Severe phenotype in infantile facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy: the road to targeted therapies

Advances in the molecular understanding of facioscapulohumeral muscular dystrophy (FSHD) have revealed that FSHD results from epigenetic de-repression of the DUX4 gene in skeletal muscle, which encodes a transcription factor that is active in early embryonic development but is normally silenced in almost all somatic tissues. These advances also led to the identification of targets for disease-altering therapies for FSHD, as well as an improved understanding of the molecular mechanism of the disease and factors that influence its progression. Together, these developments led the FSHD research community to shift its focus towards the development of disease-modifying treatments for FSHD. This Review presents advances in the molecular and clinical understanding of FSHD, discusses the potential targeted therapies that are currently being explored, some of which are already in clinical trials, and describes progress in the development of FSHD-specific outcome measures and assessment tools for use in future clinical trials.

Correlation between whole body muscle MRI and functional measures in paediatric patients with facioscapulohumeral muscular dystrophy

Symptoms and severity of facioscapulohumeral muscular dystrophy (FSHD) can vary greatly, even within the same family. Clinical trial readiness requires accurate and reliable methods of assessing disease stage and progression. MRI has not previously been assessed as a disease biomarker in paediatric FSHD. Eleven patients with FSHD1 underwent whole body muscle MRI. Pre-selected muscles were analysed by a paediatric radiologist using the semi-quantitative Mercuri/Kim method. Within each domain (oedema, fat replacement, atrophy) scores for each muscle were then summated to give each participant three cumulative domain scores. The same participants had functional measures scored: FSHD-CSS (Ricci), FSHD-CS (Lamperti), FSHD-COM, PUL2.0, MFM-32, 6MWT, myometry and manual muscle testing. Pearson coefficient was calculated to determine strength of correlation. The scores for atrophy and fat replacement showed strong correlation with functional outcome measures, particularly FSHD-CSS, FSHD-CS and FSHD-COM. In contrast, muscle oedema correlated poorly with all functional outcome measures, with no relationship seen to the 6MWT. This study of eleven children suggests that semi-quantitative visual Mercuri score utilising fat replacement or atrophy on whole body muscle MRI correlates strongly with disease-specific functional measures and may be a useful measure of disease severity in paediatric FSHD.

Gastrointestinal cancer occurs as extramuscular manifestation in FSHD1 patients

Facioscapulohumeral dystrophy type1 (FSHD1) patients with a shortened D4Z4 repeat containing the DUX4 gene have a broad spectrum of clinical manifestations. In addition, high expression of DUX4 protein with an aberrant C terminus is frequently identified in B cell acute lymphoblastic leukemia. We investigated clinical manifestations in 31 FSHD1 patients and 30 non-affected individuals. Gastrointestinal cancers (gastric and colorectal cancers) increased after the age of 40 years and were more frequently observed in FSHD1 patients (n = 10) than in non-affected individuals (n = 2, p = 0.0217), though the incidence of cancers occurring in non-gastrointestinal tissues of FSHD1 patients was the same as that of non-affected individuals (p > 0.999). These comorbidities of FSHD1 patients were not associated with D4Z4 repeat number. Our results suggest that gastrointestinal cancers are among the extramuscular manifestations of adult FSHD1 patients, and do not depend on D4Z4 repeat number.

Knocking Down DUX4 in Immortalized Facioscapulohumeral Muscular Dystrophy Patient-Derived Muscle Cells

The third most common muscular dystrophy in the world, facioscapulohumeral muscular dystrophy (FSHD), is an inherited disorder characterized by distinct asymmetric, progressive skeletal muscle weakness that begins in the upper body and spreads to other regions with age. It is caused by mutations that induce aberrant expression of the DUX4 gene in skeletal muscle. DUX4 is highly cytotoxic in skeletal muscle, dysregulating numerous signaling pathways as a result of its transcription factor activity. A promising set of approaches being developed to treat FSHD uses antisense oligonucleotides (AOs) to inhibit DUX4 transcript expression. Both steric-blocking and gapmer AOs have been shown to induce efficient DUX4 transcript knockdown in vitro and in vivo. Here, we describe a protocol that allows reliable screening of DUX4-targeting AOs through the evaluation of DUX4 transcript expression by quantitative real-time polymerase chain reaction. We also describe methods to assess the efficacy of these AOs by looking at their effect on the expression of DUX4 downstream target and potential off-target genes, as well as on the amelioration of in vitro muscle cell phenotypes.

Facioscapulohumeral muscular dystrophy: genetics, gene activation and downstream signalling with regard to recent therapeutic approaches: an update

Whilst a disease-modifying treatment for Facioscapulohumeral muscular dystrophy (FSHD) does not exist currently, recent advances in complex molecular pathophysiology studies of FSHD have led to possible therapeutic approaches for its targeted treatment. Although the underlying genetics of FSHD have been researched extensively, there remains an incomplete understanding of the pathophysiology of FSHD in relation to the molecules leading to DUX4 gene activation and the downstream gene targets of DUX4 that cause its toxic effects. In the context of the local proximity of chromosome 4q to the nuclear envelope, a contraction of the D4Z4 macrosatellite induces lower methylation levels, enabling the ectopic expression of DUX4. This disrupts numerous signalling pathways that mostly result in cell death, detrimentally affecting skeletal muscle in affected individuals. In this regard different options are currently explored either to suppress the transcription of DUX4 gene, inhibiting DUX4 protein from its toxic effects, or to alleviate the symptoms triggered by its numerous targets.

Genetic Approaches for the Treatment of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by progressive, asymmetric muscle weakness at the face, shoulders, and upper limbs, which spreads to the lower body with age. It is the third most common inherited muscular disorder worldwide. Around 20% of patients are wheelchair-bound, and some present with extramuscular manifestations. FSHD is caused by aberrant expression of the double homeobox protein 4 (DUX4) gene in muscle. DUX4 codes for a transcription factor which, in skeletal muscle, dysregulates numerous signaling activities that culminate in cytotoxicity. Potential treatments for FSHD therefore aim to reduce the expression of DUX4 or the activity of its toxic protein product. In this article, we review how genetic approaches such as those based on oligonucleotide and genome editing technologies have been developed to achieve these goals. We also outline the challenges these therapies are facing on the road to translation, and discuss possible solutions and future directions.

DUX4 Transcript Knockdown with Antisense 2'-O-Methoxyethyl Gapmers for the Treatment of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by a progressive, asymmetric weakening of muscles, starting with those in the upper body. It is caused by aberrant expression of the double homeobox protein 4 gene (DUX4) in skeletal muscle. FSHD is currently incurable. We propose to develop a therapy for FSHD using antisense 2'-O-methoxyethyl (2'-MOE) gapmers, to knock down DUX4 mRNA expression. Using immortalized patient-derived muscle cells and local intramuscular injections in the FLExDUX4 FSHD mouse model, we showed that our designed 2'-MOE gapmers significantly reduced DUX4 transcript levels in vitro and in vivo, respectively. Furthermore, in vitro, we observed significantly reduced expression of DUX4-activated downstream targets, restoration of FSHD signature genes by RNA sequencing, significant improvements in myotube morphology, and minimal off-target activity. This work facilitates the development of a promising candidate therapy for FSHD and lays down the foundation for in vivo systemic treatment studies.

Therapeutic Approaches in Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common types of muscular dystrophy, affecting roughly one in 8000 individuals. The complex underlying genetics and poor mechanistic understanding has caused a bottleneck in therapeutic development. Until the discovery of DUX4 and its causal role in FSHD, most trials were untargeted with limited results. Emerging approaches can learn from these early trials to increase their chance of success. Here, we explore the evolution of FSHD clinical trials from nonspecific anabolic or anti-inflammatory/oxidant strategies to cutting-edge molecular therapies targeting DUX4, and we discuss the importance of clinical outcome measures. With combined advances across multiple facets of FSHD research, the field is now poised to accelerate the process of therapeutic discovery and testing.

Promising Perspective to Facioscapulohumeral Muscular Dystrophy Treatment: Nutraceuticals and Phytochemicals

Facioscapulohumeral Muscular Dystrophy (FSHD) is in the top three list of all dystrophies with an approximate 1:8000 incidence. It is not a life-threatening disease; however, the progression of the disease extends over being wheelchair bound. Despite some drug trials continuing, including DUX4 inhibition, TGF-ß inhibition and resokine which promote healthier muscle, there is not an applicable treatment option for FSHD today. Still, there is a need for new agents to heal, stop or at least slow down muscle wasting. Current FSHD studies involving nutraceuticals as vitamin C, vitamin E, coenzyme Q10, zinc, selenium, and phytochemicals as curcumin or genistein, daidzein flavonoids provide promising treatment strategies. In this review, we present the clinical and molecular nature of FSHD and focus on nutraceuticals and phytochemicals that may alleviate FSHD. In the light of the association of impaired pathophysiological FSHD pathways with nutraceuticals and phytochemicals according to the literature, we present both studied and novel approaches that can contribute to FSHD treatment.

Designed U7 snRNAs inhibit DUX4 expression and improve FSHD-associated outcomes in DUX4 overexpressing cells and FSHD patient myotubes

Facioscapulohumeral muscular dystrophy (FSHD) arises from epigenetic changes that de-repress the DUX4 gene in muscle. The full-length DUX4 protein causes cell death and muscle toxicity, and therefore we hypothesize that FSHD therapies should center on inhibiting full-length DUX4 expression. In this study, we developed a strategy to accomplish DUX4 inhibition using U7-small nuclear RNA (snRNA) antisense expression cassettes (called U7-asDUX4). These non-coding RNAs were designed to inhibit production or maturation of the full-length DUX4 pre-mRNA by masking the DUX4 start codon, splice sites, or polyadenylation signal. In so doing, U7-asDUX4 snRNAs operate similarly to antisense oligonucleotides. However, in contrast to oligonucleotides, which are limited by poor uptake in muscle and a requirement for lifelong repeated dosing, U7-asDUX4 snRNAs can be packaged within myotropic gene therapy vectors and may require only a single administration when delivered to post-mitotic cells in vivo. We tested several U7-asDUX4s that reduced DUX4 expression in vitro and improved DUX4-associated outcomes. Inhibition of DUX4 expression via U7-snRNAs could be a new prospective gene therapy approach for FSHD or be used in combination with other strategies, like RNAi therapy, to maximize DUX4 silencing in individuals with FSHD.

Multi-Omics Identifies Circulating miRNA and Protein Biomarkers for Facioscapulohumeral Dystrophy

The development of therapeutics for muscle diseases such as facioscapulohumeral dystrophy (FSHD) is impeded by a lack of objective, minimally invasive biomarkers. Here we identify circulating miRNAs and proteins that are dysregulated in early-onset FSHD patients to develop blood-based molecular biomarkers. Plasma samples from clinically characterized individuals with early-onset FSHD provide a discovery group and are compared to healthy control volunteers. Low-density quantitative polymerase chain reaction (PCR)-based arrays identify 19 candidate miRNAs, while mass spectrometry proteomic analysis identifies 13 candidate proteins. Bioinformatic analysis of chromatin immunoprecipitation (ChIP)-seq data shows that the FSHD-dysregulated DUX4 transcription factor binds to regulatory regions of several candidate miRNAs. This panel of miRNAs also shows ChIP signatures consistent with regulation by additional transcription factors which are up-regulated in FSHD (FOS, EGR1, MYC, and YY1). Validation studies in a separate group of patients with FSHD show consistent up-regulation of miR-100, miR-103, miR-146b, miR-29b, miR-34a, miR-454, miR-505, and miR-576. An increase in the expression of S100A8 protein, an inflammatory regulatory factor and subunit of calprotectin, is validated by Enzyme-Linked Immunosorbent Assay (ELISA). Bioinformatic analyses of proteomics and miRNA data further support a model of calprotectin and toll-like receptor 4 (TLR4) pathway dysregulation in FSHD. Moving forward, this panel of miRNAs, along with S100A8 and calprotectin, merit further investigation as monitoring and pharmacodynamic biomarkers for FSHD.

Early-Onset Infantile Facioscapulohumeral Muscular Dystrophy: A Timely Review

Facioscapulohumeral muscular dystrophy (FSHD)-the worldwide third most common inherited muscular dystrophy caused by the heterozygous contraction of a 3.3 kb tandem repeat (D4Z4) on a chromosome with a 4q35 haplotype-is a progressive genetic myopathy with variable onset of symptoms, distribution of muscle weakness, and clinical severity. While much is known about the clinical course of adult FSHD, data on the early-onset infantile phenotype, especially on the progression of the disease, are relatively scarce. Contrary to the classical form, patients with infantile FSHD more often have a rapid decline in muscle wasting and systemic features with multiple extramuscular involvements. A rough correlation between the phenotypic severity of FSHD and the D4Z4 repeat size has been reported, and the majority of patients with infantile FSHD obtain a very short D4Z4 repeat length (one to three copies, EcoRI size 10-14 kb), in contrast to the classical, slowly progressive, form of FSHD (15-38 kb). With the increasing identifications of case reports and the advance in genetic diagnostics, recent studies have suggested that the infantile variant of FSHD is not a genetically separate entity but a part of the FSHD spectrum. Nevertheless, many questions about the clinical phenotype and natural history of infantile FSHD remain unanswered, limiting evidence-based clinical management. In this review, we summarize the updated research to gain insight into the clinical spectrum of infantile FSHD and raise views to improve recognition and understanding of its underlying pathomechanism, and further, to advance novel treatments and standard care methods.

Inhibition of DUX4 expression with antisense LNA gapmers as a therapy for facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), characterized by progressive muscle weakness and deterioration, is genetically linked to aberrant expression of DUX4 in muscle. DUX4, in its full-length form, is cytotoxic in nongermline tissues. Here, we designed locked nucleic acid (LNA) gapmer antisense oligonucleotides (AOs) to knock down DUX4 in immortalized FSHD myoblasts and the FLExDUX4 FSHD mouse model. Using a screening method capable of reliably evaluating the knockdown efficiency of LNA gapmers against endogenous DUX4 messenger RNA in vitro, we demonstrate that several designed LNA gapmers selectively and effectively reduced DUX4 expression with nearly complete knockdown. We also found potential functional benefits of AOs on muscle fusion and structure in vitro. Finally, we show that one of the LNA gapmers was taken up and induced effective silencing of DUX4 upon local treatment in vivo. The LNA gapmers developed here will help facilitate the development of FSHD therapies.

DUX4 Signalling in the Pathogenesis of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a disabling inherited muscular disorder characterized by asymmetric, progressive muscle weakness and degeneration. Patients display widely variable disease onset and severity, and sometimes present with extra-muscular symptoms. There is a consensus that FSHD is caused by the aberrant production of the double homeobox protein 4 (DUX4) transcription factor in skeletal muscle. DUX4 is normally expressed during early embryonic development, and is then effectively silenced in all tissues except the testis and thymus. Its reactivation in skeletal muscle disrupts numerous signalling pathways that mostly converge on cell death. Here, we review studies on DUX4-affected pathways in skeletal muscle and provide insights into how understanding these could help explain the unique pathogenesis of FSHD.

Neuromuscular Diseases of the Newborn

The peripheral nervous system (PNS) is composed of motor neurons, nerve roots, plexuses, peripheral nerves (motor, sensory and autonomic), neuromuscular junction, and skeletal muscles. Disorders of the PNS in neonates most frequently cause weakness, hypotonia, and contractures, which may be generalized or focal. Since these findings may also occur with brain and spinal cord lesions, key features of the history and neurologic exam, together with diagnostic testing, are helpful in reaching a diagnosis. This review covers the diagnostic approach to PNS disorders in the neonate and includes a discussion of representative diseases of the motor neuron, brachial plexus, peripheral nerves, neuromuscular junction, and muscles. The importance of reaching a precise genetic diagnosis is highlighted with a discussion of current and emerging treatments for neonatal PNS diseases, particularly spinal muscular atrophy.

The Genetics and Epigenetics of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, provides a powerful model of the complex interplay between genetic and epigenetic mechanisms of chromatin regulation. FSHD is caused by dysregulation of a macrosatellite repeat, either by contraction of the repeat or by mutations in silencing proteins. Both cases lead to chromatin relaxation and, in the context of a permissive allele, aberrant expression of the DUX4 gene in skeletal muscle. DUX4 is a pioneer transcription factor that activates a program of gene expression during early human development, after which its expression is silenced in most somatic cells. When misexpressed in FSHD skeletal muscle, the DUX4 program leads to accumulated muscle pathology. Epigenetic regulators of the disease locus represent particularly attractive therapeutic targets for FSHD, as many are not global modifiers of the genome, and altering their expression or activity should allow correction of the underlying defect.

Clinical features of facioscapulohumeral muscular dystrophy 1 in childhood

AIM

To explore the clinical course of patients presenting with facioscapulohumeral dystrophy type 1 (FSHD1) in childhood, with a view to identifying areas where they differed from older patients and where extra support or monitoring might be required.

METHOD

A retrospective case-notes review of children with FSHD1 seen at a tertiary paediatric neuromuscular centre between 2002 and 2016 was performed. Data collected included age at and nature of presentation, path to diagnosis, genetic testing results, motor function, and occurrence of extramuscular features and complications.

RESULTS

Eighteen children (11 females, seven males; mean [SD] age at latest review 13y 10mo [3y 9mo], range 8-19y) from 16 families were identified. Age at onset of FSHD1 correlated with the size of deletion (r=0.81) and most presentations were in children either younger than 5 years or older than 10 years. Children with onset before 5 years were more likely to present with non-muscular symptoms and to develop extramuscular pathology, including developmental and psychiatric issues, hearing or visual impairments, and problems involving respiratory function and nutrition. No cases of epilepsy or cardiac arrhythmia were identified but two children died.

INTERPRETATION

The complexity and severity of FSHD1 presenting in early childhood underlines the importance of a multidisciplinary approach to the disorder.

WHAT THIS PAPER ADDS

Young children often present with non-muscular pathology in facioscapulohumeral dystrophy type 1 (FSHD1), especially hearing loss. Age at onset in paediatric FSHD1 appears bimodal: under 5 years or in adolescence. Prolonged delays to diagnosis are common. Children with very early-onset FSHD1 may require nutritional and/or respiratory support. Developmental and psychiatric comorbidities are common.

Transgenic zebrafish model of DUX4 misexpression reveals a developmental role in FSHD pathogenesis

Facioscapulohumeral dystrophy type 1 (FSHD-1) is the most common autosomal dominant form of muscular dystrophy with a prevalence of ∼1 in 8000 individuals. It is considered a late-onset form of muscular dystrophy and leads to asymmetric muscle weakness in the facial, scapular, trunk and lower extremities. The prevalent hypothesis on disease pathogenesis is explained by misexpression of a germ line, primate-specific transcription factor DUX4-fl (double homeobox 4, full-length isoform) linked to the chromosome 4q35. In vitro and in vivo studies have demonstrated that very low levels of DUX4-fl expression are sufficient to induce an apoptotic and/or lethal phenotype, and therefore modeling of the disease has proved challenging. In this study, we expand upon our previously established injection model of DUX4 misexpression in zebrafish and describe a DUX4-inducible transgenic zebrafish model that better recapitulates the expression pattern and late onset phenotype characteristic of FSHD patients. We show that an induced burst of DUX4 expression during early development results in the onset of FSHD-like phenotypes in adulthood, even when DUX4 is no longer detectable. We also utilize our injection model to study long-term consequences of DUX4 expression in those that fail to show a developmental phenotype. Herein, we introduce a hypothesis that DUX4 expression during developmental stages is sufficient to induce FSHD-like phenotypes in later adulthood. Our findings point to a developmental role of DUX4 misexpression in the pathogenesis of FSHD and should be factored into the design of future therapies.

Genotype-phenotype correlations in FSHD

BACKGROUND

Facial-scapular-humeral myodystrophy Landouzy-Dejerine (FSHD) is an autosomal dominant disease, the basis of its pathogenesis is ectopic expression of the transcription factor DUX4 in skeletal muscle. There are two types of the disease: FSHD1 (MIM:158900) and FSHD2 (MIM: 158901), which have different genetic causes but are phenotypically indistinguishable. In FSHD1, partial deletion of the D4Z4 repeats on the 4th chromosome affects the expression of DUX4, whereas FSHD2 is caused by the mutations in the protein regulating the methylation status of chromatin - SMCHD1. High variability of clinical picture, both intra - and inter-family indicates a large number of factors influencing clinical picture. There are key genetic, epigenetic and gender factors that influence the expressivity and penetrance of the disease. Using only one of these factors allows just a rough prediction of the course of the disease, which indicates the combined effect of all of the factors on the DUX4 expression and on the clinical picture.

RESULTS

In this paper, we analyzed the impact of genetic, epigenetic and gender differences on phenotype and the possibility of using them for disease prognosis and family counselling.

CONCLUSIONS

Key pathogenesis factors have been identified for FSHD. However, the pronounced intra - and inter-family polymorphism of manifestations indicates a large number of modifiers of the pathological process, many of which remain unknown.

Early onset as a marker for disease severity in facioscapulohumeral muscular dystrophy

OBJECTIVE

To assess the relation between age at onset and disease severity in facioscapulohumeral muscular dystrophy (FSHD).

METHODS

In this prospective cross-sectional study, we matched adult patients with FSHD with an early disease onset with 2 sex-matched FSHD control groups with a classic onset; the first group was age matched, and the second group was disease duration matched. Genetic characteristics, muscle performance, respiratory functioning, hearing loss, vision loss, epilepsy, educational level, and work status were compared with the 2 control groups.

RESULTS

Twenty-eight patients with early-onset FSHD were age (n = 28) or duration (n = 27) matched with classic-onset patients. Patients with early-onset FSHD had more severe muscle weakness (mean FSHD clinical score 11 vs 5 in the age-matched and 9 in the duration-matched group, p < 0.05) and a higher frequency of wheelchair dependency (57%, 0%, and 30%, respectively, p < 0.05). In addition, systemic features were more frequent in early-onset FSHD, most important, hearing loss, decreased respiratory function and spinal deformities. There was no difference in work status. Genetically, the shortest D4Z4 repeat arrays (2-3 units) were found exclusively in the early-onset group, and the largest repeat arrays (8-9 units) were found only in the classic-onset groups. De novo mutations were more frequent in early-onset patients (46% vs 4%).

CONCLUSIONS

Patients with early-onset FSHD more often have severe muscle weakness and systemic features. The disease severity is greater than in patients with classic-onset FSHD who are matched for disease duration, suggesting that the progression is faster in early-onset patients.

Facioscapulohumeral Dystrophy in Childhood: A Nationwide Natural History Study

OBJECTIVE

Facioscapulohumeral dystrophy (FSHD) is one of the most frequent heritable muscular dystrophies, with a large variety in age at onset and disease severity. The natural history and molecular characteristics of FSHD in childhood are incompletely understood. Our objective is to clinically and genetically characterize FSHD in childhood.

METHODS

We performed a nationwide, single-investigator, natural history study on FSHD in childhood.

RESULTS

Multiple-source recruitment resulted in 32 patients with FSHD (0-17 years), leading to an estimated prevalence of 1 in 100,000 children in The Netherlands. This series of 32 children with FSHD revealed a heterogeneous phenotype and genotype in childhood. The phenotypic hallmarks of FSHD in childhood are: facial weakness with normal or only mildly affected motor performance, decreased functional exercise capacity (6-minute walk test), lumbar hyperlordosis, and increased echo intensity on muscle ultrasonography. In addition, pain and fatigue were frequent and patients experienced a lower quality of life compared to healthy peers. In contrast to the literature on early-onset FSHD, systemic features such as hearing loss and retinal and cardiac abnormalities were infrequent and subclinical, and epilepsy and intellectual disability were absent. Genotypically, patients had a mean D4Z4 repeat array of 5 units (range, 2-9), and 14% of the mutations were de novo.

INTERPRETATION

FSHD in childhood is more prevalent than previously known and the genotype resembles classic FSHD. Importantly, FSHD mainly affects functional exercise capacity and quality of life in children. As such, these results are paramount for counseling, clinical management, and stratification in clinical research. Ann Neurol 2018;84:635-645.

A 22-year follow-up reveals a variable disease severity in early-onset facioscapulohumeral dystrophy

AIM

To assess the long-term natural course of early-onset facioscapulohumeral dystrophy (FSHD), which is important for patient management and trial-readiness, and is currently lacking.

METHODS

We had the unique opportunity to evaluate 10 patients with early-onset FSHD after 22 years follow-up. Patients underwent a semi-structured interview, physical examination and additional genotyping.

RESULTS

Nine initial study participants (median age 37 years) were included, one patient died shortly after first publication. At first examination, one patient was wheelchair dependent, one patient walked aided, and eight patients walked unaided. After 22 years, four patients were wheelchair dependent, three walked aided, and two walked unaided. Systemic features, including hearing loss (56%), intellectual disability (44%), and a decreased respiratory function (56%), were frequent. Patients participated socially and economically with most patients living in a regular house (n = 6) and/or having a paid job (n = 4).

DISCUSSION

Patients with early-onset FSHD generally had a severe phenotype compared to classical onset FSHD. However, after 22 years of follow up they showed a wide variation in severity and, despite these physical limitations, participated socially and economically. These observations are important for patient management and should be taken into account in clinical trials.

A Pediatric Review of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral dystrophy is one of the most common forms of muscular dystrophies worldwide. It is a complex and heterogeneous disease secondary to insufficient epigenetic repression of D4Z4 repeats and aberrant expression of DUX4 in skeletal muscles. Type 1 facioscapulohumeral muscular dystrophy (FSHD) is caused by contraction of D4Z4 repeats on 4q35, whereas type 2 FSHD is associated with mutations of the SMCHD1 or DNMT3B gene in the presence of a disease-permissive 4qA haplotype. Classical FSHD is a slowly progressive disorder with gradual-onset of muscle atrophy and a descending pattern of muscle weakness. In contrast, early-onset FSHD is associated with a large deletion of D4Z4 repeats and a more severe disease phenotype, including early loss of independent ambulation as well as extramuscular manifestations, such as retinal vasculopathy, hearing loss, and central nervous system (CNS) involvement. However, the correlation between D4Z4 repeats and disease severity remains imprecise. The current standard of care guidelines offers comprehensive assessment and symptomatic management of secondary complications. Several clinical trials are currently underway for FSHD. New and emerging treatments focus on correcting the transcriptional misregulation of D4Z4 and reversing the cytotoxic effects of DUX4. Other potential therapeutic targets include reduction of inflammation, improving muscle mass, and activating compensatory molecular pathways. The utility of disease-modifying treatments will depend on selection of sensitive clinical endpoints as well as validation of muscle magnetic resonance imaging (MRI) and other biomarkers to detect meaningful changes in disease progression. Correction of the epigenetic defects using new gene editing as well as other DUX4 silencing technologies offers potential treatment options for many individuals with FSHD.

A multinational study on motor function in early-onset FSHD

OBJECTIVES

To investigate motor function associations with age, sex, and D4Z4 repeats among participants with early-onset facioscapulohumeral muscular dystrophy (FSHD) type 1 as defined by weakness onset before 10 years of age.

METHODS

We collected standardized motor assessments, including manual muscle testing (MMT), quantitative muscle testing, functional motor evaluations, and clinical severity scores (CSSs), at 12 Cooperative International Neuromuscular Research Group centers. To measure associations, we used linear regression models adjusted for sex, evaluation age, age at onset of weakness, and D4Z4 repeats.

RESULTS

Among 52 participants (60% female, mean age 22.9 ± 14.7 years), weakness was most pronounced in the shoulder and abdominal musculature. Older enrollment age was associated with greater CSSs (p = 0.003). When adjusted for enrollment age, sex, and D4Z4 repeats, younger age at onset of facial weakness was associated with greater CSSs, slower velocities in timed function tests, and lower MMT scores (p < 0.05).

CONCLUSION

Significant clinical variability was observed in early-onset FSHD. Earlier age at onset of facial weakness was associated with greater disease severity. Longitudinal assessments are needed to determine the rate of disease progression in this population.

A cre-inducible DUX4 transgenic mouse model for investigating facioscapulohumeral muscular dystrophy

The Double homeobox 4 (DUX4) gene is an important regulator of early human development and its aberrant expression is causal for facioscapulohumeral muscular dystrophy (FSHD). The DUX4-full length (DUX4-fl) mRNA splice isoform encodes a transcriptional activator; however, DUX4 and its unique DNA binding preferences are specific to old-world primates. Regardless, the somatic cytotoxicity caused by DUX4 expression is conserved when expressed in cells and animals ranging from fly to mouse. Thus, viable animal models based on DUX4-fl expression have been difficult to generate due in large part to overt developmental toxicity of low DUX4-fl expression from leaky transgenes. We have overcome this obstacle and here we report the generation and initial characterization of a line of conditional floxed DUX4-fl transgenic mice, FLExDUX4, that is viable and fertile. In the absence of cre, these mice express a very low level of DUX4-fl mRNA from the transgene, resulting in mild phenotypes. However, when crossed with appropriate cre-driver lines of mice, the double transgenic offspring readily express DUX4-fl mRNA, protein, and target genes with the spatiotemporal pattern of nuclear cre expression dictated by the chosen system. When cre is expressed from the ACTA1 skeletal muscle-specific promoter, the double transgenic animals exhibit a developmental myopathy. When crossed with tamoxifen-inducible cre lines, DUX4-mediated pathology can be induced in adult animals. Thus, the appearance and progression of pathology can be controlled to provide readily screenable phenotypes useful for assessing therapeutic approaches targeting DUX4-fl mRNA and protein. Overall, the FLExDUX4 line of mice is quite versatile and will allow new investigations into mechanisms of DUX4-mediated pathophysiology as well as much-needed pre-clinical testing of DUX4-targeted FSHD interventions in vivo.

[Clinical and genetic characteristics of facioscapulohumeral muscular dystrophy Landuzi-Dezherina type 1]

AIM

To describe clinical and genetic characteristics of patients from the Russian population with a variety of phenotypic variants of facioscapulohumeral muscular dystrophy Landuzi-Dezherina type 1 (FSHD 1).

MATERIAL AND METHODS

The material for the study were blood samples of 16 patients from 15 unrelated families residing in the territory of the Russian Federation, between the ages of 6 to 66 years, with symptoms of FSHD. Diagnosis was based on genealogical data analysis, neurological examination, electroneuromyographic study, indicators of activity of creatine phosphokinase (CPK) in the blood serum and molecular genetic analysis of the results, aimed at the analysis of macrosatellite D4Z4 repeats on chromosome 4.

RESULTS AND CONCLUSION

The study established the diagnosis of FSHD1 in 75% of patients. The correlation of the severity and phenotypic spectrum of FSHD1 with the age of onset was found. There was the significant clinical heterogeneity even among the 1st degree relatives in the same family. The correlation between macrosatellite D4Z4 repeats and clinical features of FSHD1 described previously in the literature was not observed.

Early onset facioscapulohumeral dystrophy - a systematic review using individual patient data

Infantile or early onset is estimated to occur in around 10% of all facioscapulohumeral dystrophy (FSHD) patients. Although small series of early onset FSHD patients have been reported, comprehensive data on the clinical phenotype is missing. We performed a systematic literature search on the clinical features of early onset FSHD comprising a total of 43 articles with individual data on 227 patients. Additional data from four cohorts was provided by the authors. Mean age at reporting was 18.8 years, and 40% of patients were wheelchair-dependent at that age. Half of the patients had systemic features, including hearing loss (40%), retinal abnormalities (37%) and developmental delay (8%). We found an inverse correlation between repeat size and disease severity, similar to adult-onset FSHD. De novo FSHD1 mutations were more prevalent than in adult-onset FSHD. Compared to adult FSHD, our findings indicate that early onset FSHD is overall characterized by a more severe muscle phenotype and a higher prevalence of systemic features. However, similar as in adults, a significant clinical heterogeneity was observed. Based on this, we consider early onset FSHD to be on the severe end of the FSHD disease spectrum. We found natural history studies and treatment studies to be very scarce in early onset FSHD, therefore longitudinal studies are needed to improve prognostication, clinical management and trial-readiness.

Estrogens enhance myoblast differentiation in facioscapulohumeral muscular dystrophy by antagonizing DUX4 activity

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder that is characterized by extreme variability in symptoms, with females being less severely affected than males and presenting a higher proportion of asymptomatic carriers. The sex-related factors involved in the disease are not known. Here, we have utilized myoblasts isolated from FSHD patients (FSHD myoblasts) to investigate the effect of estrogens on muscle properties. Our results demonstrated that estrogens counteract the differentiation impairment of FSHD myoblasts without affecting cell proliferation or survival. Estrogen effects are mediated by estrogen receptor β (ERβ), which reduces chromatin occupancy and transcriptional activity of double homeobox 4 (DUX4), a protein whose aberrant expression has been implicated in FSHD pathogenesis. During myoblast differentiation, we observed that the levels and activity of DUX4 increased progressively and were associated with its enhanced recruitment in the nucleus. ERβ interfered with this recruitment by relocalizing DUX4 in the cytoplasm. This work identifies estrogens as a potential disease modifier that underlie sex-related differences in FSHD by protecting against myoblast differentiation impairments in this disease.

Facioscapulohumeral dystrophy in children: design of a prospective, observational study on natural history, predictors and clinical impact (iFocus FSHD)

Background

Facioscapulohumeral muscular dystrophy (FSHD; OMIM 158900 & 158901) is a progressive skeletal muscle dystrophy, characterized by an autosomal dominant inheritance pattern. One of the major unsolved questions in FSHD is the marked clinical heterogeneity, ranging from asymptomatic individuals to severely affected patients with an early onset. An estimated 10 % of FSHD patients have an early onset (onset before 10 years of age) and are traditionally classified as infantile FSHD. This subgroup is regarded as severely affected and extra-muscular symptoms, such as hearing loss and retinopathy, are frequently described. However, information on the prevalence, natural history and clinical management of early onset FSHD is currently lacking, thereby hampering adequate patient counselling and management. Therefore, a population-based prospective cohort study on FSHD in children is highly needed.

Methods/design

This explorative study aims to recruit all children (aged 0–17 years) with a genetically confirmed diagnosis of FSHD in The Netherlands. The children will be assessed at baseline and at 2-year follow-up. The general aim of the study is the description of the clinical features and genetic characteristics of this paediatric cohort. The primary outcome is the motor function as measured by the Motor Function Measure. Secondary outcomes include quantitative and qualitative description of the clinical phenotype, muscle imaging, genotyping and prevalence estimations. The ultimate objective will be a thorough description of the natural history, predictors of disease severity and quality of life in children with FSHD.

Discussion

The results of this population-based study are vital for adequate patient management and clinical trial-readiness. Furthermore, this study is expected to provide additional insight in the epigenetic and environmental disease modifying factors. In addition to improve counselling, this could contribute to unravelling the aetiology of FSHD.

Trial registration

clinicaltrials.gov NCT02625662.

Transgenic Drosophila for Investigating DUX4 and FRG1, Two Genes Associated with Facioscapulohumeral Muscular Dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is typically an adult onset dominant myopathy. Epigenetic changes in the chromosome 4q35 region linked to both forms of FSHD lead to a relaxation of repression and increased somatic expression of DUX4-fl (DUX4-full length), the pathogenic alternative splicing isoform of the DUX4 gene. DUX4-fl encodes a transcription factor expressed in healthy testis and pluripotent stem cells; however, in FSHD, increased levels of DUX4-fl in myogenic cells lead to aberrant regulation of target genes. DUX4-fl has proven difficult to study in vivo; thus, little is known about its normal and pathogenic roles. The endogenous expression of DUX4-fl in FSHD-derived human muscle and myogenic cells is extremely low, exogenous expression of DUX4-fl in somatic cells rapidly induces cytotoxicity, and, due in part to the lack of conservation beyond primate lineages, viable animal models based on DUX4-fl have been difficult to generate. By contrast, the FRG1 (FSHD region gene 1), which is linked to FSHD, is evolutionarily conserved from invertebrates to humans, and has been studied in several model organisms. FRG1 expression is critical for the development of musculature and vasculature, and overexpression of FRG1 produces a myopathic phenotype, yet the normal and pathological functions of FRG1 are not well understood. Interestingly, DUX4 and FRG1 were recently linked when the latter was identified as a direct transcriptional target of DUX4-FL. To better understand the pathways affected in FSHD by DUX4-fl and FRG1, we generated transgenic lines of Drosophila expressing either gene under control of the UAS/GAL4 binary system. Utilizing these lines, we generated screenable phenotypes recapitulating certain known consequences of DUX4-fl or FRG1 overexpression. These transgenic Drosophila lines provide resources to dissect the pathways affected by DUX4-fl or FRG1 in a genetically tractable organism and may provide insight into both muscle development and pathogenic mechanisms in FSHD.

Facioscapulohumeral muscular dystrophy as a model for epigenetic regulation and disease

SIGNIFICANCE

Aberrant epigenetic regulation is an integral aspect of many diseases and complex disorders. Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, is caused by disrupted genetic and epigenetic regulation of a macrosatellite repeat. FSHD provides a powerful model to investigate disease-relevant epigenetic modifiers and general mechanisms of epigenetic regulation that govern gene expression.

RECENT ADVANCES

In the context of a genetically permissive allele, the one aspect of FSHD that is consistent across all known cases is the aberrant epigenetic state of the disease locus. In addition, certain mutations in the chromatin regulator SMCHD1 (structural maintenance of chromosomes hinge-domain protein 1) are sufficient to cause FSHD2 and enhance disease severity in FSHD1. Thus, there are multiple pathways to generate the epigenetic dysregulation required for FSHD.

CRITICAL ISSUES

Why do some individuals with the genetic requirements for FSHD develop disease pathology, while others remain asymptomatic? Similarly, disease progression is highly variable among individuals. What are the relative contributions of genetic background and environmental factors in determining disease manifestation, progression, and severity in FSHD? What is the interplay between epigenetic factors regulating the disease locus and which, if any, are viable therapeutic targets?

FUTURE DIRECTIONS

Epigenetic regulation represents a potentially powerful therapeutic target for FSHD. Determining the epigenetic signatures that are predictive of disease severity and identifying the spectrum of disease modifiers in FSHD are vital to the development of effective therapies.

Early-onset facioscapulohumeral muscular dystrophy type 1 with some atypical features

Facioscapulohumeral muscular dystrophy cases with facial weakness before the age of 5 and signs of shoulder weakness by the age of 10 are defined as early onset. Contraction of the D4Z4 repeat on chromosome 4q35 is causally related to facioscapulohumeral muscular dystrophy type 1, and the residual size of the D4Z4 repeat shows a roughly inverse correlation with the severity of the disease. Contraction of the D4Z4 repeat on chromosome 4q35 is believed to induce a local change in chromatin structure and consequent transcriptional deregulation of 4qter genes. We present early-onset cases in the Polish population that amounted to 21% of our total population with facioscapulohumeral muscular dystrophy. More than 27% of them presented with severe phenotypes (wheelchair dependency). The residual D4Z4 repeat sizes ranged from 1 to 4 units. In addition, even within early-onset facioscapulohumeral muscular dystrophy type 1 phenotypes, some cases had uncommon features (head drop, early disabling contractures, progressive ptosis, and respiratory insufficiency and cardiomyopathy).

Low penetrance in facioscapulohumeral muscular dystrophy type 1 with large pathological D4Z4 alleles: a cross-sectional multicenter study

Background

Facioscapulohumeral muscular dystrophy type 1(FSHD1) is an autosomal dominant disorder associated with the contraction of D4Z4 less than 11 repeat units (RUs) on chromosome 4q35. Penetrance in the range of the largest alleles is poorly known. Our objective was to study the penetrance of FSHD1 in patients carrying alleles ranging between 6 to10 RUs and to evaluate the influence of sex, age, and several environmental factors on clinical expression of the disease.

Methods

A cross-sectional multicenter study was conducted in six French and one Swiss neuromuscular centers. 65 FSHD1 affected patients carrying a 4qA allele of 6–10 RUs were identified as index cases (IC) and their 119 at-risk relatives were included. The age of onset was recorded for IC only. Medical history, neurological examination and manual muscle testing were performed for each subject. Genetic testing determined the allele size (number of RUs) and the 4qA/4qB allelic variant. The clinical status of relatives was established blindly to their genetic testing results. The main outcome was the penetrance defined as the ratio between the number of clinically affected carriers and the total number of carriers.

Results

Among the relatives, 59 carried the D4Z4 contraction. At the clinical level, 34 relatives carriers were clinically affected and 25 unaffected. Therefore, the calculated penetrance was 57% in the range of 6–10 RUs. Penetrance was estimated at 62% in the range of 6–8 RUs, and at 47% in the range of 9–10 RUs. Moreover, penetrance was lower in women than men. There was no effect of drugs, anesthesia, surgery or traumatisms on the penetrance.

Conclusions

Penetrance of FSHD1 is low for largest alleles in the range of 9–10 RUs, and lower in women than men. This is of crucial importance for genetic counseling and clinical management of patients and families.

Skeletal muscle imaging in facioscapulohumeral muscular dystrophy, pattern and asymmetry of individual muscle involvement

To better understand postural and movement disabilities, the pattern of total body muscle fat infiltration was analyzed in a large group of patients with facioscapulohumeral muscular dystrophy. Additionally, we studied whether residual D4Z4 repeat array length adjusted for age and gender could predict the degree of muscle involvement. Total body computed tomography scans of 70 patients were used to assess the degree of fat infiltration of 42 muscles from neck to ankle level on a semi-quantitative scale. Groups of muscles that highly correlated regarding fat infiltration were identified using factor analysis. Linear regression analysis was performed using muscle fat infiltration as the dependent variable and D4Z4 repeat length and age as independent variables. A pattern of muscle fat infiltration in facioscapulohumeral muscular dystrophy could be constructed. Trunk muscles were most frequently affected. Of these, back extensors were more frequently affected than previously reported. Asymmetry in muscle involvement was seen in 45% of the muscles that were infiltrated with fat. The right-sided upper extremity showed significantly higher scores for fat infiltration compared to the left side, which could not be explained by handedness. It was possible to explain 29% of the fat infiltration based on D4Z4 repeat length, corrected for age and gender. Based on our results we conclude that frequent involvement of fat infiltration in back extensors, in addition to the abdominal muscles, emphasizes the extent of trunk involvement, which may have a profound impact on postural control even in otherwise mildly affected patients.

Muscular dystrophies and other genetic myopathies

With advances in the genetics of muscle disease, the term, muscular dystrophy, has expanded to include mutations in an increasing large list of genes. This review discusses the genetics, pathophysiology, and potential treatments of the most common forms of muscular dystrophy: Duchenne muscular dystrophy, Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. Other forms of muscular dystrophy and other genetic muscle disorders are also discussed to provide an overview of this complex clinical problem.

The muscular dystrophies

PURPOSE OF REVIEW

With transition to the genetic era, the number of muscular dystrophies has grown significantly, but so too has our understanding of their pathogenic underpinnings. Clinical features associated with each muscular dystrophy still guide us to the diagnosis. However, improved diagnostic abilities refine and expand phenotypic and genotypic correlates. This article discusses the epidemiology, clinical features, and diagnosis of these disorders.

RECENT FINDINGS

Some important recent advancements include (1) a much greater understanding of the pathogenetic pathways underlying facioscapulohumeral muscular dystrophy and myotonic dystrophy type 1; (2) the publication of diagnostic and treatment guidelines for Duchenne muscular dystrophy; and (3) further clarification of the many genetic muscle disorders presenting a limb-girdle pattern of weakness.

SUMMARY

Muscular dystrophies are genetic, progressive, degenerative disorders with the primary symptom of muscle weakness. Duchenne, Becker, facioscapulohumeral, and myotonic muscular dystrophies are most prevalent and tend to have distinctive features helpful in diagnosis. The limb-girdle, Emery-Dreifuss, and oculopharyngeal muscular dystrophies are less common but often may also be diagnosed on the basis of phenotype. Researchers hope to help patients with future discoveries effective in slowing or halting disease progression, reversing or preventing underlying mechanisms, and repairing previously damaged muscle.

Infantile facioscapulohumeral muscular dystrophy revisited: Expansion of clinical phenotypes in patients with a very short EcoRI fragment

Contrary to the classical form, infantile facioscapulohumeral muscular dystrophy (FSHD) usually denotes a severe phenotype and is frequently associated with extramuscular involvements. To elucidate the genotype-phenotype correlation in this severe subgroup, we identified a cohort of nine patients with infantile FSHD who also carried a very short (10-13kb) EcoRI fragment. Their current age ranged from 8 to 33 years and age of onset ranged from 0.4 to 5 years. One patient even manifested his first FSHD-related symptoms at as early as 5 months of age, including inability to smile, poor response to call, and infantile spasms. To date, four patients were wheelchair-bound and six patients had asymmetric weakness. Sensorineural hearing loss and abnormal fundoscopic findings were observed in eight and all of patients respectively. Three with the smallest EcoRI fragments (10-11kb, with normal length being 50-300kb) had mental retardation. Two of these had epilepsy. Cardiac arrhythmias were found in five patients. Restrictive ventilatory defects were observed in seven patients, with one progressing to chronic respiratory failure. Two had swallowing difficulties; one of these required gastrostomy. We identified several rarely reported phenotypes in infantile FSHD, including cardiac arrhythmia, respiratory insufficiency, and swallowing difficulties. There seems to be a correlation between the severity of phenotype and the very short EcoRI fragment in the chromosome 4q35 region. We conclude that the high frequency of multi-organ involvements in this severe FSHD variant suggests the need for an early and multidisciplinary intervention.

Progressive muscular dystrophies

Infancy- or childhood-onset muscular dystrophies may be associated with profound loss of muscle function, affecting ambulation, posture, cardiac and respiratory functions, while those of late onset may be mild and associated with slight weakness or fatigability induced by effort. In addition to the distribution of muscle weakness, symptoms, and course of the disease, the diagnosis of muscular dystrophy is usually ascertained by histological findings. There is connective tissue proliferation in the perimysium and endomysium, variation in muscle fiber size, cytoarchitectural alterations of myofibers such as internal nuclei, myofibrillar whorls, and fiber splitting and lobulation, but, most of all, degeneration and regeneration of myofibers. Causes of muscular dystrophies characterized by muscle weakness and wasting are heterogeneous and include dysfunction of diverse genetic pathways and genes encoding proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. Duchenne and Becker muscular dystrophies are prototypes illustrating advances in the field of myology. Limb-girdle muscular dystrophies (LGMDs) are clinically and genetically heterogeneous, some with autosomal dominant (LGMD1) and others with autosomal recessive (LGMD2) inheritance. Neither clinical and genetic grounds nor biopsy patterns are specific enough to distinguish them, but two common denominators are: (1) weakness and wasting predominating in pelvic and shoulder girdle muscles, with occasional involvement of the myocardium; and (2) necrosis and regeneration of myofibers. While identification of genetic causes and molecular diagnosis are increasingly improved, especially with the advent of new generation sequencing technologies, optimized care, information for the family, and prevention, including genetic counseling and prenatal diagnosis, require multidisciplinary follow-up with genetic, pediatric, and psychological involvement.

Genetic counseling and testing for FSHD (facioscapulohumeral muscular dystrophy) in the Israeli population

Facioscapulohumeral muscular dystrophy (FSHD), is a dominantly inherited, late onset, progressive disease. At present, no treatment or prevention of symptoms are available. There is considerable clinical variability, even within families. The gene whose defect causes FSHD has not been identified, but molecular diagnosis can be made by analyzing D4Z4 repeat length on chromosome 4q35. The results can support or rule out the clinical diagnosis of FSHD, but there are also "gray zone", non-conclusive results. During the years 2000-6, 66 individuals (including 7 asymptomatic individuals), were tested in our institute for D4Z4 repeat number. In 77% of the cases the results were conclusive: two thirds of them supported a diagnosis of FSHD while in a third this diagnosis was ruled out. In 23% the results were in the gray zone. Cognitive involvement was rare, occurring only when the D4Z4 repeat size was very small (<15 kb). Maximal utilization of the existing molecular test for FSHD demands detailed clinical and family pedigree information. We recommend that comprehensive genetic counseling always be given before and after molecular testing for FSHD, in addition to the neurological follow-up. Presymptomatic testing should only be offered when complete molecular evaluation can be offered, including 4qA and 4qB variant analysis.

Epilepsy, speech delay, and mental retardation in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common muscular dystrophies which is related to the deletion of tandem repeats on chromosome 4q35. Extramuscular features such as hearing loss, retinopathy, mental retardation, and epilepsy, may be observed in patients carrying large 4q35 deletions resulting in fragment sizes less than 12 kilobases (kb) (normal >35 kb). We report on a family affected by FSHD carrying a small 4q35 deletion and residual fragments length of 17 kb, presenting with epilepsy (three patients), speech delay (two), and mental retardation (one). In all patients semeiology of seizures and interictal EEG anomalies were congruent with a localization-related epilepsy possibly involving the temporal lobe. In conclusion, we provide further evidences that extramuscular findings such as epilepsy, speech delay, and mental retardation may occur in those patients carrying smaller 4q35 deletions, suggesting that a close correlation between 4q35 fragment size and clinical severity in FSHD is therefore not constant. Moreover, a review of the literature and our observations seem to suggest that focal epilepsies, likely related to the temporal lobe in the present family, represent the main type of epilepsy occurring in children with FSHD.

The cell biology of disease: FSHD: copy number variations on the theme of muscular dystrophy

In humans, copy number variations (CNVs) are a common source of phenotypic diversity and disease susceptibility. Facioscapulohumeral muscular dystrophy (FSHD) is an important genetic disease caused by CNVs. It is an autosomal-dominant myopathy caused by a reduction in the copy number of the D4Z4 macrosatellite repeat located at chromosome 4q35. Interestingly, the reduction of D4Z4 copy number is not sufficient by itself to cause FSHD. A number of epigenetic events appear to affect the severity of the disease, its rate of progression, and the distribution of muscle weakness. Indeed, recent findings suggest that virtually all levels of epigenetic regulation, from DNA methylation to higher order chromosomal architecture, are altered at the disease locus, causing the de-regulation of 4q35 gene expression and ultimately FSHD.