Facioscapulohumeral muscular dystrophy: muscle fiber type analysis with particular reference to small angular fibers

An up-to-date myopathologic characterisation of facioscapulohumeral muscular dystrophy type 1 muscle biopsies shows sarcolemmal complement membrane attack complex deposits and increased skeletal muscle regeneration

The aim of this study was to identify key routinely used myopathologic biomarkers of FSHD1. Needle muscle biopsies were taken in 34 affected muscles (m. quadriceps femoris (QF), n = 20, m. tibialis anterior (TA), n = 13, m. biceps brachii, n = 1) from 22 patients (age, 53.5 (10) years; M = 12, F = 10). Eleven patients had more than one biopsy (2xQF, n = 1; QF+TA, n = 9; 2xQF+TA, n = 1). Histochemistry, immunoperoxidase, and immunofluorescence stainings were performed and compared to age and muscle type matched muscle specimens of 11 healthy controls. Myopathologic features observed in our FSHD1 cohort were internalized nuclei, type 1 fibre hypertrophy and NADH central clearances/cores. We observed a prominent inflammatory response with MAC deposits, MHC I expression, and muscle regeneration that correlated with the inflammatory score. Our up-to-date characterization of FSHD1 points towards MHC I, MAC, and embryonic Myosin Heavy Chain/muscle regeneration as useful myopathologic readouts of FSHD1.

The double homeodomain protein DUX4c is associated with regenerating muscle fibers and RNA-binding proteins

BACKGROUND

 We have previously demonstrated that double homeobox 4 centromeric (DUX4C) encoded for a functional DUX4c protein upregulated in dystrophic skeletal muscles. Based on gain- and loss-of-function studies we have proposed DUX4c involvement in muscle regeneration. Here, we provide further evidence for such a role in skeletal muscles from patients affected with facioscapulohumeral muscular dystrophy (FSHD).

METHODS

DUX4c was studied at RNA and protein levels in FSHD muscle cell cultures and biopsies. Its protein partners were co-purified and identified by mass spectrometry. Endogenous DUX4c was detected in FSHD muscle sections with either its partners or regeneration markers using co-immunofluorescence or in situ proximity ligation assay.

RESULTS

We identified new alternatively spliced DUX4C transcripts and confirmed DUX4c immunodetection in rare FSHD muscle cells in primary culture. DUX4c was detected in nuclei, cytoplasm or at cell-cell contacts between myocytes and interacted sporadically with specific RNA-binding proteins involved, a.o., in muscle differentiation, repair, and mass maintenance. In FSHD muscle sections, DUX4c was found in fibers with unusual shape or central/delocalized nuclei (a regeneration feature) staining for developmental myosin heavy chain, MYOD or presenting intense desmin labeling. Some couples of myocytes/fibers locally exhibited peripheral DUX4c-positive areas that were very close to each other, but in distinct cells. MYOD or intense desmin staining at these locations suggested an imminent muscle cell fusion. We further demonstrated DUX4c interaction with its major protein partner, C1qBP, inside myocytes/myofibers that presented features of regeneration. On adjacent muscle sections, we could unexpectedly detect DUX4 (the FSHD causal protein) and its interaction with C1qBP in fusing myocytes/fibers.

CONCLUSIONS

DUX4c upregulation in FSHD muscles suggests it contributes not only to the pathology but also, based on its protein partners and specific markers, to attempts at muscle regeneration. The presence of both DUX4 and DUX4c in regenerating FSHD muscle cells suggests DUX4 could compete with normal DUX4c functions, thus explaining why skeletal muscle is particularly sensitive to DUX4 toxicity. Caution should be exerted with therapeutic agents aiming for DUX4 suppression because they might also repress the highly similar DUX4c and interfere with its physiological role.

Persistent Fibroadipogenic Progenitor Expansion Following Transient DUX4 Expression Provokes a Profibrotic State in a Mouse Model for FSHD

FSHD is caused by loss of silencing of the DUX4 gene, but the DUX4 protein has not yet been directly detected immunohistologically in affected muscle, raising the possibility that DUX4 expression may occur at time points prior to obtaining adult biopsies for analysis, with consequent perturbations of muscle being responsible for disease progression. To test the extent to which muscle can regenerate following DUX4-mediated degeneration, we employed an animal model with reversible DUX4 expression, the iDUX4pA;HSA mouse. We find that muscle histology does recover substantially after DUX4 expression is switched off, with the extent of recovery correlating inversely with the duration of prior DUX4 expression. However, despite fairly normal muscle histology, and recovery of most cytological parameters, the fibroadipogenic progenitor compartment, which is significantly elevated during bouts of fiber-specific DUX4 expression, does not return to basal levels, even many weeks after a single burst of DUX4 expression. We find that muscle that has recovered from a DUX4 burst acquires a propensity for severe fibrosis, which can be revealed by subsequent cardiotoxin injuries. These results suggest that a past history of DUX4 expression leads to maintained pro-fibrotic alterations in the cellular physiology of muscle, with potential implications for therapeutic approaches.

Facioscapulohumeral dystrophy weakened sarcomeric contractility is mimicked in induced pluripotent stem cells-derived innervated muscle fibres

BACKGROUND

Facioscapulohumeral dystrophy (FSHD) is a late-onset autosomal dominant form of muscular dystrophy involving specific groups of muscles with variable weakness that precedes inflammatory response, fat infiltration, and muscle atrophy. As there is currently no cure for this disease, understanding and modelling the typical muscle weakness in FSHD remains a major milestone towards deciphering the disease pathogenesis as it will pave the way to therapeutic strategies aimed at correcting the functional muscular defect in patients.

METHODS

To gain further insights into the specificity of the muscle alteration in this disease, we derived induced pluripotent stem cells from patients affected with Types 1 and 2 FSHD but also from patients affected with Bosma arhinia and microphthalmia. We differentiated these cells into contractile innervated muscle fibres and analysed their transcriptome by RNA Seq in comparison with cells derived from healthy donors. To uncover biological pathways altered in the disease, we applied MOGAMUN, a multi-objective genetic algorithm that integrates multiplex complex networks of biological interactions (protein-protein interactions, co-expression, and biological pathways) and RNA Seq expression data to identify active modules.

RESULTS

We identified 132 differentially expressed genes that are specific to FSHD cells (false discovery rate < 0.05). In FSHD, the vast majority of active modules retrieved with MOGAMUN converges towards a decreased expression of genes encoding proteins involved in sarcomere organization (P value 2.63e^-12 ), actin cytoskeleton (P value 9.4e^-5 ), myofibril (P value 2.19e^-12 ), actin-myosin sliding, and calcium handling (with P values ranging from 7.9e^-35 to 7.9e^-21 ). Combined with in vivo validations and functional investigations, our data emphasize a reduction in fibre contraction (P value < 0.0001) indicating that the muscle weakness that is typical of FSHD clinical spectrum might be associated with dysfunction of calcium release (P value < 0.0001), actin-myosin interactions, motor activity, mechano-transduction, and dysfunctional sarcomere contractility.

CONCLUSIONS

Identification of biomarkers of FSHD muscle remain critical for understanding the process leading to the pathology but also for the definition of readouts to be used for drug design, outcome measures, and monitoring of therapies. The different pathways identified through a system biology approach have been largely overlooked in the disease. Overall, our work opens new perspectives in the definition of biomarkers able to define the muscle alteration but also in the development of novel strategies to improve muscle function as it provides functional parameters for active molecule screening.

Improving molecular and histopathology in diaphragm muscle of the double transgenic ACTA1-MCM/FLExDUX4 mouse model of FSHD with systemic antisense therapy

Facioscapulohumeral muscular dystrophy (FSHD) is a rare muscle dystrophy causing muscle weakness initially in the face, shoulders and upper arms, and extended to lower body muscles as the disease progresses. Respiratory restriction in FSHD is increasingly reported to be more common and severe than previously thought, with the involvement of diaphragm weakness in pulmonary insufficiency being under debate. As aberrant expression of the double homeobox 4 (DUX4) gene is the prime cause of FSHD, we and others have developed numerous strategies and reported promising results on downregulating DUX4 expression in both cellular and animal models of FSHD. However, the effect of DUX4 and anti-DUX4 approaches on diaphragm muscle has not been elucidated. Here we show that toxic DUX4 expression causes pathology that affects the diaphragm of ACTA1-MCM/FLExDUX4 mouse model of FSHD at both molecular and histological levels. Of importance, a systemic antisense treatment that suppresses DUX4 and target genes expression by 50% significantly improves muscle regeneration and muscle fibrosis, and prevents modification in myofiber type composition, supporting its development as a treatment for FSHD.

A pediatric case report and literature review of facioscapulohumeral muscular dystrophy type1

RATIONALE

Early-onset facioscapulohumeral muscular dystrophy (FSHD) is defined as facial weakness before the age of 5 and shoulder weakness before the age of 10. Early-onset facioscapulohumeral muscular dystrophy is relatively rare in the clinic. This onset is relatively early, the symptoms are serious, and it is likely to be accompanied by retinal vascular disease, sensorineural deafness, epilepsy and other extramuscular multisystem diseases. We report the clinical characteristics of 2 patients with early-onset facial and shoulder brachial muscular dystrophy to improve clinicians' understanding of this particular condition.

PATIENT CONCERNS

We report 2 pediatric patients with FSHD type 1. Patient 1 is an 11-year-old boy with reduced facial expression for 9 years and proximal muscle weakness for 6 years. Patient 2 is a 4-year and 6-month-old girl with developmental delay for 3 years and facial weakness for 1 year.

DIAGNOSIS

According to the clinical manifestations and molecular genetic testing (such as Southern blot analysis), the patients were diagnosed with early-onset FSHD1.

INTERVENTIONS

The patients received cocktail therapy (vitamin B1 tablets, vitamin B2 tablets, vitamin B6 tablets, vitamin C tablets, vitamin E tablets, idebenone tablets, etc.) to improve their muscle metabolism.

OUTCOMES

Both patients' condition did not improve after being given cocktail treatment. According to a recent follow-up, the symptoms of facial weakness and proximal muscle weakness were aggravated.

LESSONS

Early-onset FSHD presents early and has frequent systemic features, and it is a severe subtype of FSHD. Early identification and genetic diagnosis should be performed to improve patient prognosis.

Pathomechanisms and biomarkers in facioscapulohumeral muscular dystrophy: roles of DUX4 and PAX7

Facioscapulohumeral muscular dystrophy (FSHD) is characterised by progressive skeletal muscle weakness and wasting. FSHD is linked to epigenetic derepression of the subtelomeric D4Z4 macrosatellite at chromosome 4q35. Epigenetic derepression permits the distal-most D4Z4 unit to transcribe DUX4, with transcripts stabilised by splicing to a poly(A) signal on permissive 4qA haplotypes. The pioneer transcription factor DUX4 activates target genes that are proposed to drive FSHD pathology. While this toxic gain-of-function model is a satisfying "bottom-up" genotype-to-phenotype link, DUX4 is rarely detectable in muscle and DUX4 target gene expression is inconsistent in patients. A reliable biomarker for FSHD is suppression of a target gene score of PAX7, a master regulator of myogenesis. However, it is unclear how this "top-down" finding links to genomic changes that characterise FSHD and to DUX4. Here, we explore the roles and interactions of DUX4 and PAX7 in FSHD pathology and how the relationship between these two transcription factors deepens understanding via the immune system and muscle regeneration. Considering how FSHD pathomechanisms are represented by "DUX4opathy" models has implications for developing therapies and current clinical trials.

Reduced specific force in patients with mild and severe facioscapulohumeral muscular dystrophy

BACKGROUND

Specific force, that is the amount of force generated per unit of muscle tissue, is reduced in patients with facioscapulohumeral muscular dystrophy (FSHD). The causes of reduced specific force and its relation with FSHD disease severity are unknown.

METHODS

Quantitative muscle magnetic resonance imaging (MRI), measurement of voluntary maximum force generation and quadriceps force-frequency relationship, and vastus lateralis muscle biopsies were performed in 12 genetically confirmed patients with FSHD and 12 controls.

RESULTS

Specific force was reduced by ~33% in all FSHD patients independent of disease severity. Quadriceps force-frequency relationship shifted to the right in severe FSHD compared to controls. Fiber type distribution in vastus lateralis muscle biopsies did not differ between groups.

CONCLUSIONS

Reduced quadriceps specific force is present in all FSHD patients regardless of disease severity or fatty infiltration. Early myopathic changes, including fibrosis, and non-muscle factors, such as physical fatigue and musculoskeletal pain, may contribute to reduced specific force.

Skeletal muscle regeneration in facioscapulohumeral muscular dystrophy is correlated with pathological severity

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant myopathy characterized by slowly progressive skeletal muscle weakness and wasting. While a regenerative response is often provoked in many muscular dystrophies, little is known about whether a regenerative response is regularly elicited in FSHD muscle, prompting this study. For comparison, we also examined the similarly slowly progressing myotonic dystrophy type 2 (DM2). To first investigate regeneration at the transcriptomic level, we used the 200 human gene Hallmark Myogenesis list. This myogenesis biomarker was elevated in FSHD and control healthy myotubes compared to their myoblast counterparts, so is higher in myogenic differentiation. The myogenesis biomarker was also elevated in muscle biopsies from most independent FSHD, DM2 or Duchenne muscular dystrophy (DMD) studies compared to control biopsies, and on meta-analysis for each condition. In addition, the myogenesis biomarker was a robust binary discriminator of FSHD, DM2 and DMD from controls. We also analysed muscle regeneration at the protein level by immunolabelling muscle biopsies for developmental myosin heavy chain. Such immunolabelling revealed one or more regenerating myofibres in 76% of FSHD muscle biopsies from quadriceps and 91% from tibialis anterior. The mean proportion of regenerating myofibres per quadriceps biopsy was 0.48%, significantly less than 1.72% in the tibialis anterior. All DM2 muscle biopsies contained regenerating myofibres, with a mean of 1.24% per biopsy. Muscle regeneration in FSHD was correlated with the pathological hallmarks of fibre size variation, central nucleation, fibrosis and necrosis/regeneration/inflammation. In summary, the regenerative response in FSHD muscle biopsies correlates with the severity of pathology.

Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral Muscular Dystrophy is a common form of muscular dystrophy that presents clinically with progressive weakness of the facial, scapular, and humeral muscles, with later involvement of the trunk and lower extremities. While typically inherited as autosomal dominant, facioscapulohumeral muscular dystrophy (FSHD) has a complex genetic and epigenetic etiology that has only recently been well described. The most prevalent form of the disease, FSHD1, is associated with the contraction of the D4Z4 microsatellite repeat array located on a permissive 4qA chromosome. D4Z4 contraction allows epigenetic derepression of the array, and possibly the surrounding 4q35 region, allowing misexpression of the toxic DUX4 transcription factor encoded within the terminal D4Z4 repeat in skeletal muscles. The less common form of the disease, FSHD2, results from haploinsufficiency of the SMCHD1 gene in individuals carrying a permissive 4qA allele, also leading to the derepression of DUX4, further supporting a central role for DUX4. How DUX4 misexpression contributes to FSHD muscle pathology is a major focus of current investigation. Misexpression of other genes at the 4q35 locus, including FRG1 and FAT1, and unlinked genes, such as SMCHD1, has also been implicated as disease modifiers, leading to several competing disease models. In this review, we describe recent advances in understanding the pathophysiology of FSHD, including the application of MRI as a research and diagnostic tool, the genetic and epigenetic disruptions associated with the disease, and the molecular basis of FSHD. We discuss how these advances are leading to the emergence of new approaches to enable development of FSHD therapeutics. © 2017 American Physiological Society. Compr Physiol 7:1229-1279, 2017.

Whole-body magnetic resonance imaging evaluation of facioscapulohumeral muscular dystrophy

INTRODUCTION

Facioscapulohumeral muscular dystrophy (FSHD) is a hereditary disorder that causes progressive muscle wasting. Increasing knowledge of the pathophysiology of FSHD has stimulated interest in developing biomarkers of disease severity.

METHODS

Two groups of MRI scans were analyzed: whole-body scans from 13 subjects with FSHD; and upper and lower extremity scans from 34 subjects with FSHD who participated in the MYO-029 clinical trial. Muscles were scored for fat infiltration and edema-like changes. Fat infiltration scores were compared with muscle strength and function.

RESULTS

The analysis revealed a distinctive pattern of both frequent muscle involvement and frequent sparing in FSHD. Averaged fat infiltration scores for muscle groups in the legs correlated with quantitative muscle strength and 10-meter walk times.

CONCLUSIONS

Advances in MRI technology allow for acquisition of rapid, high-quality, whole-body imaging in diffuse muscle disease. This technique offers a promising disease biomarker in FSHD and other muscle diseases.

Dominant lethal pathologies in male mice engineered to contain an X-linked DUX4 transgene

Facioscapulohumeral muscular dystrophy (FSHD) is an enigmatic disease associated with epigenetic alterations in the subtelomeric heterochromatin of the D4Z4 macrosatellite repeat. Each repeat unit encodes DUX4, a gene that is normally silent in most tissues. Besides muscular loss, most patients suffer retinal vascular telangiectasias. To generate an animal model, we introduced a doxycycline-inducible transgene encoding DUX4 and 3' genomic DNA into a euchromatic region of the mouse X chromosome. Without induction, DUX4 RNA was expressed at low levels in many tissues and animals displayed a variety of unexpected dominant leaky phenotypes, including male-specific lethality. Remarkably, rare live-born males expressed DUX4 RNA in the retina and presented a retinal vascular telangiectasia. By using doxycycline to induce DUX4 expression in satellite cells, we observed impaired myogenesis in vitro and in vivo. This mouse model, which shows pathologies due to FSHD-related D4Z4 sequences, is likely to be useful for testing anti-DUX4 therapies in FSHD.

Facioscapulohumeral Muscular Dystrophy: More Complex than it Appears

Facioscapulohumeral muscular dystrophy (FSHD) has been classified as an autosomal dominant myopathy, linked to rearrangements in an array of 3.3 kb tandemly repeated DNA elements (D4Z4) located at the 4q subtelomere (4q35). For the last 20 years, the diagnosis of FSHD has been confirmed in clinical practice by the detection of one D4Z4 allele with a reduced number (≤8) of repeats at 4q35. Although wide inter- and intra-familial clinical variability was found in subjects carrying D4Z4 alleles of reduced size, this DNA testing has been considered highly sensitive and specific. However, several exceptions to this general rule have been reported. Specifically, FSHD families with asymptomatic relatives carrying D4Z4 reduced alleles, FSHD genealogies with subjects affected with other neuromuscular disorders and FSHD affected patients carrying D4Z4 alleles of normal size have been described. In order to explain these findings, it has been proposed that the reduction of D4Z4 repeats at 4q35 could be pathogenic only in certain chromosomal backgrounds, defined as "permissive" specific haplotypes. However, our most recent studies show that the current DNA signature of FSHD is a common polymorphism and that in FSHD families the risk of developing FSHD for carriers of D4Z4 reduced alleles (DRA) depends on additional factors besides the 4q35 locus. These findings highlight the necessity to re-evaluate the significance and the predictive value of DRA, not only for research but also in clinical practice. Further clinical and genetic analysis of FSHD families will be extremely important for studies aiming at dissecting the complexity of FSHD.

Morpholino treatment improves muscle function and pathology of Pitx1 transgenic mice

Paired-like homeodomain transcription factor 1 (PITX1) was proposed to be part of the disease mechanisms of facioscapulohumeral muscular dystrophy (FSHD). We generated a tet-repressible muscle-specific Pitx1 transgenic mouse model which develops phenotypes of muscular dystrophy after the PITX1 expression is induced. In this study, we attempted to block the translation of PITX1 protein using morpholinos. Three groups of the transgenic mice received intravenous injections of phosphorodiamidate morpholino oligomers (PMO) (100 mg/kg), octaguanidinium dendrimer-conjugated morpholino (vivo-morpholino) (10 mg/kg), or phosphate-buffered saline (PBS) after the PITX1 expression was induced. Immunoblotting data showed that PITX1 expression in the triceps and quadriceps was significantly reduced 70% and 63% by the vivo-morpholino treatment, respectively. Muscle pathology of the mice treated with the vivo-morpholino was improved by showing 44% fewer angular-shaped atrophic myofibers. Muscle function determined by grip strength was significantly improved by the vivo-morpholino treatment. The study showed that systemic delivery of the vivo-morpholino reduced the PITX1 expression and improved the muscle phenotypes. Aberrant expression of DUX4 from the last unit of the D4Z4 array has been proposed to be the cause of FSHD. The findings of this study suggest that the same principle may be applied to suppress the aberrantly expressed DUX4 in FSHD.

Muscle regeneration and inflammation in patients with facioscapulohumeral muscular dystrophy

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate whether inflammation and regeneration are prominent in mildly affected muscles of patients with facioscapulohumeral muscular dystrophy type 1A (FSHD1A). Inflammation in muscle has been suggested by MRI studies in patients with FSHD1A.

METHODS

We analysed immunohistological and histological stains of muscle biopsies from 24 patients with FSHD1A, using 10 patients with Becker muscular dystrophy (BMD) for comparison.

RESULTS

Internalized nuclei were more prevalent in BMD (23.7 ± 10.8%) vs FSHD1A (6.3 ± 6.8%; P < 0.001), indicating more past regenerating fibres in BMD. Recently regenerating fibres, expressing neonatal myosin heavy chain and vimentin, did not differ significantly between patients with FSHD1A (1.1 ± 2.9%) and patients with BMD (1.8 ± 1.9%). Regeneration was not correlated with the number of KpnI restriction fragment repeats, an FSHD1A-defining genotype property within the D4Z4 locus, or overall disease severity in patients with FSHD1A. Macrophages were more prevalent in FSHD1A (0.50 ± 0.63 per mm(2) ) vs BMD (0.07 ± 0.07 per mm(2) ), whereas inflammatory T cells were equally infrequent.

CONCLUSIONS

Macrophages were more prevalent in patients with FSHD1A and could be an important pathogenic mechanism for the initiation of the dystrophic process. Furthermore, regeneration was unrelated to genotype and disease severity in FSHD1A.

Conditional over-expression of PITX1 causes skeletal muscle dystrophy in mice

Paired-like homeodomain transcription factor 1 (PITX1) was specifically up-regulated in patients with facioscapulohumeral muscular dystrophy (FSHD) by comparing the genome-wide mRNA expression profiles of 12 neuromuscular disorders. In addition, it is the only known direct transcriptional target of the double homeobox protein 4 (DUX4) of which aberrant expression has been shown to be the cause of FSHD. To test the hypothesis that up-regulation of PITX1 contributes to the skeletal muscle atrophy seen in patients with FSHD, we generated a tet-repressible muscle-specific Pitx1 transgenic mouse model in which expression of PITX1 in skeletal muscle can be controlled by oral administration of doxycycline. After PITX1 was over-expressed in the skeletal muscle for 5 weeks, the mice exhibited significant loss of body weight and muscle mass, decreased muscle strength, and reduction of muscle fiber diameters. Among the muscles examined, the tibialis anterior, gastrocnemius, quadricep, bicep, tricep and deltoid showed significant reduction of muscle mass, while the soleus, masseter and diaphragm muscles were not affected. The most prominent pathological change was the development of atrophic muscle fibers with mild necrosis and inflammatory infiltration. The affected myofibers stained heavily with NADH-TR with the strongest staining in angular-shaped atrophic fibers. Some of the atrophic fibers were also positive for embryonic myosin heavy chain using immunohistochemistry. Immunoblotting showed that the p53 was up-regulated in the muscles over-expressing PITX1. The results suggest that the up-regulation of PITX1 followed by activation of p53-dependent pathways may play a major role in the muscle atrophy developed in the mouse model.

Asymptomatic elevation of serum creatine kinase leading to the diagnosis of 4q35 facioscapulohumeral muscular dystrophy

Persistent, asymptomatic (hyperCKemia) may be the prelude to, or the sole manifestation of, a neuromuscular disease. However, the clinical spectrum of facioscapulohumeral muscular dystrophy (FSHD) ranges from asymptomatic individuals with minimal clinical signs to patients who are wheelchair-bound. We describe a patient with persistent, asymptomatic hyperCKemia who received the diagnosis of 4q35 FSHD after a thorough stepwise investigation.

Evaluation of morphological and functional regeneration of rat nerve-muscle units after temporary and permanent tubulization

We compared the ability of temporary and permanent tubing to achieve morphological and functional recovery of nerve-muscle units, following experimental nerve transection (8-mm gap) in rat tibial nerve. Electrical stimulation of the sciatic nerve was used to analyze tension output, evoked electromyogram and conduction-transmission time (CTT) of denervated nerve-muscle units. Morphological analysis of the nerve and muscle was also performed. Within 6 weeks, the nerve gap had been bridged by a thin nerve trunk, and a few myelinated fibers were observed, although there was still no functional recovery. The rats were divided into two groups: permanent tubing (PT) and temporary tubing (TT; tubing subsequently removed). At 10 weeks after the operation, the TT group showed apparently greater thickness of regenerated nerve trunks, significantly higher tension output of plantar flexors, shorter CTT, and heavier muscle mass. These results were consistent with the presence of myelinated fibers in the regenerated nerve trunks, as shown histologically. Thus, removal of the silicone chamber results in faster and better recovery than tubing left permanently in place.

Limited myogenic response to a single bout of weight-lifting exercise in old rats

The purpose of the present study was to compare the myogenic response of hindlimb muscles in young (14-20 wk of age) and old (>120 wk of age) rats with a single exhaustive bout of heavy resistance weight lifting. [(3)H]thymidine and [(14)C]leucine labeling were monitored for up to 2 wk after the exercise bout to estimate serial changes in mitotic activity and the level of amino acid uptake and myosin synthesis. Histological, histochemical, and immunohistochemical [anti-5-bromo-2'-deoxyuridine and myogenic determination genes (MyoD)] analyses of whole muscles and analysis of muscle-specific gene expression (MyoD) using Western blotting and RT-PCR were performed. Old rats showed significant muscle atrophy and a lower exercise capacity than young rats. Exercise-induced muscle damage, as assessed in histological sections, and increases in serum creatine kinase activity were evident in both young and old exercised groups. Mitotic activity was increased in young, but not old, rats 2 days after exercise. There was a biphasic increase in [(14)C]leucine uptake during the 14 days postexercise (peaks at 1-4 and 10 days) in young rats: only the first peak was observed in old rats. There was a lower uptake of [(14)C]leucine in the myosin fraction and an impaired expression of MyoD at the protein (immunohistochemistry and Western blotting) and mRNA (RT-PCR) levels in old rats throughout the postexercise period. These results demonstrate a reduced reparative capability of muscle in response to a single bout of exercise in old compared with young rats.

Early-onset facioscapulohumeral muscular dystrophy: two case reports

This report concerns two patients with facioscapulohumeral muscular dystrophy (FSHD) whose facial weakness began in infancy. In both patients, biopsied muscle histology showed mild myogenic changes accompanied by some regenerating and some small angular fibers, while endomysial inflammatory cellular infiltration was observed in Patient 1. The finding that our very young patients had muscle histopathological findings compatible with classical FSHD supports the previously expressed view that muscle histopathology is not related to either age or duration of the disease. Although Patient 2 was a sporadic case, both patients had the abnormal EcoRI DNA fragment detected by Southern blot analysis with probes p13E-11 and pFR-1, a finding compatible with FSHD. This indicates that gene analysis of sporadic cases must be as significant as that of familial cases. This report on patients with very early-onset and with common muscle histopathological and molecular genetic findings should contribute to widening the clinical spectrum of FSHD.

Familial facioscapulohumeral muscular dystrophy: phenotypic diversity and genetic abnormality

We report two cases showing facioscapulohumeral muscular dystrophy (FSHD) with phenotypic diversity but the same genetic abnormality detected by a p13E-11 probe. The proband, a 26-year-old woman, showed an early onset, tortuosity of retinal arterioles and respiratory failure. The 53-year-old mother of the proband had limb-girdle (L-G) type muscular weakness with very mild facial involvement. Muscle biopsy showed perivascular cell infiltration in both patients. These cases suggest that the phenotypic diversity ranges from L-G type weakness to severe respiratory failure in FSHD family.

Monomelic muscle atrophy

Two patients with slowly progressive muscle atrophy limited to only one leg are reported. They had pes equinovarus deformity and muscle weakness in the affected leg but no symptom in the other limbs. Muscle biopsies from the affected leg showed dystrophic changes consisting of variation in muscle fiber size, endomysial fibrosis, and necrotic and regenerating fibers. Dystrophin was normally expressed at the surface membrane of the muscle fibers. These two patients possibly had a variant of distal muscular dystrophy, though a neural influence could not be completely excluded.