Distal Hyperlaxity Research Articles

Homozygous splice variant (c.1741-6G>A) of the COL6A1 gene in three patients with Ullrich congenital muscular dystrophy

The three major collagen VI genes: COL6A1, COL6A2, and COL6A3 encode microfibrillar components of extracellular matrices in multiple tissues including muscles and tendons. Pathogenic variants in the collagen VI genes cause collagen VI-related dystrophies representing a continuum of conditions from Bethlem myopathy at the milder end to Ullrich congenital muscular dystrophy at the more severe end. Here we describe a pathogenic variant in the COL6A1 gene (NM_001848.3; c.1741-6G>A) found in homozygosity in three patients with Ullrich congenital muscular dystrophy. The patients suffered from severe muscle impairment characterised by proximal weakness, distal hyperlaxity, joint contractures, wheelchair-dependency, and use of nocturnal non-invasive ventilation. The pathogenicity was verified by RNA analyses showing that the variant induced aberrant splicing leading to a frameshift and loss of function. The analyses were in line with immunocytochemistry studies of patient-derived skin fibroblasts and muscle tissue demonstrating impaired secretion of collagen VI into the extracellular matrix. Thereby, we add the variant c.1741-6G>A to the list of pathogenic, recessive, splice variants in COL6A1 causing Ullrich congenital muscular dystrophy. The variant is listed in ClinVar as of “uncertain significance” and “likely benign” and may presumably have been overlooked in other patients.

Griscelli syndrome type 1: a novel pathogenic variant, and review of literature.

Griscelli syndrome type 1 (GS1) is a rare inherited autosomal recessive disease caused by a deleterious variant in the MYO5A gene and characterized by general hypopigmentation, neurological symptoms, motor disability, hypotonia, and vision abnormality. Only nine pathogenic variants in the MYO5A gene have been confirmed in association with the GS1. All of the reported pathogenic variants are truncating. Herein, two siblings from a consanguineous Iranian family with abnormal pigmentation and neurological symptoms were referred for genetic counseling. Whole-exome sequencing (WES) revealed a novel homozygous truncating variant c.1633_1634delAA (p.Asn545Glnfs*10) in the MYO5A gene, which was completely co-segregated with the phenotype in all affected and unaffected family members. Computational analysis and protein modeling demonstrated the deleterious effects of this variant on the structure and function of the protein. The variant, according to ACMG guidelines, was classified as pathogenic. Besides the novelty of the identified variant, our patients manifested more severe clinical symptoms and presented distal hyperlaxity in all four limbs, which was a new finding. In conclusion, we expanded the mutational and phenotypic spectrum of the GS1. Moreover, by studying clinical manifestations in all molecularly confirmed reported cases, provided a comprehensive overview of clinical presentation, and attempted to find a genotype-phenotype correlation.

Personalized in vitro Extracellular Matrix Models of Collagen VI-Related Muscular Dystrophies.

Collagen VI-related dystrophies (COL6-RDs) are a group of rare congenital neuromuscular dystrophies that represent a continuum of overlapping clinical phenotypes that go from the milder Bethlem myopathy (BM) to the severe Ullrich congenital muscular dystrophy, for which there is no effective treatment. Mutations in one of the three Collagen VI genes alter the incorporation of this protein into the extracellular matrix (ECM), affecting the assembly and the structural integrity of the whole fibrillar network. Clinical hallmarks of COL6-RDs are secondary to the ECM disruption and include muscle weakness, proximal joint contractures, and distal hyperlaxity. Although some traits have been identified in patients’ ECMs, a correlation between the ECM features and the clinical phenotype has not been established, mainly due to the lack of predictive and reliable models of the pathology. Herein, we engineered a new personalized pre-clinical model of COL6-RDs using cell-derived matrices (CDMs) technology to better recapitulate the complexity of the native scenario. We found that CDMs from COL6-RD patients presented alterations in ECM structure and composition, showing a significantly decreased Collagen VI secretion, especially in the more severe phenotypes, and a decrease in Fibrillin-1 inclusion. Next, we examined the Collagen VI-mediated deposition of Fibronectin in the ECM, finding a higher alignment, length, width, and straightness than in patients with COL6-RDs. Overall, these results indicate that CDMs models are promising tools to explore the alterations that arise in the composition and fibrillar architecture due to mutations in Collagen VI genes, especially in early stages of matrix organization. Ultimately, CDMs derived from COL6-RD patients may become relevant pre-clinical models, which may help identifying novel biomarkers to be employed in the clinics and to investigate novel therapeutic targets and treatments.

COLLAGEN RELATED MUSCLE DISEASES: EP.59 Genetic etiology of retractile myopathies in a cohort of 80 children under 11 years following NGS analysis

The retractile myopathies consist of rare diseases with skeletal muscles and connective tissue damages. They are mostly characterized by progressive muscle weakness, joint contractures and distal hyperlaxity. A rigid spine, dropped head, scoliosis or skin involvement can distinguish some of them. The purpose of this study is the detection of gene causative variants responsible for retractile myopathies in a cohort of 80 pediatric patients sequenced by Next-Generation Sequencing (NGS). This retrospective study includes patients followed between June 2015 until March 2021 in French neuromuscular reference centers. All the referred patients of the cohort were under 11 years old and developed the first symptoms at birth or in early childhood, mostly exhibiting hypotonia for newborn patients or limb girdle myopathy, joint contractures and distal hyperlaxity for children. Genetic testing used targeted NGS panel including 30 genes associated with retractile and hyperlaxity myopathies. Among the 80 analysed patients, 40 could benefit of a disease-causing genetic etiology (50%). Among the 30 genes, 14 genes were involved. The most frequently mutated genes include the group of the COL6 genes (37.5% of patients with COL6A1, COL6A2 and COL6A3) and TTN (17.5% of patients). Interestingly, two patients were mutated in PLOD1 gene, each carrying a homozygous variant. Among the families where heritability could be analysed, eight patients exhibited a de novo dominant variant (20% of the children). In conclusion, the increased accessibility to NGS improves the field of children patients with a genetic diagnosis up to 50%. Furthermore, we confirm the interest of integrating PLOD1 gene into this panel as it was involved in 5% of patients. This allows better orientation of medical care and genetic counseling for these families.

OMICs AND AI APPROACHES FOR MUSCLE DISEASES: O.05 Whole exome sequencing identifies compound heterozygous missense variants in the LOXL4 gene: a novel candidate cause of contractural myopathy

Joint contractures are recurrent and sometimes prominent features in neuromuscular disorders, most notably in extracellular matrix (ECM)-related myopathies, such as COL6-related disorders (COL6-RD). Here, we report a patient with an atypical clinical presentation of congenital arthrogryposis, associated with distal hyperlaxity, proximal muscle deficit, dysphonia, dysphagia, mild ptosis and preserved respiratory function. At age 15, a COL6-RD was evoked and immunostaining of cutaneous fibroblasts from the patient revealed a subtle impairment of COLVI secretion; however, no mutation in the COL6A1-3 genes was identified.

EP.122Recurrent pneumothorax in an adult case of Ullrich congenital muscular dystrophy – case report and review of literature

Collagen VI related muscular dystrophy is caused by dominant or recessive mutations in the COL6A1, COL6A2 or COL6A3 genes and comprises of a spectrum of rare neuromuscular disorders including the early-onset and more severe Ulrich congenital muscular dystrophy, the milder adult form of Bethlem myopathy and an intermediate phenotype. They are characterised clinically by progressive muscle weakness, distal hyperlaxity, joint contractures and respiratory insufficiency. Respiratory failure develops with progression of the condition and is caused by respiratory muscle (diaphragm and intercostal) weakness as well as spinal and thoracic deformities. Intrinsic lung disease is not common, but pneumothorax, occurring as a single event or as recurrent episodes is being increasingly recognised in these patients. Our patient is a 22 year old female with Ulrich congenital muscular dystrophy caused by heterozygous mutation in exon 9 of COL6A1 gene. She was known to have a restrictive lung defect with scoliosis since childhood. Nocturnal ventilatory support was initiated at the age of 18 following a sleep study showing evidence of hypoventilation. She developed a spontaneous left sided pneumothorax at 21 years old, requiring intercostal drain (ICD) insertion followed by chemical pleurodesis via ICD. A contralateral spontaneous pneumothorax occurred 8 months later, which was complicated by PEA arrest requiring intubation and ventilation; followed by a protracted recovery period. This case is being presented to increase the awareness of a potentially life threatening complication associated with this condition. A first presentation of spontaneous pneumothorax in these patients should lead to careful assessment of lung parenchymal changes and consideration of definitive pre-emptive contralateral intervention.

P.42 - Congenital muscular dystrophy in Taiwan: a referral center experience

Congenital muscular dystrophy (CMD) is a heterogeneous disease entity. The detailed clinical manifestation and causative gene for each subgroup of CMD are quite variable. This study aims to analyze the phenotypes and genotypes of Taiwanese patients with CMD as the epidemiology of CMD varies among populations and has been scantly described in Asia. A total of 48 patients suspected to have CMD were screened and categorized by histochemistry and immunohistochemistry studies. Different genetic analyses, including next-generation sequencing (NGS), were used. We identified 17 patients with sarcolemma-specific collagen VI deficiency (SSCD), 6 patients with merosin deficiency, two with reduced alpha-dystroglycan staining, and two with striking lymphocyte infiltration in addition to dystrophic change on muscle pathology. Fourteen in 15 patients with SSCD whose DNA were available, were shown to have COL6A1, COL6A2 or COL6A3 mutations by NGS analysis; all presented with marked distal hyperlaxity and normal intelligence. All six patients with merosin deficiency carried mutations in LAMA2. The clinical features were relatively uniform that were compatible with previous studies, except for higher proportion of mental retardation with epilepsy. With reduced alpha-dystroglycan staining, one patient was found to carry mutations in POMT1 while another patient carried mutations in TRAPPC11. LMNA mutations were found in the two patients with inflammatory change on muscle pathology. They were clinically characterized by neck flexion limitation and early joint contracture, but no cardiac problem had developed yet. Our study showed that muscle pathology remains helpful in guiding further molecular analyses by direct sequencing of certain genes or by target capture/NGS as a second-tier diagnostic tool, and is crucial for establishing the genotype-phenotype correlation. We also determined the frequencies of the different types of CMD in our cohort which is important for the development of a specific care system for each disease.

Pneumothoraces in collagen VI-related dystrophy: a case series and recommendations for management.

Collagen VI-related dystrophy (collagen VI-RD) is a rare neuromuscular condition caused by mutations in the COL6A1, COL6A2 or COL6A3 genes. The phenotypic spectrum includes early-onset Ullrich congenital muscular dystrophy, adult-onset Bethlem myopathy and an intermediate phenotype. The disorder is characterised by distal hyperlaxity and progressive muscle weakness, joint contractures and respiratory insufficiency. Respiratory insufficiency is attributed to chest wall contractures, scoliosis, impaired diaphragmatic function and intercostal muscle weakness. To date, intrinsic parenchymal lung disease has not been implicated in the inevitable respiratory decline of these patients.This series focuses on pneumothorax, an important but previously under-recognised disease manifestation of collagen VI-RD.We describe two distinct clinical presentations within collagen VI-RD patients with pneumothorax. The first cohort consists of neonates and children with a single pneumothorax in the setting of large intrathoracic pressure changes. The second group is made up of adult patients with recurrent pneumothoraces, associated with chest computed tomography scan evidence of parenchymal lung disease. We describe treatment challenges in this unique population with respect to expectant observation, tube thoracostomy and open pleurodesis.Based on this experience, we offer recommendations for early identification of lung disease in collagen VI-RD and definitive intervention.

Comprehensive target capture/next-generation sequencing as a second-tier diagnostic approach for congenital muscular dystrophy in Taiwan.

PurposeCongenital muscular dystrophy (CMD) is a heterogeneous disease entity. The detailed clinical manifestation and causative gene for each subgroup of CMD are quite variable. This study aims to analyze the phenotypes and genotypes of Taiwanese patients with CMD as the epidemiology of CMD varies among populations and has been scantly described in Asia.MethodsA total of 48 patients suspected to have CMD were screened and categorized by histochemistry and immunohistochemistry studies. Different genetic analyses, including next-generation sequencing (NGS), were selected, based on the clinical and pathological findings.ResultsWe identified 17 patients with sarcolemma-specific collagen VI deficiency (SSCD), 6 patients with merosin deficiency, two with reduced alpha-dystroglycan staining, and two with striking lymphocyte infiltration in addition to dystrophic change on muscle pathology. Fourteen in 15 patients with SSCD, were shown to have COL6A1, COL6A2 or COL6A3 mutations by NGS analysis; all showed marked distal hyperlaxity and normal intelligence but the overall severity was less than in previously reported patients from other populations. All six patients with merosin deficiency had mutations in LAMA2. They showed relatively uniform phenotype that were compatible with previous studies, except for higher proportion of mental retardation with epilepsy. With reduced alpha-dystroglycan staining, one patient was found to carry mutations in POMT1 while another patient carried mutations in TRAPPC11. LMNA mutations were found in the two patients with inflammatory change on muscle pathology. They were clinically characterized by neck flexion limitation and early joint contracture, but no cardiac problem had developed yet.ConclusionMuscle pathology remains helpful in guiding further molecular analyses by direct sequencing of certain genes or by target capture/NGS as a second-tier diagnostic tool, and is crucial for establishing the genotype-phenotype correlation. We also determined the frequencies of the different types of CMD in our cohort which is important for the development of a specific care system for each disease.

G.P.265: Nebulin-related nemaline myopathy: Clinical and histopathological spectrum in Argentinean patients

Nebulin (NEB) is a sarcomeric structural protein. Mutations in NEB genes particularly cause autosomal recessive nemaline myopathy (NM) and core-rod myopathy. Clinical presentations range from a severe neonatal form to a mild adult-onset form as part of the different diagnosis of distal myopathy. We describe the clinical, histopathological, and molecular findings of three patients with different phenotypes of NEB gene mutations. Case 1: A 5-year-old boy with distal finger retractions, hypotonia, and motor development delay since birth with mainly distal general weakness and hyperlaxity. At age 1 he developed progressive respiratory difficulties needing ongoing invasive ventilation by tracheostomy. He was never able to walk. Spine surgery was performed at 4years. Cognitive development was normal. Quadriceps muscle biopsy showed NM consisting of rod structures, type 1 predominance and atrophy. Exome sequencing showed mutations in exon 139 and 172. Case 2: A 2.5-year-old girl presenting with motor developmental delay, hypomimia, and hypotonia since birth. At 18months of age she walked independently and steppage gait was noticed. She is still improving. Deltoid biopsy showed NM consisting of rod structures and type 1 predominance. Exome sequencing showed mutations in intron 12 and exon 150. Case 3: A 22-year-old girl had frequent falls since she started to walk at 1year, linked to distal hyperlaxity, as well as distal weakness, arreflexia, and steppagge gait. Slow symptom progression was seen. EMG ruled out neuropathic disease and muscle biopsy showed rod and core structures with type 1 predominance. Exome sequencing showed mutations in exon 129 and exon 74 to exon144. Conclusion: NEB-related NM has a broad clinical spectrum particularly including congenital and distal myopathy forms that may mimic a neurogenic process. Our three patients presented with predominantly distal weakness and muscle biopsies showed rod or core-rod myopathies.

Ullrich congenital muscular dystrophy: clinicopathological features, natural history and pathomechanism(s)

Collagen VI is widely distributed throughout extracellular matrices (ECMs) in various tissues. In skeletal muscle, collagen VI is particularly concentrated in and adjacent to basement membranes of myofibers. Ullrich congenital...

P.1.7 Contiguous gene syndrome causing ColVI myopathy, dysmorphism, frontal atrophy and diaphragmatic hernia

Collagen VI (Col6) deficiency results in a broad spectrum of clinical manifestations ranging from Ullrich Congenital Muscular Dystrophy (UCMD) to Bethlem Myopathy with intermediate phenotypes. The COL6A3 gene encodes the α3(VI) subunit and maps to chromosome 2 in one of the most commonly deleted subtelomeric region, del2q37. UCMD is not classically associated with central nervous system involvement. However, some cases with intellectual disability have been reported, without any molecular explanation. We report the case of a 4-year-old boy born to unrelated French parents presenting with hypotonia, torticollis and club foot at birth. He had a motor delay (walked unaided at 3 years). Diaphragmatic hernia was discovered fortuitously and surgically corrected at 2y10m. At 3 years, he presented facial (mostly oral) and proximal weakness, distal hyperlaxity, no retractions and pectus excavatum. Moreover, we noted a mild facial dysmorphism with prominent forehead, down-slanted eyes, thin upper lip and low-set big ears. Scars from the diaphragmatic and muscle biopsy surgeries were slightly hypertrophic. The evolution was marked by seizures and two episodes of spontaneous fractures. Plasma CK levels were normal and the muscle biopsy findings were not specific. Cerebral MRI showed atrophy of the frontal lobe. Given the muscular phenotype, collagen VI immunolabeling was studied in cultured fibroblasts and demonstrated reduced Col secretion associated with intracytoplasmic retention. Currently aged 4y3m, the patient presents a positive evolution regarding motor and intellectual development. Interestingly, CGH array revealed a de novo translocation (2;4) with 2qter deletion (2q37.2–q37.3) and genomic gain at 4qter (4q35.1–q35.2), resulting in deletion of one COL6A3 allele. This is to our knowledge the 1st case report of a patient with Col6 myopathy phenotype associated with central nervous system involvement ascribed to a contiguous gene syndrome involving the COL6A3 locus.

P.1.21 Congenital muscular dystrophy phenotype with excess of neuromuscular spindles in a 5-year old girl

We report on a 5-year-old girl who presents with an association between a congenital muscular dystrophy, and very peculiar abnormalities on muscle biopsy. The girl was the second child from healthy non related Algerian parents and has now a healthy younger brother. Family history was not informative. Weak fetal movements and polyhydramnios were noticed during the pregnancy. At birth, the child presented with moderate hypotonia, pectus excavatum, mild dysmorphia, club foot, adducted thumbs and generalized proximal arthrogryposis. The girl showed normal intelligence. She had acquired a sitting position, but no ambulation or standing position. She presented with severe shoulder, hip and knee contractures contrasting with distal hyperlaxity. In addition, there was severe cyphosis and a mild scoliosis. Weakness was axial, proximal and distal, facial musculature being mostly spared. A mild right strabismus was noted. The child also presents with mitral valve dysplasia with insufficiency that required surgical correction. There was no need for ventilatory support. Whole Body Muscular MRI demonstrated a diffuse hypotrophy of muscles without selective pattern of involvement. No abnormalities suggestive of collagen VI-related myopathy or other known myopathies were identified. Immunolabelling of collagen VI in cultured fibroblasts demonstrated the absence of secretion and intracytoplasmic retention, but no mutation was detected in the COL6A1-3 genes. Muscle biopsy especially showed a dense conjunctive tissue harboring numerous ovoid formations corresponding to the neuromuscular spindle. There were only few “extrafusal” muscle fibres. No necrotic regenerative fibers were observed. To our knowledge, this pathological aspect on the biopsy has only been described in patients with HRAS mutations (test ongoing), but in contrast with the previously reported cases, the child does not present organomegaly or hypertrophic cardiomegaly and is still living at five years of age.

Clinical and mutation analyses of a Chinese family with Bethlem myopathy

To explore the clinical features and gene mutation of a Chinese family with Bethlem myopathy in three generations. The clinical data of proband and his family members was collected. Genomic DNA from the patient and his family members was extracted routinely from peripheral blood leukocytes. Polymerase chain reaction and DNA direct sequencing were employed to analyze COL6A1, A2 and A3 genes to determine the mutation. And the relationship between genotype and phenotype was analyzed. Furthermore, the patient's skin fibroblast was cultured and immunofluorescent staining was performed with anti-collagen VI antibody. And the expression pattern of type VI collagen in extracellular matrix between the control and the patient's fibroblast was compared. In this family, 9 patients conformed to the clinical diagnosis of Bethlem myopathy. The features included motor development delay after late infantile period, generalized muscle weakness, walking unstability, distal hyper laxity, proximal joint contractures, skin changes (including hypertrophic scars) and normal intellectual development. Serum creatine kinase (CK) level became mildly elevated and electromyography showed myogenic injury. Disease progressed slowly but the lifespan was not affected. Mutation in exon 2 of COL6A1 gene with c.111-129 deletion was detected in 7 patients in this family. Immunofluorescent staining of type VI collagen in cultured skin fibroblast showed reduced expression of collagen VI in extracellular matrix in the patient compared with the control. Our study has defined the clinical features of Bethlem myopathy. According to molecular genetic analysis, 7 patients in this family have in-frame deletion mutations of COL6A1 and they conform to autosomal dominant inheritance. And genetic counseling and prenatal diagnosis are available. This is the first Chinese report of Bethlem myopathy family.

166th ENMC International Workshop on Collagen type VI-related Myopathies, 22–24 May 2009, Naarden, The Netherlands

Twenty-four clinicians, basic scientists and representatives of a patient advocacy organisation and pharmaceutical companies from 8 countries (Australia, England, France, Germany, Italy, Switzerland, Turkey, USA) gathered in Naarden, The Netherlands, to discuss the group of neuromuscular disorders caused by the deficiency of collagen type VI (ColVI), collectively termed ColVI-related myopathies. This meeting focused on three main areas: (1) the great heterogeneity observed at the genetic and clinical levels and the resulting complexity of the molecular diagnosis; (2) the pathophysiological mechanisms linking mutations in the COL6A genes to muscle pathology; (3) the current strategies for therapeutic interventions which have led to the design of upcoming clinical trials. Two sessions were also dedicated to existing and future databases, and to outcome measures.

Ullrich Congenital Dystrophy and Bethlem Myopathy: Current Knowledge on the Clinical Spectrum, Pathogenesis, and Future Therapeutic Avenues of Collagen VI Related Muscular Dystrophies

Ullrich congenital muscular dystrophy (UCMD) is a genetically and clinically heterogeneous muscle disorder causing severe muscle weakness with proximal joint contractures and distal hyperlaxity linked to collagen VI deficiency. It was initially described within the wider group of muscular congenital dystrophies. Collagen VI is an extracellular matrix protein forming a microfibrillar network. The protein is composed of three different α-chains encoded by separate genes named COL6A1, COL6A2, and COL6A3 in humans. Mutations of collagen VI gene are also responsible for Bethlem myopathy (BM), a relatively mild dominantly inherited disorder characterised by proximal weakness and distal joint contractures that was previously believed to be a completely separate entity. The pathogenesis of both diseases is still poorly understood. However, some recent data, obtained from experiments mouse models and from human myoblast cultures provide valuable insights into the pathogenesis of UCMD. A potential mitochondrial involvement may become the focus of specific therapeutic approaches. In this review we emphasise the typical clinical and biochemical findings that will help the paediatrician to identify collagenopathies within the complex diagnostic group of congenital muscular dystrophies, and outline the current understanding of UCMD pathogenesis, management, and potential therapeutic avenues. © 2009 Bentham Science Publishers Ltd.

Ullrich congenital muscular dystrophy: Report of nine cases from India

Ullrich congenital muscular dystrophy (UCMD) is a unique congenital disorder characterized clinically by generalized muscle weakness, contractures of the proximal joints and hyperextensibility of the distal joints and begins from birth or early infancy. We prospectively evaluated nine cases of classical UCMD and recorded the clinical phenotypic characteristics and the histopathological findings. There were eight boys and one girl child with classical features of severe muscle weakness, prominent proximal contractures, distal hyperlaxity and prominent calcanei. Immunohistochemistry for Collagen VI A1 done on seven cases showed total absence of labeling in six while sarcolemmal-specific deficiency was noted in one case confirming the diagnosis of UCMD. Interestingly, all our patients were noted to have near total absence of major palmar and plantar creases, and instead there were fine mesh-like lines in addition to the soft velvety skin on the palms and soles suggestive of altered collagen arrangements in the skin. Hitherto, this clinical finding has not been described in UCMD in the English literature.

G.P.1.03 Important variability in clinical severity in a family with Col VI-related myopathy: Potential implication of digenism?

Collagen VI-related muscle disorders, due to mutations in the 3 genes encoding Collagen VI, regroup Ullrich congenital muscular dystrophy, characterized by early onset generalized muscle weakness, marked proximal contractures and distal hyperlaxity, and Bethlem myopathy, a progressive myopathy, mostly proximal, with a moderate muscle weakness and contractures. Contractures are also prominent during early childhood in Emery-Dreifuss muscular dystrophy caused by mutations in Lamin A/C gene (LMNA). We report here a family with symptoms overlapping between both COL VI related disorders and EDMD. The father and mother were clinically normal. Their two children (35-year-old daughter and 32-year-old son) showed similar type of clinical presentation but with a wide range in the clinical severity. For both, clinical symptoms appeared at 3 years of age, with progressive motor deficit and multiple retractions (axial and limbs -proximal and distal-). The evolution was markedly more severe for the son who was wheelchair-bound at 11 years. Muscle biopsies of the son and daughter performed at 13 and 25 years old, showed dystrophic changes and partial deficit in collagen VI immunostaining, with entirely or partially negative fibres. The father’s muscle biopsy showed similar findings but much more subtle. Studies on cultured skin fibroblasts also showed more pronounced collagen VI deficits in the children as compared to the father. Genetic studies revealed 2 different missense COL6A2 mutations in the father (p.Ala698Val in exon 26 affecting the C1 globular domain) and mother (p.Arg830Glu in exon 28 affecting the C2 globular domain), which were both transmitted to the children. Interestingly, the father and his daughter presented a new mutation in the LMNA gene (p.Gly523Arg). We hypothesize that the LMNA mutation could play a “protective” role in the daughter in regard of the COL6 mutations which could explain the difference in the clinical severity of the two children.

Exon skipping mutations in collagen VI are common and are predictive for severity and inheritance

Mutations in the genes encoding collagen VI (COL6A1, COL6A2, and COL6A3) cause Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), two related conditions of differing severity. BM is a relatively mild dominantly inherited disorder characterized by proximal weakness and distal joint contractures. UCMD was originally regarded as an exclusively autosomal recessive condition causing severe muscle weakness with proximal joint contractures and distal hyperlaxity. We and others have subsequently modified this model when we described UCMD patients with heterozygous in-frame deletions acting in a dominant-negative way. Here we report 10 unrelated patients with a UCMD clinical phenotype and de novo dominant negative heterozygous splice mutations in COL6A1, COL6A2, and COL6A3 and contrast our findings with four UCMD patients with recessively acting splice mutations and two BM patients with heterozygous splice mutations. We find that the location of the skipped exon relative to the molecular structure of the collagen chain strongly correlates with the clinical phenotype. Analysis by immunohistochemical staining of muscle biopsies and dermal fibroblast cultures, as well as immunoprecipitation to study protein biosynthesis and assembly, suggests different mechanisms each for exon skipping mutations underlying dominant UCMD, dominant BM, and recessive UCMD. We provide further evidence that de novo dominant mutations in severe UCMD occur relatively frequently in all three collagen VI chains and offer biochemical insight into genotype-phenotype correlations within the collagen VI-related disorders by showing that severity of the phenotype depends on the ability of mutant chains to be incorporated in the multimeric structure of collagen VI.

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.