Muscle eosinophilia is a hallmark of chronic disease in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive myopathy caused by the aberrant increased expression of the DUX4 retrogene in skeletal muscle cells. The DUX4 gene encodes a transcription factor that functions in zygotic genome activation and then is silenced in most adult somatic tissues. DUX4 expression in FSHD disrupts normal muscle cell function; however, the downstream pathogenic mechanisms are still unclear. Histologically, FSHD affected muscles show a characteristic dystrophic phenotype that is often accompanied by a pronounced immune cell infiltration, but the role of the immune system in FSHD is not understood. Previously, we used ACTA1;FLExDUX4 FSHD-like mouse models varying in severity as discovery tools to identify increased Interleukin 6 and microRNA-206 levels as serum biomarkers for FSHD disease severity. In this study, we use the ACTA1;FLExDUX4 chronic FSHD-like mouse model to provide insight into the immune response to DUX4 expression in skeletal muscles. We demonstrate that these FSHD-like muscles are enriched with the chemoattractant eotaxin and the cytotoxic eosinophil peroxidase, and exhibit muscle eosinophilia. We further identified muscle fibers with positive staining for eosinophil peroxidase in human FSHD muscle. Our data supports that skeletal muscle eosinophilia is a hallmark of FSHD pathology.

The DUX4-HIF1α Axis in Murine and Human Muscle Cells: A Link More Complex Than Expected

FacioScapuloHumeral muscular Dystrophy (FSHD) is one of the most prevalent inherited muscle disorders and is linked to the inappropriate expression of the DUX4 transcription factor in skeletal muscles. The deregulated molecular network causing FSHD muscle dysfunction and pathology is not well understood. It has been shown that the hypoxia response factor HIF1α is critically disturbed in FSHD and has a major role in DUX4-induced cell death. In this study, we further explored the relationship between DUX4 and HIF1α. We found that the DUX4 and HIF1α link differed according to the stage of myogenic differentiation and was conserved between human and mouse muscle. Furthermore, we found that HIF1α knockdown in a mouse model of DUX4 local expression exacerbated DUX4-mediated muscle fibrosis. Our data indicate that the suggested role of HIF1α in DUX4 toxicity is complex and that targeting HIF1α might be challenging in the context of FSHD therapeutic approaches.

A longitudinal study of disease progression in facioscapulohumeral muscular dystrophy (FSHD)

INTRODUCTION/AIMS

In preparation for clinical trials, it is important to better understand how disease burden changes over time in facioscapulohumeral muscular dystrophy (FSHD) and to assess the capability of select metrics to detect these changes. This study aims to evaluate FSHD disease progression over 1 year and to examine the sensitivity of several outcome measures in detecting changes during this interval.

METHODS

We conducted a 12-month prospective observational study of 41 participants with FSHD. Participants were evaluated at baseline, 6 months, and 12 months with serial strength testing (manual muscle testing or MMT and maximum voluntary isometric contraction testing or MVICT), functional testing (FSHD-Composite Outcome Measure or FSHD-COM, FSHD Clinical Severity Score or CSS, and FSHD Evaluation Score or FES), sleep and fatigue assessments, lean body mass measurements, respiratory testing, and the FSHD-Health Index patient-reported outcome. Changes in these outcome measures were assessed over the 12-month period. Associations between changes in outcome measures and both age and sex were also examined.

RESULTS

In a 12-month period, FSHD participant function remained largely stable with a mild worsening of strength, measured by MMT and standardized MVICT scores, and a mild loss in lean body mass.

DISCUSSION

The abilities and disease burden of adults with FSHD are largely static over a 12-month period with participants demonstrating a mild average reduction in some measures of strength. Selection of patients, outcome measures, and trial duration should be carefully considered during the design and implementation of future clinical studies involving FSHD patients.

Characterization of D4Z4 alleles and assessment of de novo cases in Facioscapulohumeral dystrophy (FSHD) in a cohort of Italian families

Facioscapulohumeral dystrophy (FSHD) is an autosomal dominant disease, although 10%-30% of cases are sporadic. However, this percentage may include truly de novo patients (carrying a reduced D4Z4 allele that is not present in either of the parents) and patients with apparently sporadic disease resulting from mosaicism, non-penetrance, or complex genetic situations in either patients or parents. In this study, we characterized the D4Z4 Reduced Alleles (DRA) and evaluated the frequency of truly de novo cases in FSHD1 in a cohort of DNA samples received consecutively for FSHD-diagnostic from 100 Italian families. The D4Z4 testing revealed that 60 families reported a DRA compatible with FSHD1 (1-10 RU). The DRA co-segregated with the disease in most cases. Five families with truly de novo cases were identified, suggesting that this condition may be slightly lower (8%) than previously reported. In addition, D4Z4 characterization in the investigated families showed 4% of mosaic cases and 2% with translocations. This study further highlighted the importance of performing family studies for clarifying apparently sporadic FSHD cases, with significant implications for genetic counseling, diagnosis, clinical management, and procreative choices for patients and families.

Autosomal dominant in cis D4Z4 repeat array duplication alleles in facioscapulohumeral dystrophy

Facioscapulohumeral dystrophy (FSHD) has a unique genetic aetiology resulting in partial chromatin relaxation of the D4Z4 macrosatellite repeat array on 4qter. This D4Z4 chromatin relaxation facilitates inappropriate expression of the transcription factor DUX4 in skeletal muscle. DUX4 is encoded by a retrogene that is embedded within the distal region of the D4Z4 repeat array. In the European population, the D4Z4 repeat array is usually organized in a single array that ranges between 8 and 100 units. D4Z4 chromatin relaxation and DUX4 derepression in FSHD is most often caused by repeat array contraction to 1-10 units (FSHD1) or by a digenic mechanism requiring pathogenic variants in a D4Z4 chromatin repressor like SMCHD1, combined with a repeat array between 8 and 20 units (FSHD2). With a prevalence of 1.5% in the European population, in cis duplications of the D4Z4 repeat array, where two adjacent D4Z4 arrays are interrupted by a spacer sequence, are relatively common but their relationship to FSHD is not well understood. In cis duplication alleles were shown to be pathogenic in FSHD2 patients; however, there is inconsistent evidence for the necessity of an SMCHD1 mutation for disease development. To explore the pathogenic nature of these alleles we compared in cis duplication alleles in FSHD patients with or without pathogenic SMCHD1 variant. For both groups we showed duplication-allele-specific DUX4 expression. We studied these alleles in detail using pulsed-field gel electrophoresis-based Southern blotting and molecular combing, emphasizing the challenges in the characterization of these rearrangements. Nanopore sequencing was instrumental to study the composition and methylation of the duplicated D4Z4 repeat arrays and to identify the breakpoints and the spacer sequence between the arrays. By comparing the composition of the D4Z4 repeat array of in cis duplication alleles in both groups, we found that specific combinations of proximal and distal repeat array sizes determine their pathogenicity. Supported by our algorithm to predict pathogenicity, diagnostic laboratories should now be furnished to accurately interpret these in cis D4Z4 repeat array duplications, alleles that can easily be missed in routine settings.

snRNA-seq analysis in multinucleated myogenic FSHD cells identifies heterogeneous FSHD transcriptome signatures associated with embryonic-like program activation and oxidative stress-induced apoptosis

The sporadic nature of DUX4 expression in FSHD muscle challenges comparative transcriptome analyses between FSHD and control samples. A variety of DUX4 and FSHD-associated transcriptional changes have been identified, but bulk RNA-seq strategies prohibit comprehensive analysis of their spatiotemporal relation, interdependence and role in the disease process. In this study, we used single-nucleus RNA-sequencing of nuclei isolated from patient- and control-derived multinucleated primary myotubes to investigate the cellular heterogeneity in FSHD. Taking advantage of the increased resolution in snRNA-sequencing of fully differentiated myotubes, two distinct populations of DUX4-affected nuclei could be defined by their transcriptional profiles. Our data provides insights into the differences between these two populations and suggests heterogeneity in two well-known FSHD-associated transcriptional aberrations: increased oxidative stress and inhibition of myogenic differentiation. Additionally, we provide evidence that DUX4-affected nuclei share transcriptome features with early embryonic cells beyond the well-described cleavage stage, progressing into the 8-cell and blastocyst stages. Altogether, our data suggests that the FSHD transcriptional profile is defined by a mixture of individual and sometimes mutually exclusive DUX4-induced responses and cellular state-dependent downstream effects.

Physical activity practiced at a young age is associated with a less severe subsequent clinical presentation in facioscapulohumeral muscular dystrophy

BACKGROUND

In facioscapulohumeral muscular dystrophy (FSHD), it is not known whether physical activity (PA) practiced at young age is associated with the clinical presentation of disease. To assess this issue, we performed a retrospective cohort study concerning the previous practice of sports and, among them, those with medium-high cardiovascular commitment in clinically categorized carriers of a D4Z4 reduced allele (DRA).

METHODS

People aged between 18 and 60 were recruited as being DRA carriers. Subcategory (classical phenotype, A; incomplete phenotype, B; asymptomatic carriers, C; complex phenotype, D) and FSHD score, which measures muscle functional impairment, were assessed for all participants. Information on PAs was retrieved by using an online survey dealing with the practice of sports at a young age.

RESULTS

368 participants were included in the study, average age 36.6 years (SD = 9.4), 47.6% male. The FSHD subcategory A was observed in 157 (42.7%) participants with average (± SD) FSHD score of 5.8 ± 3.0; the incomplete phenotype (category B) in 46 (12.5%) participants (average score 2.2 ± 1.7) and the D phenotype in 61 (16.6%, average score 6.5 ± 3.8). Asymptomatic carriers were 104 (subcategory C, 28.3%, score 0.0 ± 0.2). Time from symptoms onset was higher for patients with A (15.8 ± 11.1 years) and D phenotype (13.3 ± 11.9) than for patients with B phenotype (7.3 ± 9.0). The practice of sports was associated with lower FSHD score (-17%) in participants with A phenotype (MR = 0.83, 95% CI = 0.73-0.95, p = 0.007) and by 33% in participants with D phenotype (MR = 0.67, 95% CI = 0.51-0.89, p = 0.006). Conversely, no improvement was observed in participants with incomplete phenotype with mild severity (B).

CONCLUSIONS

PAs at a young age are associated with a lower clinical score in the adult A and D FSHD subcategories. These results corroborate the need to consider PAs at the young age as a fundamental indicator for the correct clinical stratification of the disease and its possible evolution.

Face to Face: deciphering facial involvement in inclusion body myositis

OBJECTIVE

The objective of this study is to evaluate the frequency and characteristics of facial involvement in inclusion body myositis (IBM) patients and to compare it to the one previously described in facioscapulohumeral dystrophy (FSHD) patients.

METHODS

Thirty-two IBM patients were included and compared to 29 controls and 39 FSHD patients. All participants were recorded in a video as they performed a series of seven facial tasks. Five raters independently assessed facial weakness using both a qualitative evaluation and a semi-quantitative facial weakness score (FWS).

RESULTS

IBM patients had higher FWS than controls (7.89 ± 7.56 vs 1.06 ± 0.88, p < 0.001). Twenty IBM patients (63%) had a facial weakness with a FWS above the maximum value for controls. All facial tasks were significantly more impaired in IBM patients compared to controls (p < 0.001), task 2 evaluating orbiculari oculi muscle weakness being the most affected. IBM patients with facial weakness reported more swallowing troubles than IBM patients without facial weakness (p = 0.03). FSHD patients displayed higher FWS than IBM patients (12.16 ± 8.37 vs 7.89 ± 7.56, p = 0.01) with more pronounced facial asymmetry (p = 0.01). FWS inter-rater ICC was 0.775.

CONCLUSION

This study enabled us to estimate the frequency of facial impairment in IBM in more than half of patients, to detail its characteristics and to compare them with those of FSHD patients. The standardized, semi-quantitative FWS is an interesting diagnostic help in IBM as it appeared more sensitive than qualitative evaluation to detect mild facial weakness.

Herpesviruses mimic zygotic genome activation to promote viral replication

DUX4 is a germline transcription factor and a master regulator of zygotic genome activation. During early embryogenesis, DUX4 is crucial for maternal to zygotic transition at the 2-8-cell stage in order to overcome silencing of genes and enable transcription from the zygotic genome. In adult somatic cells, DUX4 expression is silenced and its activation in adult muscle cells causes the genetic disorder Facioscapulohumeral Muscular Dystrophy (FSHD). Here we show that herpesviruses from alpha-, beta- and gamma-herpesvirus subfamilies as well as papillomaviruses actively induce DUX4 expression to promote viral transcription and replication. We demonstrate that HSV-1 immediate early proteins directly induce expression of DUX4 and its target genes including endogenous retroelements, which mimics zygotic genome activation. We further show that DUX4 directly binds to the viral genome and promotes viral transcription. DUX4 is functionally required for herpesvirus infection, since genetic depletion of DUX4 by CRISPR/Cas9 abrogates viral replication. Our results show that herpesviruses induce DUX4 expression and its downstream germline-specific genes and retroelements, thus mimicking an early embryonic-like transcriptional program that prevents epigenetic silencing of the viral genome and facilitates herpesviral gene expression.

Optical Genome Mapping for the Molecular Diagnosis of Facioscapulohumeral Muscular Dystrophy: Advancement and Challenges

Facioscapulohumeral muscular dystrophy (FSHD) is the second most common muscular dystrophy in adults, and it is associated with local D4Z4 chromatin relaxation, mostly via the contraction of the D4Z4 macrosatellite repeat array on chromosome 4q35. In this study, we aimed to investigate the use of Optical Genome Mapping (OGM) as a diagnostic tool for testing FSHD cases from the UK and India and to compare OGM performance with that of traditional techniques such as linear gel (LGE) and Pulsed-field gel electrophoresis (PFGE) Southern blotting (SB). A total of 6 confirmed and 19 suspected FSHD samples were processed with LGE and PFGE, respectively. The same samples were run using a Saphyr Genome-Imaging Instrument (1-color), and the data were analysed using custom EnFocus FSHD analysis. OGM was able to confirm the diagnosis of FSHD1 in all FSHD1 cases positive for SB (n = 17), and D4Z4 sizing highly correlated with PFGE-SB (p < 0.001). OGM correctly identified cases with mosaicism for the repeat array contraction (n = 2) and with a duplication of the D4Z4 repeat array. OGM is a promising new technology able to unravel structural variants in the genome and seems to be a valid tool for diagnosing FSHD1.

Epigenetic profiling of the D4Z4 locus: Optimization of the protocol for studying DNA methylation at single CpG site level

The alteration of epigenetic modifications, including DNA methylation, can contribute to the etiopathogenesis and progression of many diseases. Among them, facioscapulohumeral dystrophy (FSHD) is a muscular disorder characterized by the loss of repressive epigenetic features affecting the D4Z4 locus (4q35). As a consequence, these alterations are responsible for DNA hypomethylation and a transcriptional-active chromatin conformation change that, in turn, lead to the aberrant expression of DUX4 in muscle cells. In the present study, methylation levels of 29 CpG sites of the DR1 region (within each repeat unit of the D4Z4 macrosatellite) were assessed on 335 subjects by employing primers designed for enhancing the performance of the assay. First, the DR1 original primers were optimized by adding M13 oligonucleotide tails. Moreover, the DR1 reverse primer was replaced with a degenerate one. As a result, the protocol optimization allowed a better sequencing resolution and a more accurate evaluation of DR1 methylation levels. Moreover, the assessment of the repeatability of measurements proved the reliability and robustness of the assay. The optimized protocol emerges as an excellent method to detect methylation levels compatible with FSHD.

Three-dimensional quantitative muscle ultrasound in patients with facioscapulohumeral dystrophy and myotonic dystrophy

INTRODUCTION/AIMS

Ultrasound imaging of muscle tissue conventionally results in two-dimensional sampling of tissue. For heterogeneously affected muscles, a sampling error using two-dimensional (2D) ultrasound can therefore be expected. In this study, we aimed to quantify and extend ultrasound imaging findings in neuromuscular disorders by using three-dimensional quantitative muscle ultrasound (3D QMUS).

METHODS

Patients with facioscapulohumeral dystrophy (n = 31) and myotonic dystrophy type 1 (n = 16) were included in this study. After physical examination, including Medical Research Council (MRC) scores, the tibialis anterior muscle was scanned with automated ultrasound. QMUS parameters were calculated over 15 cm of the length of the tibialis anterior muscle and were compared with a healthy reference data set.

RESULTS

With 3D QMUS local deviations from the healthy reference could be detected. Significant Pearson correlations (P < .01) between MRC score and QMUS parameters in male patients (n = 23) included the mean echo intensity (EI) (0.684), the standard deviation of EI (0.737), and the residual attenuation (0.841). In 91% of all patients, mean EI deviated by more than 1 standard deviation from the healthy reference. In general, the proportion of muscle tissue with a Z score >1 was about 50%.

DISCUSSION

In addition to mean EI, multiple QMUS parameters reported in this study are potential biomarkers for pathology. Besides a moderate correlation of mean EI with muscle weakness, two other parameters showed strong correlations: standard deviation of EI and residual attenuation. Local detection of abnormalities makes 3D QMUS a promising method that can be used in research and potentially for clinical evaluation.

Apabetalone, a Clinical-Stage, Selective BET Inhibitor, Opposes DUX4 Target Gene Expression in Primary Human FSHD Muscle Cells

Facioscapulohumeral dystrophy (FSHD) is a muscle disease caused by inappropriate expression of the double homeobox 4 (DUX4) gene in skeletal muscle, and its downstream activation of pro-apoptotic transcriptional programs. Inhibitors of DUX4 expression have the potential to treat FSHD. Apabetalone is a clinical-stage bromodomain and extra-terminal (BET) inhibitor, selective for the second bromodomain on BET proteins. Using primary human skeletal muscle cells from FSHD type 1 patients, we evaluated apabetalone for its ability to counter DUX4's deleterious effects and compared it with the pan-BET inhibitor JQ1, and the p38 MAPK inhibitor-and DUX4 transcriptional repressor-losmapimod. We applied RNA-sequencing and bioinformatic analysis to detect treatment-associated impacts on the transcriptome of these cells. Apabetalone inhibited the expression of DUX4 downstream markers, reversing hallmarks of FSHD gene expression in differentiated muscle cells. JQ1, but not apabetalone, was found to induce apoptosis. While both BET inhibitors modestly impacted differentiation marker expression, they did not affect myotube fusion. Losmapimod also reduced expression of DUX4 target genes but differed in its impact on FSHD-associated pathways. These findings demonstrate that apabetalone inhibits DUX4 target gene expression and reverses transcriptional programs that contribute to FSHD pathology, making this drug a promising candidate therapeutic for FSHD.

MATR3 is an endogenous inhibitor of DUX4 in FSHD muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common neuromuscular disorders and has no cure. Due to an unknown molecular mechanism, FSHD displays overlapping manifestations with the neurodegenerative disease amyotrophic lateral sclerosis (ALS). FSHD is caused by aberrant gain of expression of the transcription factor double homeobox 4 (DUX4), which triggers a pro-apoptotic transcriptional program resulting in inhibition of myogenic differentiation and muscle wasting. Regulation of DUX4 activity is poorly known. We identify Matrin 3 (MATR3), whose mutation causes ALS and dominant distal myopathy, as a cellular factor controlling DUX4 expression and activity. MATR3 binds to the DUX4 DNA-binding domain and blocks DUX4-mediated gene expression, rescuing cell viability and myogenic differentiation of FSHD muscle cells, without affecting healthy muscle cells. Finally, we characterize a shorter MATR3 fragment that is necessary and sufficient to directly block DUX4-induced toxicity to the same extent as the full-length protein. Collectively, our data suggest MATR3 as a candidate for developing a treatment for FSHD.

Whole exome sequencing highlights rare variants in CTCF, DNMT1, DNMT3A, EZH2 and SUV39H1 as associated with FSHD

Introduction: Despite the progress made in the study of Facioscapulohumeral Dystrophy (FSHD), the wide heterogeneity of disease complicates its diagnosis and the genotype-phenotype correlation among patients and within families. In this context, the present work employed Whole Exome Sequencing (WES) to investigate known and unknown genetic contributors that may be involved in FSHD and may represent potential disease modifiers, even in presence of a D4Z4 Reduced Allele (DRA). Methods: A cohort of 126 patients with clinical signs of FSHD were included in the study, which were characterized by D4Z4 sizing, methylation analysis and WES. Specific protocols were employed for D4Z4 sizing and methylation analysis, whereas the Illumina® Next-Seq 550 system was utilized for WES. The study included both patients with a DRA compatible with FSHD diagnosis and patients with longer D4Z4 alleles. In case of patients harboring relevant variants from WES, the molecular analysis was extended to the family members. Results: The WES data analysis highlighted 20 relevant variants, among which 14 were located in known genetic modifiers (SMCHD1, DNMT3B and LRIF1) and 6 in candidate genes (CTCF, DNMT1, DNMT3A, EZH2 and SUV39H1). Most of them were found together with a permissive short (4-7 RU) or borderline/long DRA (8-20 RU), supporting the possibility that different genes can contribute to disease heterogeneity in presence of a FSHD permissive background. The segregation and methylation analysis among family members, together with clinical findings, provided a more comprehensive picture of patients. Discussion: Our results support FSHD pathomechanism being complex with a multigenic contribution by several known (SMCHD1, DNMT3B, LRIF1) and possibly other candidate genes (CTCF, DNMT1, DNMT3A, EZH2, SUV39H1) to disease penetrance and expressivity. Our results further emphasize the importance of extending the analysis of molecular findings within the proband's family, with the purpose of providing a broader framework for understanding single cases and allowing finer genotype-phenotype correlations in FSHD-affected families.

The FSHD muscle-blood biomarker: a circulating transcriptomic biomarker for clinical severity in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a prevalent, incurable skeletal myopathy. Clinical trials for FSHD are hindered by heterogeneous biomarkers poorly associated with clinical severity, requiring invasive muscle biopsy. Macroscopically, FSHD presents with slow fatty replacement of muscle, rapidly accelerated by inflammation. Mis-expression of the transcription factor DUX4 is currently accepted to underlie pathogenesis, and mechanisms including PAX7 target gene repression have been proposed. Here, we performed RNA-sequencing on MRI-guided inflamed and isogenic non-inflamed muscle biopsies from the same clinically characterized FSHD patients (n = 24), alongside isogenic peripheral blood mononucleated cells from a subset of patients (n = 13) and unaffected controls (n = 11). Multivariate models were employed to evaluate the clinical associations of five published FSHD transcriptomic biomarkers. We demonstrated that PAX7 target gene repression can discriminate control, inflamed and non-inflamed FSHD muscle independently of age and sex (P < 0.013), while the discriminatory power of DUX4 target genes was limited to distinguishing FSHD muscle from control. Importantly, the level of PAX7 target gene repression in non-inflamed muscle associated with clinical assessments of FSHD severity (P = 0.04). DUX4 target gene biomarkers in FSHD muscle showed associations with lower limb fat fraction and D4Z4 array length but not clinical assessment. Lastly, PAX7 target gene repression in FSHD muscle correlated with the level in isogenic peripheral blood mononucleated cells (P = 0.002). A refined PAX7 target gene biomarker comprising 143/601 PAX7 target genes computed in peripheral blood (the FSHD muscle-blood biomarker) associated with clinical severity in FSHD patients (P < 0.036). Our new circulating biomarker validates as a classifier of clinical severity in an independent data set of 54 FSHD patient and 29 matched control blood samples, with improved power in older patients (P = 0.03). In summary, we present the minimally invasive FSHD muscle-blood biomarker of FSHD clinical severity valid in patient muscle and blood, of potential use in routine disease monitoring and clinical trials.

Facioscapulohumeral Muscular Dystrophy is Associated With Altered Myoblast Proteome Dynamics

Proteomic studies in facioscapulohumeral muscular dystrophy (FSHD) could offer new insight into disease mechanisms underpinned by post-transcriptional processes. We used stable isotope (deuterium oxide; D2O) labeling and peptide mass spectrometry to investigate the abundance and turnover rates of proteins in cultured muscle cells from two individuals affected by FSHD and their unaffected siblings (UASb). We measured the abundance of 4420 proteins and the turnover rate of 2324 proteins in each (n = 4) myoblast sample. FSHD myoblasts exhibited a greater abundance but slower turnover rate of subunits of mitochondrial respiratory complexes and mitochondrial ribosomal proteins, which may indicate an accumulation of "older" less viable mitochondrial proteins in myoblasts from individuals affected by FSHD. Treatment with a 2'-O-methoxyethyl modified antisense oligonucleotide targeting exon 3 of the double homeobox 4 (DUX4) transcript tended to reverse mitochondrial protein dysregulation in FSHD myoblasts, indicating the effect on mitochondrial proteins may be a DUX4-dependent mechanism. Our results highlight the importance of post-transcriptional processes and protein turnover in FSHD pathology and provide a resource for the FSHD research community to explore this burgeoning aspect of FSHD.

Compromised nonsense-mediated RNA decay results in truncated RNA-binding protein production upon DUX4 expression

Nonsense-mediated RNA decay (NMD) degrades transcripts carrying premature termination codons. NMD is thought to prevent the synthesis of toxic truncated proteins. However, whether loss of NMD results in widespread production of truncated proteins is unclear. A human genetic disease, facioscapulohumeral muscular dystrophy (FSHD), features acute inhibition of NMD upon expression of the disease-causing transcription factor, DUX4. Using a cell-based model of FSHD, we show production of truncated proteins from physiological NMD targets and find that RNA-binding proteins are enriched for aberrant truncations. The NMD isoform of one RNA-binding protein, SRSF3, is translated to produce a stable truncated protein, which is detected in FSHD patient-derived myotubes. Ectopic expression of truncated SRSF3 confers toxicity, and its downregulation is cytoprotective. Our results delineate the genome-scale impact of NMD loss. This widespread production of potentially deleterious truncated proteins has implications for FSHD biology as well as other genetic diseases where NMD is therapeutically modulated.

Molecular and Phenotypic Changes in FLExDUX4 Mice

Facioscapulohumeral muscular dystrophy (FSHD) is caused by the aberrant expression of the double homeobox 4 (DUX4) gene. The FLExDUX4 mouse model carries an inverted human DUX4 transgene which has leaky DUX4 transgene expression at a very low level. No overt muscle pathology was reported before 16 weeks. The purpose of this study is to track and characterize the FLExDUX4 phenotypes for a longer period, up to one year old. In addition, transcriptomic changes in the muscles of 2-month-old mice were investigated using RNA-seq. The results showed that male FLExDUX4 mice developed more severe phenotypes and at a younger age in comparison to the female mice. These include lower body and muscle weight, and muscle weakness measured by grip strength measurements. Muscle pathological changes were observed at older ages, including fibrosis, decreased size of type IIa and IIx myofibers, and the development of aggregates containing TDP-43 in type IIb myofibers. Muscle transcriptomic data identified early molecular changes in biological pathways regulating circadian rhythm and adipogenesis. The study suggests a slow progressive change in molecular and muscle phenotypes in response to the low level of DUX4 expression in the FLExDUX4 mice.

Five-year follow-up study on quantitative muscle magnetic resonance imaging in facioscapulohumeral muscular dystrophy: The link to clinical outcome

BACKGROUND

It is unclear how changes in quantitative muscle magnetic resonance imaging (MRI) relate to changes in clinical outcome in facioscapulohumeral muscular dystrophy (FSHD), although this information is crucial for optimal use of MRI as imaging biomarker in trials. We therefore assessed muscle MRI and clinical outcome measures in a large longitudinal prospective cohort study.

METHODS

All patients were assessed by MRI at baseline and at 5-year follow-up, employing 2pt-Dixon and turbo inversion recovery magnitude (TIRM) sequences, after which fat fraction and TIRM positivity of 19 leg muscles were determined bilaterally. The MRI compound score (CoS) was defined as the mean fat fraction of all muscles weighted for cross-sectional area. Clinical outcome measures included the Ricci-score, FSHD clinical score (FSHD-CS), MRC sumscore (MRC-SS), and motor-function-measure (MFM).

RESULTS

We included 105 FSHD patients [mean age 54 ± 14 years, median Ricci-score 7 (range 0-10)]. The median change over 5 years' time in the MRI-CoS was 2.0% (range -4.6 to +12.1; P < 0.001). The median change over 5 years' time in clinical outcome measures was small in all measures, with z-scores ranging from 5.0 to 7.2 (P < 0.001). The change in MRI-CoS correlated with change in FSHD-CS and Ricci-score (ρ = 0.25, respectively; ρ = 0.23, P < 0.05). The largest median increase in MRI-CoS was seen in baseline subgroups with an MRI-CoS 20-40% (6.1%), with ≥2 TIRM positive muscles (3.5%) or with an FSHD-CS 5-10 (3.1%).

CONCLUSIONS

This 5-year study showed significant changes in MRI and clinical outcome measures and a significant correlation between changes in MRI-CoS and changes in clinical outcome measures. In addition, we identified subgroups of patients that are most prone to radiological disease progression. This knowledge further establishes quantitative MRI parameters as prognostic biomarkers in FSHD and as efficacy biomarkers in upcoming clinical trials.

Methylation of the 4q35 D4Z4 repeat defines disease status in facioscapulohumeral muscular dystrophy

Genetic diagnosis of facioscapulohumeral muscular dystrophy (FSHD) remains a challenge in clinical practice as it cannot be detected by standard sequencing methods despite being the third most common muscular dystrophy. The conventional diagnostic strategy addresses the known genetic parameters of FSHD: the required presence of a permissive haplotype, a size reduction of the D4Z4 repeat of chromosome 4q35 (defining FSHD1) or a pathogenic variant in an epigenetic suppressor gene (consistent with FSHD2). Incomplete penetrance and epistatic effects of the underlying genetic parameters as well as epigenetic parameters (D4Z4 methylation) pose challenges to diagnostic accuracy and hinder prediction of clinical severity. In order to circumvent the known limitations of conventional diagnostics and to complement genetic parameters with epigenetic ones, we developed and validated a multistage diagnostic workflow that consists of a haplotype analysis and a high-throughput methylation profile analysis (FSHD-MPA). FSHD-MPA determines the average global methylation level of the D4Z4 repeat array as well as the regional methylation of the most distal repeat unit by combining bisulphite conversion with next-generation sequencing and a bioinformatics pipeline and uses these as diagnostic parameters. We applied the diagnostic workflow to a cohort of 148 patients and compared the epigenetic parameters based on FSHD-MPA to genetic parameters of conventional genetic testing. In addition, we studied the correlation of repeat length and methylation level within the most distal repeat unit with age-corrected clinical severity and age at disease onset in FSHD patients. The results of our study show that FSHD-MPA is a powerful tool to accurately determine the epigenetic parameters of FSHD, allowing discrimination between FSHD patients and healthy individuals, while simultaneously distinguishing FSHD1 and FSHD2. The strong correlation between methylation level and clinical severity indicates that the methylation level determined by FSHD-MPA accounts for differences in disease severity among individuals with similar genetic parameters. Thus, our findings further confirm that epigenetic parameters rather than genetic parameters represent FSHD disease status and may serve as a valuable biomarker for disease status.

Smartphone and Wearable Sensors for the Estimation of Facioscapulohumeral Muscular Dystrophy Disease Severity: Cross-sectional Study

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive neuromuscular disease. Its slow and variable progression makes the development of new treatments highly dependent on validated biomarkers that can quantify disease progression and response to drug interventions.

OBJECTIVE

We aimed to build a tool that estimates FSHD clinical severity based on behavioral features captured using smartphone and remote sensor data. The adoption of remote monitoring tools, such as smartphones and wearables, would provide a novel opportunity for continuous, passive, and objective monitoring of FSHD symptom severity outside the clinic.

METHODS

In total, 38 genetically confirmed patients with FSHD were enrolled. The FSHD Clinical Score and the Timed Up and Go (TUG) test were used to assess FSHD symptom severity at days 0 and 42. Remote sensor data were collected using an Android smartphone, Withings Steel HR+, Body+, and BPM Connect+ for 6 continuous weeks. We created 2 single-task regression models that estimated the FSHD Clinical Score and TUG separately. Further, we built 1 multitask regression model that estimated the 2 clinical assessments simultaneously. Further, we assessed how an increasingly incremental time window affected the model performance. To do so, we trained the models on an incrementally increasing time window (from day 1 until day 14) and evaluated the predictions of the clinical severity on the remaining 4 weeks of data.

RESULTS

The single-task regression models achieved an R² of 0.57 and 0.59 and a root-mean-square error (RMSE) of 2.09 and 1.66 when estimating FSHD Clinical Score and TUG, respectively. Time spent at a health-related location (such as a gym or hospital) and call duration were features that were predictive of both clinical assessments. The multitask model achieved an R² of 0.66 and 0.81 and an RMSE of 1.97 and 1.61 for the FSHD Clinical Score and TUG, respectively, and therefore outperformed the single-task models in estimating clinical severity. The 3 most important features selected by the multitask model were light sleep duration, total steps per day, and mean steps per minute. Using an increasing time window (starting from day 1 to day 14) for the FSHD Clinical Score, TUG, and multitask estimation yielded an average R² of 0.65, 0.79, and 0.76 and an average RMSE of 3.37, 2.05, and 4.37, respectively.

CONCLUSIONS

We demonstrated that smartphone and remote sensor data could be used to estimate FSHD clinical severity and therefore complement the assessment of FSHD outside the clinic. In addition, our results illustrated that training the models on the first week of data allows for consistent and stable prediction of FSHD symptom severity. Longitudinal follow-up studies should be conducted to further validate the reliability and validity of the multitask model as a tool to monitor disease progression over a longer period.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04999735; https://www.clinicaltrials.gov/ct2/show/NCT04999735.

Facioscapulohumeral Disease as a myodevelopmental disease: Applying Ockham's razor to its various features

 Facioscapulohumeral muscular dystrophy (FSHD) is an exclusively human neuromuscular disease. In the last decades the cause of FSHD was identified: the loss of epigenetic repression of the D4Z4 repeat on chromosome 4q35 resulting in inappropriate transcription of DUX4. This is a consequence of a reduction of the array below 11 units (FSHD1) or of a mutation in methylating enzymes (FSHD2). Both require the presence of a 4qA allele and a specific centromeric SSLP haplotype. Muscles become involved in a rostro-caudally order with an extremely variable progression rate. Mild disease and non-penetrance in families with affected individuals is common. Furthermore, 2% of the Caucasian population carries the pathological haplotype without clinical features of FSHD.In order to explain the various features of FSHD we applied Ockham's Razor to all possible scenarios and removed unnecessary complexities. We postulate that early in embryogenesis a few cells escape epigenetic silencing of the D4Z4 repeat. Their number is assumed to be roughly inversely related to the residual D4Z4 repeat size. By asymmetric cell division, they produce a rostro-caudal and medio-lateral decreasing gradient of weakly D4Z4-repressed mesenchymal stem cells. The gradient tapers towards an end as each cell-division allows renewed epigenetic silencing. Over time, this spatial gradient translates into a temporal gradient based on a decreasing number of weakly silenced stem cells. These cells contribute to a mildly abnormal myofibrillar structure of the fetal muscles. They also form a downward tapering gradient of epigenetically weakly repressed satellite cells. When activated by mechanical trauma, these satellite cells de-differentiate and express DUX4. When fused to myofibrils they contribute to muscle cell death in various ways. Over time and dependent on how far the gradient reaches the FSHD phenotype becomes progressively manifest. We thus hypothesize FSHD to be a myodevelopmental disease with a lifelong attempt to restore DUX4 repression.

Outcomes of Scapulothoracic Fusion in Patients with Facioscapulohumeral Dystrophy: A Comparison of Allograft versus Autograft Bone Grafting

BACKGROUND

Scapulothoracic fusion (ST) for Facioscapulohumeral Muscular Dystrophy (FSHD) is an established treatment that corrects scapular instability, though has high reported complication rates. The purpose of our study was to characterize the outcomes of ST fusion for FSHD in a large patient cohort and to compare the outcomes of bone grafting types and fixation techniques. Our hypothesis is that union rates do not differ by bone graft type during ST fusion.

METHODS

A retrospective chart review was undertaken for patients receiving ST fusion at multiple institutions performed by a single surgeon from a period of 2013 to 2020 with minimum 2-year follow-up. Patient demographics, surgical technique, time to union, complications, and clinical outcomes including patient reported outcome measures (PROMs) were recorded. Univariate and multivariate statistics including regression analyses were performed to compare pre- and postoperative outcomes.

RESULTS

Fifty patients with 54 ST fusions (n=4 bilateral) and an average follow-up of 5.8 years (SD 1.6) were included for analysis. Active forward elevation (77 degrees versus 124 degrees; p<0.00001) and abduction (60 degrees versus 90 degrees; p<0.00001) both improved significantly after fusion. Average internal rotation after fusion was L3-L4. VAS pain (2.6 versus 1.2; p<0.00001), SSV (33 versus 76; p<0.00001), and ASES (41.8 versus 76.1; p<0.00001) all improved significantly postoperatively. Fifty percent (n=27/54) of patients received treatment with cerclage versus Luque (n=27/54) wires, while 53.7% (n=29/54) received femoral head allograft versus 46.3% (n=25/54) iliac crest autograft. Average radiographic time to healing was 11.1 (SD 3.2) weeks with no incidence of non-union and did not significantly differ by bone graft type (p=0.26) or technique (p=0.20). There was a complication rate of 24.1% including seroma (n=3), superficial infection (n=2), transient neurologic injury (n=2), hemothorax (n=1), rib fracture (n=1), pneumothorax (n=1), and shortness of breath (n=1), though none requiring reoperations. There was no significant difference in the rate of postoperative complications when comparing surgical technique (p=0.81) and bone graft type (p=0.93). There were no independently predictive factors influencing the rate of postoperative complications by multivariate regression. Regression analysis showed that postoperative ASES score was independently associated with preoperative ASES score (p<0.0001), iliac crest autograft (p<0.011), and presence of complications (p<0.043).

CONCLUSION

Patients receiving ST fusion for FSHD demonstrate globally improved active motion and PROMS. Fusion construct or type of bone graft does not affect time to union or complication rates. Surgeons should be aware of a relatively high complication rate in the early postoperative period.

The effect of tibialis anterior weakness on foot drop and toe clearance in patients with facioscapulohumeral dystrophy

BACKGROUND

Facioscapulohumeral dystrophy is a genetic disease characterized by progressive muscle weakness leading to a complex combination of postural instability, foot drop during swing and compensatory strategies during gait that have been related to an increased risk of falling. The aim is to assess the effect of tibialis anterior muscle weakness on foot drop and minimum toe clearance of patients with facioscapulohumeral dystrophy during gait.

METHODS

Eight patients allocated to a subgroup depending on the severity of tibialis anterior muscle weakness, assessed by manual muscle testing (i.e., severe and mild weakness), and eight matched control participants underwent gait analysis at self-selected walking speeds.

FINDINGS

Walking speed, for all facioscapulohumeral dystrophy patients, and step length, for patients with severe weakness only, were significantly decreased compared to control participants. Minimum toe clearance was similar across all groups, but its variability was increased only for patients with severe weakness. A greater foot drop was systematically observed for patients with severe weakness during swing and only in late swing for patients with mild weakness. Individual strategies to compensate for foot drop remain unclear and may depend on other muscle impairment variability.

INTERPRETATION

Although all patients were able to control the average height of their foot trajectory during swing, patients with severe tibialis anterior muscle weakness exhibited increased foot drop and minimum toe clearance variability. Manual muscle testing is a simple, cheap and effective method to assess tibialis anterior muscle weakness and seems promising to identify facioscapulohumeral dystrophy patients with an increased risk of tripping.

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.

A Targeted Approach for Evaluating DUX4-Regulated Proteins as Potential Serum Biomarkers for Facioscapulohumeral Muscular Dystrophy Using Immunoassay Proteomics

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive myopathy caused by misexpression of the double homeobox 4 (DUX4) embryonic transcription factor in skeletal muscle. Identifying quantitative and minimally invasive FSHD biomarkers to report on DUX4 activity will significantly accelerate therapeutic development.

OBJECTIVE

The goal of this study was to analyze secreted proteins known to be induced by DUX4 using the commercially available Olink Proteomics platform in order to identify potential blood-based molecular FSHD biomarkers.

METHODS

We used high-throughput, multiplex immunoassays from Olink Proteomics to measure the levels of several known DUX4-induced genes in a cellular myoblast model of FSHD, in FSHD patient-derived myotube cell cultures, and in serum from individuals with FSHD. Levels of other proteins on the Olink Proteomics panels containing these DUX4 targets were also examined in secondary exploratory analysis.

RESULTS

Placental alkaline phosphatase (ALPP) levels correlated with DUX4 expression in both cell-based FSHD systems but did not distinguish FSHD patient serum from unaffected controls.

CONCLUSIONS

ALPP, as measured with the Olink Proteomics platform, is not a promising FSHD serum biomarker candidate but could be utilized to evaluate DUX4 activity in discovery research efforts.

Radiomics and machine learning applied to STIR sequence for prediction of quantitative parameters in facioscapulohumeral disease

Purpose

Quantitative Muscle MRI (qMRI) is a valuable and non-invasive tool to assess disease involvement and progression in neuromuscular disorders being able to detect even subtle changes in muscle pathology. The aim of this study is to evaluate the feasibility of using a conventional short-tau inversion recovery (STIR) sequence to predict fat fraction (FF) and water T2 (wT2) in skeletal muscle introducing a radiomic workflow with standardized feature extraction combined with machine learning algorithms.

Methods

Twenty-five patients with facioscapulohumeral muscular dystrophy (FSHD) were scanned at calf level using conventional STIR sequence and qMRI techniques. We applied and compared three different radiomics workflows (WF1, WF2, WF3), combined with seven Machine Learning regression algorithms (linear, ridge and lasso regression, tree, random forest, k-nearest neighbor and support vector machine), on conventional STIR images to predict FF and wT2 for six calf muscles.

Results

The combination of WF3 and K-nearest neighbor resulted to be the best predictor model of qMRI parameters with a mean absolute error about ± 5 pp for FF and ± 1.8 ms for wT2.

Conclusion

This pilot study demonstrated the possibility to predict qMRI parameters in a cohort of FSHD subjects starting from conventional STIR sequence.

D4Z4 Methylation Levels Combined with a Machine Learning Pipeline Highlight Single CpG Sites as Discriminating Biomarkers for FSHD Patients

The study describes a protocol for methylation analysis integrated with Machine Learning (ML) algorithms developed to classify Facio-Scapulo-Humeral Dystrophy (FSHD) subjects. The DNA methylation levels of two D4Z4 regions (DR1 and DUX4-PAS) were assessed by an in-house protocol based on bisulfite sequencing and capillary electrophoresis, followed by statistical and ML analyses. The study involved two independent cohorts, namely a training group of 133 patients with clinical signs of FSHD and 150 healthy controls (CTRL) and a testing set of 27 FSHD patients and 25 CTRL. As expected, FSHD patients showed significantly reduced methylation levels compared to CTRL. We utilized single CpG sites to develop a ML pipeline able to discriminate FSHD subjects. The model identified four CpGs sites as the most relevant for the discrimination of FSHD subjects and showed high metrics values (accuracy: 0.94, sensitivity: 0.93, specificity: 0.96). Two additional models were developed to differentiate patients with lower D4Z4 size and patients who might carry pathogenic variants in FSHD genes, respectively. Overall, the present model enables an accurate classification of FSHD patients, providing additional evidence for DNA methylation as a powerful disease biomarker that could be employed for prioritizing subjects to be tested for FSHD.

Morpho-Functional Macular Assessment in a Case of Facioscapulohumeral Muscular Dystrophy: Photoreceptor Degeneration as Possible Cause for Reduced Visual Acuity over Three Years of Follow-Up

BACKGROUND

Autosomal-dominant facioscapulohumeral muscular dystrophy (FSHD) is a muscular dystrophy with associated retinal abnormalities such as retinal vessel tortuosity, focal retinal pigment epithelium defect and large telangiectasia vessels.

METHODS

Case report of an FSHD 16-year-old female referred for blurred vision in both eyes (20/40), evening fever and shoulder muscle weakness over the past month preceding assessment. A multimodal assessment including visual acuity (VA), microperimetry (MP), multifocal electroretinogram (mfERG), optical coherence tomography (OCT), fluorescein angiography (FA) and fundus autofluorescence (FAF) was performed.

RESULTS

OCT showed pseudocyst macular abnormalities and disruption of the photoreceptor layer with no signs of macular ischemia/exudation. Macular function showed foveal impairment recorded by mfERG and MP as a reduction of the response amplitude density and retinal sensitivity, respectively. No medical treatment was prescribed. After three years, patient's VA slightly improved to 20/32. OCT showed resolution of bilateral pseudocyst macular changes and persistence of photoreceptor disruption. By contrast, mfERG recordings remained abnormal for impaired foveal function and microperimetry mean sensitivity was reduced as well.

CONCLUSIONS

This multimodal assessment showed persistent VA impairment at three years follow-up associated to abnormal foveal function and reduced retinal sensitivity, with spontaneous resolution of morphological macular changes, suggesting a retinal neurodegenerative process on the basis of the disease.

Antagonism Between DUX4 and DUX4c Highlights a Pathomechanism Operating Through β-Catenin in Facioscapulohumeral Muscular Dystrophy

Aberrant expression of the transcription factor DUX4 from D4Z4 macrosatellite repeats on chromosome 4q35, and its transcriptome, associate with pathogenesis in facioscapulohumeral muscular dystrophy (FSHD). Forced DUX4 expression halts skeletal muscle cell proliferation and induces cell death. DUX4 binds DNA via two homeodomains that are identical in sequence to those of DUX4c (DUX4L9): a closely related transcriptional regulator encoded by a single, inverted, mutated D4Z4 unit located centromeric to the D4Z4 macrosatellite array on chromosome 4. However, the function and contribution of DUX4c to FSHD pathogenesis are unclear. To explore interplay between DUX4, DUX4c, and the DUX4-induced phenotype, we investigated whether DUX4c interferes with DUX4 function in human myogenesis. Constitutive expression of DUX4c rescued the DUX4-induced inhibition of proliferation and reduced cell death in human myoblasts. Functionally, DUX4 promotes nuclear translocation of β-CATENIN and increases canonical WNT signalling. Concomitant constitutive expression of DUX4c prevents β-CATENIN nuclear accumulation and the downstream transcriptional program. DUX4 reduces endogenous DUX4c levels, whereas constitutive expression of DUX4c robustly suppresses expression of DUX4 target genes, suggesting molecular antagonism. In line, DUX4 expression in FSHD myoblasts correlates with reduced DUX4c levels. Addressing the mechanism, we identified a subset of genes involved in the WNT/β-CATENIN pathway that are differentially regulated between DUX4 and DUX4c, whose expression pattern can separate muscle biopsies from severely affected FSHD patients from healthy. Finally, blockade of WNT/β-CATENIN signalling rescues viability of FSHD myoblasts. Together, our study highlights an antagonistic interplay whereby DUX4 alters cell viability via β-CATENIN signalling and DUX4c counteracts aspects of DUX4-mediated toxicity in human muscle cells, potentially acting as a gene modifier for FSHD severity. Importantly, direct DUX4 regulation of the WNT/β-CATENIN pathway informs future therapeutic interventions to ameliorate FSHD pathology.

Randomized phase 2 study of ACE-083, a muscle-promoting agent, in facioscapulohumeral muscular dystrophy

Introduction/Aims

Facioscapulohumeral muscular dystrophy (FSHD) is a slowly progressive muscular dystrophy without approved therapies. In this study we evaluated whether locally acting ACE‐083 could safely increase muscle volume and improve functional outcomes in adults with FSHD.

Methods

Participants were at least 18 years old and had FSHD1/FSHD2. Part 1 was open label, ascending dose, assessing safety and tolerability (primary objective). Part 2 was randomized, double‐blind for 6 months, evaluating ACE‐083240 mg/muscle vs placebo injected bilaterally every 3 weeks in the biceps brachii (BB) or tibialis anterior (TA) muscles, followed by 6 months of open label. Magnetic resonance imaging measures included total muscle volume (TMV; primary objective), fat fraction (FF), and contractile muscle volume (CMV). Functional measures included 6‐minute walk test, 10‐meter walk/run, and 4‐stair climb (TA group), and performance of upper limb midlevel/elbow score (BB group). Strength, patient‐reported outcomes (PROs), and safety were also evaluated.

Results

Parts 1 and 2 enrolled 37 and 58 participants, respectively. Among 55 participants evaluable in Part 2, the least‐squares mean (90% confidence interval, analysis of covariance) treatment difference for TMV was 16.4% (9.8%‐23.0%) in the BB group (P < .0001) and 9.5% (3.2%‐15.9%) in the TA group (P = .01). CMV increased significantly in the BB and TA groups and FF decreased in the TA group. There were no consistent improvements in functional or PRO measures in either group. The most common adverse events were mild or moderate injection‐site reactions.

Discussion

Significant increases in TMV with ACE‐083 vs placebo did not result in consistent functional or PRO improvements with up to 12 months of treatment.

The DUX4 protein is a co-repressor of the progesterone and glucocorticoid nuclear receptors

DUX4 is a transcription factor required during early embryonic development in placental mammals. In this work we provide evidence that DUX4 is a co-repressor of nuclear receptors (NRs) of progesterone (PR) and glucocorticoids (GR). The DUX4 C-ter and N-ter regions, including the nuclear localization signals and homeodomain motifs, contribute to the corepressor activity of DUX4 on PR and GR. Immunoprecipitation studies, using total protein extracts of cells expressing tagged versions of DUX4 and GR, support that these proteins are physically associated. Our studies suggest that DUX4 could modulate gene expression by coregulating the activity of hormone NRs. This is the first report highlighting a potential endocrine role for DUX4.

Interaction between mesenchymal stem cells and myoblasts in the context of facioscapulohumeral muscular dystrophy contributes to the disease phenotype

Facioscapulohumeral muscular dystrophy (FSHD) is a genetic disease associated with ectopic expression of the DUX4 gene in skeletal muscle. Muscle degeneration in FSHD is accompanied by muscle tissue replacement with fat and connective tissue. Expression of DUX4 in myoblasts stimulates mesenchymal stem cells (MSC) migration via the CXCR4‐CXCL12 axis. MSCs participate in adipose and connective tissue formation and can contribute to fibrosis. Here we studied the interaction between myoblasts and MSCs and the consequences of this interaction in the FSHD context. We used cell motility assays and coculture of MSCs with myoblasts to study their mutual effects on cell migration, differentiation, proliferation, and extracellular matrix formation. The growth medium conditioned by FSHD myoblasts stimulated MSCs migration 1.6‐fold (p < 0.04) compared to nonconditioned medium. Blocking the CXCL12‐CXCR4 axis with the CXCR4 inhibitor (AMD3100) or neutralizing antibodies to CXCL12 abolished this effect. FSHD myoblasts stimulated MSC proliferation 1.5−2 times (p < 0.05) compared to control myoblasts, while the presence of MSCs impaired myoblast differentiation. Under inflammatory conditions, medium conditioned by FSHD myoblasts stimulated collagen secretion by MSCs 2.2‐fold as compared to the nonconditioned medium, p < 0.03. FSHD myoblasts attract MSCs via the CXCL12‐CXCR4 axis, stimulate MSC proliferation and collagen secretion by MSCs. Interaction between MSCs and FSHD myoblasts accounts for several important aspects of FSHD pathophysiology. The CXCL12‐CXCR4 axis may serve as a potential target to improve the state of the diseased muscles.

Corrigendum: Sarcopenic Obesity in Facioscapulohumeral Muscular Dystrophy

[This corrects the article DOI: 10.3389/fphys.2020.01008.].

Development and validation of the patient-reported "Facial Function Scale" for facioscapulohumeral muscular dystrophy

PURPOSE

Facial weakness and its functional consequences are an often underappreciated clinical feature of facioscapulohumeral muscular dystrophy (FSHD) by healthcare professionals and researchers. This is at least in part due to the fact that there are few adequate clinical outcome measures available.

METHODS

We developed the Facial Function Scale, a Rasch-built questionnaire on the functional disabilities relating to facial weakness in FSHD. A preliminary 33-item questionnaire was created based on semi-structured interviews with 16 FSHD patients and completed by 119 patients. For reliability studies, 73 patients completed it again after a two-week interval. Data were subjected to semi-automated Rasch analysis to select the most appropriate item set to fit model expectations.

RESULTS

This resulted in a 25-item unidimensional, linear-weighted questionnaire with high internal consistency (person separation index = 0.92) and test-retest reliability (patients' locations ICC = 0.98 and items' locations ICC = 0.99). Good external construct validity scores were obtained through correlation with the Communicative Participation Item Bank questionnaire, examiner-reported Facial Weakness Score and facial weakness subscale of the FSHD evaluation score (respectively r = 0.733, r = -0.566, and r = 0.441, all p < 0.001).

CONCLUSIONS

This study provides a linear-weighted, clinimetrically sound, patient-reported outcome measure on the functional disabilities relating to facial weakness in FSHD, to enable further research on this relevant topic.Implications for rehabilitationFacial weakness and its functional consequences are an often underappreciated clinical feature of facioscapulohumeral muscular dystrophy (FSHD), both in symptomatic treatment and in research.To enable the development and testing of therapeutic symptomatic interventions for facial weakness, clinical outcome measures are required.This study provides a linear-weighted, clinimetrically sound, patient-reported outcome measure on the functional disabilities relating to facial weakness in FSHD patients.

Proximity ligation assay to detect DUX4 protein in FSHD1 muscle: a pilot study

OBJECTIVE

Aberrant expression in skeletal muscle of DUX4, a double homeobox transcription factor, underlies pathogenesis in facioscapulohumeral muscular dystrophy (FSHD). Although previous studies of FSHD muscle biopsies detected mRNAs encoding DUX4 and its target genes, no studies had reported detection of DUX4 protein. Our objective was to develop a proximity ligation assay (PLA) for DUX4 and to determine if this assay could detect DUX4 protein in FSHD muscle sections.

RESULTS

We developed a PLA protocol using two DUX4 antibodies previously reported by Stephen Tapscott's group: P2G4, a mouse mAb specific for an epitope in the N-terminal region, and E5-5, a rabbit mAb specific for an epitope in the C-terminal region, in combination with commercial PLA secondary reagents. We validated the DUX4 PLA using cultured human myogenic cells in which DUX4 was ectopically expressed in a small fraction of nuclei. Using this two primary mAb PLA on an FSHD1 biceps biopsy, we observed nuclei with apparent DUX4 PLA signals associated with a small subset of myofibers (~ 0.05-0.1%). Though a limited pilot study, these results suggest that the two primary mAb PLA protocol could be useful for detecting DUX4 protein in FSHD muscle biopsies.

Baroreflex sensitivity in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a common form of muscular dystrophy, is caused by a genetic mutation that alters DUX4 gene expression. This mutation contributes to significant skeletal muscle loss. Although it is suggested that cardiac muscle may be spared, people with FSHD have demonstrated autonomic dysregulation. It is unknown if baroreflex function, an important regulator of blood pressure (BP), is impaired in people with FSHD. We examined if baroreflex sensitivity (BRS) is blunted in patients with FSHD. Thirty minutes of resting BP, heart rate, and cardiovagal BRS were measured in 13 patients with FSHD (age: 50 ± 13 years, avg ± SD) and 17 sex- and age-matched controls (age: 47 ± 14 years, p > 0.05). People with FSHD were less active (Activity Metabolic Index, AMI) (FSHD: 24 ± 30; controls: 222 ± 175 kcal/day; p < 0.001) but had a similar body mass index compared with controls (FSHD: 27 ± 4; controls: 27 ± 4 kg/m2 ; p > 0.05). BRSup (hypertensive response), BRSdown (hypotensive response), and total BRS were similar between groups (BRSup: FSHD: 12 ± 8; controls: 12 ± 5 ms/mmHg; BRSdown: FSHD: 10 ± 4; controls: 13 ± 6 ms/mmHg; BRS: FSHD: 14 ± 9; controls: 13 ± 6 ms/mmHg; p > 0.05). Mean arterial pressure was similar between groups (FSHD: 96 ± 7; controls: 91 ± 6mmHg). Individuals with FSHD had an elevated heart rate compared with controls (FSHD: 65 ± 8; controls: 59 ± 8 BPM; p = 0.03), but when co-varied for AMI, this relationship disappeared (p = 0.39). These findings suggest that BRS is not attenuated in people with FSHD, but an elevated heart rate may be due to low physical activity levels, a potential consequence of limited mobility.

The evolution of DUX4 gene regulation and its implication for facioscapulohumeral muscular dystrophy

Double homeobox 4 (DUX4) is an early embryonic transcription factor whose expression in the skeletal muscle causes facioscapulohumeral muscular dystrophy (FSHD). Despite decades of research, our knowledge of FSHD and DUX4 biology is incomplete, and the disease has currently no cures or targeted therapies. The unusual evolutionary origin of DUX4, its extensive epigenetic and post-transcriptional gene regulation, and various feedback regulatory loops that control its expression and function all contribute to the highly complex nature of FSHD pathogenesis. In this minireview, I synthesize the current state of knowledge in DUX4 and FSHD biology to highlight key areas where further research is needed to better understand DUX4 regulation. I also emphasize post-transcriptional regulation of and by DUX4 via changes in RNA and protein stability that might underlie key features of FSHD pathophysiology. Finally, I discuss the various feedback loops involved in DUX4 regulation and the context-specific consequences of its expression, which could be key to developing novel therapeutic approaches to combat FSHD.

RIPK3-mediated cell death is involved in DUX4-mediated toxicity in facioscapulohumeral dystrophy

BACKGROUND

Facioscapulohumeral dystrophy (FSHD) is caused by mutations leading to the aberrant expression of the DUX4 transcription factor in muscles. DUX4 was proposed to induce cell death, but the involvement of different death pathways is still discussed. A possible pro-apoptotic role of DUX4 was proposed, but as FSHD muscles are characterized by necrosis and inflammatory infiltrates, non-apoptotic pathways may be also involved.

METHODS

We explored DUX4-mediated cell death by focusing on the role of one regulated necrosis pathway called necroptosis, which is regulated by RIPK3. We investigated the effect of necroptosis on cell death in vitro and in vivo experiments using RIPK3 inhibitors and a RIPK3-deficient transgenic mouse model.

RESULTS

We showed in vitro that DUX4 expression causes a caspase-independent and RIPK3-mediated cell death in both myoblasts and myotubes. In vivo, RIPK3-deficient animals present improved body and muscle weights, a reduction of the aberrant activation of the DUX4 network genes, and an improvement of muscle histology.

CONCLUSIONS

These results provide evidence for a role of RIPK3 in DUX4-mediated cell death and open new avenues of research.

DUX4 Role in Normal Physiology and in FSHD Muscular Dystrophy

In the last decade, the sequence-specific transcription factor double homeobox 4 (DUX4) has gone from being an obscure entity to being a key factor in important physiological and pathological processes. We now know that expression of DUX4 is highly regulated and restricted to the early steps of embryonic development, where DUX4 is involved in transcriptional activation of the zygotic genome. While DUX4 is epigenetically silenced in most somatic tissues of healthy humans, its aberrant reactivation is associated with several diseases, including cancer, viral infection and facioscapulohumeral muscular dystrophy (FSHD). DUX4 is also translocated, giving rise to chimeric oncogenic proteins at the basis of sarcoma and leukemia forms. Hence, understanding how DUX4 is regulated and performs its activity could provide relevant information, not only to further our knowledge of human embryonic development regulation, but also to develop therapeutic approaches for the diseases associated with DUX4. Here, we summarize current knowledge on the cellular and molecular processes regulated by DUX4 with a special emphasis on FSHD muscular dystrophy.

The Italian National Registry for FSHD: an enhanced data integration and an analytics framework towards Smart Health Care and Precision Medicine for a rare disease

Background

The Italian Clinical network for FSHD (ICNF) has established the Italian National Registry for FSHD (INRF), collecting data from patients affected by Facioscapulohumeral dystrophy (FSHD) and their relatives. The INRF has gathered data from molecular analysis, clinical evaluation, anamnestic information, and family history from more than 3500 participants.

Methods

A data management framework, called Mediator Environment for Multiple Information Sources (MOMIS) FSHD Web Platform, has been developed to provide charts, maps and search tools customized for specific needs. Patients’ samples and their clinical information derives from the Italian Clinical network for FSHD (ICNF), a consortium consisting of fourteen neuromuscular clinics distributed across Italy. The tools used to collect, integrate, and visualize clinical, molecular and natural history information about patients affected by FSHD and their relatives are described.

Results

The INRF collected the molecular data regarding FSHD diagnosis conducted on 7197 subjects and identified 3362 individuals carrying a D4Z4 Reduced Allele (DRA): 1634 were unrelated index cases. In 1032 cases the molecular testing has been extended to 3747 relatives, 1728 carrying a DRA. Since 2009 molecular analysis has been accompanied by clinical evaluation based standardized evaluation protocols. In the period 2009–2020, 3577 clinical forms have been collected, 2059 follow the Comprehensive Clinical Evaluation form (CCEF). The integration of standardized clinical information and molecular data has made possible to demonstrate the wide phenotypic variability of FSHD. The MOMIS (Mediator Environment for Multiple Information Sources) data integration framework allowed performing genotype–phenotype correlation studies, and generated information of medical importance either for clinical practice or genetic counseling.

Conclusion

The platform implemented for the FSHD Registry data collection based on OpenClinica meets the requirement to integrate patient/disease information, as well as the need to adapt dynamically to security and privacy concerns. Our results indicate that the quality of data collection in a multi-integrated approach is fundamental for clinical and epidemiological research in a rare disease and may have great value in allowing us to redefine diagnostic criteria and disease markers for FSHD. By extending the use of the MOMIS data integration framework to other countries and the longitudinal systematic collection of standardized clinical data will facilitate the understanding of disease natural history and offer valuable inputs towards trial readiness. This approach is of high significance to FSHD medical community and also to rare disease research in general.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02100-z.

Clinical and Molecular Spectrum of Muscular Dystrophies (MDs) with Intellectual Disability (ID): a Comprehensive Overview

Muscular dystrophies encompass a wide and heterogeneous subset of hereditary myopathies that manifest by the structural or functional abnormalities in the skeletal muscle. Some pathogenic mutations induce a dysfunction or loss of proteins that are critical for the stability of muscle cells, leading to progressive muscle degradation and weakening. Several studies have well-established cognitive deficits in muscular dystrophies which are mainly due to the disruption of brain-specific expression of affected muscle proteins. We provide a comprehensive overview of the types of muscular dystrophies that are accompanied by intellectual disability by detailed consulting of the main libraries. The current paper focuses on the clinical and molecular evidence about Duchenne, congenital, limb-girdle, and facioscapulohumeral muscular dystrophies as well as myotonic dystrophies. Because these syndromes impose a heavy burden of psychological and financial problems on patients, their families, and the health care community, a thorough examination is necessary to perform timely psychological and medical interventions and thus improve the quality of life.

A 20-year Clinical and Genetic Neuromuscular Cohort Analysis in Lebanon: An International Effort

BACKGROUND

Clinical and molecular data on the occurrence and frequency of inherited neuromuscular disorders (NMD) in the Lebanese population is scarce.

OBJECTIVE

This study aims to provide a retrospective overview of hereditary NMDs based on our clinical consultations in Lebanon.

METHODS

Clinical and molecular data of patients referred to a multi-disciplinary consultation for neuromuscular disorders over a 20-year period (1999-2019) was reviewed.

RESULTS

A total of 506 patients were diagnosed with 62 different disorders encompassing 10 classes of NMDs. 103 variants in 49 genes were identified. In this cohort, 81.4%of patients were diagnosed with motor neuron diseases and muscular dystrophies, with almost half of these described with spinal muscular atrophy (SMA) (40.3%of patients). We estimate a high SMA incidence of 1 in 7,500 births in Lebanon. Duchenne and Becker muscular dystrophy were the second most frequently diagnosed NMDs (17%of patients). The latter disorders were associated with the highest number of variants (39) identified in this study. A highly heterogeneous presentation of Limb Girdle Muscular Dystrophy and Charcot-Marie-Tooth disease was notably identified. The least common disorders (5.5%of patients) involved congenital, metabolic, and mitochondrial myopathies, congenital myasthenic syndromes, and myotonic dystrophies. A review of the literature for selected NMDs in Lebanon is provided.

CONCLUSIONS

Our study indicates a high prevalence and underreporting of heterogeneous forms of NMDs in Lebanon- a major challenge with many novel NMD treatments in the pipeline. This report calls for a regional NMD patient registry.

Identification of candidate miRNA biomarkers for facioscapulohumeral muscular dystrophy using DUX4-based mouse models

Facioscapulohumeral muscular dystrophy (FSHD) is caused by misexpression of DUX4 in skeletal myocytes. As DUX4 is the key therapeutic target in FSHD, surrogate biomarkers of DUX4 expression in skeletal muscle are critically needed for clinical trials. Although no natural animal models of FSHD exist, transgenic mice with inducible DUX4 expression in skeletal muscles rapidly develop myopathic phenotypes consistent with FSHD. Here, we established a new, more-accurate FSHD-like mouse model based on chronic DUX4 expression in a small fraction of skeletal myonuclei that develops pathology mimicking key aspects of FSHD across its lifespan. Utilizing this new aged mouse model and DUX4-inducible mouse models, we characterized the DUX4-related microRNA signatures in skeletal muscles, which represent potential biomarkers for FSHD. We found increased expression of miR-31-5p and miR-206 in muscles expressing different levels of DUX4 and displaying varying degrees of pathology. Importantly, miR-206 expression is significantly increased in serum samples from FSHD patients compared with healthy controls. Our data support miR-31-5p and miR-206 as new potential regulators of muscle pathology and miR-206 as a potential circulating biomarker for FSHD.

This article has an associated First Person interview with the first author of the paper.

Summary: Candidate miRNA biomarkers for facioscapulohumeral muscular dystrophy (FSHD) were identified using FSHD-like mouse models that present cumulative pathology from chronic expression of DUX4 in skeletal muscles and confirmed in FSHD patient serum.

Precise Epigenetic Analysis Using Targeted Bisulfite Genomic Sequencing Distinguishes FSHD1, FSHD2, and Healthy Subjects

The true prevalence of facioscapulohumeral muscular dystrophy (FSHD) is unknown due to difficulties with accurate clinical evaluation and the complexities of current genetic diagnostics. Interestingly, all forms of FSHD are linked to epigenetic changes in the chromosome 4q35 D4Z4 macrosatellite, suggesting that epigenetic analysis could provide an avenue for sequence-based FSHD diagnostics. However, studies assessing DNA methylation at the FSHD locus have produced conflicting results; thus, the utility of this technique as an FSHD diagnostic remains controversial. Here, we critically compared two protocols for epigenetic analysis of the FSHD region using bisulfite genomic sequencing: Jones et al., that contends to be individually diagnostic for FSHD1 and FSHD2, and Gaillard et al., that can identify some changes in DNA methylation levels between groups of clinically affected FSHD and healthy subjects, but is not individually diagnostic for any form of FSHD. We performed both sets of assays on the same genetically confirmed samples and showed that this discrepancy was due strictly to differences in amplicon specificity. We propose that the epigenetic status of the FSHD-associated D4Z4 arrays, when accurately assessed, is a diagnostic for genetic FSHD and can readily distinguish between healthy, FSHD1 and FSHD2. Thus, epigenetic diagnosis of FSHD, which can be performed on saliva DNA, will greatly increase accessibility to FSHD diagnostics for populations around the world.

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.

Relating SMCHD1 structure to its function in epigenetic silencing

The structural maintenance of chromosomes hinge domain containing protein 1 (SMCHD1) is a large multidomain protein involved in epigenetic gene silencing. Variations in the SMCHD1 gene are associated with two debilitating human disorders, facioscapulohumeral muscular dystrophy (FSHD) and Bosma arhinia microphthalmia syndrome (BAMS). Failure of SMCHD1 to silence the D4Z4 macro-repeat array causes FSHD, yet the consequences on gene silencing of SMCHD1 variations associated with BAMS are currently unknown. Despite the interest due to these roles, our understanding of the SMCHD1 protein is in its infancy. Most knowledge of SMCHD1 function is based on its similarity to the structural maintenance of chromosomes (SMC) proteins, such as cohesin and condensin. SMC proteins and SMCHD1 share similar domain organisation and affect chromatin conformation. However, there are important differences between the domain architectures of SMC proteins and SMCHD1, which distinguish SMCHD1 as a non-canonical member of the family. In the last year, the crystal structures of the two key domains crucial to SMCHD1 function, the ATPase and hinge domains, have emerged. These structures reveal new insights into how SMCHD1 may bind and regulate chromatin structure, and address how amino acid variations in SMCHD1 may contribute to BAMS and FSHD. Here, we contrast SMCHD1 with canonical SMC proteins, and relate the ATPase and hinge domain structures to their roles in SMCHD1-mediated epigenetic silencing and disease.