Autosomal Recessive Limb-girdle Muscular Dystrophy Research Articles

Can we differentiate patients with dysferlinopathies and inflammatory myopathies by ultrasound? A discriminant analysis study.

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of diseases that are characterized by inflammation and muscle weakness. Dysferlinopathies are autosomal recessive limb-girdle muscular dystrophies caused by mutations in DYSF, which share a similar clinical presentation and histopathological inflammatory changes. To determine the sonographic differences between dysferlinopathies and IIM and whether these differences allow their classification. This observational, cross-sectional, and analytical study evaluated 20 muscles from 11 patients with dysferlinopathies and 11 patients with IIM. The patients were matched for age, sex, and disease duration. Clinical and laboratory variables were analyzed. Semi-quantitative scales were used to weigh the gray scale and power Doppler muscle abnormalities. Descriptive statistics were computed and discriminant analysis was performed to determine the ultrasound variables that best predicted the final diagnosis. Forty muscles were evaluated. Atrophy and higher Heckmatt scale scores were observed in patients with dysferlinopathies. A set of three muscles (biceps/brachialis, quadriceps, and gastrocnemius) had a diagnostic accuracy of 100% (sensitivity, 100%; specificity, 100%; canonical coefficient, 0.733 p < 0.001). A set of two formulas was used to classify both diseases correctly. In the present study, scanning of three muscle groups showed high diagnostic accuracy in differentiating dysferlinopathies from MII. Ultrasound can be used as an initial test in patients with suspected muscle disease or as an additional tool to support diagnosis in controversial cases.

Single-centre experience with autosomal recessive limb-girdle muscular dystrophy: case series and literature review.

Limb-girdle muscular dystrophy (LGMD) is a group of myopathies that lead to progressive muscle weakness, predominantly involving the shoulder and pelvic girdles; it has a heterogeneous genetic etiology, with variation in the prevalence of subtypes according to the ethnic backgrounds and geographic origins of the populations. The aim of the present study was to analyze a series of patients with autosomal recessive LGMD (LGMD-R) to contribute to a better characterization of the disease and to find the relative proportion of the different subtypes in a Southern Brazil cohort. The sample population consisted of 36 patients with LGMD-R. A 9-gene targeted next-generation sequencing panel revealed variants in 23 patients with LGMD (64%), and it identified calpainopathy (LGMD-R1) in 26%, dysferlinopathy (LGMD-R2) in 26%, sarcoglycanopathies (LGMD-R3-R5) in 13%, telethoninopathy (LGMD-R7) in 18%, dystroglicanopathy (LGMD-R9) in 13%, and anoctaminopathy (LGMD-R12) in 4% of the patients. In these 23 patients with LGMD, there were 27 different disease-related variants in the ANO5, CAPN3, DYSF, FKRP, SGCA, SGCB, SGCG, and TCAP genes. There were different causal variants in different exons of these genes, except for the TCAP gene, for which all patients carried the p.Gln53* variant, and the FKRP gene, which showed recurrence of the p.Leu276Ile variant. We analyzed the phenotypic, genotypic and muscle immunohistochemical features of this Southern Brazilian cohort.

Identification of a shared, common haplotype segregating with an SGCB c.544 T > G mutation in Indian patients affected with sarcoglycanopathy

Sarcoglycanopathy is the most frequent form of autosomal recessive limb-girdle muscular dystrophies caused by mutations in SGCB gene encoding beta-sarcoglycan proteins. In this study, we describe a shared, common haplotype co-segregating in 14 sarcoglycanopathy cases from 13 unrelated families from south Indian region with the likely pathogenic homozygous mutation c.544 T > G (p.Thr182Pro) in SGCB. Haplotype was reconstructed based on 10 polymorphic markers surrounding the c.544 T > G mutation in the cases and related family members as well as 150 unrelated controls from Indian populations using PLINK1.9. We identified haplotype H1 = G, A, G, T, G, G, A, C, T, G, T at a significantly higher frequency in cases compared to related controls and unrelated control Indian population. Upon segregation analysis within the family pedigrees, H1 is observed to co-segregate with c.544 T > G in a homozygous state in all the pedigrees of cases except one indicating a probable event of founder effect. Furthermore, Identical-by-descent and inbreeding coefficient analysis revealed relatedness among 33 new pairs of seemingly unrelated individuals from sarcoglycanopathy cohort and a higher proportion of homozygous markers, thereby indicating common ancestry. Since all these patients are from the south Indian region, we suggest this region to be a primary target of mutation screening in patients diagnosed with sarcoglycanopathy.

Disease modeling and gene correction of LGMDR21 iPSCs elucidates the role of POGLUT1 in skeletal muscle maintenance, regeneration, and the satellite cell niche

Autosomal recessive limb-girdle muscular dystrophy 21 (LGMDR21) is caused by pathogenic variants in protein O-glucosyltransferase 1 (POGLUT1), which is responsible for O-glucosylation of specific epidermal growth factor (EGF) repeats found in ∼50 mammalian proteins, including Notch receptors. Previous data from patient biopsies indicated that impaired Notch signaling, reduction of muscle stem cells, and accelerated differentiation are probably involved in disease etiopathology. Using patient induced pluripotent stem cells (iPSCs), their corrected isotypes, and control iPSCs, gene expression profiling indicated dysregulation of POGLUT1, NOTCH, muscle development, extracellular matrix (ECM), cell adhesion, and migration as involved pathways. They also exhibited reduced invitro POGLUT1 enzymatic activity and NOTCH signaling as well as defective myogenesis, proliferation, migration and differentiation. Furthermore, invivo studies demonstrated significant reductions in engraftment, muscle stem cell formation, PAX7 expression, and maintenance, along with an increased percentage of mislocalized PAX7+ cells in the interstitial space. Gene correction in patient iPSCs using CRISPR-Cas9 nickase led to the rescue of the maininvitro and invivo phenotypes. These results demonstrate the efficacy of iPSCs and gene correction in disease modeling and rescue of the phenotypes and provide evidence of the involvement of muscle stem cell niche localization, PAX7 expression, and cell migration as possible mechanisms in LGMDR21.

Exome Sequencing Identifies a Novel SGCA Gene Mutation in an Iranian Family with Limb Girdle Muscular Dystrophy: A Case Report

Introduction: Autosomal recessive limb-girdle muscular dystrophy (LGMD) is a rare congenital muscular dystrophy type. This inherited disease is one of the most common diseases resulting in severe physical health problems for infants. Genetic studies have shown that several gene mutations cause limb-girdle muscular dystrophy. This study aimed to report the case of a 10-year-old boy from an Iranian consanguineous family diagnosed with congenital muscular dystrophy and a causative genetic abnormality. Case Presentation: In this report, whole exome sequencing (WES) followed by Sanger sequencing was performed to diagnose the possible genetic defects in patients with LGMD. A novel homozygous disease-causing SGCA gene mutation (p.A107fs:c.319-329del) was found in exon 10 (NM_000023.4). Both parents were heterozygous for the detected mutation. Conclusions: It was concluded that the identified SGCA gene mutation was a pathogenic variant causing autosomal recessive LGMD.

Large Region of Homozygous (ROH) Identified in Indian Patients with Autosomal Recessive Limb-Girdle Muscular Dystrophy with p.Thr182Pro Variant in SGCB Gene

The sarcoglycanopathies are autosomal recessive limb-girdle muscular dystrophies (LGMDs) caused by the mutations in genes encoding the α, β, γ, and δ proteins which stabilizes the sarcolemma of muscle cells. The clinical phenotype is characterized by progressive proximal muscle weakness with childhood onset. Muscle biopsy findings are diagnostic in confirming dystrophic changes and deficiency of one or more sarcoglycan proteins. In this study, we summarized 1,046 LGMD patients for which a precise diagnosis was identified using targeted sequencing. The most frequent phenotypes identified in the patients are LGMDR1 (19.7%), LGMDR4 (19.0%), LGMDR2 (17.5%), and MMD1 (14.5%). Among the reported genes, each of CAPN3, SGCB, and DYSF variants was reported in more than 10% of our study cohort. The most common variant SGCB p.Thr182Pro was identified in 146 (12.5%) of the LGMD patients, and in 97.9% of these patients, the variant was found to be homozygous. To understand the genetic structure of the patients carrying SGCB p.Thr182Pro, we genotyped 68 LGMD patients using a whole genome microarray. Analysis of the array data identified a large ~1 Mb region of homozygosity (ROH) (chr4:51817441-528499552) suggestive of a shared genomic region overlapping the recurrent missense variant and shared across all 68 patients. Haplotype analysis identified 133 marker haplotypes that were present in ~85.3% of the probands as a double allele and absent in all random controls. We also identified 5 markers (rs1910739, rs6852236, rs13122418, rs13353646, and rs6554360) which were present in a significantly higher proportion in the patients compared to random control set ( n = 128 ) and the population database. Of note, admixture analysis was suggestive of greater proportion of West Eurasian/European ancestry as compared to random controls. Haplotype analysis and frequency in the population database indicate a probable event of founder effect. Further systematic study is needed to identify the communities and regions where the SGCB p.Thr182Pro variant is observed in higher proportions. After identifying these communities and//or region, a screening program is needed to identify carriers and provide them counselling.

Editors' Note: Prospective Natural History Study in 24 Adult Patients With LGMDR12 Over 2 Years of Follow-up: Quantitative MRI and Clinical Outcome Measures.

De Wel et al. prospectively studied 24 patients with autosomal recessive limb-girdle muscular dystrophy type 12 (LGMDR12). Patients with LGMDR12 had no appreciable clinical worsening over a 2-year period according to repeated standardized clinical assessments, such as the 6-minute walk distance, 10-meter walk test, or Medical Research Council sum scores of muscle power. However, for patients with LGMDR12 and intermediate-stage fatty replacement of muscle tissue (20%–70% proton density fat fraction), there was a significant worsening of Biodex Isometric Dynamometry even after 1 year. The investigators conclude this quantitative tool may be useful in monitoring clinical progression and response to targeted treatments for LGMDR12. Dr. Kawada expresses a concern regarding lead-time bias in the cohort (unclear time of disease onset in a recessive condition) which may have confounded any differences in the various qualitative and quantitative assessments over time. In response, the investigators confirmed that patients were included at the time of clinical symptom onset. Both investigators agree that sex-related differences in disease progression are less well understood, and additional studies are suggested to explore reasons for the variability in prognosis between sexes and age groups. De Wel et al. prospectively studied 24 patients with autosomal recessive limb-girdle muscular dystrophy type 12 (LGMDR12). Patients with LGMDR12 had no appreciable clinical worsening over a 2-year period according to repeated standardized clinical assessments, such as the 6-minute walk distance, 10-meter walk test, or Medical Research Council sum scores of muscle power. However, for patients with LGMDR12 and intermediate-stage fatty replacement of muscle tissue (20%–70% proton density fat fraction), there was a significant worsening of Biodex Isometric Dynamometry even after 1 year. The investigators conclude this quantitative tool may be useful in monitoring clinical progression and response to targeted treatments for LGMDR12. Dr. Kawada expresses a concern regarding lead-time bias in the cohort (unclear time of disease onset in a recessive condition) which may have confounded any differences in the various qualitative and quantitative assessments over time. In response, the investigators confirmed that patients were included at the time of clinical symptom onset. Both investigators agree that sex-related differences in disease progression are less well understood, and additional studies are suggested to explore reasons for the variability in prognosis between sexes and age groups.

LGMDR1 with Prominent Limb–Joint Contractures and Inflammatory Changes Misdiagnosed as Scleromyositis with a Novel CAPN3 Mutation: A Case Report

Muscle diseases with prominent limb–joint contractures (LJCs) are a subgroup of rare neuromuscular disorders. Prominent LJCs are not specific to genetic myopathies. Myositis can also induce severe contractures, especially in the late stages. We report the case of a 12-year-old girl with a 3-year history of painful muscular weakness with generalized LJCs. The inflammatory pattern associated with positive anti-PM/ Scl antibodies on muscle biopsy allowed us to initially retain the diagnosis of scleromyositis. After 12 months of corticosteroids and immunosuppressive treatment, there was no clinical improvement, and creatine kinase levels remained high (over 10 times the normal value). A second muscle biopsy showed persistent inflammatory infiltrate with the appearance of dystrophic features. Immunohistochemical analysis showed the absence of class 1 major histocompatibility complex expression on muscle fibres, raising the possibility of the diagnosis of muscular dystrophy. Whole-exome sequencing revealed a missense homozygous novel mutation c.386G&gt;T (p.Arg129Ile) on the calpain 3 gene, finally confirming the diagnosis of autosomal recessive limb–girdle muscular dystrophy recessive type 1 (or calpainopathy). This case report highlights the diagnostic challenges and the importance of a comprehensive evaluation in cases of muscle diseases with prominent LJCs.

Homozygous Inversion on Chromosome 13 Involving SGCG Detected by Short Read Whole Genome Sequencing in a Patient Suffering from Limb-Girdle Muscular Dystrophy.

New techniques in molecular genetic diagnostics now allow for accurate diagnosis in a large proportion of patients with muscular diseases. Nevertheless, many patients remain unsolved, although the clinical history and/or the muscle biopsy give a clear indication of the involved genes. In many cases, there is a strong suspicion that the cause must lie in unexplored gene areas, such as deep-intronic or other non-coding regions. In order to find these changes, next-generation sequencing (NGS) methods are constantly evolving, making it possible to sequence entire genomes to reveal these previously uninvestigated regions. Here, we present a young woman who was strongly suspected of having a so far genetically unsolved sarcoglycanopathy based on her clinical history and muscle biopsy. Using short read whole genome sequencing (WGS), a homozygous inversion on chromosome 13 involving SGCG and LINC00621 was detected. The breakpoint in intron 2 of SGCG led to the absence of γ-sarcoglycan, resulting in the manifestation of autosomal recessive limb-girdle muscular dystrophy 5 (LGMDR5) in the young woman.

Improvement in childhood limb-girdle muscular dystrophy with Ayurvedic management

The Limb-Girdle Muscular Dystrophies (LGMDs) include a heterogeneous group of disorders characterized by the progressive wasting and weakness of the proximal limb-girdle muscles. Sarcoglycanopathies are forms of LGMD that result from defect in the sarcoglycan complex. Ayurveda explains the condition in the line of Srotorodha (~obstructive pathology occurring in channels), especially at the Mamsa dhatu (~muscle tissue) level. This is the case report of an eight year old male child of autosomal recessive LGMD with no relevant family history. The patient was presented with gradual onset of proximal muscle weakness in all four limbs for two years along with pseudohypertrophy of bilateral calf muscles. He had elevated Creatine Phosphokinase (CPK) level and the genetic test findings revealed a homozygous missense variation in exon 2 of the SGCA gene. He visited the outpatient department of the tertiary Government Ayurveda Hospital and Ayurveda medications were administered along with dietary advices for two months followed by in-patient management for one month. There was a significant improvement in the clinical findings assessed by the Vignos scale of lower extremity and Barthel index along with reduction in the level of CPK value after three months of Ayurvedic management. Significant improvement in this short period of management substantiates the benefit of Ayurvedic medicines in the management of LGMD.

Molecular landscape of DYSF mutations in dysferlinopathy: From a Chinese multicenter analysis to a worldwide perspective.

Dysferlinopathy is one of the most common subgroup of autosomal recessive limb-girdle muscular dystrophies that is caused by mutations in DYSF gene. However, there is currently no worldwide comprehensive genetic analysis of DYSF variants. Through a national multicenter collaborative effort in China, we identified 222 DYSF variants with 40 novel variants from 245 patients. We then integrated DYSF variants from disease-related genetic databases including LOVD (n = 1020) and Clinvar (n = 1179), to depict the global landscape of disease-related DYSF variants. Normal-population-derived DSYF variants from gnomAD (n = 4318) and ChinaMAP (n = 13,330) were also analyzed in comparison. In Chinese patients, gender instead of genotype showed influence on the onset age of dysferlinopathy, with males showing an earlier age of onset. After integrative analysis, we identified two hotspot DYSF mutations, c.2997G>T in world patients and c.1375dup in Chinese patients, respectively. Both the pathogenic and likely pathogenic variants scattered on the whole gene length of DYSF. However, three specific domains (C2F-C2G-TM, DysF, and C2B-Ferl-C2C) contained variants at higher frequencies than reported in both the databases and Chinese patients. This study comprehensively collected available DYSF variant data, which may pave way for genetic counselling and future clinical trial design for gene therapies in dysferlinopathy.

Аutosomal recessive limb-girdle muscular dystrophy type 2A: two cases in Ukraine with different age of onset

The paper reports on two cases of young women from Ukraine with autosomal recessive limb-girdle muscular dystrophy type 2A with different age of symptoms onset and an absence of any family history presented with gradual onset of proximal muscle weakness in four limbs and thinning of shoulders, arms and thighs. Both patients had elevated creatine phosphokinase level and c.550delA mutations in CAPN3 gene. Sequence analysis and deletion/duplication testing of the 159 genes from skeletal muscles disease testing panel of 5-year-old girl identified deletion of exon 8 (heterozygous) and c.550delA (p.Thr184Argfs*36) mutation (heterozygous), were in CAPN3 gene. Magnetic Resonance Imaging of soft tissue of the proximal lower extremities was performed which showed signs of symmetrical atrophic changes in the major adductor muscle, the long and short adductor muscles, the semitendinosus muscle of the thigh, as a manifestations of autosomal recessive limb-girdle muscular dystrophy type 2A. Homozygous, pathogenic variant of the defect in the CAPN3 gene c.550del (p.Thr184Argfs * 36) was identified in a 25-year-old woman. Type 2A is the most common form of limb-girdle muscular dystrophy, accounting for about 30% of cases. The autosomal recessive limb-girdle muscular dystrophy type 2A is on caused by mutations in the CAPN3 gene, and it is characterized by selective atrophy and weakness of proximal limb and girdle muscles. The age of onset of muscle weakness is extremely variable; the most common being between 8 and 15 years, although it can range between 2 and 50 years. The diagnosis can be suspected by findings on a muscle biopsy or when a doctor experienced in muscular dystrophy examines you. A serum creatine kinase blood test may also show raised levels which indicate a problem in the muscles. The diagnosis has to be confirmed by means of identifying a mutation in the CAPN3 gene which is done on a deoxyribonucleic acid sample from a blood test. To date there are no specific treatments for limb-girdle muscular dystrophy, however careful management of the symptoms of the condition can improve a person’s quality of life. Joint contractures (tightening) can occur in limb-girdle muscular dystrophy and therefore regular physiotherapy is recommended.

LGMD: EP.177 Clinical and genetic spectrum of a large cohort of delta-sarcoglycan muscular dystrophy.

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3-6) that are caused by mutations in the SGCA, SGCB, SGCG and SGCD genes. Delta-sarcoglycanopathy (LGMDR6) is the least frequent of all sarcoglycanopaphies and it is considered an ultra-rare disease. Our aim was to characterize the clinical and genetic data of a large cohort of LGMDR6 patients and to investigate whether genetic or protein expression data could predict the severity of the disease. We contacted a total of 90 different neuromuscular units/neurology departments over the world and collected demographic, genetic, clinical and remaining protein expression in muscle biopsy data of patients with a genetic confirmed diagnosis of LGMDR6. We contacted more than 90 pediatric and adult neuromuscular units/neurology departments around the world and identified 23 patients from 9 different countries after reviewing genetic data of more than 10.000 patients with a neuromuscular disorder. There was a history of consanguinity in 87% of the patients and 52.2% of patients had another affected relative. Ninety-one percent of the patients were symptomatic at the time of the analysis. Upper and lower limb proximal muscle weakness was the most common presenting symptom. Distal muscle weakness was observed early on the progression of the disease. Cardiac involvement was observed in 5 patients (21.7%) and 4 patients (17.4%) required non-invasive ventilation. Sixty percent of patients were wheelchair-bound since a mean age of 14.6 years old. Patients with an undetectable expression of the sarcoglycan complex measure by muscle immunohistochemistry have a significant early onset of the disease and early age of lost ambulation compared to patients with residual protein expression. This study confirms that delta-sarcoglycanopathy is an ultra-rare neuromuscular condition and describes the clinical and molecular data of the largest cohort of patients reported so far. International collaboration has been crucial to collect these data. Our results show that this is a very severe and quickly progressive disease characterized by global muscle weakness affecting proximal and distal muscles of the limbs. As happen with other types of sarcoglycanopathy, there is a correlation between remaining protein expression, age at onset and disease's severity.

Clinical and genetic spectrum of a large cohort of patients with δ-sarcoglycan muscular dystrophy.

Sarcoglycanopathies include four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. Delta-sarcoglycanopathy (LGMDR6) is the least frequent and is considered an ultra-rare disease. Our aim was to characterize the clinical and genetic spectrum of a large international cohort of LGMDR6 patients and to investigate whether or not genetic or protein expression data could predict a disease’s severity.This is a retrospective study collecting demographic, genetic, clinical and histological data of patients with genetically confirmed LGMDR6 including protein expression data from muscle biopsies.We contacted 128 paediatric and adult neuromuscular units around the world that reviewed genetic data of patients with a clinical diagnosis of a neuromuscular disorder. We identified 30 patients with a confirmed diagnosis of LGMDR6 of which 23 patients were included in this study. Eighty-seven per cent of the patients had consanguineous parents. Ninety-one per cent of the patients were symptomatic at the time of the analysis. Proximal muscle weakness of the upper and lower limbs was the most common presenting symptom. Distal muscle weakness was observed early over the course of the disease in 56.5% of the patients. Cardiac involvement was reported in five patients (21.7%) and four patients (17.4%) required non-invasive ventilation. Sixty per cent of patients were wheelchair-bound since early teens (median age of 12.0 years). Patients with absent expression of the sarcoglycan complex on muscle biopsy had a significant earlier onset of symptoms and an earlier age of loss of ambulation compared to patients with residual protein expression.This study confirmed that delta-sarcoglycanopathy is an ultra-rare neuromuscular condition and described the clinical and molecular characteristics of the largest yet-reported collected cohort of patients. Our results showed that this is a very severe and quickly progressive disease characterized by generalized muscle weakness affecting predominantly proximal and distal muscles of the limbs. Similar to other forms of sarcoglycanopathies, the severity and rate of progressive weakness correlates inversely with the abundance of protein on muscle biopsy.

Compound heterozygous CAPN3 variants identified inafamily with limb-girdle muscular dystrophy recessive 1.

Limb-girdle muscular dystrophy recessive 1 (LGMDR1), a rare subtype of muscular dystrophy, is characterized by progressive muscle weakness and degeneration with a predominant presentation on the shoulder, pelvic and proximal limb muscles. Variants in calcium-activated neutral proteinase 3 (CAPN3), which encodes an enzyme, calpain 3, are considered the major cause of LGMDR1. The present study was conducted to identify the variants responsible for clinical symptoms in a Chinese patient with limb-girdle muscular dystrophies (LGMDs) and explore its genotype-phenotype associations. A series of clinical examinations were conducted, including blood tests and magnetic resonance imaging scans of the lower legs, electromyography and muscle biopsy on the proband diagnosed with muscular dystrophies. Genomic DNA was extracted from the peripheral blood of a three-person family with LGMDs and pathogenic variants detected by whole-exome sequencing (WES) were verified by Sanger sequencing. The WES of this patient revealed compound heterozygous variants in CAPN3, c.2120A>G/p.(Asp707Gly) in exon 20 and c.2201_2202delAT/p.(Tyr734*) in exon 21, which were inherited from his parents and absent from 200 control individuals of similar ethnic origin, indicating that these variants are the pathogenic triggers of the LGMDR1 phenotype. Notably, these CAPN3 sequence variants were related to LGMDR1 pathogenesis in this three-person family. The newly discovered c.2201_2202delAT/p.(Tyr734*) expands the current CAPN3 variant spectrum, improving the understanding of the conditions required to develop molecular diagnostic tools and for genetic counseling, particularly for families with a history of autosomal recessive LGMDs.

LIMB GIRDLE MUSCULAR DYSTROPHIES: P.150 Four individuals with a homozygous mutation in exon 1f of the PLEC gene and associated myasthenic features

Mutations in the PLEC gene have been associated with multiple phenotypes depending on the location of the mutation and isoform affected. A phenotype of autosomal recessive limb-girdle muscular dystrophy [LGMDR17 plectin-related(MIM613723)] was previously reported in three consanguineous Turkish families carrying an homozygous mutation c.1_9del in exon 1f. We identified the known homozygous c.1_9del mutation in the PLEC gene in four unrelated females from consanguineous families of Turkish origin.

FROM THE SPINAL CORD TO THE MUSCLE: O.10 European collaboration on the clinical and genetic spectrum of sarcoglycan-deficient muscular dystrophy

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutation in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with sarcoglycanopathies created a European network. The aim of this study in to determine the clinical and genetic spectrum of a large cohort of European patients with sarcoglycanopathy from this European network.

LIMB GIRDLE MUSCULAR DYSTROPHIES: P.145 Prevalence of CAPN3 mutations in Limb-girdle muscular dystrophy type 2A: From a multi-center analysis in China to a worldwide perspective

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a rare autosomal recessive limb-girdle muscular dystrophy caused by mutations in CAPN3 gene. To date, no systemic evaluation was performed to investigate the mutational distribution and the hot spot regions. We retrospectively reviewed CAPN3 gene mutations from 124 Chinese patients recruited from four diagnostic centers (2012 January to 2019 September). Then we integrated the multicenter analysis with open-source databases (Clinvar, LOVD, gnomAD) and annotated the combined dataset (Ref: NM_000070.3). Functional evaluating tools (SIFT, PolyPhen, dbscSNV and MaxEntScan) were used to analyze the pathogenicity of the mutations. We evaluated the frequency and distribution of allelic CAPN3 mutation in LGMD2A patients. In the allelic mutational dataset from Chinese cohort (n=112), 62 novel mutations (55.4%) were identified according to ClinVar. The most prevalent mutation in China was c.2120A>G (18.9%) while the previous reported hotspot in LOVD was c.550del. Functional analysis with Polyphen and dbscSNV revealed a higher deleterious effect in Chinese cohort in comparison to the reported data (PolyPhen: g= 0.52, p < 0.0001; dbscSNV: g=0.49, p = 0.0036). After integrating the Chinese data with reported alleles (n= 467 in total), mutations in exon 1 (8.9%) and exon 10 (8.0%) of CAPN3 had the highest frequencies, while missense and frameshift mutations accounted for the majority of mutations. CAPN3 mutations had a high frequency in Exon 1 and 10 among LGMD2A patients. Exon 1 encodes the muscle-specific NS region of Calpain-3 protein while Exon 10 corresponds to Protease Core subdomain 2 (PC2). The frequent mutational regions revealed in the LGMD2A patients.

LIMB GIRDLE MUSCULAR DYSTROPHIES: P.142 The age at loss of ambulation among patients with limb-girdle muscular dystrophy (LGMD) subtype 2: A systematic review

Patients with autosomal recessive LGMD subtype 2 (LGMD2) may experience severe mobility impairments (including loss of ambulation [LOA]). As clinical heterogeneity exists among patients with LGMD, the objective was to synthesize data on the timing of LOA among patients with LGMD2, particularly calpainopathy (LGMD2A), dysferlinopathy (LGMD2B/Miyoshi myopathy [MM]), and sarcoglycanopathies (LGMD2C-F). In this systematic review, a study-specific search strategy was implemented in MEDLINE and EMBASE in September 2019. Outcomes of interest included mean (standard deviation [SD]) or median (95% confidence interval [CI]) age at LOA/wheelchair dependency by key LGMD2 subtype (LGMD2A-F); summary estimates were derived from studies reporting grouped mean, grouped median, and patient-level data. Of 2,929 abstracts, 20 studies reported age at LOA/wheelchair dependency among patients with target LGMD2 subtypes. Nineteen studies reported data to derive mean (SD) age at LOA (n=175), at 28.3 (12.1) years. LOA occurred earliest among patients with sarcoglycanopathies: at 11.5 (1.9; LGMD2F, n=4); 13.1 (3.8; LGMD2E, n=9); 14.5 (2.1; LGMD2D, n=2); and 16.2 (5.4; LGMD2C, n=17) years. Age at LOA was later among those with LGMD2A (29.1 [10.1], n=109) and LGMD2B/MM (38.9 [10.9] years, n=34). One study reported median (95%CI) ages at LOA by LGMD2 subtype (n=271). LOA also occurred earliest among those with LGMD2C-F (18 [14-22] years; n=65), followed by patients with LGMD2A (45 [37-53] years; n=106), and LGMD2B (56 years, n=100); note median estimates were reported from a sample where not everyone had experienced LOA. This study characterizes the timing of LOA among patients with LGMD2; variability was observed across subtypes. Limitations to reported data precluded calculating the proportion of patients remaining ambulant over time; also, descriptions of how wheelchair use was classified were limited. Nonetheless, these data provide a greater understanding of the timing of LOA in LGMD2.

New genotype-phenotype correlations in a large European cohort of patients with sarcoglycanopathy

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with LGMDR3-6 created a European Sarcoglycanopathy Consortium. The aim of the present study was to determine the clinical and genetic spectrum of a large cohort of patients with sarcoglycanopathy in Europe. This was an observational retrospective study. A total of 33 neuromuscular centres from 13 different European countries collected data of the genetically confirmed patients with sarcoglycanopathy followed-up at their centres. Demographic, genetic and clinical data were collected for this study. Data from 439 patients from 13 different countries were collected. Forty-three patients were not included in the analysis because of insufficient clinical information available. A total of 159 patients had a confirmed diagnosis of LGMDR3, 73 of LGMDR4, 157 of LGMDR5 and seven of LGMDR6. Patients with LGMDR3 had a later onset and slower progression of the disease. Cardiac involvement was most frequent in LGMDR4. Sixty per cent of LGMDR3 patients carried one of the following mutations, either in a homozygous or heterozygous state: c.229C>T, c.739G>A or c.850C>T. Similarly, the most common mutations in LMGDR5 patients were c.525delT or c.848G>A. In LGMDR4 patients the most frequent mutation was c.341C>T. We identified onset of symptoms before 10 years of age and residual protein expression lower than 30% as independent risk factors for losing ambulation before 18 years of age, in LGMDR3, LGMDR4 and LGMDR5 patients. This study reports clinical, genetic and protein data of a large European cohort of patients with sarcoglycanopathy. Improving our knowledge about these extremely rare autosomal recessive forms of LGMD was helped by a collaborative effort of neuromuscular centres across Europe. Our study provides important data on the genotype-phenotype correlation that is relevant for the design of natural history studies and upcoming interventional trials in sarcoglycanopathies.