Immunohistochemical analysis of calpain 3: advantages and limitations in diagnosing LGMD2A

Diagnostic muscle biopsies in the era of genetics: the added value of myopathology in a selection of limb-girdle muscular dystrophy patients

In the second most common dystrophy associated with predominant pelvic and shoulder girdle muscle weakness termed Limb-Girdle Muscular Dystrophy (LGMD), genetic complexity, large phenotypic variability, and clinical overlap can result in extensive diagnostic delays in certain individuals. In view of the large strides genetics has taken in this day and age, we address the question if muscle biopsies can still provide diagnostic evidence of substance for these patients. We reviewed and reanalyzed muscle biopsy characteristics in a cohort of LGMD patient pairs in which gene variants were picked up in CAPN3, FKRP, TTN, and ANO5, using histochemical-immunohistochemical-and immunofluorescent staining, and western blotting. We found that not the nature and severity of inflammatory changes, but the changed properties of the dystrophin complex were the most valuable assets to differentiate LGMD from myositis. Proteomic evaluation brought both primary and secondary deficiencies to light, which could be equally revealing for diagnosis. Though a muscle biopsy might, at present, not always be strictly necessary anymore, it still represents an irrefutable asset when the genetic diagnosis is complicated.

Immunohistochemistry of sarcolemmal membrane-associated proteins in formalin-fixed and paraffin-embedded skeletal muscle tissue: a promising tool for the diagnostic evaluation of common muscular dystrophies

BACKGROUND

The analysis of fresh frozen muscle specimens is standard following routine muscle biopsy, but this service is not widely available in countries with limited medical facilities, such as Thailand. Nevertheless, immunohistochemistry (IHC) analysis is essential for the diagnosis of patients with a strong clinical suspicion of muscular dystrophy, in the absence of mutations detected by molecular genetics. As the successful labelling of sarcolemmal membrane-associated proteins in formalin-fixed and paraffin-embedded (FFPE) muscle sections using IHC staining has rarely been described, this study aimed to develop a reproducible IHC method for such an analysis.

METHODS

Thirteen cases were studied from the files of the Department of Pathology, Mahidol University. Diagnoses included three Duchenne muscular dystrophy (DMD), one Becker muscular dystrophy (BMD), one dysferlinopathy, and several not-specified muscular dystrophies. IHC was performed on FFPE sections at different thicknesses (3 μm, 5 μm, and 8 μm) using the heat-mediated antigen retrieval method with citrate/EDTA buffer, followed by an overnight incubation with primary antibodies at room temperature. Antibodies against spectrin, dystrophin (rod domain, C-terminus, and N-terminus), dysferlin, sarcoglycans (α, β, and γ), and β-dystroglycan were used. Frozen sections were tested in parallel for comparative analysis.

RESULTS

Antibodies labelling spectrin, dystrophin (rod domain and C-terminus), dysferlin, sarcoglycans (α, β, and γ), and β-dystroglycan clearly exhibited sarcolemmal staining in FFPE sections. However, staining of FFPE sections using the antibody directed against the N-terminus of dystrophin was unsuccessful. The absence of labeling for dystrophins and dysferlin in FFPE sections was documented in all three DMD patients and the dysferlinopathy patient. The BMD diagnosis could not be made using IHC in FFPE sections alone because of a lack of staining for the dystrophin N-terminus, indicating a limitation of this method.

CONCLUSIONS

We developed a reliable and reproducible IHC technique using FFPE muscle. This could become a valuable tool for the diagnosis of some muscular dystrophies, dystrophinopathies, sarcoglycanopathies (LGMD2D, LGMD2E, and LGMD2C), and dysferlinopathy, especially in situations where the analysis of fresh frozen muscle samples is not routinely available.

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.

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.

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.

Titin mutation segregates with hereditary myopathy with early respiratory failure

In 2001, we described an autosomal dominant myopathy characterized by neuromuscular ventilatory failure in ambulant patients. Here we describe the underlying genetic basis for the disorder, and we define the neuromuscular, respiratory and radiological phenotype in a study of 31 mutation carriers followed for up to 31 years. A combination of genome-wide linkage and whole exome sequencing revealed the likely causal genetic variant in the titin (TTN) gene (g.274375T>C; p.Cys30071Arg) within a shared haplotype of 2.93 Mbp on chromosome 2. This segregated with the phenotype in 21 individuals from the original family, nine subjects in a second family with the same highly selective pattern of muscle involvement on magnetic resonance imaging and a third familial case with a similar phenotype. Comparing the mutation carriers revealed novel features not apparent in our original report. The clinical presentation included predominant distal, proximal or respiratory muscle weakness. The age of onset was highly variable, from early adulthood, and including a mild phenotype in advanced age. Muscle weakness was earlier onset and more severe in the lower extremities in nearly all patients. Seven patients also had axial muscle weakness. Respiratory function studies demonstrated a gradual deterioration over time, reflecting the progressive nature of this condition. Cardiomyopathy was not present in any of our patients despite up to 31 years of follow-up. Magnetic resonance muscle imaging was performed in 21 affected patients and revealed characteristic abnormalities with semitendinosus involvement in 20 of 21 patients studied, including 3 patients who were presymptomatic. Diagnostic muscle histopathology most frequently revealed eosinophilic inclusions (inclusion bodies) and rimmed vacuoles, but was non-specific in a minority of patients. These findings have important clinical implications. This disease should be considered in patients with adult-onset proximal or distal myopathy and early respiratory failure, even in the presence of non-specific muscle pathology. Muscle magnetic resonance imaging findings are characteristic and should be considered as an initial investigation, and if positive should prompt screening for mutations in TTN. With 363 exons, screening TTN presented a major challenge until recently. However, whole exome sequencing provides a reliable cost-effective approach, providing the gene of interest is adequately captured.

An analysis of exome sequencing for diagnostic testing of the genes associated with muscle disease and spastic paraplegia

In this study, we assess exome sequencing (ES) as a diagnostic alternative for genetically heterogeneous disorders. Because ES readily identified a previously reported homozygous mutation in the CAPN3 gene for an individual with an undiagnosed limb girdle muscular dystrophy, we evaluated ES as a generalizable clinical diagnostic tool by assessing the targeting efficiency and sequencing coverage of 88 genes associated with muscle disease (MD) and spastic paraplegia (SPG). We used three exome-capture kits on 125 individuals. Exons constituting each gene were defined using the UCSC and CCDS databases. The three exome-capture kits targeted 47-92% of bases within the UCSC-defined exons and 97-99% of bases within the CCDS-defined exons. An average of 61.2-99.5% and 19.1-99.5% of targeted bases per gene were sequenced to 20X coverage within the CCDS-defined MD and SPG coding exons, respectively. Greater than 95-99% of targeted known mutation positions were sequenced to ≥1X coverage and 55-87% to ≥20X coverage in every exome. We conclude, therefore, that ES is a rapid and efficient first-tier method to screen for mutations, particularly within the CCDS annotated exons, although its application requires disclosure of the extent of coverage for each targeted gene and supplementation with second-tier Sanger sequencing for full coverage.

From proteins to genes: immunoanalysis in the diagnosis of muscular dystrophies

Muscular dystrophies are a large heterogeneous group of inherited diseases that cause progressive muscle weakness and permanent muscle damage. Very few muscular dystrophies show sufficient specific clinical features to allow a definite diagnosis. Because of the currently limited capacity to screen for numerous genes simultaneously, muscle biopsy is a time and cost-effective test for many of these disorders. Protein analysis interpreted in correlation with the clinical phenotype is a useful way of directing genetic testing in many types of muscular dystrophies. Immunohistochemistry and western blot are complementary techniques used to gather quantitative and qualitative information on the expression of proteins involved in this group of diseases. Immunoanalysis has a major diagnostic application mostly in recessive conditions where the absence of labelling for a particular protein is likely to indicate a defect in that gene. However, abnormalities in protein expression can vary from absence to very subtle reduction. It is good practice to test muscle biopsies with antibodies for several proteins simultaneously and to interpret the results in context. Indeed, there is a degree of direct or functional association between many of these proteins that is reflected by the presence of specific secondary abnormalities that are of value, especially when the diagnosis is not straightforward.

Limb-girdle muscular dystrophy 2A

Limb-girdle muscular dystrophy type 2A (LGMD2A) is caused by mutations in the gene CAPN3 located in the chromosome region 15q15.1-q21.1. To date more than 300 mutations have been described. This gene encodes for a 94-kDa nonlysosomal calcium-dependent cysteine protease and its function in skeletal muscle is not fully understood. It seems that calpain-3 has an unusual zymogenic activation that involves, among other substrates, cytoskeletal proteins. Calpain-3 is thought to interact with titin and dysferlin. Calpain-3 deficiency produces abnormal sarcomeres that lead eventually to muscle fiber death. Hip adductors and gluteus maximus are the earliest clinically affected muscles. No clinical differences have been reported depending on the type of mutation in the CAPN3 gene. The muscle biopsy shows variability of fiber size, interstitial fibrosis, internal nuclei, lobulated fibers, and, in some cases, presence of eosinophils. Recent gene expression profiling studies have shown upregulation of interleukin-32 and immunoglobulin genes, which may explain the eosinophilic infiltration. Two mouse knockout models of CAPN3 have been characterized. There are no curative treatments for this disease. However, experimental therapeutics using mouse models conclude that adeno-associated virus (AAV) vectors seem to be one of the best approaches because of their efficiency and persistency of gene transfer.

Muscular dystrophies: an update on pathology and diagnosis

Muscular dystrophies are clinically, genetically, and molecularly a heterogeneous group of neuromuscular disorders. Considerable advances have been made in recent years in the identification of causative genes, the differentiation of the different forms and in broadening the understanding of pathogenesis. Muscle pathology has an important role in these aspects, but correlation of the pathology with clinical phenotype is essential. Immunohistochemistry has a major role in differential diagnosis, particularly in recessive forms where an absence or reduction in protein expression can be detected. Several muscular dystrophies are caused by defects in genes encoding sarcolemmal proteins, several of which are known to interact. Others are caused by defects in nuclear membrane proteins or enzymes. Assessment of both primary and secondary abnormalities in protein expression is useful, in particular the hypoglycosylation of alpha-dystroglycan. In dominantly inherited muscular dystrophies it is rarely possible to detect a change in the expression of the primary defective protein; an exception to this is caveolin-3.

Reverse protein arrays as novel approach for protein quantification in muscular dystrophies

The definite molecular diagnosis in patients with muscular dystrophies often requires the assessment of muscular expression of multiple proteins in small amounts of muscle tissue. The sample material obtained in muscle biopsies is limited and the measurement of multiple proteins is often restricted to conventional, non-quantitative assays, i.e. immunohistochemistry and immunoblotting. Here, we demonstrate that reverse protein arrays are a novel and excellent material-saving method for the measurement and quantification of changes in protein expression between healthy and diseased muscle tissue as well as cultured primary myotubes. We evaluated a set of antibodies and found reproducible differences between Duchenne muscular dystrophy/limb-girdle muscular dystrophy patients and control samples for dystrophin, the sarcoglycans and the dystroglycans. As little as 10 mg of tissue is sufficient for the analysis of all diagnostically relevant proteins. The average coefficient of variation calculated for the sample signals confirmed that the method is highly reproducible. Thus, our experiments provide strong evidence that quantitative protein detection from very small amounts of muscle tissue is possible using reverse protein arrays. This technology may not only be of interest for diagnostic purposes, but also for protein quantification of multiple, follow-up biopsies during clinical trials when protein expression in muscle is considered an important outcome measure or biomarker.