A family-based study into penetrance in facioscapulohumeral muscular dystrophy type 1

Posttranscriptional RNA stabilization of telomeric RNAs FRG2, DBE-T, D4Z4 at human 4q35 in response to genotoxic stress and D4Z4 macrosatellite repeat length

BACKGROUND

Reduced copy number of the D4Z4 macrosatellite at human chromosome 4q35 is associated with facioscapulohumeral muscular dystrophy (FSHD). A pervasive idea is that chromatin alterations at the 4q35 locus following D4Z4 repeat unit deletion lead to disease via inappropriate expression of nearby genes. Here, we sought to analyze transcription and chromatin characteristics at specific regions of 4q35 and how these are affected by D4Z4 deletions and exogenous stresses.

RESULTS

We found that the 4q subtelomere is subdivided into discrete domains, each with characteristic chromatin features associated with distinct gene expression profiles. Centromeric genes within 4q35 (SLC25A4, FAT1 and FRG1) display active histone marks at their promoters. In contrast, poised or repressed markings are present at telomeric loci including FRG2, DBE-T and D4Z4. We discovered that these discrete domains undergo region-specific chromatin changes upon treatment with chromatin enzyme inhibitors or genotoxic drugs. We demonstrated that the 4q35 telomeric FRG2, DBE-T and D4Z4-derived transcripts are induced upon DNA damage to levels inversely correlated with the D4Z4 repeat number, are stabilized through posttranscriptional mechanisms upon DNA damage and are bound to chromatin.

CONCLUSION

Our study reveals unforeseen biochemical features of RNAs from clustered transcription units within the 4q35 subtelomere. Specifically, the FRG2, DBE-T and D4Z4-derived transcripts are chromatin-associated and are stabilized posttranscriptionally after induction by genotoxic stress. Remarkably, the extent of this response is modulated by the copy number of the D4Z4 repeats, raising new hypotheses about their regulation and function in human biology and disease.

Clinical and genetic characteristics based on the Japanese patient registry for facioscapulohumeral muscular dystrophy: a nationwide analysis

The Japanese patient registry for facioscapulohumeral muscular dystrophy (FSHD) was launched in September 2020, enrolling patients genetically confirmed to have FSHD. This study aimed to analyze clinical and genetic characteristics based on data from the Japanese FSHD registry. Core items were collected from the TREAT-NMD FSHD dataset, version 1.0. By the end of June 2024, over 200 patients were enrolled, with 161 successfully registered after confirmation. Among them, 156 had FSHD1 and 5 had FSHD2; 81 had affected family members; 116 were ambulatory; 73 had respiratory dysfunction; 22 required mechanical ventilation; 8 had cardiac dysfunction; 4 had retinopathy; and 22 had hearing loss. In patients with FSHD1, the median number of D4Z4 repeats was four, with a low proportion of long repeats. D4Z4 repeat counts influenced age at disease onset, site-specific muscle weakness onset, respiratory function, retinopathy, and hearing loss. Notably, female patients were more likely to have early facial weakness and hearing loss. Our data suggest population diversity in D4Z4 repeat numbers and sex differences. We aim to collaborate with patient groups to enroll more participants and gather more accurate epidemiological data, including cases of FSHD2. Additionally, we plan to investigate racial differences through international collaboration.

Age at onset mediates genetic impact on disease severity in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy type 1 (FSHD1) patients exhibit marked variability in both age at onset (AAO) and disease severity. Early onset FSHD1 patients are at an increased risk of severe weakness, and early onset has been tentatively linked to the length of D4Z4 repeat units (RUs) and methylation levels. The present study explored potential relationships among genetic characteristics, AAO and disease severity in FSHD1. This retrospective and observational cohort study was conducted at the Fujian Neuromedical Centre (FNMC) in China. Genetically confirmed participants with FSHD1 recruited from 2001 to 2023 underwent distal D4Z4 methylation assessment. Disease severity was assessed by FSHD clinical score, age-corrected clinical severity score (ACSS) and onset age of lower extremity involvement. Mediation analyses were used to explore relationships among genetic characteristics, AAO and disease severity. Finally, machine learning was employed to explore AAO prediction in FSHD1. A total of 874 participants (including 804 symptomatic patients and 70 asymptomatic carriers) were included. Multivariate Cox regression analyses indicated that male gender, low DUZ4 RUs, low CpG6 methylation levels, non-mosaic mutation and de novo mutation were independently associated with early onset in FSHD1. Early onset patients (AAO < 10 years) had both a significantly higher proportion and an earlier median onset age of lower extremity involvement compared to the typical adolescent onset (10 ≤ AAO < 20 years), typical adult onset (20 ≤ AAO < 30 years) and late onset (AAO ≥ 30 years) subgroups. AAO was negatively correlated with both clinical score and ACSS. We found that AAO exerted mediation effects, accounting for 12.2% of the total effect of D4Z4 RUs and CpG6 methylation levels on ACSS and 38.6% of the total effect of D4Z4 RUs and CpG6 methylation levels on onset age of lower extremity involvement. A random forest model that incorporated variables including gender, age at examination, inheritance pattern, mosaic mutation, D4Z4 RUs and D4Z4 methylation levels (at CpG3, CpG6 and CpG10 loci) performed well for AAO prediction. The predicted AAO (pAAO) was negatively correlated with ACSS (Spearman's ρ = -0.692). Our study revealed independent contributions from D4Z4 RUs, D4Z4 methylation levels, mosaic mutation and inheritance pattern on AAO variation in FSHD1. AAO mediates effects of D4Z4 RUs and methylation levels on disease severity. The pAAO values from our random forest model informatively reflect disease severity, offering insights that can support efficacious patient management.

Facioscapulohumeral muscular dystrophy type 1 combined with becker muscular dystrophy: a family case report

Facioscapulohumeral muscular dystrophy type 1 (FSHD1) and Becker muscular dystrophy (BMD) are distinct disorders caused by different genetic variations and exhibiting different inheritance patterns. The co-occurrence of both conditions within the same family is rare. In this case report, the proband was a 10 year-old boy who presented with eye and mouth orbicular muscles, shoulder and proximal upper and lower limbs weakness. Genetic testing showed that the number of D4Z4 repeat units in the sub-terminal region 4qA of chromosome 4q35 in the proband was only 4 (normal value ≥ 11) and, at the same time, a heterozygous deletion was found in exons 13-29 of DMD gene in the proband, thus the diagnosis was clinically and genetically compatible with both FSHD1 and BMD. Pedigree investigation revealed that his maternal grandmother, mother, aunt and cousin also had muscle weakness in the face, shoulders and limbs. Genetic testing confirmed that each of the four relatives had four D4Z4 repeats in the 4qA region, and all of them carried a heterozygous deletion in exons 13-29 of DMD. Based on the X-linked features of DMD/BMD, the maternal grandmother, mother, and aunt were diagnosed with FSHD1 combined with DMD deletion carriers, and the male cousin was diagnosed with FSHD1 combined with BMD. This study identifies a family with a co-occurrence of clinically overt FSHD1 and BMD, which has important reference value for the diagnosis and treatment of hereditary myopathies.

Double trouble: a comprehensive study into unrelated genetic comorbidities in adult patients with Facioscapulohumeral Muscular Dystrophy Type I

Facioscapulohumeral dystrophy type 1 (FSHD1) displays prominent intra- and interfamilial variability, which complicates the phenotype-genotype correlation. In this retrospective study, we investigated FSHD1 patients classified as category D according to the Comprehensive Clinical Evaluation Form (CCEF), a category defined by FSHD patients showing uncommon clinical features, to identify genetic causes explaining these uncommon phenotypes. Demographics, clinical data and clinical scales of FSHD1 patients were retrospectively evaluated. Patients were divided into four CCEF categories, and comparisons between groups were performed. In category D, when uncommon features suggested the presence of an unrelated genetic disease, a more extensive collection of data was performed. 157 FSHD1 patients were included in the study (82 males, 75 females) with mean age of 52.1 ± 13.5 years at the time of the study. D4Z4 repeat sizes ranged between 2 and 10 RU. According to the CCEF, 114 patients were classified into category A, 8 into category B and C each, and 27 into category D. In category D, 9 patients presented uncommon features related to commonly acquired comorbidities, whereas in the remaining 18 patients, all but two with upper-sized FSHD1 D4Z4 repeats (7-10 RU), we suspected an unrelated genetic neurological disease based on clinical phenotype. In 14/18 patients, we identified FSHD-unrelated genetic causes, most often unrelated repeat expansion disorders. This emphasizes the need of careful clinical and genetic work-up to avoid confusion between FSHD-intrinsic clinical variability and clinical features unrelated to the disease.

The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound

INTRODUCTION/AIMS

One of the most distinct clinical features of facioscapulohumeral muscular dystrophy (FSHD) is facial weakness. It leads to diminished facial expression and functional impairments. Despite its clinical relevance, little else is known about orofacial muscle involvement. We therefore evaluated orofacial muscle involvement in a sizeable cohort of FSHD participants with muscle ultrasound.

METHODS

Muscle ultrasound images of the following orofacial muscles were scored visually and quantitatively: depressor anguli oris (DAO), orbicularis oris (OO), buccinator, temporalis, masseter, digastric, zygomaticus major and minor bilaterally, and the geniohyoid. Reliability analyses of both visual and quantitative evaluations were performed. Ultrasound results were correlated with other measures: the FSHD clinical score, facial weakness score, and facial function scale.

RESULTS

We included 107 FSHD participants (male 54%; age 52 ± 14 years), of whom 92% showed signs of facial weakness. The reliability of visual ultrasound analysis varied widely (κ 0.0-1.0). Quantitative ultrasound reliability was high (intraclass correlation analysis ≥ 0.96). The DAO, buccinator, OO, temporalis, and zygomaticus minor muscles were affected most often (15%-39%). The digastric, geniohyoid, zygomaticus major, and masseter muscles were least often affected (<5%). The ultrasound compound score correlated weakly to moderately with other outcome measures used (ρ = 0.3-0.7).

DISCUSSION

This study adds to the understanding of orofacial weakness in FSHD, confirming the involvement of the muscles of facial expression in FSHD using ultrasound. We showed that orofacial muscle ultrasound is feasible and reliable when quantitatively assessed. Future studies should evaluate orofacial muscle ultrasound longitudinally, alongside clinical and patient-reported facial weakness outcome measures, to assess their potential as outcome measures.

Deciphering the Complexity of FSHD: A Multimodal Approach as a Model for Rare Disorders

Rare diseases are heterogeneous diseases characterized by various symptoms and signs. Due to the low prevalence of such conditions (less than 1 in 2000 people), medical expertise is limited, knowledge is poor and patients' care provided by medical centers is inadequate. An accurate diagnosis is frequently challenging and ongoing research is also insufficient, thus complicating the understanding of the natural progression of the rarest disorders. This review aims at presenting the multimodal approach supported by the integration of multiple analyses and disciplines as a valuable solution to clarify complex genotype-phenotype correlations and promote an in-depth examination of rare disorders. Taking into account the literature from large-scale population studies and ongoing technological advancement, this review described some examples to show how a multi-skilled team can improve the complex diagnosis of rare diseases. In this regard, Facio-Scapulo-Humeral muscular Dystrophy (FSHD) represents a valuable example where a multimodal approach is essential for a more accurate and precise diagnosis, as well as for enhancing the management of patients and their families. Given their heterogeneity and complexity, rare diseases call for a distinctive multidisciplinary approach to enable diagnosis and clinical follow-up.

The first genetically confirmed cohort of Facioscapulohumeral Muscular Dystrophy from Northern India

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common form of hereditary myopathy. Sixty per cent of the world's population lives in Asia, so a significant percentage of the world's FSHD participants is expected to live there. To date, most FSHD studies have involved individuals of European descent, yet small-scale studies of East-Asian populations suggest that the likelihood of developing FSHD may vary. Here, we present the first genetically confirmed FSHD cohort of Indian ancestry, which suggests a pathogenic FSHD1 allele size distribution intermediate between European and North-East Asian populations and more asymptomatic carriers of 4 unit and 5 unit FSHD1 alleles than observed in European populations. Our data provides important evidence of differences relevant to clinical diagnostics and underscores the need for global FSHD participation in research and trial-ready Indian FSHD cohorts.

French National Protocol for diagnosis and care of facioscapulohumeral muscular dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common genetically inherited myopathies in adults. It is characterized by incomplete penetrance and variable expressivity. Typically, FSHD patients display asymmetric weakness of facial, scapular, and humeral muscles that may progress to other muscle groups, particularly the abdominal and lower limb muscles. Early-onset patients display more severe muscle weakness and atrophy, resulting in a higher frequency of associated skeletal abnormalities. In these patients, multisystem involvement, including respiratory, ocular, and auditory, is more frequent and severe and may include the central nervous system. Adult-onset FSHD patients may also display some degree of multisystem involvement which mainly remains subclinical. In 95% of cases, FSHD patients carry a pathogenic contraction of the D4Z4 repeat units (RUs) in the subtelomeric region of chromosome 4 (4q35), which leads to the expression of DUX4 retrogene, toxic for muscles (FSHD1). Five percent of patients display the same clinical phenotype in association with a mutation in the SMCHD1 gene located in chromosome 18, inducing epigenetic modifications of the 4q D4Z4 repeated region and expression of DUX4 retrogene. This review highlights the complexities and challenges of diagnosing and managing FSHD, underscoring the importance of standardized approaches for optimal patient outcomes. It emphasizes the critical role of multidisciplinary care in addressing the diverse manifestations of FSHD across different age groups, from skeletal abnormalities in early-onset cases to the often-subclinical multisystem involvement in adults. With no current cure, the focus on alleviating symptoms and slowing disease progression through coordinated care is paramount.

Best practice guidelines on genetic diagnostics of facioscapulohumeral muscular dystrophy: Update of the 2012 guidelines

The gold standard for facioscapulohumeral muscular dystrophy (FSHD) genetic diagnostic procedures was published in 2012. With the increasing complexity of the genetics of FSHD1 and 2, the increase of genetic testing centers, and the start of clinical trials for FSHD, it is crucial to provide an update on our knowledge of the genetic features of the FSHD loci and renew the international consensus on the molecular testing recommendations. To this end, members of the FSHD European Trial Network summarized the evidence presented during the 2022 ENMC meeting on Genetic diagnosis, clinical outcome measures, and biomarkers. The working group additionally invited genetic and clinical experts from the USA, India, Japan, Australia, South-Africa, and Brazil to provide a global perspective. Six virtual meetings were organized to reach consensus on the minimal requirements for genetic confirmation of FSHD1 and FSHD2. Here, we present the clinical and genetic features of FSHD, specific features of FSHD1 and FSHD2, pros and cons of established and new technologies (Southern blot in combination with either linear or pulsed-field gel electrophoresis, molecular combing, optical genome mapping, FSHD2 methylation analysis and FSHD2 genotyping), the possibilities and challenges of prenatal testing, including pre-implantation genetic testing, and the minimal requirements and recommendations for genetic confirmation of FSHD1 and FSHD2. This consensus is expected to contribute to current clinical management and trial-readiness for FSHD.

The complementary use of muscle ultrasound and MRI in FSHD: Early versus later disease stage follow-up

OBJECTIVES

Muscle MRI and ultrasound provide complementary techniques for characterizing muscle changes and tracking disease progression in facioscapulohumeral muscular dystrophy (FSHD). In this cohort study, we provide longitudinal data that compares both imaging modalities head-to-head.

METHODS

FSHD patients were assessed at baseline and after five years. Standardized muscle MRI and ultrasound images of five leg muscles were assessed bilaterally. Fat replacement was quantified using MRI fat-fraction (FF) and ultrasound Heckmatt and echogenicity z-scores (EZ-score). Muscle edema was evaluated using T2-weighted turbo inversion recovery magnitude (TIRM) MRI.

RESULTS

Twenty FSHD patients were included. Muscles with normal baseline imaging showed increases in ultrasound EZ-scores (≥1; in 17%) more often than MRI FF increases (≥10%; in 7%) over time. Muscles with only baseline ultrasound abnormalities often showed considerable FF increases (in 22%), and TIRM positivity at follow-up (44%). Muscles with increased FF at baseline showed stable (80%) or increasing FF (20%) over time. EZ-scores of those muscles either increased (23%), decreased (33%) or remained stable (44%).

CONCLUSIONS

Muscle ultrasound may capture accelerated pathological muscle changes in FSHD in early disease, while muscle MRI appears better-suited to detecting and monitoring pathology in later stages.

SIGNIFICANCE

Our results help establish each techniques' optimal use as imaging biomarker.

Establishing the role of muscle ultrasound as an imaging biomarker in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a hereditary muscle disease, that causes weakness and wasting of skeletal muscles. In this cross-sectional cohort-study on FSHD patients, we assessed muscle ultrasound findings and their relation to clinical outcome measures, evaluating the role of ultrasound as biomarker in FSHD. We included 115 genetically confirmed FSHD patients (52% males, age-range 22-80 years). They were subjected to a standardized muscle ultrasound protocol of seven truncal and upper- and lower extremity muscles bilaterally. Muscle images were scored using the Heckmatt scale. Muscle echogenicity was quantified using z-scores. Compound echogenicity and Heckmatt scores were calculated. Nearly all patients (94%) had one or multiple muscles with an increased echogenicity z-score. The trapezius muscle was most severely affected, followed by the rectus femoris muscle. Both compound ultrasound scores strongly with multiple clinical outcome measures (ρ 0.68-0.79, p < 0.001). While most muscles showed a high level of agreement between the echogenicity z-score and Heckmatt score (>95%), the tibialis anterior and gastrocnemius muscle showed lower levels of agreement (82 and 92%). In conclusion, our study confirms the use of muscle ultrasound as clinical severity biomarker and provides a solid base for future longitudinal studies to establish ultrasound as a monitoring biomarker in FSHD.

Deciphering D4Z4 CpG methylation gradients in fascioscapulohumeral muscular dystrophy using nanopore sequencing

Fascioscapulohumeral muscular dystrophy (FSHD) is caused by a unique genetic mechanism that relies on contraction and hypomethylation of the D4Z4 macrosatellite array on the Chromosome 4q telomere allowing ectopic expression of the DUX4 gene in skeletal muscle. Genetic analysis is difficult because of the large size and repetitive nature of the array, a nearly identical array on the 10q telomere, and the presence of divergent D4Z4 arrays scattered throughout the genome. Here, we combine nanopore long-read sequencing with Cas9-targeted enrichment of 4q and 10q D4Z4 arrays for comprehensive genetic analysis including determination of the length of the 4q and 10q D4Z4 arrays with base-pair resolution. In the same assay, we differentiate 4q from 10q telomeric sequences, determine A/B haplotype, identify paralogous D4Z4 sequences elsewhere in the genome, and estimate methylation for all CpGs in the array. Asymmetric, length-dependent methylation gradients were observed in the 4q and 10q D4Z4 arrays that reach a hypermethylation point at approximately 10 D4Z4 repeat units, consistent with the known threshold of pathogenic D4Z4 contractions. High resolution analysis of individual D4Z4 repeat methylation revealed areas of low methylation near the CTCF/insulator region and areas of high methylation immediately preceding the DUX4 transcriptional start site. Within the DUX4 exons, we observed a waxing/waning methylation pattern with a 180-nucleotide periodicity, consistent with phased nucleosomes. Targeted nanopore sequencing complements recently developed molecular combing and optical mapping approaches to genetic analysis for FSHD by adding precision of the length measurement, base-pair resolution sequencing, and quantitative methylation analysis.

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.

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.

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.

Facioscapulohumeral Muscular Dystrophy

PURPOSE OF REVIEW

This article reviews the current knowledge on the clinical characteristics and disease mechanism of facioscapulohumeral muscular dystrophy (FSHD), as well as advances in targeted therapy development.

RECENT FINDINGS

FSHD has a wide range of severity, yet a distinct phenotype characterized by weakness of the facial, shoulder, and upper arm muscles, followed by weakness of the trunk and leg muscles. It can be caused by two genetic mechanisms that share a common downstream pathway, namely, the epigenetic derepression and subsequent misexpression of the myotoxic DUX4 transcription factor. Treatment is currently supportive and outlined in evidence-based guidelines. Advances in the understanding of the pathogenic mechanism of FSHD are paving the way for targeted therapy development. Approaches for targeted therapies to reduce DUX4 expression that are currently being explored include small molecules, antisense oligonucleotides, vector-based RNA interference, and gene therapy. In anticipation of more clinical trials, "clinical trial preparedness," including the development of sensitive biomarkers and clinical outcome measures, are needed.

SUMMARY

The cornerstones of the diagnosis of FSHD are clinical observation and genetic testing. Management is currently supportive, but progress in the understanding of the disease mechanism has shifted the field of FSHD toward targeted therapy development.

A feasibility study of noninvasive prenatal diagnosis in facioscapulohumeral muscular dystrophy type 1 in a Chinese family

Objective: To demonstrate the feasibility of haplotype-based noninvasive prenatal diagnosis of Facioscapulohumeral Muscular Dystrophy type 1 (FSHD1). Methods: Bionano optical mapping was used to identify the D4Z4 structural variation of the genomic DNA sample from the proband affected with FSHD1. In addition, based on the technique of next generation sequencing, the pathogenic haplotype was determined by using trio strategy through genotyping his parents, and also fetal inheritance of paternal haplotypes was then deduced using the Hidden Markov Model. Results: Bionano optical mapping analysis revealed that the proband has only three D4Z4 repeats left in the 4q35 chromosomal region and a disease-permitting 4qA haplotype. The other normal allele of the proband contains 29 D4Z4 repeats and also a 4qA haplotype. The noninvasive cell-free fetal DNA (cffDNA)-based haplotype analysis suggested that the fetus inherited the pathogenic allele from his father and thus was predicted to be affected by FSHD1. In addition, Bionano optical mapping also demonstrated the presence of the pathogenic allele in the fetus by interrogating the genomic DNA from the amniotic fluid cells. Conclusion: Our study showed the cffDNA-based haplotyping was feasible for the noninvasive prenatal diagnosis of FSHD1, which is able to provide earlier testing results with a lower risk of miscarriage and infection than invasive techniques.

Facioscapulohumeral muscular dystrophy-Reproductive counseling, pregnancy, and delivery in a complex multigenetic disease

Reproductive counseling in facioscapulohumeral muscular dystrophy (FSHD) can be challenging due to the complexity of its underlying genetic mechanisms and due to incomplete penetrance of the disease. Full understanding of the genetic causes and potential inheritance patterns of both distinct FSHD types is essential: FSHD1 is an autosomal dominantly inherited repeat disorder, whereas FSHD2 is a digenic disorder. This has become even more relevant now that prenatal diagnosis and preimplantation genetic diagnosis options are available for FSHD1. Pregnancy and delivery outcomes in FSHD are usually favorable, but clinicians should be aware of the risks. We aim to provide clinicians with case-based strategies for reproductive counseling in FSHD, as well as recommendations for pregnancy and delivery.

Prevalence and disease progression of genetically-confirmed facioscapulohumeral muscular dystrophy type 1 (FSHD1) in China between 2001 and 2020: a nationwide population-based study

BACKGROUND

Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is a rare disease, which is often underdiagnosed due to its heterogeneous presentations and complex molecular genetic basis, leading to a lack of population-based epidemiology data, especially of prevalence and disease progression.

METHODS

Fujian Neuromedical Centre (FNMC) is a diagnosis centre for clinical-genetic FSHD in China, and the only one employing pulsed-field gel electrophoresis (PFGE)-based Southern blotting for all FSHD1 genetic tests. Three sources distributed across all six spatial zones in China, were used to obtain information regarding FSHD1 events, namely, FNMC, Genetic and Myopathy Group (branches of the Neurology Society of the Chinese Medical Association), and "FSHD-China" (an organization supported by FSHD patients). During 2001-2020, all genetically-confirmed FSHD1 from China were registered in FNMC. Follow-up was conducted in the 20-year period to obtain data on disease progression, which was mainly described in terms of independent ambulation loss.

FINDINGS

Of the 1,744 FSHD1 genetic tests (total test number 1,802) included in the analysis, 997 (57.2%) patients from 620 families were diagnosed with FSHD1. The estimated prevalence of genetically-confirmed FSHD1 in China is 0.75 per million (95% confidence interval [CI], 0.70-0.79) during 2001-2020, with 0.78 (95% CI, 0.72-0.85) in males and 0.71 (95% CI, 0.65-0.78) in females. The estimated prevalence increased from 0.22 (95% CI, 0.19-0.26) per million in 2001-2015 to 0.53 (95% CI, 0.49-0.57) per million in 2016-2020 (p < 0.001). The prevalence in Fujian province was 7.10 per million, 4.66 per million, and 2.44 per million, during 2001-2020, 2001-2015, and 2016-2020, respectively. Among the 861 symptomatic plus asymptomatic patients of the total 997 patients, the median onset age at first-ever muscle weakness was 16 years of age (range 1-81); the median number of contracted D4Z4 repeats was 5 units (range 1-9); the median 4qA-allele-specific methylation level was 41% (range 14%-69%). Of the 977 symptomatic patients followed-up during 2001-2020, 117 patients (12.0%) lost independent ambulation. The expected duration from onset of first-ever muscle weakness to onset of independent ambulation loss was 40 years. The group with loss of independent ambulation had a smaller number of contracted D4Z4 repeats (p < 0.001) and had an earlier onset age of first-ever muscle weakness (p < 0.001) compared to the group without loss of independent ambulation.

INTERPRETATION

Our research captures the largest genetically-confirmed FSHD1 population worldwide, to calculate its prevalence of 0.75 per million in China from 2001 to 2020. Approximately 12.0% of symptomatic plus asymptomatic patients of FSHD1 will lose independent ambulation in 40 years from onset of first-ever muscle weakness.

FUNDING

This work has been supported by the grants (U2005201, 81870902, N.W.) and (81974193, 81671237, Z.Q.W.) from the National Natural Science Foundation of China; Joint Funds for the Innovation of Science and Technology of Fujian Province (2018Y9082) (N.W.), and the Key Clinical Specialty Discipline Construction Program of Fujian (N.W.).

Penetrance estimation of PRRT2 variants in paroxysmal kinesigenic dyskinesia and infantile convulsions

Proline-rich transmembrane protein 2 (PRRT2) is the leading cause of paroxysmal kinesigenic dyskinesia (PKD), benign familial infantile epilepsy (BFIE), and infantile convulsions with choreoathetosis (ICCA). Reduced penetrance of PRRT2 has been observed in previous studies, whereas the exact penetrance has not been evaluated well. The objective of this study was to estimate the penetrance of PRRT2 and determine its influencing factors. We screened 222 PKD index patients and their available relatives, identified 39 families with pathogenic or likely pathogenic (P/LP) PRRT2 variants via Sanger sequencing, and obtained 184 PKD/BFIE/ICCA families with P/LP PRRT2 variants from the literature. Penetrance was estimated as the proportion of affected variant carriers. PRRT2 penetrance estimate was 77.6% (95% confidence interval (CI) 74.5%-80.7%) in relatives and 74.5% (95% CI 70.2%-78.8%) in obligate carriers. In addition, we first observed that penetrance was higher in truncated than in non-truncated variants (75.8% versus 50.0%, P = 0.01), higher in Asian than in Caucasian carriers (81.5% versus 68.5%, P = 0.004), and exhibited no difference in gender or parental transmission. Our results are meaningful for genetic counseling, implying that approximately three-quarters of PRRT2 variant carriers will develop PRRT2-related disorders, with patients from Asia or carrying truncated variants at a higher risk.

Diagnostic magnetic resonance imaging biomarkers for facioscapulohumeral muscular dystrophy identified by machine learning

BACKGROUND

The diagnosis of facioscapulohumeral muscular dystrophy (FSHD) can be challenging in patients not displaying the classical phenotype or with atypical clinical features. Despite the identification by magnetic resonance imaging (MRI) of selective patterns of muscle involvement, their specificity and added diagnostic value are unknown.

METHODS

We aimed to identify the radiological features more useful to distinguish FSHD from other myopathies and test the diagnostic accuracy of MRI. A retrospective cohort of 295 patients (187 FSHD, 108 non-FSHD) studied by upper and lower-limb muscle MRI was analyzed. Scans were evaluated for the presence of 15 radiological features. A random forest machine learning algorithm was used to identify the most relevant for FSHD diagnosis. Different patterns were created by their combination and diagnostic accuracy of each of them was tested.

RESULTS

The combination of trapezius involvement and bilateral subscapularis muscle sparing achieved the best diagnostic accuracy (0.89, 95% Confidence Interval [0.85-0.92]) with 0.90 [0.85-0.94] sensitivity and 0.88 [0.80-0.93] specificity. This pattern correctly identified 91% atypical FSHD patients of our cohort. The combination of trapezius involvement, bilateral subscapularis and iliopsoas sparing and asymmetric involvement of upper and lower-limb muscles was pathognomonic for FSHD, yielding a specificity of 0.99 [0.95-1.00].

CONCLUSIONS

We identified MRI patterns that showed a high diagnostic power in promptly discriminating FSHD from other muscle disorders, with comparable performance irrespective of typical or atypical clinical features. Upper girdle in addition to lower-limb muscle imaging should be extensively implemented in the diagnostic workup to support or exclude a diagnosis of FSHD.

Adenine base editing of the DUX4 polyadenylation signal for targeted genetic therapy in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is caused by chromatin relaxation of the D4Z4 repeat resulting in misexpression of the D4Z4-encoded DUX4 gene in skeletal muscle. One of the key genetic requirements for the stable production of full-length DUX4 mRNA in skeletal muscle is a functional polyadenylation signal (ATTAAA) in exon three of DUX4 that is used in somatic cells. Base editors hold great promise to treat DNA lesions underlying genetic diseases through their ability to carry out specific and rapid nucleotide mutagenesis even in postmitotic cells such as skeletal muscle. In this study, we present a simple and straightforward strategy for mutagenesis of the somatic DUX4 polyadenylation signal by adenine base editing in immortalized myoblasts derived from independent FSHD-affected individuals. We show that mutating this critical cis-regulatory element results in downregulation of DUX4 mRNA and its direct transcriptional target genes. Our findings identify the somatic DUX4 polyadenylation signal as a therapeutic target and represent the first step toward clinical application of the CRISPR-Cas9 base editing platform for FSHD gene therapy.

Herbal medicine significantly improved muscle function in a patient with type 1 facioscapulohumeral muscular dystrophy: A case report

BACKGROUND AND AIM

Facioscapulohumeral muscular dystrophy (FSHD) is a common muscular disorder. At present, treatments for FSHD have limited effects on the muscle function of patients. A famous Chinese medicine formula, Buzhong Yiqi (BZYQ), has shown promising effects on several muscular diseases, but evidence regarding its effect on FSHD is lacking. This study aimed to examine the effect of BZYQ on FSHD.

CASE PRESENTATION

A 15-year-old girl suffered from progressive muscle weakness, with a genetically confirmed diagnosis of FSHD. Except for routine FSHD management, the patient received BZQY every day. The muscle strength of the patient remarkably increased after discharge.

CONCLUSIONS

This study was novel in reporting a significant improvement in muscle function in a patient with FSHD treated with an integrated approach of BZYQ and routine management. Therefore, BZYQ might be a potential treatment for FSHD, requiring further investigations.

Phenotypic Variability Among Patients With D4Z4 Reduced Allele Facioscapulohumeral Muscular Dystrophy

IMPORTANCE

Facioscapulohumeral muscular dystrophy (FSHD) is considered an autosomal dominant disorder, associated with the deletion of tandemly arrayed D4Z4 repetitive elements. The extensive use of molecular analysis of the D4Z4 locus for FSHD diagnosis has revealed wide clinical variability, suggesting that subgroups of patients exist among carriers of the D4Z4 reduced allele (DRA).

OBJECTIVE

To investigate the clinical expression of FSHD in the genetic subgroup of carriers of a DRA with 7 to 8 repeat units (RUs).

DESIGN, SETTING, AND PARTICIPANTS

This multicenter cross-sectional study included 422 carriers of DRA with 7 to 8 RUs (187 unrelated probands and 235 relatives) from a consecutive sample of 280 probands and 306 relatives from the Italian National Registry for FSHD collected between 2008 and 2016. Participants were evaluated by the Italian Clinical Network for FSHD, and all clinical and molecular data were collected in the Italian National Registry for FSHD database. Data analysis was conducted from January 2017 to June 2018.

MAIN OUTCOMES AND MEASURES

The phenotypic classification of probands and relatives was obtained by applying the Comprehensive Clinical Evaluation Form which classifies patients in the 4 following categories: (1) participants presenting facial and scapular girdle muscle weakness typical of FSHD (category A, subcategories A1-A3), (2) participants with muscle weakness limited to scapular girdle or facial muscles (category B, subcategories B1 and B2), (3) asymptomatic or healthy participants (category C, subcategories C1 and C2), and (4) participants with myopathic phenotypes presenting clinical features not consistent with FSHD canonical phenotype (category D, subcategories D1 and D2).

RESULTS

A total of 187 probands (mean [SD] age at last neurological examination, 53.5 [15.2] years; 103 [55.1%] men) and 235 relatives (mean [SD] age at last neurologic examination, 45.1 [17.0] years; 104 [44.7%] men) with a DRA with 7 to 8 RUs and a molecular diagnosis of FSHD were evaluated. Of 187 probands, 99 (52.9%; 95% CI, 45.7%-60.1%) displayed the classic FSHD phenotype, whereas 86 (47.1%; 95% CI, 39.8%-54.3%) presented incomplete or atypical phenotypes. Of 235 carrier relatives from 106 unrelated families, 124 (52.8%; 95% CI, 46.4%-59.7%) had no motor impairment, whereas a small number (38 [16.2%; 95% CI, 9.8%-23.1%]) displayed the classic FSHD phenotype, and 73 (31.0%; 95% CI, 24.7%-38.0%) presented with incomplete or atypical phenotypes. In 37 of 106 families (34.9%; 95% CI, 25.9%-44.8%), the proband was the only participant presenting with a myopathic phenotype, while only 20 families (18.9%; 95% CI, 11.9%-27.6%) had a member with autosomal dominant FSHD.

CONCLUSIONS AND RELEVANCE

This study found large phenotypic variability associated with individuals carrying a DRA with 7 to 8 RUs, in contrast to the indication that a positive molecular test is the only determining aspect for FSHD diagnosis. These findings suggest that carriers of a DRA with 7 to 8 RUs constitute a genetic subgroup different from classic FSHD. Based on these results, it is recommended that clinicians use the Comprehensive Clinical Evaluation Form for clinical classification and, whenever possible, study the extended family to provide the most adequate clinical management and genetic counseling.

Clinical and genetic features of somatic mosaicism in facioscapulohumeral dystrophy

PURPOSE

To analyse the clinical spectrum, genetic features, specific D4Z4 hypomethylation status and genotype-phenotype correlations for somatic mosaicism in facioscapulohumeral dystrophy (FSHD).

METHODS

This was a prospective, hospital-based, case-control, observational study of 35 participants with FSHD with somatic mosaicism recruited over 10 years, with 17 penetrant patients and 18 non-penetrant mutation carriers. This study also included a univariate comparison of 17 paired mosaic and non-mosaic patients with FSHD.

RESULTS

Mosaic participants with FSHD varied in age of diagnosis (median 45; range 15-65 years), muscle strength (FSHD clinical score median 0; range 0-10 points), clinical severity (age-corrected clinical severity score (ACSS) median 0; range 0-467 points), D4Z4 repeats (median 3; range 2-5 units), mosaic proportion (median 55%; range 27%-72%) and D4Z4 methylation extent (median 49.82%; range 27.17%-64.51%). The genotypic severity scale and D4Z4 methylation extent were significantly associated with ACSS (p₁=0.003; p₂=0.002). Among the matched pairs, the 17 mosaic patients had shorter D4Z4 repeats, lower FSHD clinical scores and lower ACSS than non-mosaic patients. Additionally, 34 of 35 (97%) participants carried two mosaic arrays, while a single patient had three mosaic arrays (3%). Two cases also carried four-type non-mosaic arrays on chromosome 10 (translocation configuration).

CONCLUSIONS

Broadly, this large mosaic FSHD cohort exhibited significant clinical heterogeneity and relatively slight disease severity. Both genotypic severity scale and D4Z4 hypomethylation status served as modifiers of clinical phenotypes. Consistent with previous reports, mitotic interchromosomal/intrachromosomal gene conversion without crossover was here identified as a major genetic mechanism underlying mosaic FSHD.

Beatmung bei neuromuskulären Erkrankungen

Neuromuskuläre Erkrankungen betreffen das erste und zweite Motoneuron, die peripheren Nerven, die neuromuskulären Übertragung und die Muskelzelle. Es handelt sich um eine heterogene Gruppe von erblichen, degenerativen und autoimmunen Erkrankungen. Eine korrekte diagnostische Einordnung ist erforderlich, da zentralnervöse, kardiale, endokrine und weitere Begleitsymptome vorliegen können und für einige Erkrankungen bereits medikamentöse Therapien zur Verfügung stehen. Neuromuskuläre Erkrankungen haben eine große Bedeutung in der neuromuskulären Beatmungsmedizin. Die respiratorische Symptomatik resultiert in der Regel aus Paresen der am Atmen, Schlucken oder Husten beteiligten Muskulatur mit konsekutiver ventilatorischer Insuffienz, Dysphagie bis hin zur Speichelaspiration und Sekretretention. Mittels eines strukturierte Sekretmanagements und einer effektive nichtinvasive oder invasive Beatmungstherapie können neuromuskuläre Patienten viele Jahre mit guter Lebensqualität überleben. Themen dieses Kapitels sind ein Überblick über die neuromuskulären Erkrankungen, die Indikationen und Strategien der nichtinvasiven und der invasiven Beatmung und eine ausführliche Darstellung beatmungsmedizinisch besonders relevanter neuromuskulärer Erkrankungen wie der amyotrophe Lateralsklerose, des Guillain-Barré-Syndroms, der Myasthenia gravis und der Critical-Illness-Polyneuropathie/-Myopathie.

Estimating the age at onset distribution of the asymptomatic stage of a genetic disease based on pedigree data

Information on the age at onset distribution of the asymptomatic stage of a disease can be of paramount importance in early detection and timely management of that disease. However, accurately estimating this distribution is challenging, because the asymptomatic stage is difficult to recognize for the patient and is often detected as an incidental finding or in case of recommended screening; the age at onset is often interval-censored. In this paper, we propose a method for the estimation of the age at onset distribution of the asymptomatic stage of a genetic disease based on ascertained pedigree data that take into account the way the data are ascertained to overcome selection bias. Simulation studies show that the estimates seem to be asymptotically unbiased. Our work is motivated by the analysis of data on facioscapulohumeral muscular dystrophy, a genetic muscle disorder. In our application, carriers of the genetic causal variant are identified through genetic screening of the relatives of symptomatic carriers and their disease status is determined by a medical examination. The estimates reveal an early age at onset of the asymptomatic stage of facioscapulohumeral muscular dystrophy.

Cis D4Z4 repeat duplications associated with facioscapulohumeral muscular dystrophy type 2

Facioscapulohumeral muscular dystrophy, known in genetic forms FSHD1 and FSHD2, is associated with D4Z4 repeat array chromatin relaxation and somatic derepression of DUX4 located in D4Z4. A complete copy of DUX4 is present on 4qA chromosomes, but not on the D4Z4-like repeats of chromosomes 4qB or 10. Normally, the D4Z4 repeat varies between 8 and 100 units, while in FSHD1 it is only 1-10 units. In the rare genetic form FSHD2, a combination of a 4qA allele with a D4Z4 repeat size of 8-20 units and heterozygous pathogenic variants in the chromatin modifier SMCHD1 causes DUX4 derepression and disease. In this study, we identified 11/79 (14%) FSHD2 patients with unusually large 4qA alleles of 21-70 D4Z4 units. By a combination of Southern blotting and molecular combing, we show that 8/11 (73%) of these unusually large 4qA alleles represent duplication alleles in which the long D4Z4 repeat arrays are followed by a small FSHD-sized D4Z4 repeat array duplication. We also show that these duplication alleles are associated with DUX4 expression. This duplication allele frequency is significantly higher than in controls (2.9%), FSHD1 patients (1.4%) and in FSHD2 patients with typical 4qA alleles of 8-20 D4Z4 units (1.5%). Segregation analysis shows that, similar to typical 8-20 units FSHD2 alleles, duplication alleles only cause FSHD in combination with a pathogenic variant in SMCHD1. We conclude that cis duplications of D4Z4 repeats explain DUX4 expression and disease presentation in FSHD2 families with unusual long D4Z4 repeats on 4qA chromosomes.

FSHD1 and FSHD2 form a disease continuum

OBJECTIVE

To compare the clinical features of patients showing a classical phenotype of facioscapulohumeral muscular dystrophy (FSHD) with genetic and epigenetic characteristics of the FSHD1 and FSHD2 loci D4Z4 and SMCHD1.

METHODS

This is a national multicenter cohort study. We measured motor strength, motor function, and disease severity by manual muscle testing sumscore, Brooke and Vignos scores, clinical severity score (CSS), and age-corrected CSS, respectively. We correlated these scores with genetic (D4Z4 repeat size and haplotype; SMCHD1 variant status) and epigenetic (D4Z4 methylation) parameters.

RESULTS

We included 103 patients: 54 men and 49 women. Among them, we identified 64 patients with FSHD1 and 20 patients with FSHD2. Seven patients had genetic and epigenetic characteristics of FSHD1 and FSHD2, all carrying repeats of 9-10 D4Z4 repeat units (RU) and a pathogenic SMCHD1 variant. In the remaining patients, FSHD was genetically excluded or remained unconfirmed. All clinically affected SMCHD1 mutation carriers had a D4Z4 repeat of 9-16 RU on a disease permissive 4qA haplotype. These patients are significantly more severely affected by all clinical scales when compared to patients with FSHD1 with upper-sized FSHD1 alleles (8-10 RU).

CONCLUSION

The overlap between FSHD1 and FSHD2 patients in the 9-10 D4Z4 RU range suggests that FSHD1 and FSHD2 form a disease continuum. The previously established repeat size threshold for FSHD1 (1-10 RU) and FSHD2 (11-20 RU) needs to be reconsidered.

CLINICALTRIALSGOV IDENTIFIER

NCT01970735.