (ER)-stress. The protein content module showed hub genes coding for different types of collagens (such as COL6A3 and COL5A2), along with MMP2 and SPARC, which are implicated in Collagen type IV catabolism and biosynthesis. Taken together, the present findings suggested that an ER stress condition may underly the inflammatory responses and apoptotic events taking place within affected PM muscles. Moreover, these results support the hypothesis of a role of the Collagen type IV in the cascade of events leading to the occurrence of WS/WB and identify novel actors probably involved in their onset.

Pathogenesis of Enamel-Renal Syndrome Associated Gingival Fibromatosis: A Proteomic Approach

The enamel renal syndrome (ERS) is a rare disorder featured by amelogenesis imperfecta, gingival fibromatosis and nephrocalcinosis. ERS is caused by bi-allelic mutations in the secretory pathway pseudokinase FAM20A. How mutations in FAM20A may modify the gingival connective tissue homeostasis and cause fibromatosis is currently unknown. We here analyzed conditioned media of gingival fibroblasts (GFs) obtained from four unrelated ERS patients carrying distinct mutations and control subjects. Secretomic analysis identified 109 dysregulated proteins whose abundance had increased (69 proteins) or decreased (40 proteins) at least 1.5-fold compared to control GFs. Proteins over-represented were mainly involved in extracellular matrix organization, collagen fibril assembly, and biomineralization whereas those under-represented were extracellular matrix-associated proteins. More specifically, transforming growth factor-beta 2, a member of the TGFβ family involved in both mineralization and fibrosis was strongly increased in samples from GFs of ERS patients and so were various known targets of the TGFβ signaling pathway including Collagens, Matrix metallopeptidase 2 and Fibronectin. For the over-expressed proteins quantitative RT-PCR analysis showed increased transcript levels, suggesting increased synthesis and this was further confirmed at the tissue level. Additional immunohistochemical and western blot analyses showed activation and nuclear localization of the classical TGFβ effector phospho-Smad3 in both ERS gingival tissue and ERS GFs. Exposure of the mutant cells to TGFB1 further upregulated the expression of TGFβ targets suggesting that this pathway could be a central player in the pathogenesis of the ERS gingival fibromatosis. In conclusion our data strongly suggest that TGFβ -induced modifications of the extracellular matrix contribute to the pathogenesis of ERS. To our knowledge this is the first proteomic-based analysis of FAM20A-associated modifications.

Collagen VI-related myopathy with scoliosis alone: A case report and literature review

BACKGROUND

Scoliosis is a complex three-dimensional deformity of spine and one of the common complications of collagen VI-related myopathy, caused by mutations in collagen type VI alpha 1 chain (COL6A1), COL6A2, and COL6A3 genes. The typical clinical presentations of collagen VI-related myopathy include weakness, hypotonia, laxity of distal joints, contractures of proximal joints, and skeletal deformities.

CASE SUMMARY

A 28-year-old female presented with scoliosis for 28 years without weakness, hypotonia, laxity of distal joints, and contracture of proximal joints. Computed tomography and magnetic resonance imaging revealed hemivertebra, butterfly vertebra, and the missing vertebral space. Patients underwent orthopedic surgery and paravertebral muscle biopsy. The Cobb angle dropped from 103.4° to 52.9°. However, the muscle biopsy showed neurogenic muscular atrophy with myogenic lesions, suggesting congenital muscular dystrophy. Gene analysis indicated that mutations in COL6A1 (c.1612-10G>A) and COL6A2 (c.115+10G>T, c.2749G>A). Immunohistochemistry staining for collagen VI displayed shallow and discontinuous. Eventually, the patient was diagnosed as collagen VI-related myopathy.

CONCLUSION

This newly found subtype of collagen VI-related myopathy has no typical manifestations; however, it is characterized by severe scoliosis and congenital vertebral deformity.

Collagen VI as a driver and disease biomarker in human fibrosis

Fibrosis of visceral organs such as the lungs, heart, kidneys and liver remains a major cause of morbidity and mortality and is also associated with many other disorders, including cancer and metabolic disease. In this review, we focus upon the microfibrillar collagen VI, which is present in the extracellular matrix (ECM) of most tissues. However, expression is elevated in numerous fibrotic conditions, such as idiopathic pulmonary disease (IPF), and chronic liver and kidney diseases. Collagen VI is composed of three subunits α1, α2 and α3, which can be replaced with alternate chains of α4, α5 or α6. The C-terminal globular domain (C5) of collagen VI α3 can be proteolytically cleaved to form a biologically active fragment termed endotrophin, which has been shown to actively drive fibrosis, inflammation and insulin resistance. Tissue biopsies have long been considered the gold standard for diagnosis and monitoring of progression of fibrotic disease. The identification of neoantigens from enzymatically processed collagen chains have revolutionised the biomarker field, allowing rapid diagnosis and evaluation of prognosis of numerous fibrotic conditions, as well as providing valuable clinical trial endpoint determinants. Collagen VI chain fragments such as endotrophin (PRO-C6), C6M and C6Mα3 are emerging as important biomarkers for fibrotic conditions.

The critical role of collagen VI in lung development and chronic lung disease

Type VI collagen (collagen VI) is an obligate extracellular matrix component found mainly in the basement membrane region of many mammalian tissues and organs, including skeletal muscle and throughout the respiratory system. Collagen VI is probably most recognized in medicine as the genetic cause of a spectrum of muscular dystrophies, including Ullrich Congenital Myopathy and Bethlem Myopathy. Collagen VI is thought to contribute to myopathy, at least in part, by mediating muscle fiber integrity by anchoring myoblasts to the muscle basement membrane. Interestingly, collagen VI myopathies present with restrictive respiratory insufficiency, thought to be due primarily to thoracic muscular weakening. Although it was recently recognized as one of the (if not the) most abundant collagens in the mammalian lung, there is a substantive knowledge gap concerning its role in respiratory system development and function. A few studies have suggested that collagen VI insufficiency is associated with airway epithelial cell survival and altered lung function. Our recent work suggested collagen VI may be a genomic risk factor for chronic lung disease in premature infants. Using this as motivation, we thoroughly assessed the role of collagen VI in lung development and in lung epithelial cell biology. Here, we describe the state-of-the-art for collagen VI cell and developmental biology within the respiratory system, and reveal its essential roles in normal developmental processes and airway epithelial cell phenotype and intracellular signaling.

Whole Organ Engineering: Approaches, Challenges, and Future Directions

End-stage organ failure remains a leading cause of morbidity and mortality across the globe. The only curative treatment option currently available for patients diagnosed with end-stage organ failure is organ transplantation. However, due to a critical shortage of organs, only a fraction of these patients are able to receive a viable organ transplantation. Those patients fortunate enough to receive a transplant must then be subjected to a lifelong regimen of immunosuppressant drugs. The concept of whole organ engineering offers a promising alternative to organ transplantation that overcomes these limitations. Organ engineering is a discipline that merges developmental biology, anatomy, physiology, and cellular interactions with enabling technologies such as advanced biomaterials and biofabrication to create bioartificial organs that recapitulate native organs in vivo. There have been numerous developments in bioengineering of whole organs over the past two decades. Key technological advancements include (1) methods of whole organ decellularization and recellularization, (2) three-dimensional bioprinting, (3) advanced stem cell technologies, and (4) the ability to genetically modify tissues and cells. These advancements give hope that organ engineering will become a commercial reality in the next decade. In this review article, we describe the foundational principles of whole organ engineering, discuss key technological advances, and provide an overview of current limitations and future directions.

Autosomal recessive Bethlem myopathy: A clinical, genetic and functional study

Bethlem myopathy represents the milder form of the spectrum of Collagen VI-related dystrophies, which are characterized by a clinical continuum between the two extremities, the Bethlem myopathy and the Ullrich congenital muscular dystrophy, and include less defined intermediate phenotypes. Bethlem myopathy is mainly an autosomal dominant disorder and the causing mutations occur in the COL6A genes encoding for the α1 (COL6A1), α2 (COL6A2) and α3 (COL6A3) chains. However, few cases of recessive inheritance have been also reported. We here describe clinical, genetic and functional findings in a recessive Bethlem myopathy family harbouring two novel pathogenic mutations in the COL6A2 gene. Two adult siblings presented with muscle weakness and wasting, elbows and Achilles tendon retractions, lumbar hyperlordosis, waddling gait and positive Gowers' sign. Muscle biopsy showed a dystrophic pattern. Molecular analysis of the COL6A2 gene revealed the novel paternally-inherited nonsense p.Gln889* mutation and the maternally-inherited p.Pro260_Lys261insProPro small insertion. Fibroblast studies in both affected patients showed the concomitant reduction in the amount of normal Collagen VI (p.Gln889*) and impairment of Collagen VI secretion and assembly (p.Pro260_Lys261insProPro). Each of the two variants behave as a recessive mutation as shown by the asymptomatic heterozygous parents, while their concomitant effects determined a relatively mild Bethlem myopathy phenotype. This study confirms the occurrence of recessive inherited Bethlem myopathy and expands the genetic heterogeneity of this group of muscle diseases.

A recurrent COL6A1 pseudoexon insertion causes muscular dystrophy and is effectively targeted by splice-correction therapies

The clinical application of advanced next-generation sequencing technologies is increasingly uncovering novel classes of mutations that may serve as potential targets for precision medicine therapeutics. Here, we show that a deep intronic splice defect in the COL6A1 gene, originally discovered by applying muscle RNA sequencing in patients with clinical findings of collagen VI-related dystrophy (COL6-RD), inserts an in-frame pseudoexon into COL6A1 mRNA, encodes a mutant collagen α1(VI) protein that exerts a dominant-negative effect on collagen VI matrix assembly, and provides a unique opportunity for splice-correction approaches aimed at restoring normal gene expression. Using splice-modulating antisense oligomers, we efficiently skipped the pseudoexon in patient-derived fibroblast cultures and restored a wild-type matrix. Similarly, we used CRISPR/Cas9 to precisely delete an intronic sequence containing the pseudoexon and efficiently abolish its inclusion while preserving wild-type splicing. Considering that this splice defect is emerging as one of the single most frequent mutations in COL6-RD, the design of specific and effective splice-correction therapies offers a promising path for clinical translation.

From Structure to Phenotype: Impact of Collagen Alterations on Human Health

The extracellular matrix (ECM) is a highly dynamic and heterogeneous structure that plays multiple roles in living organisms. Its integrity and homeostasis are crucial for normal tissue development and organ physiology. Loss or alteration of ECM components turns towards a disease outcome. In this review, we provide a general overview of ECM components with a special focus on collagens, the most abundant and diverse ECM molecules. We discuss the different functions of the ECM including its impact on cell proliferation, migration and differentiation by highlighting the relevance of the bidirectional cross-talk between the matrix and surrounding cells. By systematically reviewing all the hereditary disorders associated to altered collagen structure or resulting in excessive collagen degradation, we point to the functional relevance of the collagen and therefore of the ECM elements for human health. Moreover, the large overlapping spectrum of clinical features of the collagen-related disorders makes in some cases the patient clinical diagnosis very difficult. A better understanding of ECM complexity and molecular mechanisms regulating the expression and functions of the various ECM elements will be fundamental to fully recognize the different clinical entities.

Gene expression profiles reveal key genes for early diagnosis and treatment of adamantinomatous craniopharyngioma

Adamantinomatous craniopharyngioma (ACP) is an aggressive brain tumor that occurs predominantly in the pediatric population. Conventional diagnosis method and standard therapy cannot treat ACPs effectively. In this paper, we aimed to identify key genes for ACP early diagnosis and treatment. Datasets GSE94349 and GSE68015 were obtained from Gene Expression Omnibus database. Consensus clustering was applied to discover the gene clusters in the expression data of GSE94349 and functional enrichment analysis was performed on gene set in each cluster. The protein-protein interaction (PPI) network was built by the Search Tool for the Retrieval of Interacting Genes, and hubs were selected. Support vector machine (SVM) model was built based on the signature genes identified from enrichment analysis and PPI network. Dataset GSE94349 was used for training and testing, and GSE68015 was used for validation. Besides, RT-qPCR analysis was performed to analyze the expression of signature genes in ACP samples compared with normal controls. Seven gene clusters were discovered in the differentially expressed genes identified from GSE94349 dataset. Enrichment analysis of each cluster identified 25 pathways that highly associated with ACP. PPI network was built and 46 hubs were determined. Twenty-five pathway-related genes that overlapped with the hubs in PPI network were used as signatures to establish the SVM diagnosis model for ACP. The prediction accuracy of SVM model for training, testing, and validation data were 94, 85, and 74%, respectively. The expression of CDH1, CCL2, ITGA2, COL8A1, COL6A2, and COL6A3 were significantly upregulated in ACP tumor samples, while CAMK2A, RIMS1, NEFL, SYT1, and STX1A were significantly downregulated, which were consistent with the differentially expressed gene analysis. SVM model is a promising classification tool for screening and early diagnosis of ACP. The ACP-related pathways and signature genes will advance our knowledge of ACP pathogenesis and benefit the therapy improvement.

Mapping QTL for white striping in relation to breast muscle yield and meat quality traits in broiler chickens

Background

White striping (WS) is an emerging muscular defect occurring on breast and thigh muscles of broiler chickens. It is characterized by the presence of white striations parallel to the muscle fibers and has significant consequences for meat quality. The etiology of WS remains poorly understood, even if previous studies demonstrated that the defect prevalence is related to broiler growth and muscle development. Moreover, recent studies showed moderate to high heritability values of WS, which emphasized the role of genetics in the expression of the muscle defect. The aim of this study was to identify the first quantitative trait loci (QTLs) for WS as well as breast muscle yield (BMY) and meat quality traits using a genome-wide association study (GWAS). We took advantage of two divergent lines of chickens selected for meat quality through Pectoralis major ultimate pH (pHu) and which exhibit the muscular defect. An expression QTL (eQTL) detection was further performed for some candidate genes, either suggested by GWAS analysis or based on their biological function.

Results

Forty-two single nucleotide polymorphisms (SNPs) associated with WS and other meat quality traits were identified. They defined 18 QTL regions located on 13 chromosomes. These results supported a polygenic inheritance of the studied traits and highlighted a few pleiotropic regions. A set of 16 positional and/or functional candidate genes was designed for further eQTL detection. A total of 132 SNPs were associated with molecular phenotypes and defined 21 eQTL regions located on 16 chromosomes. Interestingly, several co-localizations between QTL and eQTL regions were observed which could suggest causative genes and gene networks involved in the variability of meat quality traits and BMY.

Conclusions

The QTL mapping carried out in the current study for WS did not support the existence of a major gene, but rather suggested a polygenic inheritance of the defect and of other studied meat quality traits. We identified several candidate genes involved in muscle metabolism and structure and in muscular dystrophies. The eQTL analyses showed that they were part of molecular networks associated with WS and meat quality phenotypes and suggested a few putative causative genes.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4598-9) contains supplementary material, which is available to authorized users.

A group of patients with Marfan's syndrome, who have finger and toe contractures, displays tendons' alterations upon an ultrasound examination: are these features common among classical Marfan patients?

The involvement of the musculoskeletal system with other mild pleiotropic manifestations represents a clinical criterion, called "systemic features," to d iagnose Marfan's syndrome. We aimed to investigate the features of the hands and feet redressable contractures present in a group of Marfan patients. In 13 patients with previously diagnosed Marfan's syndrome, an accurate clinical examination was performed. In particular the characterization of the musculoskeletal system by visual analogic scale to measure muscle pain (VAS) and muscle strength (MRC system) was carried out; the Beighton scale score was used to evaluate the articular hypermobility. Ultrasound examination (US) was performed to detect deep-superficial flexor tendons and extensor tendons of both hands, and the short and long flexor and extensor tendons of the fingers and toes in static and dynamic positions. The ImageJ program was adopted to measure a profile of tendon echo-intensity. A reduction of the thickness of all tendons was detected by US in our patients; the VAS and Beighton scale scores were in normal ranges. The profile of tendon echo-intensity showed different textural details in all Marfan patients. This study provides evidence for other contractures' localization, and for altered findings of the tendons in patients with Marfan syndrome and finger/toe contractures. These changes may be associated with structural modifications in connective tissue.

Oxidative Stress-Mediated Skeletal Muscle Degeneration: Molecules, Mechanisms, and Therapies

Oxidative stress is a loss of balance between the production of reactive oxygen species during cellular metabolism and the mechanisms that clear these species to maintain cellular redox homeostasis. Increased oxidative stress has been associated with muscular dystrophy, and many studies have proposed mechanisms that bridge these two pathological conditions at the molecular level. In this review, the evidence indicating a causal role of oxidative stress in the pathogenesis of various muscular dystrophies is revisited. In particular, the mediation of cellular redox status in dystrophic muscle by NF-κB pathway, autophagy, telomere shortening, and epigenetic regulation are discussed. Lastly, the current stance of targeting these pathways using antioxidant therapies in preclinical and clinical trials is examined.

A TALEN-Exon Skipping Design for a Bethlem Myopathy Model in Zebrafish

Presently, human collagen VI-related diseases such as Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) remain incurable, emphasizing the need to unravel their etiology and improve their treatments. In UCMD, symptom onset occurs early, and both diseases aggravate with ageing. In zebrafish fry, morpholinos reproduced early UCMD and BM symptoms but did not allow to study the late phenotype. Here, we produced the first zebrafish line with the human mutation frequently found in collagen VI-related disorders such as UCMD and BM. We used a transcription activator-like effector nuclease (TALEN) to design the col6a1^ama605003-line with a mutation within an essential splice donor site, in intron 14 of the col6a1 gene, which provoke an in-frame skipping of exon 14 in the processed mRNA. This mutation at a splice donor site is the first example of a template-independent modification of splicing induced in zebrafish using a targetable nuclease. This technique is readily expandable to other organisms and can be instrumental in other disease studies. Histological and ultrastructural analyzes of homozygous and heterozygous mutant fry and 3 months post-fertilization (mpf) fish revealed co-dominantly inherited abnormal myofibers with disorganized myofibrils, enlarged sarcoplasmic reticulum, altered mitochondria and misaligned sarcomeres. Locomotion analyzes showed hypoxia-response behavior in 9 mpf col6a1 mutant unseen in 3 mpf fish. These symptoms worsened with ageing as described in patients with collagen VI deficiency. Thus, the col6a1^ama605003-line is the first adult zebrafish model of collagen VI-related diseases; it will be instrumental both for basic research and drug discovery assays focusing on this type of disorders.

Melanocytes from Patients Affected by Ullrich Congenital Muscular Dystrophy and Bethlem Myopathy have Dysfunctional Mitochondria That Can be Rescued with Cyclophilin Inhibitors

Ullrich congenital muscular dystrophy and Bethlem myopathy are caused by mutations in collagen VI (ColVI) genes, which encode an extracellular matrix protein; yet, mitochondria play a major role in disease pathogenesis through a short circuit caused by inappropriate opening of the permeability transition pore, a high-conductance channel, which causes a shortage in ATP production. We find that melanocytes do not produce ColVI yet they bind it at the cell surface, suggesting that this protein may play a trophic role and that its absence may cause lesions similar to those seen in skeletal muscle. We show that mitochondria in melanocytes of Ullrich congenital muscular dystrophy and Bethlem myopathy patients display increased size, reduced matrix density, and disrupted cristae, findings that suggest a functional impairment. In keeping with this hypothesis, mitochondria (i) underwent anomalous depolarization after inhibition of the F-ATP synthase with oligomycin, and (ii) displayed decreased respiratory reserve capacity. The non-immunosuppressive cyclophilin inhibitor NIM811 prevented mitochondrial depolarization in response to oligomycin in melanocytes from both Ullrich congenital muscular dystrophy and Bethlem myopathy patients, and partially restored the respiratory reserve of melanocytes from one Bethlem myopathy patient. These results match our recent findings on melanocytes from patients affected by Duchenne muscular dystrophy (Pellegrini et al., 2013), and suggest that skin biopsies may represent a minimally invasive tool to investigate mitochondrial dysfunction and to evaluate drug efficacy in ColVI-related myopathies and possibly in other muscle wasting conditions like aging sarcopenia.

Nutritional status evaluation in patients affected by bethlem myopathy and ullrich congenital muscular dystrophy

Collagen VI mutations lead to disabling myopathies like Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD). We have investigated the nutritional and metabolic status of one UCMD and seven BM patients (five female, three male, mean age 31 ± 9 years) in order to find a potential metabolic target for nutritional intervention. For this study, we used standard anthropometric tools, such as BMI evaluation and body circumference measurements. All results were compared to dual-energy X-ray absorptiometry (DXA), considered the “gold standard” method. Energy intake of each patient was evaluated through longitudinal methods (7-day food diary) while resting energy expenditure (REE) was predicted using specific equations and measured by indirect calorimetry. Clinical evaluation included general and nutritional blood and urine laboratory analyses and quantitative muscle strength measurement by hand-held dynamometry. BM and UCMD patients showed an altered body composition, characterized by low free fat mass (FFM) and high fat mass (FM), allowing us to classify them as sarcopenic, and all but one as sarcopenic-obese. Another main result was the negative correlation between REE/FFM ratio (basal energy expenditure per kilograms of fat-free mass) and the severity of the disease, as defined by the muscle megascore (correlation coefficient −0.955, P-value <0.001). We postulate that the increase of the REE/FFM ratio in relation to the severity of the disease may be due to an altered and pathophysiological loss of energetic efficiency at the expense of skeletal muscle. We show that a specific metabolic disequilibrium is related to the severity of the disease, which may represent a target for a nutritional intervention in these patients.

Defective collagen VI α6 chain expression in the skeletal muscle of patients with collagen VI-related myopathies

Collagen VI is a non-fibrillar collagen present in the extracellular matrix (ECM) as a complex polymer; the mainly expressed form is composed of α1, α2 and α3 chains; mutations in genes encoding these chains cause myopathies known as Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM). The collagen VI α6 chain is a recently identified component of the ECM of the human skeletal muscle. Here we report that the α6 chain was dramatically reduced in skeletal muscle and muscle cell cultures of genetically characterized UCMD, BM and MM patients, independently of the clinical phenotype, the gene involved and the effect of the mutation on the expression of the “classical” α1α2α3 heterotrimer. By contrast, the collagen VI α6 chain was normally expressed or increased in the muscle of patients affected by other forms of muscular dystrophy, the overexpression matching with areas of increased fibrosis. In vitro treatment with TGF-β1, a potent collagen inducer, promoted the collagen VI α6 chain deposition in the ECM of normal muscle cells, whereas, in cultures derived from collagen VI-related myopathy patients, the collagen VI α6 chain failed to develop a network outside the cells and accumulated in the endoplasmic reticulum. The defect of the α6 chain points to a contribution to the pathogenesis of collagen VI-related disorders.

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Collagen VI is an ECM component of the human skeletal muscle.

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We evaluated the α6 chain in collagen VI-related and other muscular dystrophies.

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The α6 chain was reduced in collagen VI-related diseases but not in other myopathies.

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A correlation between the α6 chain and fibrosis was demonstrated in MDC1A.

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The α6 chain is involved in the pathogenesis of collagen VI diseases and fibrosis.

Diagnostic approach to the congenital muscular dystrophies

Congenital muscular dystrophies (CMDs) are early onset disorders of muscle with histological features suggesting a dystrophic process. The congenital muscular dystrophies as a group encompass great clinical and genetic heterogeneity so that achieving an accurate genetic diagnosis has become increasingly challenging, even in the age of next generation sequencing. In this document we review the diagnostic features, differential diagnostic considerations and available diagnostic tools for the various CMD subtypes and provide a systematic guide to the use of these resources for achieving an accurate molecular diagnosis. An International Committee on the Standard of Care for Congenital Muscular Dystrophies composed of experts on various aspects relevant to the CMDs performed a review of the available literature as well as of the unpublished expertise represented by the members of the committee and their contacts. This process was refined by two rounds of online surveys and followed by a three-day meeting at which the conclusions were presented and further refined. The combined consensus summarized in this document allows the physician to recognize the presence of a CMD in a child with weakness based on history, clinical examination, muscle biopsy results, and imaging. It will be helpful in suspecting a specific CMD subtype in order to prioritize testing to arrive at a final genetic diagnosis.

Oxidative stress in muscular dystrophy: from generic evidence to specific sources and targets

Muscular dystrophies (MDs) are a heterogeneous group of diseases that share a common end-point represented by muscular wasting. MDs are caused by mutations in a variety of genes encoding for different molecules, including extracellular matrix, transmembrane and membrane-associated proteins, cytoplasmic enzymes and nuclear proteins. However, it is still to be elucidated how genetic mutations can affect the molecular mechanisms underlying the contractile impairment occurring in these complex pathologies. The intracellular accumulation of reactive oxygen species (ROS) is widely accepted to play a key role in contractile derangements occurring in the different forms of MDs. However, scarce information is available concerning both the most relevant sources of ROS and their major molecular targets. This review focuses on (i) the sources of ROS, with a special emphasis on monoamine oxidase, a mitochondrial enzyme, and (ii) the targets of ROS, highlighting the relevance of the oxidative modification of myofilament proteins.

Collagen genes and exercise-associated muscle cramping

OBJECTIVE

The authors hypothesized that variants within genes, such as COL5A1, COL3A1, COL6A1, and COL12A1, that code for connective tissue components of the musculoskeletal system may modulate susceptibility to exercise-associated muscle cramping (EAMC). Specifically, the aim of this study was to investigate if the COL5A1 rs12722 (C/T), COL3A1 rs1800255 (G/A), COL6A1 rs35796750 (T/C), and COL12A1 rs970547 (A/G) polymorphisms are associated with a history of EAMC.

DESIGN

Retrospective genetic case-control association study.

SETTING

Participants were recruited at triathlon and ultra-marathon events and were asked to report physical activity, medical history, and cramping history.

PARTICIPANTS

One hundred sixteen participants with self-reported history of EAMC within the past 12 months before an ultra-endurance event were included as cases in this study (EAMC group). One hundred fifty participants with no self-reported history of previous (lifelong) EAMC were included as controls (NON group).

INTERVENTIONS

All participants were genotyped for the selected variants.

MAIN OUTCOME MEASURES

Differences in genotype frequency distributions, for COL5A1 rs12722, COL3A1 rs1800255, COL6A1 rs35796750, and COL12A1 rs970547, among the cases and controls.

RESULTS

The COL5A1 CC genotype was significantly overrepresented (P = 0.031) among the NON group (21.8%) when compared with the EAMC group (11.1%). No significant genotype differences were found for the COL3A1 (P = 0.828), COL6A1 (P = 0.300), or COL12A1 (P = 0.120) genotypes between the EAMC and NON groups.

CONCLUSIONS

This study identified, for the first time, the COL5A1 gene as a potential marker for a history of EAMC.

No association between COL3A1, COL6A1 or COL12A1 gene variants and range of motion

Approximately 64-70% of the variability in joint range of motion (ROM) is heritable. A common variant within a type V collagen (COL5A1) gene is associated with joint range of motion. Like type V collagen, types III, VI and XII collagen are also involved in fibril assembly and/or diameter regulation. Mutations within the genes that encode these proteins, COL3A1, COL6A1 and COL12A1, also cause connective tissue hypermobility disorders and phenotypes. The aim of this study was to determine if variants within these genes are associated with measures of joint range of motion. Three hundred and fifty apparently healthy and physically active Caucasian participants were recruited. Anthropometric measurements were taken. Sit-and-reach (SR), straight leg raise (SLR) and total shoulder rotation (ShTR) range of motion were measured. All participants were genotyped for COL3A1 rs1800255, COL6A1 rs35796750 and COL12A1 rs970547. COL3A1 rs1800255, COL6A1 rs35796750 and COL12A1 rs970547 were not significantly associated with sit-and-reach, straight leg raise or total shoulder rotation range of motion. Furthermore, no significant age-genotype interaction effects were identified between the variants and range of motion measurements. None of the variants investigated in this study were significantly associated with any of the measures of range of motion used. Further studies are required to identify additional intrinsic and extrinsic factors that may determine range of motion, including the genetic component.

Physical exercise stimulates autophagy in normal skeletal muscles but is detrimental for collagen VI-deficient muscles

Autophagy is a catabolic process that provides the degradation of altered/damaged organelles through the fusion between autophagosomes and lysosomes. Proper regulation of the autophagic flux is fundamental for the homeostasis of skeletal muscles in physiological conditions and in response to stress. Defective as well as excessive autophagy is detrimental for muscle health and has a pathogenic role in several forms of muscle diseases. Recently, we found that defective activation of the autophagic machinery plays a key role in the pathogenesis of muscular dystrophies linked to collagen VI. Impairment of the autophagic flux in collagen VI null (Col6a1–/–) mice causes accumulation of dysfunctional mitochondria and altered sarcoplasmic reticulum, leading to apoptosis and degeneration of muscle fibers. Here we show that physical exercise activates autophagy in skeletal muscles. Notably, physical training exacerbated the dystrophic phenotype of Col6a1–/– mice, where autophagy flux is compromised. Autophagy was not induced in Col6a1–/– muscles after either acute or prolonged exercise, and this led to a marked increase of muscle wasting and apoptosis. These findings indicate that proper activation of autophagy is important for muscle homeostasis during physical activity.

Altered trabecular bone structure and delayed cartilage degeneration in the knees of collagen VI null mice

Mutation or loss of collagen VI has been linked to a variety of musculoskeletal abnormalities, particularly muscular dystrophies, tissue ossification and/or fibrosis, and hip osteoarthritis. However, the role of collagen VI in bone and cartilage structure and function in the knee is unknown. In this study, we examined the role of collagen VI in the morphology and physical properties of bone and cartilage in the knee joint of Col6a1(-/-) mice by micro-computed tomography (microCT), histology, atomic force microscopy (AFM), and scanning microphotolysis (SCAMP). Col6a1(-/-) mice showed significant differences in trabecular bone structure, with lower bone volume, connectivity density, trabecular number, and trabecular thickness but higher structure model index and trabecular separation compared to Col6a1(+/+) mice. Subchondral bone thickness and mineral content increased significantly with age in Col6a1(+/+) mice, but not in Col6a1(-/-) mice. Col6a1(-/-) mice had lower cartilage degradation scores, but developed early, severe osteophytes compared to Col6a1(+/+) mice. In both groups, cartilage roughness increased with age, but neither the frictional coefficient nor compressive modulus of the cartilage changed with age or genotype, as measured by AFM. Cartilage diffusivity, measured via SCAMP, varied minimally with age or genotype. The absence of type VI collagen has profound effects on knee joint structure and morphometry, yet minimal influences on the physical properties of the cartilage. Together with previous studies showing accelerated hip osteoarthritis in Col6a1(-/-) mice, these findings suggest different roles for collagen VI at different sites in the body, consistent with clinical data.

An analysis of exome sequencing for diagnostic testing of the genes associated with muscle disease and spastic paraplegia

In this study, we assess exome sequencing (ES) as a diagnostic alternative for genetically heterogeneous disorders. Because ES readily identified a previously reported homozygous mutation in the CAPN3 gene for an individual with an undiagnosed limb girdle muscular dystrophy, we evaluated ES as a generalizable clinical diagnostic tool by assessing the targeting efficiency and sequencing coverage of 88 genes associated with muscle disease (MD) and spastic paraplegia (SPG). We used three exome-capture kits on 125 individuals. Exons constituting each gene were defined using the UCSC and CCDS databases. The three exome-capture kits targeted 47-92% of bases within the UCSC-defined exons and 97-99% of bases within the CCDS-defined exons. An average of 61.2-99.5% and 19.1-99.5% of targeted bases per gene were sequenced to 20X coverage within the CCDS-defined MD and SPG coding exons, respectively. Greater than 95-99% of targeted known mutation positions were sequenced to ≥1X coverage and 55-87% to ≥20X coverage in every exome. We conclude, therefore, that ES is a rapid and efficient first-tier method to screen for mutations, particularly within the CCDS annotated exons, although its application requires disclosure of the extent of coverage for each targeted gene and supplementation with second-tier Sanger sequencing for full coverage.

Animal models of muscular dystrophy

The muscular dystrophies (MDs) represent a diverse collection of inherited human disorders, which affect to varying degrees skeletal, cardiac, and sometimes smooth muscle (Emery, 2002). To date, more than 50 different genes have been implicated as causing one or more types of MD (Bansal et al., 2003). In many cases, invaluable insights into disease mechanisms, structure and function of gene products, and approaches for therapeutic interventions have benefited from the study of animal models of the different MDs (Arnett et al., 2009). The large number of genes that are associated with MD and the tremendous number of animal models that have been developed preclude a complete discussion of each in the context of this review. However, we summarize here a number of the more commonly used models together with a mixture of different types of gene and MD, which serves to give a general overview of the value of animal models of MD for research and therapeutic development.

Congenital muscular dystrophies: a brief review

Congenital muscular dystrophies (CMDs) are clinically and genetically heterogeneous neuromuscular disorders with onset at birth or in infancy in which the muscle biopsy is compatible with a dystrophic myopathy. In the past 10 years, knowledge of neuromuscular disorders has dramatically increased, particularly with the exponential boost of disclosing the genetic background of CMDs. This review will highlight the clinical description of the most important forms of CMD, paying particular attention to the main keys for diagnostic approach. The diagnosis of CMDs requires the concurrence of expertise in multiple specialties (neurology, morphology, genetics, neuroradiology) available in a few centers worldwide that have achieved sufficient experience with the different CMD subtypes. Currently, molecular diagnosis is of paramount importance not only for phenotype-genotype correlations, genetic and prenatal counseling, and prognosis and aspects of management, but also concerning the imminent availability of clinical trials and treatments.

Molecular mining of alleles in water buffalo Bubalus bubalis and characterization of the TSPY1 and COL6A1 genes

Background

Minisatellites are an integral part of eukaryotic genomes and show variation in the complexity of their organization. Besides their presence in non-coding regions, a small fraction of them are part of the transcriptome, possibly participating in gene regulation, expression and silencing. We studied the minisatellite (TGG)_n tagged transcriptome in the water buffalo Bubalus bubalis across various tissues and the spermatozoa, and characterized the genes TSPY1 and COL6A1 discovered in the process.

Results

Minisatellite associated sequence amplification (MASA) conducted using cDNA and oligonucleotide primer (TGG)₅ uncovered 38 different mRNA transcripts from somatic tissues and gonads and 15 from spermatozoa. These mRNA transcripts corresponded to several known and novel genes. The majority of the transcripts showed the highest level of expression either in the testes or spermatozoa with exception of a few showing higher expression levels in the lungs and liver. Transcript SR1, which is expressed in all the somatic tissues and gonads, was found to be similar to the Bos taurus collagen type VI alpha 1 gene (COL6A1). Similarly, SR29, a testis-specific transcript, was found to be similar to the Bos taurus testis-specific Y-encoded protein-1 representing cancer/testis antigen 78 (CT78). Subsequently, full length coding sequences (cds) of these two transcripts were obtained. Quantitative PCR (q-PCR) revealed 182-202 copies of theTSPY1 gene in water buffalo, which localized to the Y chromosome.

Conclusions

The MASA approach enabled us to identify several genes, including two of clinical significance, without screening an entire cDNA library. Genes identified with TGG repeats are not part of a specific family of proteins and instead are distributed randomly throughout the genome. Genes showing elevated expression in the testes and spermatozoa may prove to be potential candidates for in-depth characterization. Furthermore, their possible involvement in fertility or lack thereof would augment animal biotechnology.

The collagen VI-related myopathies: muscle meets its matrix

The collagen VI-related myopathy known as Ullrich congenital muscular dystrophy is an early-onset disease that combines substantial muscle weakness with striking joint laxity and progressive contractures. Patients might learn to walk in early childhood; however, this ability is subsequently lost, concomitant with the development of frequent nocturnal respiratory failure. Patients with intermediate phenotypes of collagen VI-related myopathy display a lesser degree of weakness and a longer period of ambulation than do individuals with Ullrich congenital muscular dystrophy, and the spectrum of disease finally encompasses mild Bethlem myopathy, in which ambulation persists into adulthood. Dominant and recessive autosomal mutations in the three major collagen VI genes-COL6A1, COL6A2, and COL6A3-can underlie this entire clinical spectrum, and result in deficient or dysfunctional microfibrillar collagen VI in the extracellular matrix of muscle and other connective tissues, such as skin and tendons. The potential effects on muscle include progressive dystrophic changes, fibrosis and evidence for increased apoptosis, which potentially open avenues for pharmacological intervention. Optimized respiratory management, including noninvasive nocturnal ventilation together with careful orthopedic management, are the current mainstays of treatment and have already led to a considerable improvement in life expectancy for children with Ullrich congenital muscular dystrophy.

Large genomic deletions: a novel cause of Ullrich congenital muscular dystrophy

Two mutational mechanisms are known to underlie Ullrich congenital muscular dystrophy (UCMD): heterozygous dominant negatively-acting mutations and recessively-acting loss-of-function mutations. We describe large genomic deletions on chromosome 21q22.3 as a novel type of mutation underlying recessively inherited UCMD in 2 families. Clinically unaffected parents carrying large genomic deletions of COL6A1and COL6A2also provide conclusive evidence that haploinsufficiency for COL6A1and COL6A2is not a disease mechanism for Bethlem myopathy. Our findings have important implications for the genetic evaluation of patients with collagen VI-related myopathies as well as for potential therapeutic interventions for this patient population.

The collagen VI-related myopathies Ullrich congenital muscular dystrophy and Bethlem myopathy

Mutations in the genes COL6A1, COL6A2, and COL6A3, coding for three α chains of collagen type VI, underlie a spectrum of myopathies, ranging from the severe congenital muscular dystrophy-type Ullrich (UCMD) to the milder Bethlem myopathy (BM), with disease manifestations of intermediate severity in between. UCMD is characterized by early-onset weakness, associated with pronounced distal joint hyperlaxity and the early onset or early progression of more proximal contractures. In the most severe cases ambulation is not achieved, or it may be achieved only for a limited period of time. BM may be of early or later onset, but is milder in its manifestations, typically allowing for ambulation well into adulthood, whereas typical joint contractures are frequently prominent. A genetic spectrum is emerging, with BM being caused mostly by dominantly acting mutations, although rarely recessive inheritance of BM is also possible, whereas both dominantly as well as recessively acting mutations underlie UCMD.

Congenital muscular dystrophy. Part II: a review of pathogenesis and therapeutic perspectives

The congenital muscular dystrophies (CMDs) are a group of genetically and clinically heterogeneous hereditary myopathies with preferentially autosomal recessive inheritance, that are characterized by congenital hypotonia, delayed motor development and early onset of progressive muscle weakness associated with dystrophic pattern on muscle biopsy. The clinical course is broadly variable and can comprise the involvement of the brain and eyes. From 1994, a great development in the knowledge of the molecular basis has occurred and the classification of CMDs has to be continuously up dated. In the last number of this journal, we presented the main clinical and diagnostic data concerning the different subtypes of CMD. In this second part of the review, we analyse the main reports from the literature concerning the pathogenesis and the therapeutic perspectives of the most common subtypes of CMD: MDC1A with merosin deficiency, collagen VI related CMDs (Ullrich and Bethlem), CMDs with abnormal glycosylation of alpha-dystroglycan (Fukuyama CMD, Muscle-eye-brain disease, Walker Warburg syndrome, MDC1C, MDC1D), and rigid spine syndrome, another much rare subtype of CMDs not related with the dystrophin/glycoproteins/extracellular matrix complex.

Zebrafish models of collagen VI-related myopathies

Collagen VI is an integral part of the skeletal muscle extracellular matrix, providing mechanical stability and facilitating matrix-dependent cell signaling. Mutations in collagen VI result in either Ullrich congenital muscular dystrophy (UCMD) or Bethlem myopathy (BM), with UCMD being clinically more severe. Recent studies demonstrating increased apoptosis and abnormal mitochondrial function in Col6a1 knockout mice and in human myoblasts have provided the first mechanistic insights into the pathophysiology of these diseases. However, how loss of collagen VI causes mitochondrial dysfunction remains to be understood. Progress is hindered in part by the lack of an adequate animal model for UCMD, as knockout mice have a mild motor phenotype. To further the understanding of these disorders, we have generated zebrafish models of the collagen VI myopathies. Morpholinos designed to exon 9 of col6a1 produced a severe muscle disease reminiscent of UCMD, while ones to exon 13 produced a milder phenotype similar to BM. UCMD-like zebrafish have increased cell death and abnormal mitochondria, which can be attenuated by treatment with the proton pump modifier cyclosporin A (CsA). CsA improved the motor deficits in UCMD-like zebrafish, but failed to reverse the sarcolemmal membrane damage. In all, we have successfully generated the first vertebrate model matching the clinical severity of UCMD and demonstrated that CsA provides phenotypic improvement, thus corroborating data from knockout mice supporting the use of mitochondrial permeability transition pore modifiers as therapeutics in patients, and providing proof of principle for the utility of the zebrafish as a powerful preclinical model.

Identification of a deep intronic mutation in the COL6A2 gene by a novel custom oligonucleotide CGH array designed to explore allelic and genetic heterogeneity in collagen VI-related myopathies

Background

Molecular characterization of collagen-VI related myopathies currently relies on standard sequencing, which yields a detection rate approximating 75-79% in Ullrich congenital muscular dystrophy (UCMD) and 60-65% in Bethlem myopathy (BM) patients as PCR-based techniques tend to miss gross genomic rearrangements as well as copy number variations (CNVs) in both the coding sequence and intronic regions.

Methods

We have designed a custom oligonucleotide CGH array in order to investigate the presence of CNVs in the coding and non-coding regions of COL6A1, A2, A3, A5 and A6 genes and a group of genes functionally related to collagen VI. A cohort of 12 patients with UCMD/BM negative at sequencing analysis and 2 subjects carrying a single COL6 mutation whose clinical phenotype was not explicable by inheritance were selected and the occurrence of allelic and genetic heterogeneity explored.

Results

A deletion within intron 1A of the COL6A2 gene, occurring in compound heterozygosity with a small deletion in exon 28, previously detected by routine sequencing, was identified in a BM patient. RNA studies showed monoallelic transcription of the COL6A2 gene, thus elucidating the functional effect of the intronic deletion. No pathogenic mutations were identified in the remaining analyzed patients, either within COL6A genes, or in genes functionally related to collagen VI.

Conclusions

Our custom CGH array may represent a useful complementary diagnostic tool, especially in recessive forms of the disease, when only one mutant allele is detected by standard sequencing. The intronic deletion we identified represents the first example of a pure intronic mutation in COL6A genes.

Autosomal recessive inheritance of classic Bethlem myopathy

Mutations in the collagen VI genes (COL6A1, COL6A2 and COL6A3) result in Ullrich congenital muscular dystrophy (CMD), Bethlem myopathy or phenotypes intermediate between Ullrich CMD and Bethlem myopathy. While Ullrich CMD can be caused by either recessively or dominantly acting mutations, Bethlem myopathy has thus far been described as an exclusively autosomal dominant condition. We report two adult siblings with classic Bethlem myopathy who are compound heterozygous for a single nucleotide deletion (exon 23; c.1770delG), leading to in-frame skipping of exon 23 on the maternal allele, and a missense mutation p.R830W in exon 28 on the paternal allele. The parents are carriers of the respective mutations and are clinically unaffected. The exon skipping mutation in exon 23 results in a chain incapable of heterotrimeric assembly, while p.R830W likely ameliorates the phenotype into the Bethlem range. Thus, autosomal recessive inheritance can also underlie Bethlem myopathy, supporting the notion that Ullrich CMD and Bethlem myopathy are part of a common clinical and genetic spectrum.

Predominant fiber atrophy and fiber type disproportion in early ullrich disease

Ullrich disease (congenital muscular dystrophy type Ullrich, UCMD) is a severe congenital disorder of muscle caused by recessive and dominant mutations in the three genes that encode the alpha-chains of collagen type VI. Little is known about the early pathogenesis of this myopathy. The aim of this study was to investigate early histological changes in muscle of patients with molecularly confirmed UCMD. Muscle biopsies were analyzed from 8 UCMD patients ranging in age from 6 to 30 months. Type I fiber atrophy and predominance were seen early, together with a widening of the fiber diameter spectrum, whereas no dystrophic features were apparent. A subpopulation of more severely atrophic type I fibers was apparent subsequently, including one biopsy that fulfilled the formal diagnostic criteria of histopathological fiber type disproportion (FTD). Thus, early in the disease, UCMD presents as a non-dystrophic myopathy with predominant fiber atrophy. Collagen VI mutations also qualify as a cause of fiber type disproportion.

Fibroblast autofluorescence in connective tissue disorders: a future tool for clinical and differential diagnosis?

Marfan syndrome (MFS) is an inherited disorder of connective tissue due to mutations in FBN1 (90%) and TGFBR1 and TGFBR2 (5 to 10%) genes. Clinical and differential diagnosis is difficult because of the inter- and intrafamiliar marked heterogeneity and the variable onset age of clinical manifestations. Among the disorders, in differential diagnosis, thoracic aortic aneurysm (TAA) and Ullrich scleroatonic muscular dystrophy (UCMD) are reported. We evaluate the possibility of utilizing autofluorescence (AF) analysis as a diagnostic tool in the clinical and/or differential diagnosis of MFS and related disorders and in the investigation of the molecular mechanisms involved. Both multispectral imaging autofluorescence microscopy (MIAM) and autofluorescence microspectroscopy (AMS) have been used to characterize AF emission of fibroblasts from patients affected by inherited connective tissue disorders. Our preliminary results show significant differences in AF emission between normal and pathological fibroblasts, suggesting possible improvement in diagnostics of connective tissue disorders by AF analysis.

Collagen VI glycine mutations: perturbed assembly and a spectrum of clinical severity

OBJECTIVE

The collagen VI muscular dystrophies, Bethlem myopathy and Ullrich congenital muscular dystrophy, form a continuum of clinical phenotypes. Glycine mutations in the triple helix have been identified in both Bethlem and Ullrich congenital muscular dystrophy, but it is not known why they cause these different phenotypes.

METHODS

We studied eight new patients who presented with a spectrum of clinical severity, screened the three collagen VI messenger RNA for mutations, and examined collagen VI biosynthesis and the assembly pathway.

RESULTS

All eight patients had heterozygous glycine mutations toward the N-terminal end of the triple helix. The mutations produced two assembly phenotypes. In the first patient group, collagen VI dimers accumulated in the cell but not the medium, microfibril formation in the medium was moderately reduced, and the amount of collagen VI in the extracellular matrix was not significantly altered. The second group had more severe assembly defects: some secreted collagen VI tetramers were not disulfide bonded, microfibril formation in the medium was severely compromised, and collagen VI in the extracellular matrix was reduced.

INTERPRETATION

These data indicate that collagen VI glycine mutations impair the assembly pathway in different ways and disease severity correlates with the assembly abnormality. In mildly affected patients, normal amounts of collagen VI were deposited in the fibroblast matrix, whereas in patients with moderate-to-severe disability, assembly defects led to a reduced collagen VI fibroblast matrix. This study thus provides an explanation for how different glycine mutations produce a spectrum of clinical severity.

Ullrich myopathy phenotype with secondary ColVI defect identified by confocal imaging and electron microscopy analysis

Ullrich congenital muscular dystrophy (UCMD) is clinically characterized by muscle weakness, proximal contractures and distal hyperlaxity and morphologically branded by absence or reduction of collagen VI (ColVI), in muscle and in cultured fibroblasts. The ColVI defect is generally related to COL6 genes mutations, however UCDM patients without COL6 mutations have been recently reported, suggesting genetic heterogeneity. We report comparative morphological findings between a UCMD patient harboring a homozygous COL6A2 mutation and a patient with a typical UCMD phenotype in which mutations in COL6 genes were excluded. The patient with no mutations in COL6 genes exhibited a partial ColVI defect, which was only detected close to the basal membrane of myofibers. We describe how confocal microscopy and rotary-shadowing electron microscopy may be useful to identify a secondary ColVI defect.

Variable penetrance of COL6A1 null mutations: implications for prenatal diagnosis and genetic counselling in Ullrich congenital muscular dystrophy families

Collagen VI mutations cause mild Bethlem myopathy and severe, progressive Ullrich congenital muscular dystrophy (UCMD). We identified a novel homozygous COL6A1 premature termination mutation in a UCMD patient that causes nonsense-mediated mRNA decay. Collagen VI microfibrils cannot be detected in muscle or fibroblasts. The parents are heterozygous carriers of the mutation and their fibroblasts produce reduced amounts of collagen VI. The molecular findings in the parents are analogous to those reported for a heterozygous COL6A1 premature termination mutation that causes Bethlem myopathy. However, the parents of our UCMD proband are clinically normal. The proband's brother, also a carrier, has clinical features consistent with a mild collagen VI phenotype. Following a request for prenatal diagnosis in a subsequent pregnancy we found the fetus was a heterozygous carrier indicating that it would not be affected with severe UCMD. COL6A1 premature termination mutations exhibit variable penetrance necessitating a cautious approach to genetic counselling.

Reprint of "Structural correlation between collagen VI microfibrils and collagen VI banded aggregates" [J. Struct. Biol. 154 (2006) 312-326]

Collagen VI is a component of the extracellular matrix that is able to form structural links with cells. Collagen VI monomers cross-link into tetramers that come together to form long molecular chains known as microfibrils. Collagen VI tetramers are also the most likely candidates for the formation of banded aggregates with an axial periodicity of about 105 nm that are seen in the retinas of people suffering from age-related macular degeneration and Sorsby's fundus dystrophy, in the vitreous of patients with full thickness macular holes and in the intervertebral discs of normal individuals. Here, a protocol is developed to carry out a structural comparison between the microfibrils, which are known to be made of collagen VI tetramers, and the banded aggregates. The comparison shows that the banded aggregates are easily explained as being a lateral assembly of microfibrils, thus supporting the hypothesis that they too are made of collagen VI. Understanding the role played by the collagen VI aggregates in normal and pathological conditions will help to throw light on the pathologies with which they are associated.

Congenital muscular dystrophies and the extracellular matrix

During the past decade, considerable progress in the field of congenital muscular dystrophies (CMDs) had led to the identification of a growing number of causative genes. This genetic progress has uncovered crucial pathophysiological concepts and has been instrumental in redefining clinical phenotypes. Important new pathogenic mechanisms include the disorders of O-mannosyl-linked glycosylation of alpha-dystroglycan as well as the involvement of a collagen type VI in the pathogenesis of congenital disorders of muscle. Thus, an emerging theme among gene products involved in the pathogenesis of congenital muscular dystrophy is their intimate connection to the extracellular matrix. In this review, we focus on the clinical phenotypes that we are correlating with the novel genetic and biochemical findings encountered within CMD. This correlation will frequently lead to a considerably expanded clinical spectrum associated with a given CMD gene.

Structural correlation between collagen VI microfibrils and collagen VI banded aggregates

Collagen VI is a component of the extracellular matrix that is able to form structural links with cells. Collagen VI monomers cross-link into tetramers that come together to form long molecular chains known as microfibrils. Collagen VI tetramers are also the most likely candidates for the formation of banded aggregates with an axial periodicity of about 105 nm that are seen in the retinas of people suffering from age-related macular degeneration and Sorsby's fundus dystrophy, in the vitreous of patients with full thickness macular holes and in the intervertebral discs of normal individuals. Here, a protocol is developed to carry out a structural comparison between the microfibrils, which are known to be made of collagen VI tetramers, and the banded aggregates. The comparison shows that the banded aggregates are easily explained as being a lateral assembly of microfibrils, thus supporting the hypothesis that they too are made of collagen VI. Understanding the role played by the collagen VI aggregates in normal and pathological conditions will help to throw light on the pathologies with which they are associated.

COL6A1 genomic deletions in Bethlem myopathy and Ullrich muscular dystrophy

We have identified highly similar heterozygous COL6A1 genomic deletions, spanning from intron 8 to exon 13 or intron 13, in two patients with Ullrich congenital muscular dystrophy and the milder Bethlem myopathy. The 5' breakpoints of both deletions are located within a minisatellite in intron 8. The mutations cause in-frame deletions of 66 and 84 amino acids in the amino terminus of the triple-helical domain, leading to intracellular accumulation of mutant polypeptides and reduced extracellular collagen VI microfibrils. Our studies identify a deletion-prone region in COL6A1 and suggest that similar mutations can lead to congenital muscle disorders of different clinical severity.