RESUMEN
Sarcoglycanopathies encompass four distinct forms of limb-girdle muscular dystrophies (LGMD), denoted as LGMD R3-R6, arising from mutations within the SGCA, SGCB, SGCG, and SGCD genes. The global prevalence of sarcoglycanopathies is low, making it challenging to study these diseases. The principal objective of this study was to explore the spectrum of mutations in a cohort of Russian patients with sarcoglycanopathies and to ascertain the frequency of these conditions in the Russian Federation. We conducted a retrospective analysis of clinical and molecular genetic data from 49 Russian patients with sarcoglycan genes variants. The results indicated that variants in the SGCA gene were found in 71.4% of cases, with SGCB and SGCG genes each exhibiting variants in 12.2 % of patients. SGCD gene variants were detected in 4.1% of cases. Bi-allelic pathogenic and likely pathogenic variants were identified in 46 of the 49 cases of sarcoglycanopathies: LGMD R3 (n = 34), LGMD R4 (n = 4), LGMD R5 (n = 6), and LGMD R6 (n = 2). A total of 31 distinct variants were identified, comprising 25 previously reported and 6 novel variants. Two major variants, c.229C>T and c.271G>A, were detected within the SGCA, constituting 61.4% of all mutant alleles in Russian patients with LGMD R3. Both LGMD R6 cases were caused by the homozygous nonsense variant c.493C>T p.(Arg165Ter) in the SGCD gene. The incidence of sarcoglycanopathies in the Russian Federation was estimated to be at least 1 in 4,115,039, which is lower than the reported incidence in other populations.
Asunto(s)
Mutación , Sarcoglicanopatías , Sarcoglicanos , Humanos , Sarcoglicanopatías/genética , Sarcoglicanopatías/epidemiología , Federación de Rusia/epidemiología , Masculino , Femenino , Sarcoglicanos/genética , Estudios Retrospectivos , Adulto , Niño , Adolescente , Preescolar , Adulto Joven , Estudios de Cohortes , Persona de Mediana Edad , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/epidemiologíaRESUMEN
Sarcoglycanopathies are rare autosomal recessive diseases belonging to the family of limb-girdle muscular dystrophies. They are caused by mutations in the genes coding for α-, ß-, γ-, and δ-sarcoglycan. The mutations impair the assembly of a key structural complex, which normally protects the sarcolemma of striated muscle from contraction-derived stress. Although heterogeneous, sarcoglycanopathies are characterized by progressive muscle degeneration, increased serum creatine kinase levels, loss of ambulation often during adolescence, and variable cardio-respiratory impairment. Genetic defects can impair sarcoglycan synthesis or produce a protein that is defective in folding. There is currently no effective treatment available; however, both gene replacement strategy and small molecule-based approaches show great promise and have entered or are starting to enter clinical trials.
Asunto(s)
Sarcoglicanopatías , Sarcoglicanos , Humanos , Sarcoglicanopatías/terapia , Sarcoglicanopatías/genética , Sarcoglicanopatías/metabolismo , Animales , Sarcoglicanos/genética , Sarcoglicanos/metabolismo , Terapia Genética/métodos , MutaciónRESUMEN
BACKGROUND: The Limb Girdle Muscular Dystrophies (LGMDs) are characterized by progressive weakness of the shoulder and hip girdle muscles as a result of over 30 different genetic mutations. This study is designed to develop clinical outcome assessments across the group of disorders. METHODS/DESIGN: The primary goal of this study is to evaluate the utility of a set of outcome measures on a wide range of LGMD phenotypes and ability levels to determine if it would be possible to use similar outcomes between individuals with different phenotypes. We will perform a multi-center, 12-month study of 188 LGMD patients within the established Genetic Resolution and Assessments Solving Phenotypes in LGMD (GRASP-LGMD) Research Consortium, which is comprised of 11 sites in the United States and 2 sites in Europe. Enrolled patients will be clinically affected and have mutations in CAPN3 (LGMDR1), ANO5 (LGMDR12), DYSF (LGMDR2), DNAJB6 (LGMDD1), SGCA (LGMDR3), SGCB (LGMDR4), SGCD (LGMDR6), or SGCG (LGMDR5, or FKRP-related (LGMDR9). DISCUSSION: To the best of our knowledge, this will be the largest consortium organized to prospectively validate clinical outcome assessments (COAs) in LGMD at its completion. These assessments will help clinical trial readiness by identifying reliable, valid, and responsive outcome measures as well as providing data driven clinical trial decision making for future clinical trials on therapeutic agents for LGMD. The results of this study will permit more efficient clinical trial design. All relevant data will be made available for investigators or companies involved in LGMD therapeutic development upon conclusion of this study as applicable. TRIAL REGISTRATION: Clinicaltrials.gov NCT03981289; Date of registration: 6/10/2019.
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Humanos , Distrofia Muscular de Cinturas/diagnóstico , Distrofia Muscular de Cinturas/genética , Fenotipo , Músculo Esquelético , Mutación/genética , Proteínas del Tejido Nervioso/genética , Chaperonas Moleculares/genética , Proteínas del Choque Térmico HSP40/genética , Pentosiltransferasa/genética , Anoctaminas/genéticaRESUMEN
Limb-girdle muscular dystrophy 2E/R4 is caused by mutations in the ß-sarcoglycan (SGCB) gene, leading to SGCB deficiency and consequent muscle loss. We developed a gene therapy approach based on functional replacement of the deficient SCB protein. Here we report interim results from a first-in-human, open-label, nonrandomized, phase 1/2 trial evaluating the safety and efficacy of bidridistrogene xeboparvovec, an adeno-associated virus-based gene therapy containing a codon-optimized, full-length human SGCB transgene. Patients aged 4-15 years with confirmed SGCB mutations at both alleles received one intravenous infusion of either 1.85 × 1013 vector genome copies kg-1 (Cohort 1, n = 3) or 7.41 × 1013 vector gene copies kg-1 (Cohort 2, n = 3). Primary endpoint was safety, and secondary endpoint was change in SGCB expression in skeletal muscle from baseline to Day 60. We report interim Year 2 results (trial ongoing). The most frequent treatment-related adverse events were vomiting (four of six patients) and gamma-glutamyl transferase increase (three of six patients). Serious adverse events resolved with standard therapies. Robust SGCB expression was observed: Day 60 mean (s.d.) percentage of normal expression 36.2% (2.7%) in Cohort 1 and 62.1% (8.7%) in Cohort 2. Post hoc exploratory analysis showed preliminary motor improvements using the North Star Assessment for Limb-girdle Type Muscular Dystrophies maintained through Year 2. The 2-year safety and efficacy of bidridistrogene xeboparvovec support clinical development advancement. Further studies are necessary to confirm the long-term safety and efficacy of this gene therapy. ClinicalTrials.gov registration: NCT03652259 .
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Humanos , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/metabolismo , Distrofia Muscular de Cinturas/terapia , Sarcoglicanopatías/genética , Sarcoglicanopatías/metabolismo , Sarcoglicanopatías/terapia , Músculo Esquelético/metabolismo , Terapia Genética/efectos adversos , Terapia Genética/métodosRESUMEN
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.
Asunto(s)
Sarcoglicanopatías , Sarcoglicanos , Humanos , Pueblo Asiatico , Haplotipos , Mutación , Sarcoglicanopatías/genética , Sarcoglicanos/genéticaRESUMEN
Sarcoglycanopathies, also known as limb girdle muscular dystrophy 3-6, are rare muscular dystrophies characterized, although heterogeneous, by high disability, with patients often wheelchair-bound by late adolescence and frequently developing respiratory and cardiac problems. These diseases are currently incurable, emphasizing the importance of effective treatment strategies and the necessity of animal models for drug screening and therapeutic verification. Using the CRISPR/Cas9 genome editing technique, we generated and characterized δ-sarcoglycan and ß-sarcoglycan knockout zebrafish lines, which presented a progressive disease phenotype that worsened from a mild larval stage to distinct myopathic features in adulthood. By subjecting the knockout larvae to a viscous swimming medium, we were able to anticipate disease onset. The δ-SG knockout line was further exploited to demonstrate that a δ-SG missense mutant is a substrate for endoplasmic reticulum-associated degradation (ERAD), indicating premature degradation due to protein folding defects. In conclusion, our study underscores the utility of zebrafish in modeling sarcoglycanopathies through either gene knockout or future knock-in techniques. These novel zebrafish lines will not only enhance our understanding of the disease's pathogenic mechanisms, but will also serve as powerful tools for phenotype-based drug screening, ultimately contributing to the development of a cure for sarcoglycanopathies.
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Animales , Degradación Asociada con el Retículo Endoplásmico , Pez Cebra/genética , Evaluación Preclínica de Medicamentos , LarvaRESUMEN
Genetic testing is essential for patients with a suspected hereditary myopathy. More than 50% of patients clinically diagnosed with a myopathy carry a variant of unknown significance in a myopathy gene, often leaving them without a genetic diagnosis. Limb-girdle muscular dystrophy (LGMD) type R4/2E is caused by mutations in ß-sarcoglycan (SGCB). Together, ß-, α-, γ-, and δ-sarcoglycan form a 4-protein transmembrane complex (SGC) that localizes to the sarcolemma. Biallelic loss-of-function mutations in any subunit can lead to LGMD. To provide functional evidence for the pathogenicity of missense variants, we performed deep mutational scanning of SGCB and assessed SGC cell surface localization for all 6,340 possible amino acid changes. Variant functional scores were bimodally distributed and perfectly predicted pathogenicity of known variants. Variants with less severe functional scores more often appeared in patients with slower disease progression, implying a relationship between variant function and disease severity. Amino acid positions intolerant to variation mapped to points of predicted SGC interactions, validated in silico structural models, and enabled accurate prediction of pathogenic variants in other SGC genes. These results will be useful for clinical interpretation of SGCB variants and improving diagnosis of LGMD; we hope they enable wider use of potentially life-saving gene therapy.
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Humanos , Virulencia , Distrofia Muscular de Cinturas/genética , AminoácidosRESUMEN
Muscular dystrophies are inherited neuromuscular diseases, resulting in progressive disability and often affecting life expectancy. The most severe, common types are Duchenne muscular dystrophy (DMD) and Limb-girdle sarcoglycanopathy, which cause advancing muscle weakness and wasting. These diseases share a common pathomechanism where, due to the loss of the anchoring dystrophin (DMD, dystrophinopathy) or due to mutations in sarcoglycan-encoding genes (LGMDR3 to LGMDR6), the α-sarcoglycan ecto-ATPase activity is lost. This disturbs important purinergic signaling: An acute muscle injury causes the release of large quantities of ATP, which acts as a damage-associated molecular pattern (DAMP). DAMPs trigger inflammation that clears dead tissues and initiates regeneration that eventually restores normal muscle function. However, in DMD and LGMD, the loss of ecto-ATPase activity, that normally curtails this extracellular ATP (eATP)-evoked stimulation, causes exceedingly high eATP levels. Thus, in dystrophic muscles, the acute inflammation becomes chronic and damaging. The very high eATP over-activates P2X7 purinoceptors, not only maintaining the inflammation but also tuning the potentially compensatory P2X7 up-regulation in dystrophic muscle cells into a cell-damaging mechanism exacerbating the pathology. Thus, the P2X7 receptor in dystrophic muscles is a specific therapeutic target. Accordingly, the P2X7 blockade alleviated dystrophic damage in mouse models of dystrophinopathy and sarcoglycanopathy. Therefore, the existing P2X7 blockers should be considered for the treatment of these highly debilitating diseases. This review aims to present the current understanding of the eATP-P2X7 purinoceptor axis in the pathogenesis and treatment of muscular dystrophies.
Asunto(s)
Distrofia Muscular de Duchenne , Sarcoglicanopatías , Ratones , Animales , Receptores Purinérgicos P2X7/genética , Sarcoglicanopatías/patología , Ratones Endogámicos mdx , Distrofia Muscular de Duchenne/genética , Distrofina/genética , Adenosina Trifosfato , Inflamación/patología , Músculo Esquelético/patologíaRESUMEN
Sarcoglycanopathies, limb-girdle muscular dystrophies (LGMD) caused by genetic loss-of-function of the membrane proteins sarcoglycans (SGs), are characterized by progressive degeneration of skeletal muscle. In these disorders, muscle necrosis is associated with immune-mediated damage, whose triggering and perpetuating molecular mechanisms are not fully elucidated yet. Extracellular adenosine triphosphate (eATP) seems to represent a crucial factor, with eATP activating purinergic receptors. Indeed, in vivo blockade of the eATP/P2X7 purinergic pathway ameliorated muscle disease progression. P2X7 inhibition improved the dystrophic process by restraining the activity of P2X7 receptors on immune cells. Whether P2X7 blockade can display a direct action on muscle cells is not known yet. In this study, we investigated eATP effects in primary cultures of myoblasts isolated from patients with LGMDR3 (α-sarcoglycanopathy) and in immortalized cells isolated from a patient with LGMDR5 (γ-sarcoglycanopathy). Our results demonstrated that, owing to a reduced ecto-ATPase activity and/or an enhanced release of ATP, patient cells are exposed to increased juxtamembrane concentrations of eATP and display a higher susceptivity to eATP signals. The purinoceptor P2Y2, which proved to be overexpressed in patient cells, was identified as a pivotal receptor responsible for the enhanced ATP-induced or UTP-induced Ca2+ increase in affected myoblasts. Moreover, P2Y2 stimulation in LDMDR3 muscle cells induced chemotaxis of immune cells and release of interleukin-8. In conclusion, a higher eATP concentration and sensitivity in primary human muscle cells carrying different α-SG or γ-SG loss-of-function mutations indicate that eATP/P2Y2 is an enhanced signaling axis in cells from patients with α-/γ-sarcoglycanopathy. Understanding the basis of the innate immune-mediated damage associated with the dystrophic process may be critical in overcoming the immunologic hurdles associated with emerging gene therapies for these disorders.
Asunto(s)
Adenosina Trifosfato , Sarcoglicanopatías , Humanos , Adenosina Trifosfato/metabolismo , Músculo Esquelético/metabolismo , Sarcoglicanopatías/metabolismo , Transducción de Señal , Receptores Purinérgicos P2Y2RESUMEN
Dystrophinopathy and sarcoglycanopathies are incurable diseases caused by mutations in the genes encoding dystrophin or members of the dystrophin associated protein complex (DAPC). Restoration of the missing dystrophin or sarcoglycans via genetic approaches is complicated by the downsides of personalised medicines and immune responses against re-expressed proteins. Thus, the targeting of disease mechanisms downstream from the mutant protein has a strong translational potential. Acute muscle damage causes release of large quantities of ATP, which activates P2X7 purinoceptors, resulting in inflammation that clears dead tissues and triggers regeneration. However, in dystrophic muscles, loss of α-sarcoglycan ecto-ATPase activity further elevates extracellular ATP (eATP) levels, exacerbating the pathology. Moreover, seemingly compensatory P2X7 upregulation in dystrophic muscle cells, combined with high eATP leads to further damage. Accordingly, P2X7 blockade alleviated dystrophic damage in mouse models of both dystrophinopathy and sarcoglycanopathy. Existing P2X7 blockers could be re-purposed for the treatment of these highly debilitating diseases.
Asunto(s)
Sarcoglicanopatías , Ratones , Animales , Sarcoglicanopatías/metabolismo , Sarcoglicanopatías/patología , Distrofina , Receptores Purinérgicos P2X7/metabolismo , Sarcoglicanos/genética , Sarcoglicanos/metabolismo , Adenosina Trifosfato/metabolismo , Músculo Esquelético/metabolismoRESUMEN
Sarcoglycanopathies are highly heterogeneous in terms of disease progression, muscular weakness, loss of ambulation and cardiac/respiratory involvement. Their clinical severity usually correlates with the residual protein amount, which makes protein quantification extremely relevant. Sarcoglycanopathy diagnosis is genetic, but skeletal muscle analysis - by both immunohistochemistry and Western blot (WB) - is still mandatory to establish the correct diagnostic process. Unfortunately, however, WB analysis cannot be performed if the bioptic specimen is scarce. This study provides a sensitive tool for semi-quantification of residual amount of sarcoglycans in patients affected by sarcoglycanopathies, based on immunofluorescence staining on skeletal muscle sections, image acquisition and software elaboration. We applied this method to eleven sarcoglycanopathies, seven Becker muscular dystrophies and four age-matched controls. Fluorescence data analysed in patients and compared to age-matched controls showed a significant reduction of the mutated sarcoglycan expression and a variable reduction of the other sarcoglycans. Fluorescence normalized data analysed in relation to the age of onset of the disease, showed a negative correlation of α-sarcoglycan fluorescent signal versus fibrosis in patients with an early age of onset and a negative correlation between δ-sarcoglycan signal and fibrosis in both intermediate and late age of onset groups. The availability of a method that allows objective quantification of the sarcolemmal proteins, faster and less consuming than WB analysis and able to detect low residual sarcoglycan expression with great sensitivity, proves useful to better define both patient prognosis and expected disease evolution. The proposed method could be employed also to monitor the efficacy of therapeutic interventions and during clinical trials.
Asunto(s)
Sarcoglicanopatías , Sarcoglicanos , Biopsia , Fibrosis , Técnica del Anticuerpo Fluorescente , Humanos , Músculo Esquelético/metabolismo , Sarcoglicanopatías/diagnóstico , Sarcoglicanopatías/metabolismo , Sarcoglicanopatías/patología , Sarcoglicanos/metabolismoRESUMEN
Limb-girdle muscular dystrophies (LGMD) are clinically and genetically heterogenous presentations displaying predominantly proximal muscle weakness due to the loss of skeletal muscle fibers. Beta-sarcoglycanopathy (LGMDR4) results from biallelic molecular defects in SGCB and features pediatric onset with limb-girdle involvement, often complicated by respiratory and heart dysfunction. Here we describe a patient who presented at the age of 12 years reporting high creatine kinase levels and onset of cramps after strenuous exercise. Instrumental investigations, including a muscle biopsy, pointed towards a diagnosis of beta-sarcoglycanopathy. NGS panel sequencing identified two variants in the SGCB gene, one of which (c.243+1548T>C) was found to promote the inclusion of a pseudoexon between exons 2 and 3 in the SGCB transcript. Interestingly, we detected the same genotype in a previously reported LGMDR4 patient, deceased more than twenty years ago, who had escaped molecular diagnosis so far. After the delivery of morpholino oligomers targeting the pseudoexon in patient-specific induced pluripotent stem cells, we observed the correction of the physiological splicing and partial restoration of protein levels. Our findings prompt the analysis of the c.243+1548T>C variant in suspected LGMDR4 patients, especially those harbouring monoallelic SGCB variants, and provide a further example of the efficacy of antisense technology for the correction of molecular defects resulting in splicing abnormalities.
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Niño , Humanos , Morfolinos/genética , Morfolinos/metabolismo , Músculo Esquelético/metabolismo , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/patología , Mutación , Sarcoglicanopatías/metabolismoRESUMEN
Limb girdle muscular dystrophy type 2D (LGMD2D) is characterized by progressive weakening of muscles in the hip and shoulder girdles. It is caused by a mutation in the α-sarcoglycan gene and results in absence of α-sarcoglycan in the dystrophin-glycoprotein complex. The activin type IIB receptor is involved in the activin/myostatin pathway, with myostatin being a negative regulator of muscle growth. In this study, we investigated the effects of sequestering myostatin by a soluble activin type IIB receptor (sActRIIB) on muscle growth in Sgca-null mice, modelling LGMD2D. Treatment was initiated at 3 weeks of age, prior to the disease onset, or at 9 weeks of age when already in an advanced stage of the disease. We found that early sActRIIB treatment resulted in increased muscle size. However, this led to more rapid decline of muscle function than in saline-treated Sgca-null mice. Furthermore, no histopathological improvements were seen after sActRIIB treatment. When initiated at 9 weeks of age, sActRIIB treatment resulted in increased muscle mass too, but to a lesser extent. No effect of the treatment was observed on muscle function or histopathology. These data show that sActRIIB treatment as a stand-alone therapy does not improve muscle function or histopathology in Sgca-null mice.
Asunto(s)
Miostatina , Sarcoglicanopatías , Receptores de Activinas/metabolismo , Activinas/metabolismo , Animales , Modelos Animales de Enfermedad , Ratones , Músculo Esquelético/patología , Miostatina/genética , Sarcoglicanopatías/metabolismo , Sarcoglicanos/genética , Sarcoglicanos/metabolismoRESUMEN
The clinico-genetic architecture of sarcoglycanopathies in Indian patients is reported only as short series. In the present study, we aimed to investigate the clinical picture, genetic basis, and disease progression of patients genetically confirmed to have sarcoglycanopathy. Next-generation sequencing was performed in 68 probands with suspected sarcoglycanopathy. A total of 35 different variants were detected in the sarcoglycan genes in 68 probands (M = 37; age range, 5-50 years). Consanguinity was present in 44 families. Thirty-two variants are predicted to be pathogenic/likely pathogenic, among which 25 (78.13%) are reported, and 7 (21.87%) are novel. The clinical diagnosis was confirmed in a total of 64 (94.12%) probands with biallelic variations [SGCA(n=18); SGCB(n=34); SGCG(n=7); SGCD(n=5)]. The most common mutation was c.544A > C (p.Thr182Pro) in SGCB, and detected in 20 patients (29.42%). The majority of pathogenic mutations are homozygous (n = 30; 93.75%). Variants in 4 cases are of uncertain significance. Thirty-three patients lost ambulation at a mean age of 15.12 ± 9.47 years, after 7.76 ± 5.95 years into the illness. Only 2 patients had cardiac symptoms, and one had respiratory muscle involvement. The results from this study suggest that mutations in SGCB are most common, followed by SGCA, SGCG, and SGCD. The novel variations identified in this study expand the mutational spectrum of sarcoglycanopathies. To the best of our knowledge, this is the first study from India to describe a large cohort of genetically confirmed patients with sarcoglycanopathy and report its disease progression.
Asunto(s)
Sarcoglicanopatías , Sarcoglicanos , Adolescente , Adulto , Niño , Preescolar , Progresión de la Enfermedad , Perfil Genético , Humanos , Persona de Mediana Edad , Prevalencia , Sarcoglicanopatías/epidemiología , Sarcoglicanopatías/genética , Sarcoglicanopatías/patología , Sarcoglicanos/genética , Adulto JovenRESUMEN
BACKGROUND: Mutations in the alpha-sarcoglycan gene cause limb-girdle muscular dystrophy 2D, an autosomal recessive muscle wasting disorder primarily affecting the muscles of the shoulder and pelvic girdles. To date, no previous study has collated all known mutations in alpha-sarcoglycan and mapped these to the associated phenotypes. AIMS: To examine for correlations between mutation locations, or mutation type, and the phenotype caused in all reported mutations in alpha-sarcoglycan. METHODS: We present a systematic literature review examining correlations between mutation locations, or mutation type, and the phenotype caused in all reported cases of limb-girdle muscular dystrophy 2D. RESULTS: From 134 unique genotypes collated, a strong prevalence of missense mutations (64% of all unique mutations) was found in this gene. Mutation hotspots were noted in exon three and the extracellular domain, with mutation densities varying significantly between both exons and protein domains (p ≤ 0.01). All compound heterozygous limb-girdle muscular dystrophy 2D patients with cardiac involvement contained at least one mutation in exon three, a novel finding. All non-sense mutations in alpha-sarcoglycan give a severe phenotype, as do genotypes involving a combination of exons four and five. This study confirms on a large, diverse cohort the extremely high prevalence of the c.229C > T mutation. CONCLUSIONS: This study demonstrates the vast variation in disease severity seen between patients possessing the same mutation, highlighting the difficulty identifying genotype-phenotype correlations in this condition. Novel findings including the involvement of exon three in all compound heterozygous patients who suffered from cardiomyopathy, and the severity of mutations involving exons four and five may help to guide investigations and therapeutic decisions in an era of personalised medicine.
Asunto(s)
Sarcoglicanopatías , Humanos , Sarcoglicanopatías/genética , Sarcoglicanos/genética , Exones , Fenotipo , Mutación , Estudios de Asociación GenéticaRESUMEN
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.
Asunto(s)
Distrofia Muscular de Cinturas , Distrofias Musculares , Sarcoglicanopatías , Adulto , Niño , Humanos , Debilidad Muscular , Distrofias Musculares/genética , Distrofia Muscular de Cinturas/diagnóstico , Distrofia Muscular de Cinturas/genética , Estudios Retrospectivos , Sarcoglicanopatías/genética , Sarcoglicanos/genética , Sarcoglicanos/metabolismoRESUMEN
Limb-girdle muscular dystrophies (LGMDs) represent a major group of muscle disorders. Treatment is sorely needed and currently expanding based on safety and efficacy adopting principles of single-dosing gene therapy for monogenic autosomal recessive disorders. Gene therapy has made in-roads for LGMD and this review describes progress that has been achieved for these conditions. This review first provides a background on the definition and classification of LGMDs. The major effort focuses on progress in LGMD gene therapy, from experimental studies to clinical trials. The disorders discussed include the LGMDs where the most work has been done including calpainopathies (LGMD2A/R1), dysferlinopathies (LGMD2B/R2) and sarcoglycanopathies (LGMD2C/R5, LGMD2D/R3, LGMD2E/R4). Early success in clinical trials provides a template to move the field forward and potentially apply emerging technology like CRISPR/Cas9 that may enhance the scope and efficacy of gene therapy applied to patient care.
Lay abstract Limb-girdle muscular dystrophy is a term that is applied to a group of relatively rare forms of muscular dystrophy. The term 'LGMD' was introduced in the 1950's, but there were no strict rules for defining the condition. This changed as a result of the 229th European Neuromuscular Center International Workshop in 2017 providing a clear definition and classification discussed in this article. Limb-girdle muscular dystrophy is now recognized as a genetic muscle disease with an elevated serum creatine kinase and dystrophic changes on muscle histology. Most treatments up to now rely on supportive measures for heart and lungs and assisting the physical limitations. Medications have not proven to be beneficial to stop progression of disease. This article focuses on new innovations of treatment that target the effected gene and the use special methods to replace the abnormal gene.
Asunto(s)
Distrofia Muscular de Cinturas , Sarcoglicanopatías , Humanos , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/terapiaRESUMEN
Sarcoglycanopathies are the most severe forms of autosomal recessive limb-girdle muscular dystrophies (LGMDs), constituting about 10-25% of LGMDs. The clinical phenotype is variable, but onset is usually in the first decade of life. Patients present muscle hypertrophy, elevated CK, variable muscle weaknesses, and progressive loss of ambulation. Four subtypes are known: LGMDR3, LGMDR4, LGMDR5 and LGMDR6, caused, respectively, by mutations in the SGCA, SGCB,SGCG and SGCD genes. Their four coded proteins, α-SG, ß-SG, λ-SG and δ-SG are part of the dystrophin-glycoprotein complex (DGC) present in muscle sarcolemma, which acts as a linker between the cytoskeleton of the muscle fiber and the extracellular matrix, providing mechanical support to the sarcolemma during myofiber contraction. Many different mutations have already been identified in all the sarcoglycan genes, with a predominance of some mutations in different populations. The diagnosis is currently based on the molecular screening for these mutations. Therapeutic approaches include the strategy of gene replacement mediated by a vector derived from adeno-associated virus (AAV). Pre-clinical studies have shown detectable levels of SG proteins in the muscle, and some improvement in the phenotype, in animal models. Therapeutic trials in humans are ongoing.
Asunto(s)
Sarcoglicanopatías/genética , Dependovirus , Terapia Genética , Humanos , Músculo Esquelético/metabolismo , Mutación , Fenotipo , Sarcoglicanos/genéticaRESUMEN
AIM: Since the immune system plays a role in the pathogenesis of several muscular dystrophies, we aim to characterize several muscular inflammatory features in α- (LGMD R3) and γ-sarcoglycanopathies (LGMD R5). MATERIALS AND METHODS: We explored the expression of major histocompatibility complex class I molecules (MHCI), and we analyzed the composition of the immune infiltrates in muscle biopsies from 10 patients with LGMD R3 and 8 patients with LGMD R5, comparing the results to Duchenne muscular dystrophy patients (DMD). RESULTS: A consistent involvement of the immune response was observed in sarcoglycanopathies, although it was less evident than in DMD. LGMD R3-R5 and DMD shared an abnormal expression of MHCI, and the composition of the muscular immune cell infiltrate was comparable. CONCLUSION: These findings might serve as a rationale to fine-tune a disease-specific immunomodulatory regimen, particularly relevant in view of the rapid development of gene therapy for sarcoglycanopathies.
Asunto(s)
Distrofias Musculares , Miositis , Sarcoglicanopatías , Biopsia , Humanos , Músculo Esquelético , Sarcoglicanopatías/genéticaRESUMEN
Skeletal muscle, the most abundant tissue in the body, is heterogeneous. This heterogeneity forms the basis of muscle diversity, which is reflected in the specialized functions of muscles in different parts of the body. However, these different parts are not always clearly delimitated, and this often gives rise to gradients within the same muscle and even across the body. During the last decade, several studies on muscular disorders both in mice and in humans have observed particular distribution patterns of muscle weakness during disease, indicating that the same mutation can affect muscles differently. Moreover, these phenotypical differences reveal gradients of severity, existing alongside other architectural gradients. These two factors are especially prominent in sarcoglycanopathies. Nevertheless, very little is known about the mechanism(s) driving the phenotypic diversity of the muscles affected by these diseases. Here, we will review the available literature on sarcoglycanopathies, focusing on phenotypic differences among affected muscles and gradients, characterization techniques, molecular signatures, and cell population heterogeneity, highlighting the possibilities opened up by new technologies. This review aims to revive research interest in the diverse disease phenotype affecting different muscles, in order to pave the way for new therapeutic interventions.