Evaluation of heart involvement in gamma-sarcoglycanopathy (LGMD2C). A study of ten patients

Protein glycosylation in cardiovascular health and disease

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer. Several decades ago, cell surface glycoproteins were found to have an important role in regulating ion transport across the cardiac sarcolemma. However, with very few exceptions, our understanding of how changes in protein glycosylation influence cardiovascular (patho)physiology remains remarkably limited. Therefore, in this Review, we aim to provide an overview of N-linked and O-linked protein glycosylation, including intracellular O-linked N-acetylglucosamine protein modification. We discuss our current understanding of how all forms of protein glycosylation contribute to normal cardiovascular function and their roles in cardiovascular disease. Finally, we highlight potential gaps in our knowledge about the effects of protein glycosylation on the heart and vascular system, highlighting areas for future research.

Patterns of Clinical Progression Among Patients With Autosomal Recessive Limb-Girdle Muscular Dystrophy: A Systematic Review

OBJECTIVES

As the clinical course of autosomal recessive limb-girdle muscular dystrophy (LGMDR) is highly variable, this study characterized the frequency of loss of ambulation (LOA) among patients by subtype (LGMDR1, LGMDR2, LGMDR3-6, LGMDR9, LGMDR12) and progression to cardiac and respiratory involvement among those with and without LOA.

METHODS

Systematic literature review.

RESULTS

From 2929 abstracts screened, 418 patients were identified with ambulatory status data (LOA: 265 [63.4%]). Cardiac and/or respiratory function was reported for 142 patients (34.0%; all with LOA). Among these, respiratory involvement was most frequent in LGMDR3-6 (74.1%; mean [SD] age 23.9 [11.0] years) and cardiac in LGMDR9 (73.3%; mean [SD] age 23.7 [17.7] years). Involvement was less common in patients without LOA except in LGMDR9 (71.4% respiratory and 52.4% cardiac).

CONCLUSIONS

This study described the co-occurrence of LOA, cardiac, and respiratory involvement in LGMDR and provides greater understanding of the clinical progression of LGMDR.

Dystrophin-Glycoprotein Complex Behavior in Sternocleidomastoid Muscle of High- and Low-Ranking Baboons: A Possible Phylogenetic Arrangement

The dystrophin-glycoprotein complex is a multimeric system made up of the sarcoglycan sub-complex, the sarcomplasmatic complex and the dystroglycans complex. The sarcoglycan sub-complex stabilizes the sarcolemma during muscle activity and plays a role in force transduction. This protein system is also expressed in the muscle of non-human primates such as chimpanzees and baboons, and its expression changes depending on social ranking. In fact, previous data have shown that all muscle fibers of masseter and sternocleidomastoid muscles of chimpanzees and high- ranking baboons always express sarcoglycans, while middle- and low-ranking baboons are characterized by fibers that are negative for the sarcoglycan sub-complex. Given this information, the aim of the present work was to evaluate the expression of other proteins such as laminin, beta dystroglycan and dystrophin in the sternocleidomastoid muscle of high- and low-ranking baboons. The samples were processed by immunohistochemistry; results show that in high-ranking baboons, all tested proteins were always expressed while in low-ranking baboons, fibers that were negative for sarcoglycans and beta dystroglycan have been observed. No negative fibers for laminin and dystrophin have been found in low-ranking baboons suggesting that only the transmembrane proteins of the dystrophin glycoprotein complex change in their expression and that could be correlated to a phylogenetic arrangement.

Neuromuscular diseases and their cardiac manifestations under the spectrum of cardiovascular imaging

Neuromuscular diseases (NMDs) include a broad spectrum of disorders that affect motor unit in every possible site, extending from the cell body of peripheral nerves to the muscle. The different lesion sites make this group of inherited disorders difficult to diagnose. Many NMDs, especially those involving skeletal muscles, can present significant cardiovascular complications, ranging from rhythm disturbances to the development of dilated or hypertrophic cardiomyopathy. Heart disease represents a major cause of morbidity and mortality among NMD patients, underlining the vital need for further familiarization with the pathogenesis and assessment of cardiac involvement. Cardiovascular imaging is the cornerstone for the evaluation of heart disorders in NMDs, with conventional echocardiography still offering a portable, affordable, and easily accessible solution. Meanwhile, newer echocardiographic techniques such as speckle tracking imaging in combination with cardiac magnetic resonance add new insights into further substrate characterization. The purpose of this review is to offer a brief presentation of the main NMDs and their cardiovascular complications, as well as the presentation of data that highlight the importance of cardiovascular imaging in early diagnosis, monitoring, and prognosis of these patients. Lastly, the authors provide a simple guide about which clinical features, imaging findings, and follow-up plan to adopt in each myopathic disorder.

Progression to Loss of Ambulation Among Patients with Autosomal Recessive Limb-girdle Muscular Dystrophy: A Systematic Review

Background

The impact of age at autosomal recessive limb girdle muscular dystrophy (LGMDR) onset on progression to loss of ambulation (LOA) has not been well established, particularly by subtype.

Objectives:

To describe the characteristics of patients with adult-, late childhood-, and early childhood-onset LGMDR by subtype and characterize the frequency and timing of LOA.

Methods:

A systematic review was conducted in MEDLINE, Embase and the Cochrane library. Frequency and timing of LOA in patients with LGMDR1, LGMDR2/Miyoshi myopathy (MM), LGMDR3-6, LGMDR9, and LGMDR12 were synthesized from published data.

Results:

In 195 studies, 695 (43.4%) patients had adult-, 532 (33.2%) had late childhood-, and 376 (23.5%) had early childhood-onset of disease across subtypes among those with a reported age at onset (n = 1,603); distribution of age at onset varied between subtypes. Among patients with LOA (n = 228), adult-onset disease was uncommon in LGMDR3-6 (14%) and frequent in LGMDR2/MM (42%); LGMDR3-6 cases with LOA primarily had early childhood-onset (74%). Mean (standard deviation [SD]) time to LOA varied between subtypes and was shortest for patients with early childhood-onset LGMDR9 (12.0 [4.9] years, n = 19) and LGMDR3-6 (12.3 [10.7], n = 56) and longest for those with late childhood-onset LGMDR2/MM (21.4 [11.5], n = 36).

Conclusions:

This review illustrated that patients with early childhood-onset disease tend to have faster progression to LOA than those with late childhood- or adult-onset disease, particularly in LGMDR9. These findings provide a greater understanding of progression to LOA by LGMDR subtype, which may help inform clinical trial design and provide a basis for natural history studies.

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

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

Effects of Home Mechanical Ventilation on Left Ventricular Function in Sarcoglycanopathies (Limb Girdle Muscular Dystrophies)

Cardiac and respiratory function may be impaired in sarcoglycanopathies, a subgroup of muscular dystrophies due to sarcoglycan proteins (α, β, γ, and δ) genes mutations. Management of patients with restrictive respiratory failure mainly relies on home mechanical ventilation (HMV). Little is known about the cardiac effects of prolonged mechanical ventilation in patients with muscular dystrophy and restrictive respiratory insufficiency. We aimed to assess the effects of HMV on cardiac function in sarcoglycanopathies. We retrospectively included 10 genetically proven patients with sarcoglycanopathy followed at the HMV unit of the Raymond Poincare University Hospital (4 patients with α-sarcoglycanopathy and 6 patients with γ-sarcoglycanopathy). We collected cardiorespiratory clinical baseline data and left ventricular ejection fraction (LVEF) at baseline before initiation of HMV and at the end of follow-up. At baseline, median age was 30.5 years (27 to 39) and median pulmonary vital capacity was 27% of the predicted value (21 to 36). Forty percent of the patients had documented sleep apnea. Cardiomyopathy, defined as LVEF <50%, was found in 3 patients with γ-sarcoglycanopathy. After a median follow-up of 3 years (1.0 to 4.5), there was a significant increase in LVEF after initiation of HMV, that is, 62% (48 to 65) versus 53% (45.5 to 56.5) (p = 0.0039). In conclusion, HMV in sarcoglycanopathies is not harmful and may protect left ventricular function by its thoracic physiological effects.

Natural History of Cardiac and Respiratory Involvement, Prognosis and Predictive Factors for Long-Term Survival in Adult Patients with Limb Girdle Muscular Dystrophies Type 2C and 2D

Background

Type 2C and 2D limb girdle muscular dystrophies (LGMD) are a group of autosomal recessive limb girdle muscular dystrophies manifested by proximal myopathy, impaired respiratory muscle function and cardiomyopathy. The correlation and the prognostic impact of respiratory and heart impairment are poorly described. We aimed to describe the long-term cardiac and respiratory follow-up of these patients and to determine predictive factors of cardio-respiratory events and mortality in LGMD 2C and 2D.

Methods

We reviewed the charts of 34 LGMD patients, followed from 2005 to 2015, to obtain echocardiographic, respiratory function and sleep recording data. We considered respiratory events (acute respiratory failure, pulmonary sepsis, atelectasis or pneumothorax), cardiac events (acute heart failure, significant cardiac arrhythmia or conduction block, ischemic stroke) and mortality as outcomes of interest for the present analysis.

Results

A total of 21 patients had type 2C LGMD and 13 patients had type 2D. Median age was 30 years [IQR 24–38]. At baseline, median pulmonary vital capacity (VC) was 31% of predicted value [20–40]. Median maximal inspiratory pressure (MIP) was 31 cmH₂O [IQR 20.25–39.75]. Median maximal expiratory pressure (MEP) was 30 cm H₂O [20–36]. Median left ventricular ejection fraction (LVEF) was 55% [45–64] with 38% of patients with LVEF <50%. Over a median follow-up of 6 years, we observed 38% respiratory events, 14% cardiac events and 20% mortality. Among baseline characteristics, LVEF and left ventricular end diastolic diameter (LVEDD) were associated with mortality, whilst respiratory parameters (VC, MIP, MEP) and the need for home mechanical ventilation (HMV) were associated with respiratory events.

Conclusion

In our cohort of severely respiratory impaired type 2C and 2D LGMD, respiratory morbidity was high. Cardiac dysfunction was frequent in particular in LGMD 2C and had an impact on long-term mortality.

Trial Registration

ClinicalTrials.gov NCT02501083

Heart Disease in Disorders of Muscle, Neuromuscular Transmission, and the Nerves

Little is known regarding cardiac involvement (CI) by neuromuscular disorders (NMDs). The purpose of this review is to summarise and discuss the major findings concerning the types, frequency, and severity of cardiac disorders in NMDs as well as their diagnosis, treatment, and overall outcome. CI in NMDs is characterized by pathologic involvement of the myocardium or cardiac conduction system. Less commonly, additional critical anatomic structures, such as the valves, coronary arteries, endocardium, pericardium, and even the aortic root may be involved. Involvement of the myocardium manifests most frequently as hypertrophic or dilated cardiomyopathy and less frequently as restrictive cardiomyopathy, non-compaction, arrhythmogenic right-ventricular dysplasia, or Takotsubo-syndrome. Cardiac conduction defects and supraventricular and ventricular arrhythmias are common cardiac manifestations of NMDs. Arrhythmias may evolve into life-threatening ventricular tachycardias, asystole, or even sudden cardiac death. CI is common and carries great prognostic significance on the outcome of dystrophinopathies, laminopathies, desminopathies, nemaline myopathy, myotonias, metabolic myopathies, Danon disease, and Barth-syndrome. The diagnosis and treatment of CI in NMDs follows established guidelines for the management of cardiac disease, but cardiotoxic medications should be avoided. CI in NMDs is relatively common and requires complete work-up following the establishment of a neurological diagnosis. Appropriate cardiac treatment significantly improves the overall long-term outcome of NMDs.

Sarcoglycan complex in masseter and sternocleidomastoid muscles of baboons: an immunohistochemical study

The sarcoglycan complex consists of a group of single-pass transmembrane glycoproteins that are essential to maintain the integrity of muscle membranes. Any mutation in each sarcoglycan gene causes a series of recessive autosomal dystrophin-positive muscular dystrophies. Negative fibres for sarcoglycans have never been found in healthy humans and animals. In this study, we have investigated whether the social ranking has an influence on the expression of sarcoglycans in the skeletal muscles of healthy baboons. Biopsies of masseter and sternocleidomastoid muscles were processed for confocal immunohistochemical detection of sarcoglycans. Our findings showed that baboons from different social rankings exhibited different sarcoglycan expression profiles. While in dominant baboons almost all muscles were stained for sarcoglycans, only 55% of muscle fibres showed a significant staining. This different expression pattern is likely to be due to the living conditions of these primates. Sarcoglycans which play a key role in muscle activity by controlling contractile forces may influence the phenotype of muscle fibres, thus determining an adaptation to functional conditions. We hypothesize that this intraspecies variation reflects an epigenetic modification of the muscular protein network that allows baboons to adapt progressively to a different social status.

Cardiac involvement in Dutch patients with sarcoglycanopathy: a cross-sectional cohort and follow-up study

INTRODUCTION

The aim of this study is to describe the frequency, nature, severity, and progression of cardiac abnormalities in a cohort of Dutch sarcoglycanopathy patients.

METHODS

In this cross-sectional cohort study, patients were interviewed using a standardized questionnaire and assigned a functional score. Electrocardiography (ECG), echocardiography, and 24-h ECG were performed.

RESULTS

Twenty-four patients with sarcoglycanopathy had a median age of 25 years (range, 8-59 years). Beta blockers were used by 13%, and 17% used angiotensin-converting enzyme inhibitors. ECG abnormalities were present in 5 (21%), and 4 (17%) fulfilled the criteria for dilated cardiomyopathy (DCM). There were no significant differences in median age or severity of disease between patients with or without DCM. Eleven patients were examined earlier. Median follow-up time was 10 years. Two of the 11 patients (18%) developed DCM during follow-up.

CONCLUSIONS

Seventeen percent of the patients with sarcoglycanopathy were found to have dilated cardiomyopathy. We recommend biannual cardiac monitoring, including ECG and echocardiography.

A slowly progressive form of limb-girdle muscular dystrophy type 2C associated with founder mutation in the SGCG gene in Puerto Rican Hispanics

Limb-girdle muscular dystrophy type 2C (LGMD2C) is considered one of the severe forms of childhood-onset muscular dystrophy. The geographical distribution of founder mutations in the SGCG gene has a prominent effect on the prevalence of LGMD2C in certain populations. The aim of this study was to confirm the hypothesis that the c.787G>A (p.E263K) mutation in the SGCG gene is a founder mutation among Puerto Rican Hispanics and to characterize the associated clinical and immunohistochemical phenotype. Genotyping of six polymorphic microsatellite markers internal to (D13S232) and flanking (D13S175, D13S292, D13S787, D13S1243, D13S283) the SGCG gene was performed on four unrelated Puerto Rican patients with LGMD2C. Preserved ambulation to the second decade of life was observed in at least two subjects. Immunostaining of skeletal muscle demonstrated absence of γ-sarcoglycan in all affected subjects. Two markers, D13S232 and D13S292, were highly informative and confirmed that all four families share the haplotype of the mutant allele. Our findings confirm that the E263K missense mutation in the SGCG gene is a founder mutation in Puerto Rican Hispanics. A slowly progressive disease course with prolonged preservation of ambulation can be seen in association with this mutation, providing evidence for phenotypic variability.

Left ventricular function in alpha-sarcoglycanopathy and gamma-sarcoglycanopathy

Sarcoglycanopathies are autosomic recessive muscular dystrophies, secondary to mutations of the sarcoglycan complex. Heart can be involved in sarcoglycanopathies. We sought to analyse left ventricular function in patients with alpha-sarcoglycanopathy and gamma-sarcoglycanopathy. We conducted a retrospective study that aimed to analyse clinical and echocardiographic data of patients with sarcoglycanopathies. Our study included 19 patients: eight patients with alpha-sarcoglycanopathy and 11 patients with gamma-sarcoglycanopathy. Mean age was 37.8 ± 8.7 years in alpha-sarcoglycanopathy and 36 ± 7.3 years in gamma-sarcoglycanopathy. Mean VC was, respectively, 36.3 ± 18 % in alpha-sarcoglycanopathy and 23.5 ± 6.8 % in gamma-sarcoglycanopathy (p 0.05). 1/8 patients disclosed a left ventricular dysfunction with a left ventricular ejection fraction (LVEF) <50 % in alpha-sarcoglycanopathy, whereas 5/11 patients disclosed a left ventricular dysfunction (LVEF < 50 %) in gamma-sarcoglycanopathy. LV was altered in gamma-sarcoglycanopathy than in alpha-sarcoglycanopathy (LVEF at 45.6 ± 18 vs. 59.6 ± 5.9 % p 0.018). We found a significant alteration of the left ventricular function in gamma-sarcoglycanopathy compared to alpha-sarcoglycanopathy.

The genetics of dilated cardiomyopathy

PURPOSE OF REVIEW

More than 40 different individual genes have been implicated in the inheritance of dilated cardiomyopathy. For a subset of these genes, mutations can lead to a spectrum of cardiomyopathy that extends to hypertrophic cardiomyopathy and left ventricular noncompaction. In nearly all cases, there is an increased risk of arrhythmias. With some genetic mutations, extracardiac manifestations are likely to be present. The precise genetic cause can usually not be discerned from the cardiac and/or extracardiac manifestations and requires molecular genetic diagnosis for prognostic determination and cardiac care.

RECENT FINDINGS

Newer technologies are influencing genetic testing, especially cardiomyopathy genetic testing, wherein an increased number of genes are now routinely being tested simultaneously. Although this approach to testing multiple genes is increasing the diagnostic yield, the analysis of multiple genes in one test is also resulting in a large amount of genetic information of unclear significance.

SUMMARY

Genetic testing is highly useful in the care of patients and families, as it guides diagnosis, influences care and aids in prognosis. However, the large amount of benign human genetic variation may complicate genetic results and often requires a skilled team to accurately interpret the findings.

[Heart involvement in sarcoglycanopathies]

Sarcoglycanopathies (SG) are autosomic recessive muscular dystrophies, secondary to mutations of the sarcoglycan complex. Clinical pictures include muscle weakness affecting mainly the proximal limb girdle musculature. We review heart involvement in this group of disease.

A phase I trial of adeno-associated virus serotype 1-γ-sarcoglycan gene therapy for limb girdle muscular dystrophy type 2C

γ-Sarcoglycanopathy or limb girdle muscular dystrophy type 2C is an untreatable disease caused by autosomal recessively inherited mutations of the γ-sarcoglycan gene. Nine non-ambulatory patients (two males, seven females, mean age 27 years; range 16-38 years) with del525T homozygous mutation of the γ-sarcoglycan gene and no γ-sarcoglycan immunostaining on muscle biopsy were divided into three equal groups to receive three escalating doses of an adeno-associated virus serotype 1 vector expressing the human γ-sarcoglycan gene under the control of the desmin promoter, by local injection into the extensor carpi radialis muscle. The first group received a single injection of 3 × 10(9) viral genomes in 100 µl, the second group received a single injection of 1.5 × 10(10) viral genomes in 100 µl, and the third group received three simultaneous 100-µl injections at the same site, delivering a total dose of 4.5 × 10(10) viral genomes. No serious adverse effects occurred during 6 months of follow-up. All nine patients became adeno-associated virus serotype 1 seropositive and one developed a cytotoxic response to the adeno-associated virus serotype 1 capsid. Thirty days later, immunohistochemical analysis of injected-muscle biopsy specimens showed γ-sarcoglycan expression in all three patients who received the highest dose (4.7-10.5% positively stained fibres), while real-time polymerase chain reaction detected γ-sarcoglycan messenger RNA. In one patient, γ-sarcoglycan protein was detected by western blot. For two other patients who received the low and intermediate doses, discrete levels of γ-sarcoglycan expression (<1% positively stained fibres) were also detectable. Expression of γ-sarcoglycan protein can be induced in patients with limb girdle muscular dystrophy type 2C by adeno-associated virus serotype 1 gene transfer, with no serious adverse effects.

Molecular diagnosis of muscular dystrophies, focused on limb girdle muscular dystrophies

BACKGROUND

Muscular dystrophies include a spectrum of muscle disorders, some of which are phenotypically well characterized. The identification of dystrophin as the causative factor in Duchenne muscular dystrophy has led to the development of molecular genetics and has facilitated the division of muscular dystrophies into distinct groups, among which are the 'limb girdle muscular dystrophies'.

OBJECTIVES

This article reviews the methodology to be used in the diagnosis of muscular dystrophies, focused on the groups of limb girdle muscular dystrophies, and the development of new strategies to reach a final molecular diagnosis.

METHOD

A literature review (Medline) from 1985 to the present.

CONCLUSION

Immunohistochemistry and western blotting analyses of the proteins involved in the various forms of muscular dystrophies have permitted a refined pathological approach necessary to conduct genetic studies and to offer appropriate genetic counseling. The application of molecular medicine in genetic muscular dystrophies also brings great hope to the therapeutic management of these patients.

Therapeutic possibilities in the autosomal recessive limb-girdle muscular dystrophies

Fourteen years ago, the first disease-causing mutation in a form of autosomal recessive limb-girdle muscular dystrophy was reported. Since then the number of genes has been extended to at least 14 and the phenotypic spectrum has been broadened. The generation of mouse models helped to improve our understanding of the pathogenesis of the disease and also served to study therapeutic possibilities. All autosomal recessive limb-girdle muscular dystrophies are rare diseases, which is one reason why there have been so very few controlled clinical trials. Other reasons are insufficient natural history data and the lack of standardized assessment criteria and validated outcome measures. Currently, therapeutic possibilities are mainly restricted to symptomatic treatment and the treatment of disease complications. On the other hand, new efforts in translational research and the development of molecular therapeutic approaches suggest that more promising clinical trials will be carried out in autosomal recessive limb-girdle muscular dystrophy in the next several years.

Primary myopathies and the heart

Myopathies are frequently not confined to the skeletal muscles but also involve other organs or tissues. One of the most frequently affected organ in addition to the skeletal muscle is the heart (cardiac involvement, CI). CI manifests as impulse generation or conduction defects, focal or diffuse myocardial thickening, dilation of the cardiac cavities, relaxation abnormality, hypertrophic, dilated, restrictive cardiomyopathy, apical form of hypertrophic cardiomyopathy, noncompaction, Takotsubo phenomenon, secondary valve insufficiency, intra-cardiac thrombus formation, or heart failure with systolic or diastolic dysfunction. CI occurs in dystrophinopathies, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, limb girdle muscular dystrophies, laminopathies, congenital muscular dystrophies, myotonic dystrophies, congenital myopathies, metabolic myopathies, desminopathies, myofibrillar myopathy, Barth syndrome, McLeod syndrome, Senger's syndrome, and Bethlem myopathy. Patients with myopathy should be cardiologically investigated as soon as their neurological diagnosis is established, since supportive cardiac therapy is available, which markedly influences prognosis and outcome of CI in these patients.

Costameric proteins in human skeletal muscle during muscular inactivity

Costameres are regions that are associated with the sarcolemma of skeletal muscle fibres and comprise proteins of the dystrophin-glycoprotein complex and vinculin-talin-integrin system. Costameres play both a mechanical and a signalling role, transmitting force from the contractile apparatus to the extracellular matrix in order to stabilize skeletal muscle fibres during contraction and relaxation. Recently, it was shown that bidirectional signalling occurs between sarcoglycans and integrins, with muscle agrin potentially interacting with both types of protein to enable signal transmission. Although numerous studies have been carried out on skeletal muscle diseases, such as Duchenne muscular dystrophy, recessive autosomal muscular dystrophies and other skeletal myopathies, insufficient data exist on the relationship between costameres and the pathology of the second motor nerve and between costameric proteins and muscle agrin in other conditions in which skeletal muscle atrophy occurs. Previously, we carried out a preliminary study on skeletal muscle from patients with sensitive-motor polyneuropathy, in which we analysed the distribution of sarcoglycans, integrins and agrin by immunostaining only. In the present study, we have examined the skeletal muscle fibres of ten patients with sensitive-motor polyneuropathy. We used immunofluorescence and reverse transcriptase PCR to examine the distribution of vinculin, talin and dystrophin, in addition to that of those proteins previously studied. Our aim was to characterize in greater detail the distribution and expression of costameric proteins and muscle agrin during this disease. In addition, we used transmission electron microscopy to evaluate the structural damage of the muscle fibres. The results showed that immunostaining of alpha 7B-integrin, beta 1D-integrin and muscle agrin appeared to be severely reduced, or almost absent, in the muscle fibres of the diseased patients, whereas staining of alpha 7A-integrin appeared normal, or slightly increased, compared with that in normal skeletal muscle fibres. We also observed a lower level of alpha 7B- and beta 1D-integrin mRNA and a normal, or slightly higher than normal, level of alpha 7A-integrin mRNA in the skeletal muscle fibres of the patients with sensitive-motor polyneuropathy, compared with those in the skeletal muscle of normal patients. Additionally, transmission electron microscopy of transverse sections of skeletal muscle fibres indicated that the normal muscle fibre architecture was disrupted, with no myosin present inside the actin hexagons. Based on our results, we hypothesize that skeletal muscle inactivity, such as that found after denervation, could result in a reorganization of the costameres, with alpha 7B-integrin being replaced by alpha 7A-integrin. In this way, the viability of the skeletal muscle fibre is maintained. It will be interesting to clarify, by future experimentation, the mechanisms that lead to the down-regulation of integrins and agrin in muscular dystrophies.

Reduced life span with heart and muscle dysfunction in Drosophila sarcoglycan mutants

In humans, genetically diverse forms of muscular dystrophy are associated with a disrupted sarcoglycan complex. The sarcoglycan complex resides at the muscle plasma membrane where it associates with dystrophin. There are six known sarcoglycan proteins in mammals whereas there are only three in Drosophila melanogaster. Using imprecise P element excision, we generated three different alleles at the Drosophila delta-sarcoglycan locus. Each of these deletions encompassed progressively larger regions of the delta-sarcoglycan gene. Line 840 contained a large deletion of the delta-sarcoglycan gene, and this line displayed progressive impairment in locomotive ability, reduced heart tube function and a shortened life span. In line 840, deletion of the Drosophila delta-sarcoglycan gene produced disrupted flight muscles with shortened sarcomeres and disorganized M lines. Unlike mammalian muscle where degeneration is coupled with ongoing regeneration, no evidence for regeneration was seen in this Drosophila sarcoglycan mutant. In contrast, line 28 was characterized with a much smaller deletion that affected only a portion of the cytoplasmic region of the delta-sarcoglycan protein and left intact the transmembrane and extracellular domains. Line 28 had a very mild phenotype with near normal life span, intact cardiac function and normal locomotive activity. Together, these data demonstrate the essential nature of the transmembrane and extracellular domains of Drosophila delta-sarcoglycan for normal muscle structure and function.

Left ventricular synchronization by biventricular pacing in Becker muscular dystrophy as assessed by tissue Doppler imaging

Biventricular (BiV) pacing is a promising therapy for severe heart failure. The effect of BiV pacing is cardiac resynchronization of both ventricles. Asynchrony of the ventricular contraction and restoration of cardiac synchronization can be assessed by tissue Doppler imaging. Here we describe a patient with Becker muscular dystrophy with heart failure caused by dilated cardiomyopathy in whom a BiV pacemaker was implanted.

LGMD2E patients risk developing dilated cardiomyopathy

Sarcoglycan gene mutations cause various limb-girdle muscular dystrophies. The sarcoglycans are expressed both in skeletal and cardiac muscle but, surprisingly, so far only a few sarcoglycanopathy patients have had documented cardiomyopathy. We studied six patients with beta-sarcoglycanopathy. Immunohistochemical and immunoblot analysis performed on skeletal muscle biopsies from five patients, showed the loss of all sarcoglycans in three cases and marked reduction in two patients. Non-invasive cardiac examinations revealed that three patients had cardiac involvement: one had a severe Duchenne-like dystrophy, lethal dilated cardiomyopathy, and shared the same mutation reported in another cardiomyopathic patient; the other two patients had limb-girdle dystrophy and moderate cardiac involvement (one of them has a novel gene mutation). Given the age profile of the patients studied, the 50% cardiac involvement found in our LGMD2E patients is likely to be a conservative estimate. Careful cardiac monitoring should be carried out in beta-sarcoglycanopathy patients who are at high risk of developing cardiomyopathy.

Cardiac complications of childhood myopathies

The management of individuals with a neuromuscular disorder is usually focused on the skeletal muscle weakness and resulting complications, such as respiratory failure. Long-term prognosis of a number of neuromuscular conditions is, however, also determined by the type and severity of cardiac involvement. Early recognition and treatment of the cardiovascular complications are part of the task of the multidisciplinary team involved in the care of these patients. Although for several of the common conditions, there is general consensus on the cardiac investigations and treatments, in the rarer disorders, evidence-based recommendations are not available, and suggestions from experts provide an acceptable solution. This review summarizes the recent advances in our understanding of the pathogenesis and phenotypic diversity of cardiac complications associated with pediatric myopathies and provides a rational framework for planning the monitoring and therapeutic intervention in individual conditions.

Genetic diseases of muscle

In the last twenty years, the genetic basis for most of the inherited myopathies and muscular dystrophies has been unveiled. Diseases have been found to result from loss of function of structural components of the muscle basal lamina (e.g., MCD1A), sarcolemma (e.g., the sarcoglycanopathies), nucleus (e.g., EDMD) and sarcomere (e.g., the nemaline myopathies). A few have been associated with abnormalities in the genes for muscle enzymes (e.g., calpain and fukutin). Alternate mechanisms of pathogenesis have also recently been suggested by mutations lying outside of coding regions, such as the "field effect" of chromosomal mutations in DM2. In the future, we will likely identify the genes responsible for the remaining disorders, including many of the distal myopathies. In addition, we may also find skeletal muscle diseases associated with some of the presently non-implicated muscle proteins: syntropin, dystrobrevin, epsilon-sarcoglycan and sarcospan. The next steps may be to identify and understand the relationship of modifier genes producing the phenotypic heterogeneity of many of these diseases and to characterize those and other targets for therapeutic intervention, whether by gene therapy or by pharmacological treatment.

Cardiomyopathy is independent of skeletal muscle disease in muscular dystrophy

Dystrophin and its associated proteins, the sarcoglycans, are normally expressed in heart and skeletal muscle. Mutations that alter the expression of these membrane-associated proteins lead to muscular dystrophy (MD) and cardiomyopathy in humans. Because of the timing and nature of the accompanying cardiomyopathy, it has been suggested that cardiomyopathy develops as a secondary consequence of skeletal muscle dysfunction in the muscular dystrophies. To determine whether skeletal muscle dystrophy contributes to the development of sarcoglycan-mediated cardiomyopathy, we used mice lacking gamma-sarcoglycan and inserted a transgene that "rescued" gamma-sarcoglycan expression only in skeletal muscle. Gamma-sarcoglycan was expressed in skeletal muscle under the control of the skeletal muscle-specific myosin light chain 1/3 promoter. Gamma-sarcoglycan-null mice expressing this transgene fully restore gamma-sarcoglycan expression. Furthermore, the transgene-rescued mice lack the focal necrosis and membrane permeability defects that are a hallmark of MD. Despite correction of the skeletal muscle disease, focal degeneration and membrane permeability abnormalities persisted in cardiac muscle, and notably persisted in the right ventricle. Therefore, heart and skeletal muscle defects are independent processes in sarcoglycan-mediated muscular dystrophies and, as such, therapy should target both skeletal and cardiac muscle correction to prevent sudden death due to cardiomyopathy in the muscular dystrophies.