Dystrophic Pattern Research Articles

Muscle ultrastructure and histopathological findings in a Brazilian single-centre series of genetically classified telethoninopathy patients

BackgroundTelethoninopathy or TCAP-gene related Limb Girdle Muscular Dystrophy is a rare genetic disease that was first described in Brazil. There are around 100 families reported worldwide. Due to its rarity, detailed information on muscle biopsy light and electron microscopic features are lacking.Cases presentationRetrospective study of consecutive muscle biopsies performed in patients from a Neuromuscular Outpatient Clinic between 2011 and 2023. Inclusion criteria: telethoninopathy diagnosed by both immunohistochemistry and molecular studies. Seven patients (0.7% or 7/953) were found: five male and two female, admitted from 6 to 54 years old. Detailed light and electron microscopy findings are illustrated. Muscle imaging is presented. A dystrophic pattern on muscle biopsy was found in 57% (4/7) of the patients. Other 43% (3/7) presented myopathic features such as variation in fibre calibre, nuclear internalization, rimmed vacuoles, and oxidative irregularities. Morphometry disclosed type 1 lobulated fibres that were 34%, 52%, and 57% smaller than type 2 fibres, respectively, in three patients, without type 1 fibre predominance. Electron microscopy demonstrated nuclear pseudoinclusions, pyknosis, multifocal loss of the sarcolemma, and 17 nm intrasarcoplasmic filamentous inclusions. All patients presented: (1) complete absence of the immunohistochemical expression of telethonin, and (2) the homozygous c.157C > T, p.(Gln53*) pathogenic variant in exon 2 of the TCAP gene.ConclusionAnti-telethonin immunohistochemistry may be helpful in unsolved cases with nonspecific myopathic abnormalities, specially with small type 1 lobulated fibres. Appropriate diagnosis is important for adequate genetic counselling.

The congenital muscular dystrophies

AbstractBackgroundCongenital muscular dystrophies (CMDs) are genetically and clinically heterogeneous inherited conditions. Onset is typically within the first year of life. Most CMDs are autosomal recessive, except for de novo dominant mutations in LMNA‐related muscular dystrophy and some collagen‐6‐associated disorders.ResultsCMD is characterized by progressive muscular weakness, hypotonia, multiple contractures with a variable degree, spinal stiffness, delay in motor milestones acquisition, and histologically dystrophic lesions. Also, some forms of CMD may feature structural and myelination abnormalities on brain magnetic resonance imaging, intellectual impairment, and structural abnormalities of the eye. Muscle biopsy specimens exhibit a dystrophic pattern, but the appearance is quite variable depending on the different stages and severity of the disorder. The prevalence of CMD is estimated to be one in 100 000 people. Over the last few years, with advances in molecular genetic diagnostics, knowledge about neuromuscular disorders, particularly CMDs, has increased dramatically. Thus, the incidence may be higher than originally thought.ConclusionThis article reviews the recent achievements related to the clinical, diagnostic, pathogenic, and therapeutic aspects of CMDs.

Motor Outcome Measures in Pediatric Patients with Congenital Muscular Dystrophies: A Scoping Review

Congenital muscular dystrophies (CMDs) are a heterogeneous group of genetic neuromuscular disorders. They usually occur at birth or in early childhood, with delayed acquisition of motor milestones, and diffuse muscle weakness. A dystrophic pattern is evident on the muscle biopsy. They are highly variable both in terms of severity and clinical evolution and in terms of pathogenetic biochemical mechanisms. The aim of this review is to collect and summarize the current knowledge of motor function in pediatric patients with congenital muscular dystrophies and the instruments used to assess it. This scoping review was conducted using the methodology of PRISMA (extension for Scoping Reviews, PRISMA-ScR). Two databases were queried from January 2002 to November 2022. Articles were identified based on title and abstract. Full-text papers published in peer-reviewed English-language journals were selected. It emerged that motor functional aspects are still underinvestigated in CMD patients, probably due to the rarity of these conditions and the phenotypic variability. The scales used to assess motor function are heterogeneous, as are the age groups considered. Finally, the predominant type of research design is cross-sectional; few studies analyze the progression of motor function over time. All these factors make it difficult to correlate the results of different publications and stress the need for more accurate and shared protocols for assessing motor function in these patients.

AUTOIMMUNE & INFLAMMATORY NMD: EP.01 Autoimmune necrotizing myopathy with anti-signal recognition particle antibodies in the first year of life

Autoimmune necrotizing myopathy with anti-signal recognition particle antibodies (SRP ANM) has been rarely reported in childhood. Case Reports. We report 2 patients with onset in the first years of life. Both received corticosteroids, immunoglobulins, methotrexate, hydroxychloroquine and tacrolimus. Patient 1 has clearly improved. Patient 2 was misdiagnosed as muscular dystrophy for 15 years; nevertheless, after 4 months of therapy there was mild motor improvement. Patient 1. A 6-year-old girl presented with weakness, but her parents could not recall the beginning. She had axial as well as mild to moderate limb girdle weakness. There was no systemic/skin involvement. CK levels were 2.400 UI/l. The DMD MLPA test and next-generation sequencing (NGS) did not reveal any pathogenic mutation. Muscle weakness progressed quickly in the next 3 months, suggesting an acquired myopathy, and SRP antibodies were detected. Muscle biopsy was compatible with ANM. Patient 2. A 4-year-old girl presented with weakness in lower limbs for months. Her family was consanguineous. She achieved ambulation after 18 months. She had proximal limb weakness, as well as scapular winging and calf hypertrophy. Her cognitive capacity was borderline. CK levels were >5.000U/l. MRI disclosed posterior thig involvement and focal edema, but based on the rest of clinical findings, a muscular dystrophy was suspected. Muscle biopsy performed at 5 and 10 years of age showed a dystrophic pattern with necrotic fibers and endomysial connective infiltration. Immunochemistry study for muscular dystrophies was normal. Her clinical course has progressed very slowly. She showed rigid spine and maintains independent walking. At 19 year of age, due to the negativity of the all the genetic tests performed over the time (including NGS), myositis specific autoantibodies were tested and SRP antibodies were positive. Review of the second muscle biopsy disclosed C5b-9 expression in muscle fibers. SRP ANM is under-recognized and consequently undertreated in children. Early diagnosis is crucial to improve outcome.

SINGLE-NUCLEOTIDE POLYMORPHISMS OF THE ESR1 [RS 2234693], IL-1 [RS1143627], RANKL [RS9594738] AND [RS9594759] GENES AS POSSIBLE RISK MARKERS FOR VARIOUS VARIANTS OF THE COURSE OF PERIODONTAL DISEASE IN PATIENTS BORN MACROSOMIC

The article is concerned with the research for genetic predictors of periodontal tissue diseases in individuals born to macosomіс.
 Purpose of this study is to identify the association between the polymorphic variants of the CYP19A1 [rs2414096, rs936306], ESR1 [rs2234693, rs9340799], IL-1b [rs1143627], IL-6 [rs1800796], IL-10 [rs1800896], RANKL [rs9597575] and VDR [rs 1544410, rs10735810] genes and the formation of periodontal tissue disorders with a predominance of inflammatory (periodontitis) or dystrophic (paradontosis) flow patterns in of Kharkiv and the population of adjacent district who were born by macrosomic delivery.
 Object and Methods. The molecular genetic method was used to examine 81 persons of different ages (from 18 to 55 years old) who live in the Kharkiv and adjacent districts (Ukraine). The participants in the study were divided into 3 groups. The pathological changes in periodontal tissues were recorded by the classification of periodontal diseases (M.F. Danylevskyi, 1994).
 The macrosomic-at-birth participants who were diagnosed with chronic periodontitis (of the initial, first, or second degree) were assigned to the general group with a predominance of inflammatory processes in periodontal tissues. The macrosomic-at-birth participants who were diagnosed with parodontosis (of the initial, first or second degree), were assigned to the general group with a predominance of dystrophic processes in periodontal tissues. The comparison group consisted of the individuals with a conventionally healthy periodontium.
 The DNA was isolated from the buccal epithelium. The genotyping of SNP was carried out by Real-Time PCR.
 Conclusions. 1. The risk of dystrophically-inflammatory diseases of periodontal tissues with prevalence of both dystrophic (parodontosis) and inflammatory (periodontitis) flow patterns is associated with variants of the IL-1b gene: [rs1143627] (an over-dominant model of inheritance) in individuals born macrosomic. 2. The protective effect during periodontal tissue diseases with a tendency to inflammatory course was associated with the ESR gene variants [rs 2234693] (recessive model of inheritance) and IL-1b [rs1143627] (dominant and multiplicative model of inheritance). 3. A more pronounced effect of the IL-1b gene variant: [rs1143627] on the development of processes with a tendency to inflammatory course in the periodontal tissues (additive, dominant, over-dominant and multiplicative models of inheritance versus over-dominant model of the tendency to dystrophic flow) was recorded. 4. The risk of developing of pathological processes in periodontal tissues with a tendency to a dystrophic course rather than to an inflammatory course, associated with the RANKL [rs9594738] gene variants (dominant and multiplicative models of inheritance) and RANKL [rs9594759] variant (dominant model of inheritance). 5. Analysis of variants of the ESR1 [rs 2234693], IL-1b [rs1143627] and RANKL [rs9594738], [rs95944738], [rs95944738] gene variants is proposed to be used for DNA diagnostics at the preclinical stage of the disease in order to highlight the risk group for the development of periodontal tissue disorders and increase the effectiveness of personalized preventive measures in individuals born macrosomic.

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

Bethlem myopathy (BM) represents the milder form of the spectrum of Collagen VI-related dystrophies, which are characterized by a clinical continuum between the two extremities, the BM and the Ullrich congenital muscular dystrophy, and include less defined intermediate phenotypes. BM 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 BM 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 BM phenotype. This study confirms the occurrence of recessive inherited BM and expands the genetic heterogeneity of this group of muscle diseases.

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.

Clinical and genetic spectrum of sarcoglycanopathies in a large cohort of Chinese patients

BackgroundSarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophy (LGMD2C, LGMD2D, LGMD2E, and LGMD2F) that are caused, respectively, by mutations in the SGCG, SGCA, SGCB, and SGCD genes. Knowledge about the clinical and genetic features of sarcoglycanopathies in Chinese patients is limited. The aims of this study were to investigate in detail the clinical manifestations, sarcoglycan expression, and gene mutations in Chinese patients with sarcoglycanopathies and to identify possible correlations between them.ResultsOf 3638 patients for suspected neuromuscular diseases (1733 with inherited myopathies, 1557 with acquired myopathies, and 348 unknown), 756 patients had next-generation sequencing (NGS) diagnostic panel. Twenty-five patients with sarcoglycanopathies (11.5%) were identified from 218 confirmed LGMDs, comprising 18 with LGMD2D, 6 with LGMD2E, and one with LGMD2C. One patient with LGMD2D also had Charcot-Marie-Tooth 1A. The clinical phenotypes of the patients with LGMD2D or LGMD2E were markedly heterogeneous. Muscle biopsy showed a dystrophic pattern in 19 patients and mild myopathic changes in 6. The percentage of correct prediction of genotype based on expression of sarcoglycan was 36.0% (4 LGMD2D, 4 LGMD2E, and one LGMD2C). There was a statistically significant positive correlation between reduction of α-sarcoglycan level and disease severity in LGMD2D. Thirty-five mutations were identified in SGCA, SGCB, SGCG, and PMP22, 16 of which were novel. Exon 3 of SGCA was a hotspot region for mutations in LGMD2D. The missense mutation c.662G > A (p.R221H) was the most common mutation in SGCA. Missense mutations in both alleles of SGCA were associated with a relative benign disease course. No obvious clinical, sarcoglycan expression, and genetic correlation was found in LGMD2E.ConclusionsThis study expands the clinical and genetic spectrum of sarcoglycanopathies in Chinese patients and provides evidence that disease severity of LGMD2D may be predicted by α-sarcoglycan expression and SGCA mutation.

Exon Skipping in a Dysf-Missense Mutant Mouse Model

Limb girdle muscular dystrophy 2B (LGMD2B) is without treatment and caused by mutations in the dysferlin gene (DYSF). One-third is missense mutations leading to dysferlin aggregation and amyloid formation, in addition to defects in sarcolemmal repair and progressive muscle wasting. Dysferlin-null mouse models do not allow study of the consequences of missense mutations. We generated a new mouse model (MMex38) carrying a missense mutation in exon 38 in analogy to a clinically relevant human DYSF variant (DYSF p.Leu1341Pro). The targeted mutation induces all characteristics of missense mutant dysferlinopathy, including a progressive dystrophic pattern, amyloid formation, and defects in membrane repair. We chose U7 small nuclear RNA (snRNA)-based splice switching to demonstrate a possible exon-skipping strategy in this new animal model. We show that Dysf exons 37 and 38 can successfully be skipped in vivo. Overall, the MMex38 mouse model provides an ideal tool for preclinical development of treatment strategies for dysferlinopathy.

Predictive Value and Interrater Reliability of Radiographic Factors in Neurofibromatosis Patients With Dystrophic Scoliosis

BackgroundScoliosis in patients with neurofibromatosis type I (NF1) can manifest as dystrophic or nondystrophic curves. Dystrophic scoliosis is rapidly progressive, rendering treatment challenging. Radiographic characteristics have been reported to predict dystrophic scoliosis, but their reliability and predictive value have not been well described. The purpose of this study is to assess the interobserver reliability for eight radiographic characteristics of dystrophic scoliosis and to evaluate the sensitivity and specificity of these characteristics relative to the gold standard of a definitive clinical diagnosis. MethodsSpine radiographs of 122 NF1 patients from multiple institutions were graded by five spine surgeons as dystrophic or nondystrophic, based on eight radiographic characteristics of dystrophic modulation: rib penciling, vertebral rotation, scalloping, wedging, spindling of transverse processes, short sharp angular curve, widened interpedicular distance, and atypical location. The curves were classified by each submitting institution as dystrophic or nondystrophic based on clinical outcome. Interobserver reliability analysis was performed using Fleiss kappa. ResultsFor the 122 cases, the interrater agreement among the five readers for the diagnosis of dystrophic scoliosis was good at 0.61. The agreement for individual radiographic characteristic ranged from 0.62 for wedging to 0.14 (poor) for scalloping. Surgeons underestimated the number of dystrophic curves, rating from 45% to 67% of the curve patterns as dystrophic, compared to the gold standard, which revealed 68% of the curves to be dystrophic. On multivariate analysis, rib penciling, vertebral rotation, vertebral wedging, and atypical location were significantly associated with true dystrophic status (odds ratios of 2.4, 3.0, 2.4, and 3.0, respectively). ConclusionOverall dystrophic diagnosis can be assessed by radiographic characteristics. Better understanding of the predictive value of specific radiographic features may assist in early diagnosis of patients with dystrophic NF and assist surgeons in identifying dystrophic curve patterns and instituting prompt, appropriate treatment. Level of EvidenceLevel III.

Magnetic Resonance Imaging Findings in the Muscle Tissue of Patients with Limb Girdle Muscular Dystrophy Type 2I Harboring the Founder Mutation c.545A>G in the FKRP Gene.

Limb girdle muscular dystrophy type 2I (LGMD2I) is an autosomal recessive muscular dystrophy that is rare in Asia and is caused by mutations in the fukutin-related protein gene (FKRP). The aim of this study was to determine if there are any characteristic features of muscle on magnetic resonance imaging (MRI) in patients with LGMD2I harboring the founder mutation c.545A>G in FKRP. Using MRI, we delineated changes in the thigh muscles of ten patients with genetically confirmed LGMD2I. The majority of muscle biopsy specimens showed reduced glycosylation of α-dystroglycan, decreased expression of laminin α2, and a dystrophic pattern. In our cohort, the muscles with the most severe fatty infiltration were adductor magnus and vastus intermedius, whereas the rectus femoris, sartorius, and gracilis muscles were relatively spared. In seven patients, we identified a concentric fatty infiltration pattern that was most pronounced in the vastus intermedius and vastus medialis muscles around the distal femoral diaphysis. In this disease, the initial fatty infiltration of the posterior thigh muscles gradually progresses anteriorly regardless of the founder mutation in FKRP. Muscle tissue in patients with LGMD2I who have the founder mutation c.545A>G in FKRP shows a distinctive concentric pattern of fatty infiltration and edema on MRI.

Quantitation of muscle pathology abnormalities in 18 patients with mitochondrial disorders

ABSTRACT INTRODUCTION: Mitochondrial disorders can lead to the accumulation of mitochondria in muscle fibers, as indicated by ragged red (RRF) or ragged blue fibers when stained with modified Gomori trichrome or succinate dehydrogenase (SDH+), respectively, and, absence of activity of cytochrome c oxidase, COX negative fibers (COX-). The combined COX-SDH stain (COMBO+) can reveal even more COX-deficient fibers. OBJECTIVE: To quantify RRFs, SDH+, COX-, and COMBO+ fibers in muscle biopsies with mitochondrial findings. MATERIAL AND METHODS: We retrospectively selected 18 muscle biopsies with mitochondrial abnormalities based on the Walker criteria (percentage of RRFs/COX- fibers, and clinical picture), and/or the Sleigh criteria (percentage of RRFs, SDH+, and COX- fibers). RESULTS: Females represented 83.3%, with a mean age of 38.6 years (5 months-70 years). Patients were diagnosed with chronic progressive external ophthalmoplegia (CPEO, 66.7%), proximal myopathy (22.2%), idiopathic hyperCKemia (11.1%), Kearns-Sayre syndrome (5.6%), mitochondrial encephalomyopathy with ragged red fibers and stroke-like episodes (5.6%), and a dystrophic pattern (5.6%). Some cases of CPEO were combined with proximal myopathy. The quantitative pathologic findings were: RRFs, 3.95% ± 3.17%; SDH+, 7.55% ± 6.1%; COX-, 10.9% ± 7.2%; COMBO+, 14.22% ± 12.79%. We found a slight variation in the diameter of muscle fibers, no necrosis or proliferative connective tissue, few fibers with internal nuclei, and some cases with fiber type grouping. CONCLUSION: Pathologic events, grouped in ascending order of frequency, were RRFs, SDH+ fibers, COX- fibers, and COMBO+ fibers. These data emphasize the importance of the COMBO technique in revealing occult COX deficiency in muscle fibers.

P.419 - Cataracts, cognitive impairment, and congenital myasthenic syndrome with myopathic features caused by mutation in GMPPB gene

Mutations in guanosine diphosphate mannose (GDP-mannose) pyrophosphorylase B (GMPPB) can result in muscular dystrophy variants with hypoglycosylated alfa-dystroglycan. The firsts patients described with defects in this gene showed a broad phenotypic spectrum ranging from congenital muscle weakness, eye and brain structural abnormalities and intellectual delay to adult-onset limb-girdle muscular dystrophies without mental retardation. More recently, a relationship between defects in this gene has been associated to congenital myasthenic syndromes (CMS). Here we describe three sibling, two boys and one girl, from consanguineous Egyptian family aged 17, 12 and 6 y/o, respectively, with congenital myasthenic syndrome (CMS) due to AR mutation in GMPPB gene. All 3 patients showed a homogeneous clinical picture characterized by hypotonia since the first months of life, congenital cataract, axial and proximal muscle weakness, fatigability and intellectual disability. Complementary studies showed: increased CPK, cerebral MRI with a mild increase in cerebellar foliation. EMG with a myopathic pattern and decremented pathological response of 24% was observed just in the oldest patient.Muscular biopsy showed dystrophic pattern and reduction of the expression of alpha-Dystroglycan. Therapeutic testing with anticholinesterase drugs showed and dramatic improvement in the functional test, increasing the distance in 6MWT up to 10 times in the younger patient (30 to 370mts). Genetic studied showed homozygous mutation GMPPB: c.553C>T, p.Arg185Cys. Clinical recognition of GMPPB-associated to congenital myasthenic syndrome may be complicated by the presence of myopathic features. Clinicians should keep in mind this treatable disorder since there is a dramatic response to antocholinesterase drugs even in advanced stages of the disease. Cataracts and cognitive involvement have been described in other Egyptian patients with the same mutation, suggesting a genotype-phenotype correlation.

A novel frameshift mutation in two siblings with merosin-deficient congenital muscular dystrophy

Introduction: Merosin-deficient congenital muscular dystrophy (MDC1A #607855) is an autosomal recessive disorder characterized by muscle weakness and hypotonia at birth that due to mutations in the laminin α2 (LAMA2) gene mapped to the 6q22-23 chromosomal location. Case reports: We present two siblings with elevated serum creatine kinase level, delayed motor milestones, muscle weakness and contractures of the lower limbs. The older sibling was 3 years old. She had proximal muscle weakness power of grade 3/5. Her deep tendon reflexes were absent. She had contractures on her lower limbs. Her intellectual and speech development was normal. The electromyogram showed a myopathic process. We suspected the diagnose of MDC1A and magnetic resonance imaging (MRI) revealed diffuse white matter hyperintensity supporting the diagnose. Immunohistochemical studies on the muscle biopsy showed dystrophic pattern and a completely negative reaction for merosin. The 20 months old patient was the younger sister of the first case. She had similar clinical features like her sister. Sequencing of two siblings revealed a novel homozygous frameshift mutation p.N55Mfs*16 (c.163_163delA) within the LAMA2 gene. Discussion: This mutation is leading to a premature stop codon and no reported in the literatüre. This study emphasize that in individual with congenital hypotonia, muscle weakness, elevated serum creatine kinase level and white matter abnormalities MDC1A should be kept in mind.

AAV-mediated transfer of FKRP shows therapeutic efficacy in a murine model but requires control of gene expression.

Limb Girdle Muscular Dystrophies type 2I (LGMD2I), a recessive autosomal muscular dystrophy, is caused by mutations in the Fukutin Related Protein (FKRP) gene. It has been proposed that FKRP, a ribitol-5-phosphate transferase, is a participant in α-dystroglycan (αDG) glycosylation, which is important to ensure the cell/matrix anchor of muscle fibers. A LGMD2I knock-in mouse model was generated to express the most frequent mutation (L276I) encountered in patients. The expression of FKRP was not altered neither at transcriptional nor at translational levels, but its function was impacted since abnormal glycosylation of αDG was observed. Skeletal muscles were functionally impaired from 2 months of age and a moderate dystrophic pattern was evident starting from 6 months of age. Gene transfer with a rAAV2/9 vector expressing Fkrp restored biochemical defects, corrected the histological abnormalities and improved the resistance to eccentric stress in the mouse model. However, injection of high doses of the vector induced a decrease of αDG glycosylation and laminin binding, even in WT animals. Finally, intravenous injection of the rAAV-Fkrp vector into a dystroglycanopathy mouse model due to Fukutin (Fktn) knock-out indicated a dose-dependent toxicity. These data suggest requirement for a control of FKRP expression in muscles.

Muscle biopsy with dystrophic pattern and rimmed vacuoles: GNE myopathy in a Brazilian patient

G N […] Muscle biopsy with dystrophic pattern and rimmed vacuoles: GNE myopathy in a Brazilian patient

377. AAV-Mediated Transfer of FKRP Shows Therapeutic Efficacy in a Murine Model of Limb-Girdle Muscular Dystrophy Type 2i, but Requires Tight Control of Gene Expression

Limb Girdle Muscular Dystrophies (LGMD) type 2I, a recessive autosomal muscular dystrophy, is caused by mutations in the Fukutin Related Protein (FKRP) gene. It has been proposed that FKRP, whose function remains unclear, is a participant in α-dystroglycan (αDG) glycosylation, which is important to ensure the cell/matrix anchor of muscle fibers. A knock-in mouse model of LGMD2I was generated to express the most frequent mutation (L276I) encountered in patients. The introduction of the mutation did not alter the expression of FKRP, neither at transcriptional nor at translational levels, but did alter its function since abnormal glycosylation of αDG was observed. In this model, skeletal muscles were functionally impaired from 2 months of age and a moderate dystrophic pattern was evident by histology starting from 6 months of age. Gene transfer with a rAAV2/9 vector expressing Fkrp restored the biochemical defects, corrected the histological abnormalities and improved the resistance to eccentric stress in the mouse model was obtained. However, injection of high doses of the vector induced a decrease of αDG glycosylation and laminin binding. Finally, we showed that intravenous injection of the rAAV-Fkrp vector into a dystrophic mouse model suffering of dystroglycanopathy due to skeletal muscle-specific Fukutin (Fktn) knock-out caused toxicity. The dose-dependent worsening of the dystrophic phenotype suggests requirement for a precise control of its expression.

Limb-girdle muscular dystrophy type 2A in Brazilian children.

Calpainopathy is an autosomal recessive limb girdle muscular dystrophy (LGMD2A) caused by mutations in CAPN3 gene. To present clinical and histological findings in six children with a molecular diagnosis of LGMD2A and additionally the MRI findings in two of them. We retrospectively assessed medical records of 6 patients with mutation on CAPN3 gene. All patients were female (three to 12 years). The mean of age of disease onset was 9 years. All of them showed progressive weakness with predominance in lower limbs. Other findings were scapular winging, joint contractures and calf hypertrophy. One female had a more severe phenotype than her dizygotic twin sister that was confirmed by muscle MRI. Muscle biopsies showed a dystrophic pattern in all patients. In this cohort of children with LGMD2A, the clinical aspects were similar to adults with the same disorder.

Particularités de la dystrophie musculaire de Becker et des femmes conductrices

Becker muscular dystrophy (BMD) was first described in 1955 and linked to the DMD gene in 1987. Compared to Duchenne muscular dystrophy (DMD), clinical onset of BMD usually occurs after the age of 12 and wheelchair is required after the age of 16. BMD is characterized by generalized weakness first affecting limb girdle muscles, hypertrophy of the calves and cardiomyopathy in males. Some patients have only mild symptoms such as cramps or elevated serum creatine kinases (SCK) throughout all their lives. SCK levels are usually elevated. Muscle biopsy (immunohistochemistry or immunoblotting) shows a dystrophic pattern with abnormal dystrophin staining. Diagnosis is confirmed by DMD gene sequencing. Deletions or duplications of one or several exons are identified in the majority of cases. A multidisciplinary approach is recommended for the care management of these patients with a particular attention to the cardiomyopathy, which is typically responsible for death but can be prevented by specific treatment. X-linked dilated cardiomyopathies linked to DMD gene are a phenotypic continuum of BMD. Some female carriers of DMD mutations exhibit clinical symptoms of variable severity, often milder and beginning later than in males. The cardiomyopathy is the most frequent feature that should be especially monitored in these patients. Genetic counselling should be systematically proposed.

Deletion of integrin α7 subunit does not aggravate the phenotype of laminin α2 chain-deficient mice.

Laminin-211 is a major constituent of the skeletal muscle basement membrane, exerting its biological functions by binding to cell surface receptors integrin α7β1 and dystroglycan (the latter is part of the dystrophin-glycoprotein complex). The importance of these molecules for normal muscle function is underscored by the fact that their respective deficiency leads to different forms of muscular dystrophy with different severity in humans and animal models. We recently demonstrated that laminin α2 chain and members of the dystrophin-glycoprotein complex have overlapping but non-redundant roles despite being part of the same adhesion complex. To analyse whether laminin-211 and integrin α7 subunit have non-redundant functions we generated mice deficient in laminin α2 chain and integrin α7 subunit (dy3K/itga7). We show that lack of both molecules did not exacerbate the severe phenotype of laminin α2-chain deficient animals. They displayed the same weight, survival and dystrophic pattern of muscle biopsy, with similar degree of inflammation and fibrosis. These data suggest that laminin-211 and integrin α7β1 have intersecting roles in skeletal muscle.