LGMD2A: genotype-phenotype correlations based on a large mutational survey on the calpain 3 gene

Identification of novel pathogenic variants of Calpain-3 gene in limb girdle muscular dystrophy R1

BACKGROUND

Limb Girdle Muscular Dystrophy R1 (LGMDR1) is an autosomal recessive neuromuscular disease caused by mutations in the calpain-3 (CAPN3) gene. As clinical and pathological features may overlap with other types of LGMD, therefore definite molecular diagnosis is required to understand the progression of this debilitating disease. This study aims to identify novel variants of CAPN3 gene in LGMDR1 patients.

RESULTS

Thirty-four patients with clinical and histopathological features suggestive of LGMD were studied. The muscle biopsy samples were evaluated using Enzyme histochemistry, Immunohistochemistry, followed by Western Blotting and Sanger sequencing. Out of 34 LGMD cases, 13 patients were diagnosed as LGMDR1 by immunoblot analysis, demonstrating reduced or absent calpain-3 protein as compared to controls. Variants of CAPN3 gene were also found and pathogenicity was predicted using in-silico prediction tools. The CAPN3 gene variants found in this study, included, two missense variants [CAPN3: c.1189T > C, CAPN3: c.2338G > C], one insertion-deletion [c.1688delinsTC], one splice site variant [c.2051-1G > T], and one nonsense variant [c.1939G > T; p.Glu647Ter].

CONCLUSIONS

We confirmed 6 patients as LGMDR1 (with CAPN3 variants) from our cohort and calpain-3 protein expression was significantly reduced by immunoblot analysis as compared to control. Besides the previously known variants, our study found two novel variants in CAPN3 gene by Sanger sequencing-based approach indicating that genetic variants in LGMDR1 patients may help to understand the etiology of the disease and future prognostication.

Defining clinical endpoints in limb girdle muscular dystrophy: a GRASP-LGMD study

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.

Novel Biomarkers for Limb Girdle Muscular Dystrophy (LGMD)

OBJECTIVE

To identify novel biomarkers as an alternative diagnostic tool for limb girdle muscular dystrophy (LGMD).

BACKGROUND

LGMD encompasses a group of muscular dystrophies characterized by proximal muscles weakness, elevated CK levels and dystrophic findings on muscle biopsy. Heterozygous CAPN3 mutations are associated with autosomal dominant LGMD-4, while biallelic mutations can cause autosomal recessive LGMD-1. Diagnosis is currently often based on invasive methods requiring muscle biopsy or blood tests. In most cases Western blotting (WB) analysis from muscle biopsy is essential for a diagnosis, as muscle samples are currently the only known tissues to express the full-length CAPN3 isoform.

METHODS

We analyzed CAPN3 in a cohort including 60 LGMD patients. Selected patients underwent a complete neurological examination, electromyography, muscle biopsy, and skin biopsies for primary fibroblasts isolation. The amount of CAPN3 was evaluated by WB analysis in muscle and skin tissues. The total RNA isolated from muscle, fibroblast and urine was processed, and cDNA was used for qualitative analysis. The expression of CAPN3 was investigated by qRT-PCR. The CAPN3 3D structure has been visualized and analyzed using PyMOL.

RESULTS

Among our patients, seven different CAPN3 mutations were detected, of which two were novel. After sequencing CAPN3 transcripts from fibroblast and urine, we detected different CAPN3 isoforms surprisingly including the full-length transcript. We found comparable protein levels from fibroblasts and muscle tissue; in particular, patients harboring a novel CAPN3 mutation showed a 30% reduction in protein compared to controls from both tissues.

CONCLUSIONS

Our findings showed for the first time the presence of the CAPN3 full-length transcript in urine and skin samples. Moreover, we demonstrated surprisingly comparable CAPN3 protein levels between muscle and skin samples, thus allowing us to hypothesize the use of skin biopsy and probably of urine samples as an alternative less invasive method to assess the amount of CAPN3 when molecular diagnosis turns out to be inconclusive.

Clinical features, imaging findings and molecular data of limb-girdle muscular dystrophies in a cohort of Chinese patients

BACKGROUND

Limb-girdle muscular dystrophies (LGMDs) are a group of heterogeneous inherited diseases predominantly characterized by limb-girdle muscle weakness and dystrophic changes on histological analysis. The frequency of LGMD subtypes varies among regions in China and ethnic populations worldwide. Here, we analyzed the prevalence of LGMD subtypes, their corresponding clinical manifestations, and molecular data in a cohort of LGMD patients in Southeast China.

METHODS

A total of 81 consecutive patients with clinically suspected LGMDs from 62 unrelated families across Southeast China were recruited for targeted next-generation sequencing and whole-exome sequencing from July 2017 to February 2020.

RESULTS

Among 50 patients (41 families) with LGMDs, the most common subtypes were LGMD-R2/LGMD2B (36.6%) and LGMD-R1/LGMD2A (29.3%). Dystroglycanopathies (including LGMD-R9/LGMD2I, LGMD-R11/LGMD2K, LGMD-R14/LGMD2N and LGMD-R20/LGMD2U) were the most common childhood-onset subtypes and were found in 12.2% of the families. A total of 14.6% of the families had the LGMD-R7/LGMD2G subtype, and the mutation c.26_33dupAGGTGTCG in TCAP was the most frequent (83.3%). The only patient with the rare subtype LGMD-R18/LGMD2S had TRAPPC11 mutations; had a later onset than those previously reported, and presented with proximal‒distal muscle weakness, walking aid dependency, fatty liver disease and diabetes at 33 years of age. A total of 22.0% of the patients had cardiac abnormalities, and one patient with LMNA-related muscular dystrophy/LGMD1B experienced sudden cardiac death at 37 years of age. A total of 15.4% of the patients had restrictive respiratory insufficiency. Muscle imaging in patients with LGMD-R1/LGMD2A and LGMD-R2/LGMD2B showed subtle differences, including more severe fatty infiltration of the posterior thigh muscles in those with LGMD-R1/LGMD2A and edema in the lower leg muscles in those with LGMD-R2/LGMD2B.

CONCLUSION

We determined the prevalence of different LGMD subtypes in Southeast China, described the detailed clinical manifestations and distinct muscle MRI patterns of these LGMD subtypes and reported the frequent mutations and the cardiorespiratory involvement frequency in our cohort, all of which might facilitate the differential diagnosis of LGMDs, allowing more timely treatment and guiding future clinical trials.

Genetic findings in Czech patients with limb girdle muscular dystrophy

Limb girdle muscular dystrophies (LGMD) are a genetically heterogeneous group of muscular dystrophies. The study presents an overview of molecular characteristics of a large cohort of LGMD patients who are representative of the Czech LGMD population. We present 226 LGMD probands in which 433 mutant alleles carrying 157 different variants with a supposed pathogenic effect were identified. Fifty-four variants have been described only in the Czech LGMD population so far. LGMD R1 caplain3-related is the most frequent subtype of LGMD involving 53.1% of patients with genetically confirmed LGMD, followed by LGMD R9 FKRP-related (11.1%), and LGMD R12 anoctamin5-related (7.1%). If we consider identified variants, then all but five were small-scale variants. One large gene deletion was identified in the LAMA2 gene and two deletions in each of CAPN3 and SGCG. We performed comparison our result with other published studies. The results obtained in the Czech LGMD population clearly differ from the outcome of other LGMD populations in two aspects-we have a more significant proportion of patients with LGMD R1 calpain3-related and a smaller proportion of LGMD R2 dysferlin-related.

The spectrum of hereditary neuromuscular disorders in the Pakistani population

Hereditary neuromuscular disorders (NMDs) are a broad group of clinically heterogeneous disorders with varying inheritance patterns, that are associated with over 500 implicated genes. In the context of a highly consanguineous Pakistani population, we expect that autosomal recessive NMDs may have a higher prevalence compared with patients of European descent. This is the first study to offer a detailed description of the spectrum of genes causing hereditary NMDs in the Pakistani population using NGS testing. To study the clinical and genetic profiles of patients presenting for evaluation of a hereditary neuromuscular disorder. This is a retrospective chart review of patients seen in the Neuromuscular Disorders Clinic and referred to the Genetics Clinic with a suspected hereditary neuromuscular disorder, between 2016 and 2020 at the Aga Khan University Hospital, Karachi and Mukhtiar A. Sheikh Hospital, Multan, Pakistan. The genetic testing for these patients included NGS-based single gene sequencing, NGS-based multi-gene panel and whole exome sequencing. In a total of 112 patients studied, 35 (31.3%) were female. The mean age of onset in all patients was 14.6 years (SD ±12.1 years), with the average age at presentation to the clinic of 22.4 years (SD ±14.10 years). Forty-seven (41.9%) patients had a positive genetic test result, 53 (47.3%) had one or more variants of uncertain significance (VUS), and 12 (10.7%) had a negative result. Upon further genotype-phenotype correlation and family segregation analysis, the diagnostic yield improved, with 59 (52.7%) patients reaching a diagnosis of a hereditary NMD. We also report probable founder variants in COL6A2, FKTN, GNE, and SGCB, previously reported in populations that have possible shared ancestry with the Pakistani population. Our findings reemphasizes that the rate of VUSs can be reduced by clinical correlation and family segregation studies.

Invited review: Muscle protein breakdown and its assessment in periparturient dairy cows

Mobilization of body reserves including fat, protein, and glycogen is necessary to overcome phases of negative nutrient balance typical for high-yielding dairy cows during the periparturient period. Skeletal muscle, the largest internal organ in mammals, plays a crucial role in maintaining metabolic homeostasis. However, unlike in liver and adipose tissue, the metabolic and regulatory role of skeletal muscle in the adaptation of dairy cows to the physiological needs of pregnancy and lactation has not been studied extensively. The functional integrity and quality of skeletal muscle are maintained through a constant turnover of protein, resulting from both protein breakdown and protein synthesis. Thus, muscle protein breakdown (MPB) and synthesis are intimately connected and tightly controlled to ensure proper protein homeostasis. Understanding the regulation of MPB, the catabolic component of muscle turnover, and its assessment are therefore important considerations to provide information about the timing and extent of tissue mobilization in periparturient dairy cows. Based on animal models and human studies, it is now evident that MPB occurs via the integration of 3 main systems: autophagy-lysosomal, calpain Ca²⁺-dependent cysteine proteases, and the ubiquitin-proteasome system. These 3 main systems are interconnected and do not work separately, and the regulation is complex. The ubiquitin-proteasomal system is the most well-known cellular proteolytic system and plays a fundamental role in muscle physiology. Complete degradation of a protein often requires a combination of the systems, depending on the physiological situation. Determination of MPB in dairy cows is technically challenging, resulting in a relative dearth of information. The methods for assessing MPB can be divided into either direct or indirect measurements, both having their strengths and limitations. Available information on the direct measures of MPB primarily comes from stable isotopic tracer methods and those of indirect measurements from assessing expression and activity measures of the components of the 3 MPB systems in muscle biopsy samples. Other indirect approaches (i.e., potential indicators of MPB), including ultrasound imaging and measuring metabolites from muscle degradation (i.e., 3-methylhistidine and creatinine), seem to be applicable methods and can provide useful information about the extent and timing of MPB. This review presents our current understanding, including methodological considerations, of the process of MPB in periparturient dairy cows.

Targeting the Ubiquitin-Proteasome System in Limb-Girdle Muscular Dystrophy With CAPN3 Mutations

LGMDR1 is caused by mutations in the CAPN3 gene that encodes calpain 3 (CAPN3), a non-lysosomal cysteine protease necessary for proper muscle function. Our previous findings show that CAPN3 deficiency leads to reduced SERCA levels through increased protein degradation. This work investigates the potential contribution of the ubiquitin-proteasome pathway to increased SERCA degradation in LGMDR1. Consistent with our previous results, we observed that CAPN3-deficient human myotubes exhibit reduced SERCA protein levels and high cytosolic calcium concentration. Treatment with the proteasome inhibitor bortezomib (Velcade) increased SERCA2 protein levels and normalized intracellular calcium levels in CAPN3-deficient myotubes. Moreover, bortezomib was able to recover mutated CAPN3 protein in a patient carrying R289W and R546L missense mutations. We found that CAPN3 knockout mice (C3KO) presented SERCA deficits in skeletal muscle in the early stages of the disease, prior to the manifestation of muscle deficits. However, treatment with bortezomib (0.8 mg/kg every 72 h) for 3 weeks did not rescue SERCA levels. No change in muscle proteasome activity was observed in bortezomib-treated animals, suggesting that higher bortezomib doses are needed to rescue SERCA levels in this model. Overall, our results lay the foundation for exploring inhibition of the ubiquitin-proteasome as a new therapeutic target to treat LGMDR1 patients. Moreover, patients carrying missense mutations in CAPN3 and presumably other genes may benefit from proteasome inhibition by rescuing mutant protein levels. Further studies in suitable models will be necessary to demonstrate the therapeutic efficacy of proteasome inhibition for different missense mutations.

Defining and identifying satellite cell-opathies within muscular dystrophies and myopathies

Muscular dystrophies and congenital myopathies arise from specific genetic mutations causing skeletal muscle weakness that reduces quality of life. Muscle health relies on resident muscle stem cells called satellite cells, which enable life-course muscle growth, maintenance, repair and regeneration. Such tuned plasticity gradually diminishes in muscle diseases, suggesting compromised satellite cell function. A central issue however, is whether the pathogenic mutation perturbs satellite cell function directly and/or indirectly via an increasingly hostile microenvironment as disease progresses. Here, we explore the effects on satellite cell function of pathogenic mutations in genes (myopathogenes) that associate with muscle disorders, to evaluate clinical and muscle pathological hallmarks that define dysfunctional satellite cells. We deploy transcriptomic analysis and comparison between muscular dystrophies and myopathies to determine the contribution of satellite cell dysfunction using literature, expression dynamics of myopathogenes and their response to the satellite cell regulator PAX7. Our multimodal approach extends current pathological classifications to define Satellite Cell-opathies: muscle disorders in which satellite cell dysfunction contributes to pathology. Primary Satellite Cell-opathies are conditions where mutations in a myopathogene directly affect satellite cell function, such as in Progressive Congenital Myopathy with Scoliosis (MYOSCO) and Carey-Fineman-Ziter Syndrome (CFZS). Primary satellite cell-opathies are generally characterised as being congenital with general hypotonia, and specific involvement of respiratory, trunk and facial muscles, although serum CK levels are usually within the normal range. Secondary Satellite Cell-opathies have mutations in myopathogenes that affect both satellite cells and muscle fibres. Such classification aids diagnosis and predicting probable disease course, as well as informing on treatment and therapeutic development.

Disease Progression and Mutation Pattern in a Large Cohort of LGMD R1/LGMD 2A Patients from India

Calpainopathy is caused by mutations in the CAPN3. There is only one clinical and genetic study of CAPN3 from India and none from South India. A total of 72 (male[M]:female [F] = 34:38) genetically confirmed probands from 72 independent families are included in this study. Consanguinity was present in 54.2%. The mean age of onset and duration of symptoms are 13.5 ± 6.4 and 6.3 ± 4.7 years, respectively. Positive family history occurred in 23.3%. The predominant initial symptoms were proximal lower limb weakness (52.1%) and toe walking (20.5%). At presentation, 97.2% had hip girdle weakness, 69.4% had scapular winging, and 58.3% had contractures. Follow-up was available in 76.4%, and 92.7% were ambulant at a mean age of 23.7 ± 7.6 years and duration of 4.5 years, remaining 7.3% became wheelchair-bound at 25.5 ± 5.7 years of age (mean duration = 13.5 ± 4.6), 4.1% were aged more than 40 years (duration range = 5–20). The majority remained ambulant 10 years after disease onset. Next-generation sequencing (NGS) detected 47 unique CAPN3 variants in 72 patients, out of which 19 are novel. Missense variants were most common occurring in 59.7% (homozygous = 29; Compound heterozygous = 14). In the remaining 29 patients (40.3%), at least one suspected loss of function variant was present. Common recurrent variants were c.2051–1G > T and c.2338G > C in 9.7%, c.1343G > A, c.802–9G > A, and c.1319G > A in 6.9% and c.1963delC in 5.5% of population. Large deletions were observed in 4.2%. Exon 10 mutations accounted for 12 patients (16.7%). Our study highlights the efficiency of NGS technology in screening and molecular diagnosis of limb-girdle muscular dystrophy with recessive form (LGMDR1) patients in India.

Compound heterozygous CAPN3 variants identified in a family 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.

Mutational Spectrum of CAPN3 with Genotype-Phenotype Correlations in Limb Girdle Muscular Dystrophy Type 2A/R1 (LGMD2A/LGMDR1) Patients in India

BACKGROUND

Limb girdle muscular dystrophy recessive type 1 (LGMDR1, Previously LGMD2A) is characterized by inactivating mutations in CAPN3. Despite the significant burden of muscular dystrophy in India, and particularly of LGMDR1, its genetic characterization and possible phenotypic manifestations are yet unidentified.

MATERIAL AND METHODS

We performed bidirectional CAPN3 sequencing in 95 LGMDR1 patient samples characterized by calpain-3 protein analysis, and these findings were correlated with clinical, biochemical and histopathological features.

RESULTS

We identified 84 (88.4%) cases of LGMDR1 harboring 103 CAPN3 mutations (71 novel and 32 known). At least two mutant alleles were identified in 79 (94.2%) of patients. Notably, 76% exonic variations were enriched in nine CAPN3 exons and overall, 41 variations (40%) correspond to only eight exonic and intronic mutations. Patients with two nonsense/out of frame/splice-site mutations showed significant loss of calpain-3 protein as compared to those with two missense/inframe mutations (P = 0.04). We observed a slow progression of disease and less severity in our patients compared to European population. Rarely, presenting clinical features were atypical, and mimicked other muscle diseases like FSHMD, distal myopathy and metabolic myopathies.

CONCLUSION

This is first systematic study to characterize the genetic framework of LGMDR1 in the Indian population. Preliminary calpain-3 immunoblot screening serves well to direct genetic testing. Our findings prioritized nine CAPN3 exons for LGMDR1 diagnosis in our population; therefore, a targeted-sequencing panel of nine exons could serve well for genetic diagnosis, carrier testing, counseling and clinical trial feasibility study in LGMDR1 patients in India.

Clinical and Genomic Evaluation of 207 Genetic Myopathies in the Indian Subcontinent

Objective: Inherited myopathies comprise more than 200 different individually rare disease-subtypes, but when combined together they have a high prevalence of 1 in 6,000 individuals across the world. Our goal was to determine for the first time the clinical- and gene-variant spectrum of genetic myopathies in a substantial cohort study of the Indian subcontinent.

Methods: In this cohort study, we performed the first large clinical exome sequencing (ES) study with phenotype correlation on 207 clinically well-characterized inherited myopathy-suspected patients from the Indian subcontinent with diverse ethnicities.

Results: Clinical-correlation driven definitive molecular diagnosis was established in 49% (101 cases; 95% CI, 42–56%) of patients with the major contributing pathogenicity in either of three genes, GNE (28%; GNE-myopathy), DYSF (25%; Dysferlinopathy), and CAPN3 (19%; Calpainopathy). We identified 65 variant alleles comprising 37 unique variants in these three major genes. Seventy-eight percent of the DYSF patients were homozygous for the detected pathogenic variant, suggesting the need for carrier-testing for autosomal-recessive disorders like Dysferlinopathy that are common in India. We describe the observed clinical spectrum of myopathies including uncommon and rare subtypes in India: Sarcoglycanopathies (SGCA/B/D/G), Collagenopathy (COL6A1/2/3), Anoctaminopathy (ANO5), telethoninopathy (TCAP), Pompe-disease (GAA), Myoadenylate-deaminase-deficiency-myopathy (AMPD1), myotilinopathy (MYOT), laminopathy (LMNA), HSP40-proteinopathy (DNAJB6), Emery-Dreifuss-muscular-dystrophy (EMD), Filaminopathy (FLNC), TRIM32-proteinopathy (TRIM32), POMT1-proteinopathy (POMT1), and Merosin-deficiency-congenital-muscular-dystrophy-type-1 (LAMA2). Thirteen patients harbored pathogenic variants in >1 gene and had unusual clinical features suggesting a possible role of synergistic-heterozygosity/digenic-contribution to disease presentation and progression.

Conclusions: Application of clinically correlated ES to myopathy diagnosis has improved our understanding of the clinical and genetic spectrum of different subtypes and their overlaps in Indian patients. This, in turn, will enhance the global gene-variant-disease databases by including data from developing countries/continents for more efficient clinically driven molecular diagnostics.

Molecular landscape of CAPN3 mutations in limb-girdle muscular dystrophy type R1: from a Chinese multicentre analysis to a worldwide perspective

BACKGROUND

Limb-girdle muscular dystrophy type R1 (LGMDR1) can be caused by recessive CAPN3 mutations accounting for the majority of LGMD. To date, no systemic evaluation has been performed to analyse the detrimental and normal mutations on CAPN3 and its hotspots.

METHODS

CAPN3 variants (n=112) from a total of 124 patients with LGMDR1 recruited in four centres in China were retrospectively analysed. Then external CAPN3 variants (n=2031) from online databases were integrated with our Chinese cohort data to achieve a worldwide perspective on CAPN3 mutations. According to their related phenotypes (LGMDR1 or normal), we analysed consequence, distribution, ethnicity and severity scores of CAPN3 mutations.

RESULTS

Two hotspot mutations were identified including c.2120A>G in Chinese population and c.550del in Europe. According to the integrated dataset, 521 mutations were classified as LGMDR1-related and converged on exons 1, 10, 5, 22 and 13 of CAPN3. The remaining 1585 variants were classified as normal-population related. The deleterious ratio of LGMDR1-relevant variants to total variants in each population was 0.26 on average with a maximum of 0.35 in Finns and a minimum of 0.21 in South Asians. Severity evaluation showed that Chinese LGMDR1-related variants exhibited a higher risk (Combined Annotation Dependent Depletion score +1.10) than that from database patients (p<0.001).

CONCLUSIONS

This study confirmed two hotspots and LGMDR1-related CAPN3 variants, highlighting the advantages in using a data-based comprehensive analysis to achieve a genetic landscape for patients with LGMDR1.

Heterozygous CAPN3 missense variants causing autosomal-dominant calpainopathy in seven unrelated families

AIMS

Recessive variants in CAPN3 gene are the cause of the commonest form of autosomal recessive limb girdle muscle dystrophy. However, two distinct in-frame deletions in CAPN3 (NM_000070.3:c.643_663del21 and c.598_621del15) and more recently, Gly445Arg and Arg572Pro substitutions have been linked to autosomal dominant (AD) forms of calpainopathy. We report 21 affected individuals from seven unrelated families presenting with an autosomal dominant form of muscular dystrophy associated with five different heterozygous missense variants in CAPN.

METHODS

We have used massively parallel gene sequencing (MPS) to determine the genetic basis of a dominant form of limb girdle muscular dystrophy in affected individuals from seven unrelated families.

RESULTS

The c.700G> A, [p.(Gly234Arg)], c.1327T> C [p.(Ser443Pro], c.1333G> A [p.(Gly445Arg)], c.1661A> C [p.(Tyr554Ser)] and c.1706T> C [p.(Phe569Ser)] CAPN3 variants were identified. Affected individuals presented in young adulthood with progressive proximal and axial weakness, waddling walking and scapular winging or with isolated hyperCKaemia. Muscle imaging showed fatty replacement of paraspinal muscles, variable degrees of involvement of the gluteal muscles, and the posterior compartment of the thigh and minor changes at the mid-leg level. Muscle biopsies revealed mild myopathic changes. Western blot analysis revealed a clear reduction in calpain 3 in skeletal muscle relative to controls. Protein modelling of these variants on the predicted structure of calpain 3 revealed that all variants are located in proximity to the calmodulin-binding site and are predicted to interfere with proteolytic activation.

CONCLUSIONS

We expand the genotypic spectrum of CAPN3-associated muscular dystrophy due to autosomal dominant missense variants.

Novel CAPN3 variant associated with an autosomal dominant calpainopathy

AIMS

The most common autosomal recessive limb girdle muscular dystrophy is associated with the CAPN3 gene. The exclusively recessive inheritance of this disorder has been recently challenged by the description of the recurrent variants, c.643_663del21 [p.(Ser215_Gly221del)] and c.598_612del15 [p.(Phe200_Leu204del)], associated with autosomal dominant inheritance. Our objective was to confirm the existence of autosomal dominant calpainopathies.

METHODS

Through our activity as one of the reference centres for genetic diagnosis of calpainopathies in France and the resulting collaborations through the French National Network for Rare Neuromuscular Diseases (FILNEMUS), we identified four families harbouring the same CAPN3 heterozygous variant with supposedly autosomal dominant inheritance.

RESULTS

We identified a novel dominantly inherited CAPN3 variant, c.1333G>A [p.(Gly445Arg)] in 14 affected patients from four unrelated families. The complementary phenotypic, functional and genetic findings correlate with an autosomal dominant inheritance in these families, emphasizing the existence of this novel transmission mode for calpainopathies. The mild phenotype associated with these autosomal dominant cases widens the phenotypic spectrum of calpainopathies and should therefore be considered in clinical practice.

CONCLUSIONS

We confirm the existence of autosomal dominant calpainopathies as an entity beyond the cases related to the in-frame deletions c.643_663del21 and c.598_612del15, with the identification of a novel dominantly inherited and well-documented CAPN3 missense variant, c.1333G>A [p.(Gly445Arg)]. In addition to the consequences for genetic counselling, the confirmation of an autosomal dominant transmission mode for calpainopathies underlines the importance of re-assessing other myopathies for which the inheritance is considered as strictly autosomal recessive.

Skeletal muscle: A review of molecular structure and function, in health and disease

Decades of research in skeletal muscle physiology have provided multiscale insights into the structural and functional complexity of this important anatomical tissue, designed to accomplish the task of generating contraction, force and movement. Skeletal muscle can be viewed as a biomechanical device with various interacting components including the autonomic nerves for impulse transmission, vasculature for efficient oxygenation, and embedded regulatory and metabolic machinery for maintaining cellular homeostasis. The "omics" revolution has propelled a new era in muscle research, allowing us to discern minute details of molecular cross-talk required for effective coordination between the myriad interacting components for efficient muscle function. The objective of this review is to provide a systems-level, comprehensive mapping the molecular mechanisms underlying skeletal muscle structure and function, in health and disease. We begin this review with a focus on molecular mechanisms underlying muscle tissue development (myogenesis), with an emphasis on satellite cells and muscle regeneration. We next review the molecular structure and mechanisms underlying the many structural components of the muscle: neuromuscular junction, sarcomere, cytoskeleton, extracellular matrix, and vasculature surrounding muscle. We highlight aberrant molecular mechanisms and their possible clinical or pathophysiological relevance. We particularly emphasize the impact of environmental stressors (inflammation and oxidative stress) in contributing to muscle pathophysiology including atrophy, hypertrophy, and fibrosis. This article is categorized under: Physiology > Mammalian Physiology in Health and Disease Developmental Biology > Developmental Processes in Health and Disease Models of Systems Properties and Processes > Cellular Models.

European muscle MRI study in limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A)

BACKGROUND

Limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A) is a progressive myopathy caused by deficiency of calpain 3, a calcium-dependent cysteine protease of skeletal muscle, and it represents the most frequent type of LGMD worldwide. In the last few years, muscle magnetic resonance imaging (MRI) has been proposed as a tool for identifying patterns of muscular involvement in genetic disorders and as a biomarker of disease progression in muscle diseases. In this study, 57 molecularly confirmed LGMDR1 patients from a European cohort (age range 7-78 years) underwent muscle MRI and a global evaluation of functional status (Gardner-Medwin and Walton score and ability to raise the arms).

RESULTS

We confirmed a specific pattern of fatty substitution involving predominantly the hip adductors and hamstrings in lower limbs. Spine extensors were more severely affected than spine rotators, in agreement with higher incidence of lordosis than scoliosis in LGMDR1. Hierarchical clustering of lower limb MRI scores showed that involvement of anterior thigh muscles discriminates between classes of disease progression. Severity of muscle fatty substitution was significantly correlated with CAPN3 mutations: in particular, patients with no or one "null" alleles showed a milder involvement, compared to patients with two null alleles (i.e., predicting absence of calpain-3 protein). Expectedly, fat infiltration scores strongly correlated with functional measures. The "pseudocollagen" sign (central areas of sparing in some muscle) was associated with longer and more severe disease course.

CONCLUSIONS

We conclude that skeletal muscle MRI represents a useful tool in the diagnostic workup and clinical management of LGMDR1.

Clinicogenetic lessons from 370 patients with autosomal recessive limb-girdle muscular dystrophy

Limb-girdle muscular dystrophies (LGMD) are a group of genetically heterogeneous disorders characterized by predominantly proximal muscle weakness. We aimed to characterize epidemiological, clinical and molecular data of patients with autosomal recessive LGMD2/LGMD-R in Brazil. A multicenter historical cohort study was performed at 13 centers, in which index cases and their affected relatives' data from consecutive families with genetic or pathological diagnosis of LGMD2/LGMD-R were reviewed from July 2017 to August 2018. Survival curves to major handicap for LGMD2A/LGMD-R1-calpain3-related, LGMD2B/LGMD-R2-dysferlin-related and sarcoglycanopathies were built and progressions according to sex and genotype were estimated. In 370 patients (305 families) with LGMD2/LGMD-R, most frequent subtypes were LGMD2A/LGMD-R1-calpain3-related and LGMD2B/LGMD-R2-dysferlin-related, each representing around 30% of families. Sarcoglycanopathies were the most frequent childhood-onset subtype, representing 21% of families. Five percent of families had LGMD2G/LGMD-R7-telethonin-related, an ultra-rare subtype worldwide. Females with LGMD2B/LGMD-R2-dysferlin-related had less severe progression to handicap than males and LGMD2A/LGMD-R1-calpain3-related patients with truncating variants had earlier disease onset and more severe progression to handicap than patients without truncating variants. We have provided paramount epidemiological data of LGMD2/LGMD-R in Brazil that might help on differential diagnosis, better patient care and guiding future collaborative clinical trials and natural history studies in the field.

Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans

Muscle protein breakdown (MPB) is an important metabolic component of muscle remodeling, adaptation to training, and increasing muscle mass. Degradation of muscle proteins occurs via the integration of three main systems—autophagy and the calpain and ubiquitin-proteasome systems. These systems do not operate independently, and the regulation is complex. Complete degradation of a protein requires some combination of the systems. Determination of MPB in humans is technically challenging, leading to a relative dearth of information. Available information on the dynamic response of MPB primarily comes from stable isotopic methods with expression and activity measures providing complementary information. It seems clear that resistance exercise increases MPB, but not as much as the increase in muscle protein synthesis. Both hyperaminoacidemia and hyperinsulinemia inhibit the post-exercise response of MPB. Available data do not allow a comprehensive examination of the mechanisms behind these responses. Practical nutrition recommendations for interventions to suppress MPB following exercise are often made. However, it is likely that some degree of increased MPB following exercise is an important component for optimal remodeling. At this time, it is not possible to determine the impact of nutrition on any individual muscle protein. Thus, until we can develop and employ better methods to elucidate the role of MPB following exercise and the response to nutrition, recommendations to optimize post exercise nutrition should focus on the response of muscle protein synthesis. The aim of this review is to provide a comprehensive examination of the state of knowledge, including methodological considerations, of the response of MPB to exercise and nutrition in humans.

Molecular genetic study of Calpainopathy in Iran

INTRODUCTION

Calpainopathy is an autosomal recessive form of limb girdle muscular dystrophies (LGMDs) caused by mutations in the CAPN3 gene. CAPN3 is a Ca²⁺-dependent cystein protease consisting of 821 amino acids. LGMD is a highly heterogeneous disorder and mutation identification of this disease by Sanger sequencing of all genes is expensive and time consuming. Using autozygosity mapping is an effective approach to address this issue.

METHODS

We used two sets of multiplex STR (Short tandem repeat) markers linked to CAPN3, DYSF, SGCA, SGCB, SGCG, SGCD genes following sequencing of the CAPN3 gene. In silico analysis and mutation detection in one hundred ethnically matched healthy individuals were carried out to determine the pathogenicity of novel mutations. Sequence variant interpretation was performed using the American College of Medical Genetics and Genomics (ACMG) guideline.

RESULTS

Sixteen out of 50 families linked to the CAPN3 gene. In this study, mutations were found in 14 out of 16 families including 4 novel (c.1894A > T, c.567delG, c.2254-2256delAAC, and c.2373C > T) and 9 previously reported mutations consisting of 5 missense (c.2105C > T, c.2243G > A, c.1714C > T, c.291C > A, c.956C > T), 3 splice site (c.2380 + 2 T > G, c.946-2A > G, c.380G > A), and one indel (c.2257delinsAA) mutations.

DISCUSSION

The c.2105C > T was found to be the most frequent mutation in this study. The results of this study revealed that most cases with splicing, frame shift and nonsense mutations experienced more severe clinical manifestations. Nonetheless, this should be confirmed by further studies on larger sample size.

Left ventricular deformation abnormalities in a patient with calpainopathy-a case from the three-dimensional speckle-tracking echocardiographic MAGYAR-Path Study

Calpainopathy or limb-girdle muscular dystrophy type 2A (LGMD2A) is the most common type of autosomal recessive limb-girdle muscular dystrophies. The disease is caused by mutations in the CAPN3 gene encoding calpain, a protein involved in muscle membrane remodeling and repair. This paper gives an overview of the genetic background, clinical course, and diagnosis of the disease, and presents the first case of calpainopathy in which cardiac deformation mechanics was investigated. Three-dimensional speckle-tracking echocardiography (3DSTE) demonstrated reduced left ventricular (LV) strains and increased LV apical rotation and twist, suggestive of asymptomatic subclinical LV dysfunction. Cardiac involvement has not been previously reported in calpainopathy.

Human growth hormone stabilizes walking and improves strength in a patient with dominantly inherited calpainopathy

The aim was to investigate if daily low-dose treatment with recombinant human growth hormone (somatropine) can stabilize or improve muscle strength and walking capability in a patient with dominantly inherited calpainopathy. The patient was treated with daily injections of somatropine, except for a 6-month pause, over a period of 4.5 years. Efficacy was assessed by repeated muscle dynamometry tests and 6-minute walk tests (6MWT). Strength improved in most muscle groups on treatment, deteriorated in the 6-month off treatment, and improved again when treatment was resumed. The 6MWT stabilized during the initial 18-month treatment period, then deteriorated in the 6 months off treatment and improved to pre-trial levels when treatment was resumed. The findings suggest that supplementation with somatropine, within physiological ranges, may improve muscle strength and stabilize walking capability in a patient with calpainopathy. This finding calls for testing of somatropine supplementation in muscular dystrophies in a randomized study.

Epidemiological and Molecular Characterization of a Mexican Population Isolate with High Prevalence of Limb-Girdle Muscular Dystrophy Type 2A Due to a Novel Calpain-3 Mutation

Limb-Girdle Muscular Dystrophy type 2 (LGMD2) is a group of autosomally recessive inherited disorders defined by weakness and wasting of the shoulder and pelvic girdle muscles. In the past, several population isolates with high incidence of LGMD2 arising from founder mutation effects have been identified. The aim of this work is to describe the results of clinical, epidemiologic, and molecular studies performed in a Mexican village segregating numerous cases of LGMD2. A population census was conducted in the village to identify all LGMD affected patients. Molecular analysis included genome wide homozygosity mapping using a 250K SNP Affymetrix microarray followed by PCR amplification and direct nucleotide sequencing of the candidate gene. In addition, DNA from 401 randomly selected unaffected villagers was analyzed to establish the carrier frequency of the LGMD2 causal mutation. A total of 32 LGMD2 patients were identified in the village, rendering a disease prevalence of 4.3 (CI: 2.9–5.9) cases per 1,000 habitants (1 in 232). Genome wide homozygosity mapping revealed that affected individuals shared a 6.6 Mb region of homozygosity at chromosome 15q15. The identified homozygous interval contained CAPN3, the gene responsible for LGMD2 type A (LGMD2A). Direct sequencing of this gene revealed homozygosity for a novel c.348C>A mutation (p.Ala116Asp) in DNA from all 20 affected subjects available for genetic screening, except one which was heterozygous for the mutation. In such patient, a heterozygous c.2362AG>TCATCT deletion/insertion was recognized as the second CAPN3 mutation. Western blot and autocatalytic activity analyses in protein lysates from skeletal muscle biopsy obtained from a p.Ala116Asp homozygous patient suggested that this particular mutation increased the autocatalytic activity of CAPN3. Thirty eigth heterozygotes of the p.Ala116Asp mutation were identified among 401 genotyped unaffected villagers, yielding a population carrier frequency of 1 in 11. This study demonstrates that a cluster of patients with LGMD2A in a small Mexican village arises from a novel CAPN3 founder mutation. Evidence of allelic heterogeneity is demonstrated by the recognition of an additional CAPN3 mutation in a single affected. Our study provides an additional example of genetic isolation causing a high prevalence of LGMD and of successful molecular characterization of the disease by means of homozygosity mapping. The identification of a very high carrier frequency of the LGMD2-causing mutation has implications for more rational genetic counseling in this community.

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.

OBJECTIVE

To present clinical and histological findings in six children with a molecular diagnosis of LGMD2A and additionally the MRI findings in two of them.

METHOD

We retrospectively assessed medical records of 6 patients with mutation on CAPN3 gene.

RESULTS

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.

CONCLUSION

In this cohort of children with LGMD2A, the clinical aspects were similar to adults with the same disorder.

Calpain 3 deficiency affects SERCA expression and function in the skeletal muscle

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a form of muscular dystrophy caused by mutations in calpain 3 (CAPN3). Several studies have implicated Ca²⁺ dysregulation as an underlying event in several muscular dystrophies, including LGMD2A. In this study we used mouse and human myotube cultures, and muscle biopsies in order to determine whether dysfunction of sarco/endoplasmatic Ca²⁺-ATPase (SERCA) is involved in the pathology of this disease. In CAPN3-deficient myotubes, we found decreased levels of SERCA 1 and 2 proteins, while mRNA levels remained comparable with control myotubes. Also, we found a significant reduction in SERCA function that resulted in impairment of Ca²⁺ homeostasis, and elevated basal intracellular [Ca²⁺] in human myotubes. Furthermore, small Ankyrin 1 (sAnk1), a SERCA1-binding protein that is involved in sarcoplasmic reticulum integrity, was also diminished in CAPN3-deficient fibres. Interestingly, SERCA2 protein was patently reduced in muscles from LGMD2A patients, while it was normally expressed in other forms of muscular dystrophy. Thus, analysis of SERCA2 expression may prove useful for diagnostic purposes as a potential indicator of CAPN3 deficiency in muscle biopsies. Altogether, our results indicate that CAPN3 deficiency leads to degradation of SERCA proteins and Ca²⁺ dysregulation in the skeletal muscle. While further studies are needed in order to elucidate the specific contribution of SERCA towards muscle degeneration in LGMD2A, this study constitutes a reasonable foundation for the development of therapeutic approaches targeting SERCA1, SERCA2 or sAnk1.

Natural history of LGMD2A for delineating outcome measures in clinical trials

Objective

Limb‐girdle muscular dystophy 2A (LGMD2A, OMIM) is a slowly progressive myopathy caused by the deficiency in calpain 3, a calcium‐dependent cysteine protease of the skeletal muscle.

Methods

In this study, we carried out an observational study of clinical manifestations and disease progression in genetically confirmed LGMD2A patients for up to 4 years. A total of 85 patients, aged 14–65 years, were recruited in three centers located in metropolitan France, the Basque country, and the Reunion Island. They were followed up every 6 months for 2 years and a subgroup was assessed annually thereafter for two more years. Data collected for all patients included clinical history, blood parameters, muscle strength assessed by manual muscle testing (MMT) and quantitative muscle testing, functional scores, and pulmonary and cardiac functions. In addition, CT scans of the lower limbs were performed in a subgroup of patients.

Results

Our study confirms the clinical description of a slowly progressive disorder with onset in the first or second decade of life with some degree of variability related to gender and mutation type. The null mutations lead to a more severe phenotype while compound heterozygote patients are the least affected. Muscle weakness is remarkably symmetrical and predominant in the axial muscles of the trunk and proximal muscles of the lower limb. There was a high correlation between the weakness at individual muscle level as assessed by MMT and the loss of density in CT scan analysis.

Interpretation

All the generated data will help to determine the endpoints for further clinical studies.

Clinical and Pathological Heterogeneity of Korean Patients with CAPN3 Mutations

PURPOSE

This study was designed to investigate the characteristics of Korean patients with calpainopathy.

MATERIALS AND METHODS

Thirteen patients from ten unrelated families were diagnosed with calpainopathy via direct or targeted sequencing of the CAPN3 gene. Clinical, mutational, and pathological spectra were then analyzed.

RESULTS

Nine different mutations, including four novel mutations (NM_000070: c.1524+1G>T, c.1789_1790inA, c.2184+1G>T, and c.2384C>T) were identified. The median age at symptom onset was 22 (interquartile range: 15-28). Common clinical findings were joint contracture in nine patients, winged scapula in four, and lordosis in one. However, we also found highly variable clinical features including early onset joint contractures, asymptomatic hyperCKemia, and heterogeneous clinical severity in three members of the same family. Four of nine muscle specimens revealed lobulated fibers, but three showed normal skeletal muscle histology.

CONCLUSION

We identified four novel CAPN3 mutations and demonstrated clinical and pathological heterogeneity in Korean patients with calpainopathy.

Protein and genetic diagnosis of limb girdle muscular dystrophy type 2A: The yield and the pitfalls

Limb girdle muscular dystrophy type 2A (LGMD2A) is the most frequent form of LGMD worldwide. Comprehensive clinical assessment and laboratory testing is essential for diagnosis of LGMD2A. Muscle immunoblot analysis of calpain-3 is the most useful tool to direct genetic testing, as detection of calpain-3 deficiency has high diagnostic value. However, calpain-3 immunoblot testing lacks sensitivity in about 30% of cases due to gene mutations that inactivate the enzyme. The best diagnostic strategy should be determined on a case-by-case basis, depending on which tissues are available, and which molecular and/or genetic methods are adopted. In this work we survey the current knowledge, advantages, limitations, and pitfalls of protein testing and mutation detection in LGMD2A and provide an update of genetic epidemiology.

Common recessive limb girdle muscular dystrophies differential diagnosis: why and how?

Limb girdle muscular dystrophies are heterogeneous autosomal hereditary neuromuscular disorders. They produce dystrophic changes on muscle biopsy and they are associated with mutations in several genes involved in muscular structure and function. Detailed clinical, laboratorial, imaging, diagnostic flowchart, photographs, tables, and illustrated diagrams are presented for the differential diagnosis of common autosomal recessive limb girdle muscular dystrophy subtypes diagnosed nowadays at one reference center in Brazil. Preoperative image studies guide muscle biopsy site selection. Muscle involvement image pattern differs depending on the limb girdle muscular dystrophy subtype. Muscle involvement is conspicuous at the posterior thigh in calpainopathy and fukutin-related proteinopathy; anterior thigh in sarcoglycanopathy; whole thigh in dysferlinopathy, and telethoninopathy. The precise differential diagnosis of limb girdle muscular dystrophies is important for genetic counseling, prognostic orientation, cardiac and respiratory management. Besides that, it may probably, in the future, provide specific genetic therapies for each subtype.

Limb-girdle muscular dystrophy type 2a with mutation in CAPN3: the first report in Taiwan

The autosomal recessive limb-girdle muscular dystrophy type 2A (LGMD2A) is caused by mutations in the calpain 3 (CAPN3) gene, and it is characterized by selective atrophy and weakness of proximal limb and girdle muscles. We report a 33-year-old woman with initial presentations of exercise intolerance and running difficulty at age 15 years. At presentation, waddling gait, positive Gowers' sign, and marked muscle atrophy in pelvic and leg muscles were noted. Muscle computed tomography (CT) imaging demonstrated symmetric involvement of the posterior thigh muscles with relative sparing of vastus lateralis, sartorius, and gracilis. Muscle biopsy revealed a dystrophic change and many lobulated fibers on NADH-tetrazolium reductase staining. Genetic analysis of the CAPN3 gene identified a novel homozygous mutation of c2047_2050 del4, p.Lys683fs mutation, confirming the first LGMD2A patient in Taiwan.

Dysregulation of calcium homeostasis in muscular dystrophies

Muscular dystrophies are a group of diseases characterised by the primary wasting of skeletal muscle, which compromises patient mobility and in the most severe cases originate a complete paralysis and premature death. Existing evidence implicates calcium dysregulation as an underlying crucial event in the pathophysiology of several muscular dystrophies, such as dystrophinopathies, calpainopathies or myotonic dystrophy among others. Duchenne muscular dystrophy is the most frequent myopathy in childhood, and calpainopathy or LGMD2A is the most common form of limb-girdle muscular dystrophy, whereas myotonic dystrophy is the most frequent inherited muscle disease worldwide. In this review, we summarise recent advances in our understanding of calcium ion cycling through the sarcolemma, the sarcoplasmic reticulum and mitochondria, and its involvement in the pathogenesis of these dystrophies. We also discuss some of the clinical implications of recent findings regarding Ca2+ handling as well as novel approaches to treat muscular dystrophies targeting Ca2+ regulatory proteins.

Limb-girdle muscular dystrophy subtypes: First-reported cohort from northeastern China

The relative frequencies of different subtypes of limb-girdle muscular dystrophies vary widely among different populations. We estimated the percentage of limb-girdle muscular dystrophy subtypes in Chinese people based on 68 patients with limb-girdle muscular dystrophy from the Myology Clinic, Neurology Department, First Hospital of Jilin University, China. A diagnosis of calpainopathy was made in 12 cases (17%), and dysferlin deficiency in 10 cases (15%). Two biopsies revealed α-sarcoglycan deficiency (3%), and two others revealed a lack of caveolin-3 (3%). A diagnosis of unclassified limb-girdle muscular dystrophy was made in the remaining patients (62%). The appearances of calpain 3- and dysferlin-deficient biopsies were similar, though rimmed vacuoles were unique to dysferlinopathy, while inflammatory infiltrates were present in both these limb-girdle muscular dystrophy type 2D biopsies. Macrophages were detected in seven dysferlinopathy biopsies. The results of this study suggest that the distribution of limb-girdle muscular dystrophy subtypes in the Han Chinese population is similar to that reported in the West. The less necrotic, regenerating and inflammatory appearance of limb-girdle muscular dystrophy type 2A, but with more lobulated fibers, supports the idea that calpainopathy is a less active, but more chronic disease than dysferlinopathy. Unusual features indicated an extended limb-girdle muscular dystrophy disease spectrum. The use of acid phosphatase stain should be considered in suspected dysferlinopathies. To the best of our knowledge, this is the first report to define the relative proportions of the various forms of limb-girdle muscular dystrophy in China, based on protein testing.

Autosomal recessive limb-girdle muscular dystrophies in the Czech Republic

Background

Autosomal recessive limb-girdle muscular dystrophies (LGMD2) include a number of disorders with heterogeneous etiology that cause predominantly weakness and wasting of the shoulder and pelvic girdle muscles. In this study, we determined the frequency of LGMD subtypes within a cohort of Czech LGMD2 patients using mutational analysis of the CAPN3, FKRP, SGCA, and ANO5 genes.

Methods

PCR-sequencing analysis; sequence capture and targeted resequencing.

Results

Mutations of the CAPN3 gene are the most common cause of LGMD2, and mutations in this gene were identified in 71 patients in a set of 218 Czech probands with a suspicion of LGMD2. Totally, we detected 37 different mutations of which 12 have been described only in Czech LGMD2A patients. The mutation c.550delA is the most frequent among our LGMD2A probands and was detected in 47.1% of CAPN3 mutant alleles. The frequency of particular forms of LGMD2 was 32.6% for LGMD2A (71 probands), 4.1% for LGMD2I (9 probands), 2.8% for LGMD2D (6 probands), and 1.4% for LGMD2L (3 probands).

Further, we present the first results of a new approach established in the Czech Republic for diagnosis of neuromuscular diseases: sequence capture and targeted resequencing. Using this approach, we identified patients with mutations in the DYSF and SGCB genes.

Conclusions

We characterised a cohort of Czech LGMD2 patients on the basis of mutation analysis of genes associated with the most common forms of LGMD2 in the European population and subsequently compared the occurrence of particular forms of LGMD2 among countries on the basis of our results and published studies.

Redox state and mitochondrial respiratory chain function in skeletal muscle of LGMD2A patients

Background

Calpain-3 deficiency causes oxidative and nitrosative stress-induced damage in skeletal muscle of LGMD2A patients, but mitochondrial respiratory chain function and anti-oxidant levels have not been systematically assessed in this clinical population previously.

Methods

We identified 14 patients with phenotypes consistent with LGMD2A and performed CAPN3 gene sequencing, CAPN3 expression/autolysis measurements, and insilico predictions of pathogenicity. Oxidative damage, anti-oxidant capacity, and mitochondrial enzyme activities were determined in a subset of muscle biopsies.

Results

Twenty-one disease-causing variants were detected along the entire CAPN3 gene, five of which were novel (c.338 T>C, c.500 T>C, c.1525-1 G>T, c.2115+4 T>G, c.2366 T>A). Protein- and mRNA-based tests confirmed insilico predictions and the clinical diagnosis in 75% of patients. Reductions in antioxidant defense mechanisms (SOD-1 and NRF-2, but not SOD-2), coupled with increased lipid peroxidation and protein ubiquitination, were observed in calpain-3 deficient muscle, indicating a redox imbalance primarily affecting non-mitochondrial compartments. Although ATP synthase levels were significantly lower in LGMD2A patients, citrate synthase, cytochrome c oxidase, and complex I+III activities were not different from controls.

Conclusions

Despite significant oxidative damage and redox imbalance in cytosolic/myofibrillar compartments, mitochondrial respiratory chain function is largely maintained in skeletal muscle of LGMD2A patients.

Limb-girdle muscular dystrophies: where next after six decades from the first proposal (Review)

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of disorders, which has led to certain investigators disputing its rationality. The mutual feature of LGMD is limb-girdle affection. Magnetic resonance imaging (MRI), perioral skin biopsies, blood-based assays, reverse-protein arrays, proteomic analyses, gene chips and next generation sequencing are the leading diagnostic techniques for LGMD and gene, cell and pharmaceutical treatments are the mainstay therapies for these genetic disorders. Recently, more highlights have been shed on disease biomarkers to follow up disease progression and to monitor therapeutic responsiveness in future trials. In this study, we review LGMD from a variety of aspects, paying specific attention to newly evolving research, with the purpose of bringing this information into the clinical setting to aid the development of novel therapeutic strategies for this hereditary disease. In conclusion, substantial progress in our ability to diagnose and treat LGMD has been made in recent decades, however enhancing our understanding of the detailed pathophysiology of LGMD may enhance our ability to improve disease outcome in subsequent years.

Muscle pathology in 31 patients with calpain 3 gene mutations

BACKGROUND AND PURPOSE

At present, more than 20 different forms of limb-girdle muscular dystrophies (LGMDs) are known (at least 7 autosomal dominant and 14 autosomal recessive). Although these different forms show some typical phenotypic characteristics, the existing clinical overlap makes their differential diagnosis difficult. Limb-girdle muscular dystrophy type 2 (LGMD2A) is the most prevalent LGMD in many European as well as Brazilian communities and is caused by mutations in the gene CAPN3. Laboratory testing, such as calpain immunohistochemistry and Western-blot analysis, is not totally reliable, since up to 20% of molecularly confirmed LGMD2A show normal content of calpain 3 and a third of LGMD2A biopsies have normal calpain 3 proteo-lytic activity in the muscle. Thus, genetic testing is considered as the only reliable diagnostic criterion in LGMD2A.

MATERIAL AND METHODS

In an attempt to find a correlation between genotype and muscle pathology in limb-girdle muscular dystrophy 2A we performed histopathological investigation of a group of 31 patients subdivided according to the type of pathologic CAPN3 gene mutation.

RESULTS

In all biopsies typical features of muscular dystrophy such as fiber necrosis and regeneration, variation in fiber size and fibrosis were noted. Lobulated fibers were often encountered in the muscle biopsies of LGMD2A patients. Such fibers were more frequent in patients with 550delA mutation.

CONCLUSIONS

These findings may be helpful in establishing diagnostic strategies in LGMD.

Ancestral founder mutations in calpain-3 in the Indian Agarwal community: historical, clinical, and molecular perspective

INTRODUCTION

Clinical heterogeneity of limb-girdle muscular dystrophies (LGMDs, 24 known subtypes), which includes overlapping phenotypes and varying ages of onset and morbidity, adds complexity to clinical and molecular diagnoses.

METHODS

To diagnose LGMD subtype, protein analysis, using immunohistochemistry (IHC) and immunoblotting, was followed by gene sequencing through a panel approach (simultaneous sequencing of known LGMD genes) in 9 patients from unrelated families of the Indian Agarwal community. Haplotype studies were performed by targeted SNP genotyping to establish mutation segregation.

RESULTS

We identified 2 founder mutations in CAPN3, a missense (c.2338G>C; p.D780H) and a splice-site (c.2099-1G>T) mutation, on 2 different haplotype backgrounds. The patients were either heterozygous for both or homozygous for either of these mutations.

CONCLUSIONS

Founder mutations have immediate clinical application, at least in selected population groups. Clinically available gene panels may provide a definitive molecular diagnosis for heterogeneous disorders such as LGMD.

Selective pseudohypertrophy of vastus medialis muscles associated with calpain 3 deficiency

INTRODUCTION

Calpain 3 deficiency causes limb girdle muscular dystrophy type 2A, which is one of the most common forms of limb girdle muscular dystrophy. Nevertheless, calpainopathy is not always associated with mutations in the specific gene and secondary reduction in protein expression has been described.

CASE REPORT

We report a case of a 43-year-old man who complained of thigh muscle stiffness and had muscle hypertrophy of both vastus medialis with prolonged myotonic contraction by percussion. A muscle biopsy showed dystrophic features and calpain 3 deficiency was shown by immunoblot analysis although mutations in the specific gene were not found. Known cases of secondary calpain 3 protein deficiency were ruled out and mutations in MD1 and MD2 genes were excluded.

CONCLUSIONS

This patient represents the first case of calpain 3 deficiency with selective pseudohypertrophy of vastus medialis muscles.

Late-onset axial myopathy and camptocormia in a calpainopathy carrier

Camptocormia is a debilitating gait disorder characterized by the hyperflexion of the thoracolumbar spine during the upright position. Its etiologies are heterogenous, including parkinsonism and various neuromuscular disorders. Here, we report a camptocormia patient due to a late-onset axial myopathy with numerous lobulated fibers. The patient's father reportedly had similar symptoms. Myriad lobulated fibers are common among patients with an autosomal recessive muscular dystrophy due to calpain-3 gene (CAPN3) mutations or calpainopathy. CAPN3 sequencing revealed a single c.759-761delGAA mutation. Calpainopathy carriers are generally asymptomatic. The presence of lobulated fibers in this patient suggests that camptocormia could be a manifestation of calpainopathy carrier, although the possibility of a coexisting undiagnosed myopathy cannot be excluded. The current patient should spur the evaluation of camptocormia among calpainopathy carriers.