Importance of immunohistochemical evaluation of developmentally regulated myosin heavy chains in human muscle biopsies

Our retrospective immunohistochemical study of normal quadriceps muscle biopsies shows that embryonic myosin heavy chains are down-regulated by, or soon after, birth. Fetal myosin heavy chains are down-regulated by 4-6 months. Thus the presence of an appreciable number of fibres with embryonic myosin heavy chains at birth or of fetal myosin heavy chains after 6 months of age suggests a delay in maturation or an underlying abnormality. Regenerating fibres in dystrophic muscle often co-express both embryonic and fetal myosin heavy chains but more fibres with fetal than embryonic myosin heavy chains can occur. Embryonic myosin heavy chains are a useful marker of regeneration but effects of denervation, stress, disuse, and fibre maintenance also have to be taken into account. In neurogenic disorders fibres with embryonic myosin heavy chains are rare but fetal myosin heavy chain expression is common, particularly in 5q spinal muscle atrophy. Nuclear clumps in denervated muscle show fetal and sometimes embryonic myosin heavy chains. Developmentally regulated myosins are useful for highlighting the perifascicular atrophy in juvenile dermatomyositis. Our studies highlight the importance of baseline data for embryonic and fetal myosin heavy chains in human muscle biopsies and the importance of assessing them in a spectrum of neuromuscular disorders.

Myopathology in congenital myopathies

Congenital myopathies are clinically and genetically a heterogeneous group of early onset neuromuscular disorders, characterized by hypotonia and muscle weakness. Clinical severity and age of onset are variable. Many patients are severely affected at birth while others have a milder, moderately progressive or nonprogressive phenotype. Respiratory weakness is a major clinical aspect that requires regular monitoring. Causative mutations in several genes have been identified that are inherited in a dominant, recessive or X-linked manner, or arise de novo. Muscle biopsies show characteristic pathological features such as nemaline rods/bodies, cores, central nuclei or caps. Small type 1 fibres expressing slow myosin are a common feature and may sometimes be the only abnormality. Small cores (minicores) devoid of mitochondria and areas showing variable myofibrillar disruption occur in several neuromuscular disorders including several forms of congenital myopathy. Muscle biopsies can also show more than one structural defect. There is considerable clinical, pathological and genetic overlap with mutations in one gene resulting in more than one pathological feature, and the same pathological feature being associated with defects in more than one gene. Increasing application of whole exome sequencing is broadening the clinical and pathological spectra in congenital myopathies, but pathology still has a role in clarifying the pathogenicity of gene variants as well as directing molecular analysis.

RYR1-related congenital myopathy with fatigable weakness, responding to pyridostigimine

The spectrum of RYR1 mutation associated disease encompasses congenital myopathies, exercise induced rhabdomyolysis, malignant hyperthermia susceptibility and King-Denborough syndrome. We report the clinical phenotype of two siblings who presented in infancy with hypotonia and striking fatigable ptosis. Their response to pyridostigimine was striking, but genetic screening for congenital myasthenic syndromes was negative, prompting further evaluation. Muscle MRI was abnormal with a selective pattern of involvement evocative of RYR1-related myopathy. This directed sequencing of the RYR1 gene, which revealed two heterozygous c.6721C>T (p.Arg2241X) nonsense mutations and novel c.8888T>C (p.Leu2963Pro) mutations in both siblings. These cases broaden the RYR1-related disease spectrum to include a myasthenic-like phenotype, including partial response to pyridostigimine. RYR1-related myopathy should be considered in the presence of fatigable weakness especially if muscle imaging demonstrates structural abnormalities. Single fibre electromyography can also be helpful in cases like this.

Congenital myopathies--clinical features and frequency of individual subtypes diagnosed over a 5-year period in the United Kingdom

The congenital myopathies are a group of inherited neuromuscular disorders mainly defined on the basis of characteristic histopathological features. We analysed 66 patients assessed at a single centre over a 5 year period. Of the 54 patients where muscle biopsy was available, 29 (54%) had a core myopathy (central core disease, multi-minicore disease), 9 (17%) had nemaline myopathy, 7 (13%) had myotubular/centronuclear myopathy, 2 (4%) had congenital fibre type disproportion, 6 (11%) had isolated type 1 predominance and 1 (2%) had a mixed core-rod myopathy. Of the 44 patients with a genetic diagnosis, RYR1 was mutated in 26 (59%), ACTA1 in 7 (16%), SEPN1 in 7 (16%), MTM1 in 2 (5%), NEB in 1 (2%) and TPM3 in 1 (2%). Clinically, 77% of patients older than 18 months could walk independently. 35% of all patients required ventilatory support and/or enteral feeding. Clinical course was stable or improved in 57/66 (86%) patients, whilst 4 (6%) got worse and 5 (8%) died. These findings indicate that core myopathies are the most common form of congenital myopathies and that more than half can be attributed to RYR1 mutations. The underlying genetic defect remains to be identified in 1/3 of congenital myopathies cases.

Mutations in MYH7 cause Multi-minicore Disease (MmD) with variable cardiac involvement

Central Core Disease (CCD) and Multi-minicore Disease (MmD) (the "core myopathies") have been mainly associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the selenoprotein N (SEPN1) gene. A proportion of cases remain unresolved. Mutations in MYH7 encoding the beta myosin heavy chain protein have been implicated in cardiac and, less frequently, skeletal muscle disorders. Here we report four patients from two families with a histopathological diagnosis of MmD, presenting in childhood with slowly progressive muscle weakness, more proximal in Family 1 and more distal in Family 2, and variable degrees of cardiorespiratory impairment evolving later in life. There was also a strong family history of sudden death in the first family. Muscle biopsies obtained in early childhood showed multiple minicores as the most prominent feature. Sequencing of the MYH7 gene revealed heterozygous missense mutations, c.4399C>G; p.Leu1467Val (exon 32) in Family 1 and c.4763G>C; p.Arg1588Pro (exon 34) in Family 2. These findings suggest MYH7 mutations as another cause of a myopathy with multiple cores, in particular if associated with dominant inheritance and cardiac involvement. However, clinical features previously associated with this genetic background, namely a more distal distribution of weakness and an associated cardiomyopathy, may only evolve over time.

Mutations in MYH7 cause Multi-minicore Disease (MmD) with variable cardiac involvement

Central Core Disease (CCD) and Multi-minicore Disease (MmD) (the "core myopathies") have been mainly associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the selenoprotein N (SEPN1) gene. A proportion of cases remain unresolved. Mutations in MYH7 encoding the beta myosin heavy chain protein have been implicated in cardiac and, less frequently, skeletal muscle disorders. Here we report four patients from two families with a histopathological diagnosis of MmD, presenting in childhood with slowly progressive muscle weakness, more proximal in Family 1 and more distal in Family 2, and variable degrees of cardiorespiratory impairment evolving later in life. There was also a strong family history of sudden death in the first family. Muscle biopsies obtained in early childhood showed multiple minicores as the most prominent feature. Sequencing of the MYH7 gene revealed heterozygous missense mutations, c.4399C>G; p.Leu1467Val (exon 32) in Family 1 and c.4763G>C; p.Arg1588Pro (exon 34) in Family 2. These findings suggest MYH7 mutations as another cause of a myopathy with multiple cores, in particular if associated with dominant inheritance and cardiac involvement. However, clinical features previously associated with this genetic background, namely a more distal distribution of weakness and an associated cardiomyopathy, may only evolve over time.

Relative frequency of congenital muscular dystrophy subtypes: analysis of the UK diagnostic service 2001-2008

The Dubowitz Neuromuscular Centre is the UK National Commissioning Group referral centre for congenital muscular dystrophy (CMD). This retrospective review reports the diagnostic outcome of 214 UK patients referred to the centre for assessment of 'possible CMD' between 2001 and 2008 with a view to commenting on the variety of disorders seen and the relative frequency of CMD subtypes in this patient population. A genetic diagnosis was reached in 53 of 116 patients fulfilling a strict criteria for the diagnosis of CMD. Within this group the most common diagnoses were collagen VI related disorders (19%), dystroglycanopathy (12%) and merosin deficient congenital muscular dystrophy (10%). Among the patients referred as 'possible CMD' that did not meet our inclusion criteria, congenital myopathies and congenital myasthenic syndromes were the most common diagnoses. In this large study on CMD the diagnostic outcomes compared favourably with other CMD population studies, indicating the importance of an integrated clinical and pathological assessment of this group of patients.

Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease

OBJECTIVES

Homoplasmic maternally inherited, m.14674T>C or m. 14674T>G mt-tRNA(Glu) mutations have recently been identified in reversible infantile cytochrome c oxidase deficiency (or 'benign COX deficiency'). This study sought other genetic defects that may give rise to similar presentations.

PATIENTS

Eight patients from seven families with clinicopathological features of infantile reversible cytochrome c oxidase deficiency were investigated.

METHODS

The study reviewed the diagnostic features and performed molecular genetic analyses of mitochondrial DNA and nuclear encoded candidate genes.

RESULTS

Patients presented with subacute onset of profound hypotonia, feeding difficulties and lactic acidosis within the first months of life. Although recovery was remarkable, a mild myopathy persisted into adulthood. Histopathological findings in muscle included increased lipid and/or glycogen content, ragged-red and COX negative fibres. Biochemical studies suggested more generalised abnormalities than pure COX deficiency. Clinical improvement was reflected by normalisation of lactic acidosis and histopathological abnormalities. The m.14674T>C mt-tRNA(Glu) mutation was identified in four families, but none had the m. 14674T>G mutation. Furthermore, in two families pathogenic mutations were also found in the nuclear TRMU gene which has not previously been associated with this phenotype. In one family, the genetic aetiology still remains unknown.

CONCLUSIONS

Benign COX deficiency is better described as 'reversible infantile respiratory chain deficiency'. It is genetically heterogeneous, and patients not carrying the m.14674T>C or T>G mt-tRNA(Glu) mutations may have mutations in the TRMU gene. Diagnosing this disorder at the molecular level is a significant advance for paediatric neurologists and intensive care paediatricians, enabling them to select children with an excellent prognosis for continuing respiratory support from those with severe mitochondrial presentation in infancy.

Flow cytometry analysis: a quantitative method for collagen VI deficiency screening

Mutations in COL6A1, COL6A2 and COL6A3 genes result in collagen VI myopathies: Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and intermediate phenotypes. At present, none of the existing diagnostic techniques for evaluating collagen VI expression is quantitative, and the detection of subtle changes in collagen VI expression remains challenging. We investigated flow cytometry analysis as a means of quantitatively measuring collagen VI in primary fibroblasts and compared this method with the standard method of fibroblast collagen VI immunohistochemical analysis. Eight UCMD and five BM molecularly confirmed patients were studied and compared to five controls. Flow cytometry analysis consistently detected a reduction of collagen VI of at least 60% in all UCMD cases. In BM cases the levels of collagen VI were variable but on average 20% less than controls. Flow cytometry analysis provides an alternative method for screening for collagen VI deficiency at the protein level in a quantitative, time and cost-effective manner.

RYR1 mutations are a common cause of congenital myopathies with central nuclei

OBJECTIVE

Centronuclear myopathy (CNM) is a rare congenital myopathy characterized by prominence of central nuclei on muscle biopsy. CNM has been associated with mutations in MTM1, DNM2, and BIN1 but many cases remain genetically unresolved. RYR1 encodes the principal sarcoplasmic reticulum calcium release channel and has been implicated in various congenital myopathies. We investigated whether RYR1 mutations cause CNM.

METHODS

We sequenced the entire RYR1 coding sequence in 24 patients with a diagnosis of CNM from South Africa (n = 14) and Europe (n = 10) and identified mutations in 17 patients. The most common genotypes featured compound heterozygosity for RYR1 missense mutations and mutations resulting in reduced protein expression, including intronic splice site and frameshift mutations.

RESULTS

The high incidence in South African patients (n = 12/14) in conjunction with recurrent RYR1 mutations associated with common haplotypes suggested the presence of founder effects. In addition to central nuclei, prominent histopathological findings included (often multiple) internalized nuclei and type 1 fiber predominance and hypotrophy with relative type 2 hypertrophy. Although cores were not typically seen on oxidative stains, electron microscopy revealed subtle abnormalities in most cases. External ophthalmoplegia, proximal weakness, and bulbar involvement were prominent clinical findings.

INTERPRETATION

Our findings expand the range of RYR1-related phenotypes and suggest RYR1 mutations as a common cause of congenital myopathies with central nuclei. Corresponding to recent observations in X-linked CNM, these findings indicate disturbed assembly and/or malfunction of the excitation-contraction machinery as a key mechanism in CNM and related myopathies.

Muscular dystrophies due to defective glycosylation of dystroglycan

Muscular dystrophies are a clinically and genetically heterogeneous group of disorders. Until recently most of the proteins associated with muscular dystrophies were believed to be proteins of the sarcolemma associated with reinforcing the plasma membrane or in facilitating its re-sealing following injury. In the last few years a novel and frequent pathogenic mechanism has been identified that involves the abnormal glycosylation of alpha-dystroglycan (ADG). This peripheral membrane protein undergoes complex and crucial glycosylation steps that enable it to interact with LG domain containing extracellular matrix proteins such as laminins, agrin and perlecan. Mutations in six genes (POMT1, POMT2, POMGnT1, fukutin, FKRP and LARGE) have been identified in patients with reduced glycosylation of ADG. While initially a clear correlation between gene defect and phenotype was observed for each of these 6 genes (for example, Walker Warburg syndrome was associated with mutations in POMT1 and POMT2, Fukuyama congenital muscular dystrophy associated with fukutin mutations, and Muscle Eye Brain disease associated with POMGnT1 mutations), we have recently demonstrated that allelic mutations in each of these 6 genes can result in a much wider spectrum of clinical conditions. Thus, the crucial aspect in determining the phenotypic severity is not which gene is primarily mutated, but how severely the mutation affects the glycosylation of ADG. Systematic mutation analysis of these 6 glycosyltransferases in patients with a dystroglycan glycosylation disorder identifies mutations in approximately 65% suggesting that more genes have yet to be identified.

A congenital myopathy with diaphragmatic weakness not linked to the SMARD1 locus

Severe diaphragmatic weakness in infancy is rare. Common causes include structural myopathies, neuromuscular transmission defects, or anterior horn cell dysfunction (spinal muscular atrophy with respiratory distress, SMARD1). We describe a form of infantile diaphragmatic weakness without mutations in the SMARD1 gene, in which pathological and clinical features differ from known conditions, and investigations suggest a myopathy. We identified seven cases in four families. All presented soon after birth with feeding and breathing difficulties, marked head lag, facial weakness, and preserved antigravity movements in the limbs, with arms weaker than legs. All had paradoxical breathing and paralysis of at least one hemi-diaphragm. All required gastrostomy feeding, and all became ventilator-dependent. Investigations included myopathic EMG, muscle biopsy showing myopathic changes, normal electrophysiology and no mutations in SMN1 or IGHMBP2. These seven infants are affected by a myopathic condition clinically resembling SMARD1. However, its pathogenesis appears to be a myopathy affecting predominantly the diaphragm.

A comparative analysis of collagen VI production in muscle, skin and fibroblasts from 14 Ullrich congenital muscular dystrophy patients with dominant and recessive COL6A mutations

Ullrich congenital muscular dystrophy (UCMD) is caused by recessive and dominant mutations in COL6A genes. We have analysed collagen VI expression in 14 UCMD patients. Sequencing of COL6A genes had identified homozygous and heterozygous mutations in 12 cases. Analysis of collagen VI in fibroblast cultures derived from eight of these patients showed reduced extracellular deposition in all cases and intracellular collagen VI staining in seven cases. This was observed even in cases that showed normal collagen VI labelling in skin biopsies. Collagen VI immunolabelling was reduced in all the available muscle biopsies. When comparisons were possible no correlation was seen between the extent of the reduction in the muscle and fibroblast cultures, the mode of inheritance or the severity of the clinical phenotype. Mutations affecting glycine substitutions in the conserved triple helical domain were common and all resulted in reduced collagen VI. This study expands the spectrum of collagen VI defects and shows that analysis of skin fibroblasts may be a useful technique for the detection of collagen VI abnormalities. In contrast, immunohistochemical analysis of skin biopsies may not always reveal an underlying collagen VI defect.

Non-sarcolemmal muscular dystrophies

The muscular dystrophies are characterised by progressive muscle weakness and wasting. Pathologically the hallmarks are muscle fibre degeneration and fibrosis. Several recessive forms of muscular dystrophy are caused by defects in proteins localised to the sarcolemma. However, it is now apparent that others are due to defects in a wide range of proteins including those which are either nuclear-related (Emery-Dreifuss type muscular dystrophies, oculopharyngeal muscular dystrophy), enzymatic (limb-girdle muscular dystrophy 2A, myotonic dystrophy) or sarcomeric (limb-girdle muscular dystrophies 1A and 2G). Although the clinical and molecular basis of these disorders is heterogeneous all display myopathic morphological features. These include variation in fibre size, an increase in internal nuclei, and some myofibrillar distortion. Degeneration and fibrosis occur, but usually not to the same extent as in muscular dystrophies associated with sarcolemmal protein defects. This review outlines the genetic basis of these "non-sarcolemmal" forms of dystrophy and discusses current ideas on their pathogenesis.

Disease severity in dominant Emery Dreifuss is increased by mutations in both emerin and desmin proteins

Individuals with the same genetic disorder often show remarkable differences in clinical severity, a finding generally attributed to the genetic background. We identified two patients with genetically proven Emery-Dreifuss muscular dystrophy (EDMD) who followed an unusual course and had uncommon clinicopathological findings. We hypothesized digenic inheritance and looked for additional molecular explanations. Mutations in additional separate genes were identified in both patients. The first patient was a member of a family with molecularly proven X-linked EDMD. However, the clinical features were unusually severe for this condition in the propositus: he presented at 2.5 years with severe proximal weakness and markedly elevated serum creatine kinase. Muscle weakness rapidly progressed, leading to loss of independent ambulation by the age of 12. In addition, the patient developed cardiac conduction system disease requiring pacing at the age of 11 and severe dilated cardiomyopathy in the early teens. Despite pacing, he had several syncopal episodes attributed to ventricular dysrhythmias. As these resemble the cardiac features of patients with the autosomal dominant variant of EDMD, we examined the lamin A/C gene, identifying a de-novo mutation in the propositus. The second patient had a cardioskeletal myopathy, similar to his mother who had died more than 20 years previously. Because of the dominant family history, a laminopathy was suspected and a mutation in exon 11 of the LMNA gene was identified. This mutation, however, was not present in his mother, but instead, surprisingly, was identified in his virtually asymptomatic father. Unusual accumulations of desmin found in the cardiac muscle of the propositus prompted us to examine the desmin gene in this patient, and in so doing, we identified a desmin mutation, in addition to the LMNA mutation in the propositus. These cases suggest that separate mutations in related proteins that are believed to interact, or that represent different parts of a presumed functional pathway, may synergistically contribute to disease severity in autosomal dominant EDMD. Furthermore, digenic inheritance may well contribute to the clinical severity of many other neuromuscular disorders.

Minicore myopathy with ophthalmoplegia caused by mutations in the ryanodine receptor type 1 gene

BACKGROUND

Minicore myopathy (multi-minicore disease [MmD]) is a congenital myopathy characterized by multifocal areas with loss of oxidative activity on muscle biopsy. MmD is clinically heterogeneous and distinct phenotypes have been associated with recessive mutations in either the selenoprotein N (SEPN1) or the skeletal muscle ryanodine receptor (RYR1) gene, also implicated in central core disease and malignant hyperthermia. External ophthalmoplegia is an additional finding in a subset of patients with MmD.

OBJECTIVE

To clinically and genetically examine families with MmD and external ophthalmoplegia.

METHODS

The authors investigated 11 affected individuals from 5 unrelated families. Clinical, histopathologic, and imaging studies were performed and RYR1 haplotyping and mutational analysis were carried out.

RESULTS

All patients had multiple cores involving the entire fiber diameter on longitudinal sections. Weakness and wasting in the shoulder girdle, scoliosis, moderate respiratory impairment, and feeding difficulties were prominent. In contrast to SEPN1-related myopathies, soleus was more severely affected than gastrocnemius on muscle MRI. Haplotyping suggested linkage to the RYR1 locus in informative families and mutational screening revealed four novel RYR1 mutations in three unrelated families; in addition, functional haploinsufficiency was found in one allele of two recessive cases.

CONCLUSION

These findings expand the phenotypic spectrum associated with mutations in the skeletal muscle ryanodine receptor (RYR1) gene. Recessive mutations of domains commonly affected in malignant hyperthermia appear to be particularly prevalent in multi-minicore disease with external ophthalmoplegia and might suggest a different pathomechanism from that involved in central core disease.

A and B utrophin in human muscle and sarcolemmal A-utrophin associated with tumours

Utrophin is an autosomal homologue of dystrophin, abnormal expression of which is responsible for X-linked Duchenne and Becker muscular dystrophy. In normal mature muscle utrophin is confined to blood vessels, nerves and myotendinous and neuromuscular junctions. When dystrophin is absent utrophin is abundant on the sarcolemma. This has raised the possibility that up-regulation of utrophin may be of therapeutic benefit. Two full-length transcripts of utrophin, A and B, have been identified, which are regulated by alternatively spliced 5' promoters. In dystrophic mouse muscle, the A isoform is present on the sarcolemma, whereas the B form is confined to blood vessels. We show here using immunohistochemistry and human isoform-specific antibodies that A- and B-utrophin localisation is the same in human muscle. The A isoform is present on the sarcolemma of foetal human muscle fibres, regenerating fibres, fibres deficient in dystrophin and on blood vessels and neuromuscular junctions. B-utrophin is only detected on blood vessels. We also show that muscle adjacent to some soft tissue tumours shows increased sarcolemmal utrophin-A, showing that utrophin and dystrophin can simultaneously localise to the sarcolemma and raising the possibility that factor(s) from the tumour cells or accompanying inflammatory cells may have a role in regulating utrophin.

Congenital muscular dystrophy: molecular and cellular aspects

The congenital muscular dystrophies are a clinically and genetically heterogeneous group of neuromuscular disorders. Each form has a characteristic phenotype, but there is overlap between some entities and their classification is based on a combination of clinical features and the primary or secondary protein defect. Recent studies have identified the genetic basis of a number of congenital muscular dystrophies (11 genes in total) and have recognised a novel pathological mechanism that highlights the importance of the correct posttranslational processing of proteins, in particular alpha-dystroglycan. Diagnosis of these conditions has been aided by the availability of specific antibodies for each protein and a better understanding of the protein changes that accompany each condition. In this review we present the major molecular, clinical and diagnostic aspects of each group of congenital muscular dystrophy with an emphasis in the more recent developments.

Expanding the phenotype of potassium channelopathy: severe neuromyotonia and skeletal deformities without prominent Episodic Ataxia

We report an unusual family in which the same point mutation in the voltage-gated potassium channel gene KCNA1 resulted in markedly different clinical phenotypes. The propositus presented in infancy with marked muscle stiffness, motor developmental delay, short stature, skeletal deformities, muscle hypertrophy and muscle rippling on percussion. He did not experience episodic ataxia. His mother presented some years later with typical features of Episodic Ataxia type 1 (EA1), with episodes of ataxia lasting a few minutes provoked by exercise. On examination she had myokymia, joint contractures and mild skeletal deformities. A heterozygous point mutation in the voltage-gated K(+) channel (KCNA1) gene (ACG-AGG, Thr226Arg) was found in both. We conclude that mutations in the potassium channel gene (KCNA1) can cause severe neuromyotonia resulting in marked skeletal deformities even if episodic ataxia is not prominent.

Absence of neuronal nitric oxide synthase (nNOS) as a pathological marker for the diagnosis of Becker muscular dystrophy with rod domain deletions

Immunohistochemistry using antibodies to dystrophin is the pathological basis for the diagnosis of Duchenne and Becker muscular dystrophy (DMD and BMD). While the sarcolemma of DMD muscle is negative, BMD muscle generally shows variable labelling because of the translation of a partially functional dystrophin that is localized to the sarcolemma. In rare cases, however, this labelling is equivocal and similar to that observed in controls making diagnosis difficult. We report here that in such instances immunolabelling with antibodies to the neuronal form of nitric oxide synthase (nNOS) can be useful in suspecting a dystrophinopathy with a mutation in the 'hot-spot' rod domain and help to direct molecular analysis. nNOS localizes to the sarcolemma of mature muscle fibres via several components of the dystrophin-associated protein complex (DAPC) including dystrophin but sarcolemmal nNOS is lost when dystrophin levels are very low or absent because of deletions in critical regions of the rod domain. We report three cases who presented with only mild or no muscle weakness but had elevated serum creatine kinase activity and dystrophin immunolabelling indistinguishable from normal, making a pathological diagnosis difficult. All three cases had a complete absence of sarcolemmal nNOS and were subsequently found to have an in-frame deletion in the common rod domain exons (in these cases 48, 45-51, 47-53) compatible with a BMD. In addition, we observed that nNOS appears to be developmentally regulated with the antibody used and was often absent from the sarcolemma of immature fibres. These findings demonstrate the value of including antibodies to nNOS in routine immunohistochemical studies and that absence of nNOS can be a more sensitive marker than up-regulation of utrophin for diagnosis of BMD. Immaturity of fibres, however, needs to be taken into account, especially in neonates.

Central core disease: clinical, pathological, and genetic features

Central core disease (CCD) is a dominantly inherited congenital myopathy allelic to malignant hyperthermia (MH) caused by mutations in the RYR1 gene on chromosome 19q13.1. Eleven individuals with RYR1 mutations are described. Four index cases showed features consistent with a congenital myopathy (hypotonia, delayed motor milestones, and skeletal abnormalities including congenital hip dislocation and scoliosis). All four cases and subsequently seven other family members were found to possess novel mutations in the RYR1 gene. The degree of disability varied from one clinically normal individual, to another who had never achieved independent ambulation (the only patient with a de novo mutation). Four cases showed a mild reduction in vital capacity, repeated nocturnal polysomnography showed hypoxaemia in one case. A variety of muscle biopsy features were found; central cores were absent in the youngest case, and the biopsy specimens from two others were more suggestive of mini-core myopathy. In all cases missense mutations in exons 101, 102, and 103 of the RYR1 gene on were found. Future laboratory diagnosis of suspected cases and family members will be less invasive and more accurate with DNA analysis. Clinicians, especially paediatricians and orthopaedic surgeons, should be aware of this disorder because of the potential risk of MH.

Muscle magnetic resonance imaging in patients with congenital muscular dystrophy and Ullrich phenotype

The aim of this study was to evaluate muscle magnetic resonance imaging findings in patients with congenital muscular dystrophy and Ullrich phenotype. Fifteen children with congenital muscular dystrophy and Ullrich phenotype were included in the study. All patients had collagen VI studies in muscle and, when family structure was informative, linkage studies to the collagen 6 loci. Three of the 15 patients had reduced collagen in muscle. One of the three was from an informative family and linked to one of the collagen 6 loci. Another patient was linked to one of the collagen 6 loci but had normal expression of collagen in muscle. The remaining 11 all had normal collagen expression in muscle. Only two of these 11 were from informative families and linkage to collagen 6 loci was excluded in them. All patients had muscle magnetic resonance imaging of their leg muscles using transverse T1 sequences. With the exception of the two patients in whom linkage to the collagen 6 loci was excluded, the other 13 patients showed the same pattern of selective involvement on magnetic resonance imaging of thigh muscles. This consisted of relative sparing of sartorius, gracilis, adductor longus and rectus. This pattern was also found in the case linked COL6A1/A2 locus but with normal collagen. This finding, and the striking clinical and magnetic resonance imaging concordance between patients with normal and reduced collagen VI in muscle suggest that collagen VI could still be the culprit in several cases with normal collagen expression, or alternatively a primary defect in a protein that closely interacts with collagen VI. Mutation analysis of the collagen 6 genes in cases with normal collagen VI expression is needed to resolve this issue.

Early and severe presentation of X-linked myotubular myopathy in a girl with skewed X-inactivation

X-linked myotubular myopathy is a severe congenital myopathy in males, caused by mutations in the myotubularin (MTM1) gene on chromosome Xq28. In heterozygous carriers of MTM1 mutations, clinical symptoms are usually absent or only mild. We report a 6-year-old girl presenting at birth with marked hypotonia and associated feeding and respiratory difficulties. A muscle biopsy performed at 5 months suggested a diagnosis of myotubular myopathy. On examination at 6 years she had marked facial weakness with bilateral ptosis and external ophthalmoplegia, severe axial and proximal weakness and a mild scoliosis. Muscle magnetic resonance imaging showed a distinctive pattern of muscle involvement. Molecular genetic investigation of the MTM1 gene identified a heterozygous mutation in exon 12. X-inactivation studies in lymphocytes showed an extremely skewed pattern (97:3). This case emphasizes that investigation of the MTM1 gene and X-inactivation studies are indicated in isolated females with histopathological and clinical findings suggestive of myotubular myopathy.

The spectrum of pathology in central core disease

Central core disease is a congenital myopathy with muscle weakness defined pathologically by the presence of extensive areas in muscle fibres that are devoid of oxidative enzyme activity. The gene responsible has been shown to be the ryanodine receptor 1 on chromosome 19q13 and mutations have now been identified in several patients. Some cases with the morphological defect remain molecularly undefined, particularly those studied before molecular studies were available. We have studied three families with congenital onset, each with a dominantly inherited mutation in a C-terminal exon of the ryanodine receptor 1. They illustrate the spectrum of pathology that can be observed in patients with the myopathic features of central core disease. We show that extensive fibrosis and fat may be present, type 1 fibre uniformity may occur in the absence of cores; cores may be central or peripheral, single or multiple; and that an appearance of multiple focal minicores might cause a diagnostic pathological dilemma. In addition, we show the value of immunocytochemistry in identifying cores, in particular the use of antibodies to desmin and gamma-filamin.

Autosomal recessive inheritance of RYR1 mutations in a congenital myopathy with cores

Central core disease (CCD) is a congenital myopathy due to dominant mutations in the skeletal muscle ryanodine receptor gene (RYR1). The authors report three patients from two consanguineous families with symptoms of a congenital myopathy, cores on muscle biopsy, and confirmed linkage to the RYR1 locus. Molecular genetic studies in one family identified a V4849I homozygous missense mutation in the RYR1 gene. This report suggests a congenital myopathy associated with recessive RYR1 mutations.

Collagen VI involvement in Ullrich syndrome: a clinical, genetic, and immunohistochemical study

BACKGROUND

Ullrich congenital muscular dystrophy (UCMD) is a form of merosin-positive congenital muscular dystrophy characterized by proximal contractures, distal laxity, rigidity of the spine, and respiratory complications. Recently, a deficiency of collagen VI on muscle and skin biopsy together with recessive mutations in the collagen 6A2 gene were reported in three families with UCMD. However, the clinical spectrum, frequency, and level of heterogeneity of this disorder are not known.

SUBJECTS AND METHODS

The authors studied 15 patients (aged 3 to 23.6 years) with a clinical diagnosis of UCMD. Linkage analysis to the three collagen VI genes was performed in all informative families (n = 7), whereas immunohistochemical analysis of collagen VI expression in muscle was performed in the remaining cases.

RESULTS

An immunocytochemical reduction of collagen VI was observed in six patients. Three of the six patients belonged to informative families, and haplotype analysis clearly suggested linkage to the COL6A1/2 locus in two cases and to the COL6A3 loci in the third case. In the remaining nine patients, primary collagen VI involvement was excluded based on either the linkage analysis (four families) or considered unlikely based on normal immunolabeling of collagen VI. Age and presentation at onset, the distribution and severity of weakness and contractures, and the frequency of nonambulant patients were similar in the patients with and without collagen VI involvement. Distal laxity, rigidity of the spine, scoliosis, failure to thrive, and early and severe respiratory impairment were found in all patients by the end of the first decade of life, irrespective of their maximum motor functional ability or their collagen status.

CONCLUSIONS

These results suggest that collagen VI involvement is relatively common in UCMD (40%); however, the role of this molecule was excluded in a number of cases, suggesting genetic heterogeneity of this condition.

The muscle-specific marker desmin is expressed in a proportion of human dermal fibroblasts after their exposure to galectin-1

We have previously shown that galectin-1 is a factor capable of converting mouse dermal fibroblasts to the myogenic lineage [Cell Transplant 2000;9:519]. Here, we report that human dermal fibroblasts are also capable of expressing the myogenic marker, desmin, when grown in muscle-cell-conditioned media. Furthermore, the human foetal skin cells also express this marker when grown in the presence of galectin-1. These results highlight the importance of galectin-1 in the conversion of both human and murine skin cells to a myogenic lineage. Thus galectin-1 could be an important tool for use in autologous cell therapies for the treatment of human muscular dystrophies.

Mutations in the fukutin-related protein gene (FKRP) identify limb girdle muscular dystrophy 2I as a milder allelic variant of congenital muscular dystrophy MDC1C

The limb girdle and congenital muscular dystrophies (LGMD and CMD) are characterized by skeletal muscle weakness and dystrophic muscle changes. The onset of symptoms in CMD is within the first few months of life, whereas in LGMD they can occur in late childhood, adolescence or adult life. We have recently demonstrated that the fukutin-related protein gene (FKRP) is mutated in a severe form of CMD (MDC1C), characterized by the inability to walk, leg muscle hypertrophy and a secondary deficiency of laminin alpha2 and alpha-dystroglycan. Both MDC1C and LGMD2I map to an identical region on chromosome 19q13.3. To investigate whether these are allelic disorders, we undertook mutation analysis of FKRP in 25 potential LGMD2I families, including some with a severe and early onset phenotype. Mutations were identified in individuals from 17 families. A variable reduction of alpha-dystroglycan expression was observed in the skeletal muscle biopsy of all individuals studied. In addition, several cases showed a deficiency of laminin alpha2 either by immunocytochemistry or western blotting. Unexpectedly, affected individuals from 15 families had an identical C826A (Leu276Ileu) mutation, including five that were homozygous for this change. Linkage analysis identified at least two possible haplotypes in linkage disequilibrium with this mutation. Patients with the C826A change had the clinically less severe LGMD2I phenotype, suggesting that this is a less disruptive FKRP mutation than those found in MDC1C. The spectrum of LGMD2I phenotypes ranged from infants with an early presentation and a Duchenne-like disease course including cardiomyopathy, to milder phenotypes compatible with a favourable long-term outcome.

Long mutant dystrophins and variable phenotypes: evasion of nonsense-mediated decay?

More than 98% of Duchenne muscular dystrophy (DMD) mutations result in the premature termination of the dystrophin open reading frame at various points over its 11-kb length. Despite this wide variation in coding potential (0%-98.6% of the full-length protein), the truncating mutations are associated with a surprisingly uniform severity of phenotype. This uniformity is probably attributable to ablation of the message by nonsense-mediated decay (NMD). The rare truncating mutations that occur near the 3' end of the dystrophin gene (beyond exon 70) can however result in extremely variable phenotypes (both intra- and inter-familially). We suggest that all proteins encoded by such mutant genes are capable in principle of rescuing the DMD phenotype but that NMD abrogates the opportunity to effect this rescue. The observed variability may therefore reflect an underlying variation in the efficiency of NMD between individuals. We discuss this hypothesis with particular reference to a well-characterised Becker muscular dystrophy patient with a frameshift mutation, where expression of a truncated dystrophin rescues the muscular but not mental phenotype.

Skeletal muscle pathology in autosomal dominant Emery-Dreifuss muscular dystrophy with lamin A/C mutations

We present our observations on the skeletal muscle pathology of nine cases from seven families of autosomal dominant Emery-Dreifuss muscular dystrophy (ADEDMD) with identified mutations in the lamin A/C gene, aged 2-35 years at the time of biopsy. The severity of pathological change was moderate and the most common features were variation in fibre size (hypertrophy and atrophy), an increase in internal nuclei and smaller diameter fibres with high oxidative enzyme activity. Only one case showed necrosis, which was present in two separate samples taken from the quadriceps and tibialis anterior, at different ages. Immunocytochemistry detected an age-related reduction of laminin beta1 on the muscle fibres in adolescent and adult cases. Antibodies to lamins A and A/C, and emerin did not reveal any detectable differences from controls. Electron microscopy of two out of three cases showed an abnormal distribution of heterochromatin in many fibre nuclei. Our results show that dystrophic changes in skeletal muscle are not a major feature of ADEDMD, and that nuclear abnormalities may be detected with electron microscopy. Immunodetection of reduced laminin beta1 may be a useful secondary marker in adults with this disorder, as immunocytochemistry of lamins is not yet of diagnostic use.

Neonatal arthrogryposis and absent limb muscles: a muscle developmental gene defect?

We describe a child who presented at birth with arthrogryposis. Following a muscle biopsy a diagnosis of congenital muscular dystrophy was made and a skin biopsy 12 years later confirmed the presence of merosin. Her clinical picture was unusual, however, for merosin-positive congenital muscular dystrophy. She had extreme wasting and weakness of her arms and legs. In contrast, she had good neck and trunk control, and no facial or respiratory muscle weakness. We have used magnetic resonance imaging to examine the pattern of muscle involvement in this case. No recognizable muscle could be identified in the limbs. In contrast, the axial muscles were preserved. This striking pattern of virtual absence of muscles in the limbs with sparing of the axial muscle suggests that a gene responsible for the migration and/or proliferation of limb muscle precursor cells may be involved in the disease process. It is recognized that merosin-positive congenital muscular dystrophy is a heterogeneous disease. Magnetic resonance imaging is a useful tool for examining in detail the pattern of muscle involvement and identifying individual phenotypes. Understanding more about which muscles are affected in children with congenital myopathies may provide information on the underlying pathological process and help in the search for candidate proteins and genes.

Absence of utrophin in intercalated discs of human cardiac muscle

Utrophin is the autosomal homologue of dystrophin. In normal skeletal muscle it is localised only to neuromuscular and myotendinous junctions, nerves and vascular tissue. In Xp21 muscular dystrophies, utrophin is also detected on the sarcolemma of skeletal and cardiac muscle, while dystrophin is absent or reduced. In normal cardiac muscle, some reports have demonstrated utrophin at intercalated discs and T-tubules. We have re-examined the distribution of utrophin in normal human cardiac muscle using a panel of eight monoclonal antibodies against different epitopes in N- and C-terminal domains. In contrast to previous studies, utrophin was not detected at the intercalated discs or T-tubules, although labelling of blood vessels was strong. We conclude that the primary location of utrophin in normal heart is in the vascular system. In addition, our results show that the utrophin on cardiac blood vessels is full length, similar to that of skeletal muscle blood vessels.

Abnormalities in the expression of nebulin in chromosome-2 linked nemaline myopathy

Nemaline myopathy is clinically and genetically heterogeneous. The most common autosomal recessive form affecting infants (NEM2) links to chromosome 2q, and is caused by mutations in the gene for nebulin. We have examined the immunocytochemical expression of nebulin in skeletal muscle in 11 cases of nemaline myopathy, from ten families, with linkage compatible to chromosome 2q.22, the locus for nebulin. Mutations in the gene for nebulin have been found in eight of these cases. Immunolabelling with polyclonal antibodies to C-terminal regions of nebulin was compared with antibodies to fibre-type-specific myofibrillar proteins, including myosin heavy chain isoforms and alpha-actinin isoforms. No cases showed a complete absence of C-terminal nebulin, and no enhancement of labelling of the rods was seen with conventional fluorescence microscopy. In control muscle an antibody to the M176-181 repeat region of nebulin showed higher expression in fibres with slow myosin, while ones to the serine-rich domain and to the SH3 domain showed uniform expression. In some cases of nemaline myopathy differences in these patterns were observed. Two siblings with a homozygous mutation in exon 185, that produces a stop codon, showed an absence of labelling only with the SH3 antibody, and other cases showed uneven labelling with this antibody or some fibres devoid of label. Fibre type correlations also showed differences from controls, as some fibres had a fast isoform of one protein but a slow isoform of another. These results indicate that analysis of nebulin expression may detect abnormalities in some cases linked to the corresponding locus and may help to direct molecular analysis. In addition, they may also be relevant to studies of fibre type plasticity and diversity in nemaline myopathy.

Mild phenotype of nemaline myopathy with sleep hypoventilation due to a mutation in the skeletal muscle alpha-actin (ACTA1) gene

Nemaline myopathy is a clinically and genetically heterogeneous condition. The clinical spectrum ranges from severe cases with antenatal or neonatal onset and early death to late onset cases with only slow progression. Three genes are known to cause nemaline myopathy: the genes for nebulin (NEB) on chromosome 2q22, slow alpha-tropomyosin (TPM3) on chromosome 1q21 and skeletal muscle alpha-actin (ACTA1) on chromosome 1q42. We present a 39-year-old lady with a mild form of nemaline myopathy, whom we have followed over a period of 25 years. She presented at the age of 7 years with symptoms of mild axial and proximal muscle weakness. The overall course was essentially static, but at 36 years, she went into life-threatening respiratory failure, for which she is currently treated with night-time ventilation. Muscle biopsies at 12, 17 and 39 years of age showed typical nemaline rods, particularly in type 1 fibres. Areas with unevenness of oxidative stain were present in the second and third biopsies. The presence of rods and core-like areas was confirmed on electron microscopy. There was no detectable alteration in actin expression immunocytochemically. A dominant missense mutation in the skeletal muscle alpha-actin gene (ACTA1) was found. This case illustrates the clinical and genetic heterogeneity of nemaline myopathy, and one phenotype of the wide spectrum of severity caused by mutations in the skeletal muscle alpha-actin (ACTA1) gene. In addition, it shows the diversity of pathological features that can occur in congenital myopathies due to mutations in the same gene.

Congenital muscular dystrophy with secondary merosin deficiency and normal brain MRI: a novel entity?

We describe two Scottish siblings affected by a form of congenital muscular dystrophy characterised by a severe clinical phenotype, similar to that observed in the 6q-linked merosin-deficient CMD but in whom brain MRI and cognitive development were normal. The maximal function achieved in the 2 siblings was sitting independently. Serum CK were grossly elevated and the skin and muscle biopsies showed a severe reduction of merosin in both. The normal brain MRI and normal cognitive development distinguish this form from Fukuyama congenital muscular dystrophy, muscle-eye-brain disease or other forms of CMD with secondary partial merosin deficiency and abnormal brain MRI and/or mental retardation. Linkage analysis excluded all the known loci for CMD. We propose that this may represent a novel variant of CMD.

High resolution magnetic resonance imaging of the brain in the dy/dy mouse with merosin-deficient congenital muscular dystrophy

Magnetic resonance imaging (MRI) abnormalities in the cerebral white matter are a consistent feature of merosin-deficient human congenital muscular dystrophy, a disease caused by a primary defect in the expression of the laminin alpha2 chain of merosin. To investigate the relationship between imaging changes and merosin deficiency we undertook a MRI study in the dy/dy mouse, an animal model for this form of human congenital muscular dystrophy. High resolution in vivo imaging was performed on anaesthetized animals (two homozygous dy/dy mutants and two heterozygous dy/DY controls, aged 2.5 months) in a dedicated 11.7T magnetic resonance imaging scanner. T(1) and T(2) weighted images were normal in all mice and white matter changes were not seen at a stage of maturity when MRI changes are already very striking in human patients. Cerebral MRI abnormalities do not appear to be a feature of dy/dy mice, despite the virtual absence of merosin expression in the dy/dy mouse brain. Possible causes for this absence of MRI changes, and implications for the pathogenesis of the MRI changes in humans are reviewed.

Maternal contamination at fetal muscle biopsy

Duchenne muscular dystrophy (DMD) can be diagnosed by fetal muscle biopsy and immunohistochemical staining showing the absence of dystrophin. We report a case of fetal muscle biopsy in which the needle gun was successfully fired within the fetal gluteal muscle but the sample was contaminated by maternal tissue. This was attributed to the design of the biopsy needle, allowing transient opening of the biopsy core as the needle penetrated the maternal rectus sheath, muscle, and myometrium. Histology showed tissue suggestive of maternal origin, confirmed by DNA analysis. Repeat sampling revealed fetal muscle with normal dystrophin expression. We recommend that care be taken during needle insertion to avoid maternal contamination, and tests be used to confirm the fetal source of the sample.

Immunocytochemical analysis of human muscular dystrophy

Immunocytochemistry is an essential tool for the assessment of muscle biopsies from patients with muscular dystrophy, especially the recessive forms. Antibodies can detect primary defects when there is an alteration in expression, in particular in Xp21 muscular dystrophies, Emery-Dreifuss muscular dystrophy, the limb-girdle dystrophies caused by abnormal expression of the sarcoglycans, and in the form of congenital muscular dystrophy linked to the gene for laminin alpha2. Absence of a protein is easily observed and reduction in expression can be assessed provided adequate controls and baselines are established. Assessment of secondary defects can also be of diagnostic value; they widen the understanding of pathology changes, and are helping in the development of therapeutic strategies.

An unusual case of hyperekplexia

Hyperekplexia is a rare paroxysmal disorder characterized by exaggerated startle response, hypertonia during infancy and a transient increase in tone following startle attacks. We report an unusual case of hyperekplexia in a young man. In addition to common symptoms of the condition, we found generalized spasticity persisting beyond infancy, and facial and skeletal dysmorphism. Because of an unsteady gait with frequent falls and raised serum creatine kinase levels, a congenital myopathy had been suspected in the past and an abnormal muscle biopsy had been documented. We diagnosed hyperekplexia at the age of 21 years on clinical grounds and following the response to pharmacological treatment. A mutation in the alpha1 subunit of the glycine receptor confirmed the diagnosis. A repeated needle muscle biopsy demonstrated mild myopathic changes, which we considered to be secondary to increased muscle tone. This case highlights the diagnostic difficulties of hyperekplexia, particularly in sporadic cases with unusual presentation.

Brain magnetic resonance imaging abnormalities in merosin-positive congenital muscular dystrophy

We report the brain magnetic resonance imaging (MRI) findings in 23 patients with merosin-positive congenital muscular dystrophy (CMD). Twelve patients had normal scans. Eight other children had essentially normal scans but showed mild non-specific periventricular white matter changes. Three children had structural abnormalities on imaging. The first patient, a 15-month-old boy with hypotonia, muscle weakness and global development delay, had moderate cerebellar atrophy and mild dilatation of the lateral ventricles. The second child, a 3-year-old ambulant girl with subtle learning problems, had mild cerebellar hypoplasia and a large subarachnoid space when scanned at 16 months. The third patient, a 15-year-old ambulant male with normal intelligence and complex partial seizures, had polymicrogyria of both temporoparietal lobes on brain MRI. The clinical features and motor ability of children with merosin-positive CMD are variable, although usually milder than merosin-deficient CMD. Our findings confirm that central nervous system involvement can occur in some merosin-positive cases. We suggest performing brain MRI in children with merosin-positive CMD, as this may help in our understanding of this very heterogeneous disease.

Mutations in the laminin alpha2-chain gene in two children with early-onset muscular dystrophy

We investigated two children who presented with delayed motor milestones. The first was a girl who was referred at 20 months because of developmental delay. She walked at 28 months and currently, aged 5 years, is independently mobile but has difficulty rising from the floor or going upstairs. The second was also a girl who presented at 6 weeks of age with hypotonia. Her motor milestones were delayed and she walked at the age of 2 years and 8 months and is currently independently mobile at the age of 3 years. Serum creatine kinase was elevated and a muscle biopsy showed dystrophic changes in both children. Immunohistochemistry of the laminin alpha2 chain of merosin was very similar in both cases: using a C-terminal antibody that recognizes an 80 kDa fragment, there was a mild reduction in expression on most fibres, while the staining with another antibody that recognizes a 300 kDa fragment showed a very marked reduction. Mutational analysis of the laminin alpha2 chain gene in the first patient showed that one of the two alleles had a de novo single nucleotide deletion at position 5702, causing a frameshift. In the other allele, we identified two point mutations present in cis; one was a G-->C transition at position +5 while the second was a T-->C transition at position +6 of the conserved donor splicing consensus sequence of introns 37 and 63, respectively. Transcription analysis of the corresponding cDNA region did not show any alternative splicing occurring as a result of these splice site mutations. Therefore, these mutations probably affect the splicing efficiency. Interestingly, the second child carried in both alleles the same two splicing consensus sequence mutations found in cis in the first patient. Our data provide further evidence that mutations in the laminin alpha2 chain gene are responsible not only for the severe form of congenital muscular dystrophy with onset at birth, but also for milder phenotypes, with later onset, in which the synthesis of a partially functional protein, or of a normal protein but in reduced quantity, is possible. The finding that these two unrelated patients had the same unusual mutation in common might suggest that this is a relatively commonly allele responsible for partial merosin deficiency in the UK.