Exome sequencing identifies Laing distal myopathy MYH7 mutation in a Roma family previously diagnosed with distal neuronopathy

Pathogenic variants in three families with distal muscle involvement

Three families suspected of distal hereditary motor neuropathy underwent genetic screening with the aim to identify the molecular defect underlying the disease. The description of the identification reflects the shift in molecular diagnostics that was made during the last decades. Our candidate gene approach yielded a known pathogenic variant in BSCL2 (p.Asn88Ser) in one family, and via a CMT-capture, in HSPB1 (p.Arg127Trp), in addition to five other variations in Charcot-Marie-Tooth-related genes in the proband of the second family. In the third family, using whole exome sequencing, followed by linkage-by-location, a three base pair deletion in exon 33 of MYH7 (p.Glu1508del) was found, a reported pathogenic allele albeit for a myopathy. After identification of the causative molecular defect, cardiac examination was performed for patients of the third family and this demonstrated abnormalities in three out of five affected family members. Heterogeneity and expansion of clinical phenotypes beyond known characteristics requires a wider set of genes to be screened. Whole exome/genome analysis with limited prior clinical information may therefore be used to precede a detailed clinical evaluation in cases of large families, preventing screening of a too narrow set of genes, and enabling the identification of novel disease-associated genes. In our cases, the variants had been reported, and co-segregation analysis confirmed the molecular diagnosis.

Using gene panels in the diagnosis of neuromuscular disorders: A mini-review

The diagnosis of inherited neuromuscular disorders is challenging due to their genetic and phenotypic variability. Traditionally, neurophysiology and histopathology were primarily used in the initial diagnostic approach to these conditions. Sanger sequencing for molecular diagnosis was less frequently utilized as its application was a time-consuming and cost-intensive process. The advent and accessibility of next-generation sequencing (NGS) has revolutionized the evaluation process of genetically heterogenous neuromuscular disorders. Current NGS diagnostic testing approaches include gene panels, whole exome sequencing (WES), and whole genome sequencing (WGS). Gene panels are often the most widely used, being more accessible due to availability and affordability. In this mini-review, we describe the benefits and risks of clinical genetic testing. We also discuss the utility, benefits, challenges, and limitations of using gene panels in the evaluation of neuromuscular disorders.

MYH7-related disorders in two Bulgarian families: Novel variants in the same region associated with different clinical manifestation and disease penetrance

Pathogenic variants in MYH7 cause a wide range of cardiac and skeletal muscle diseases with childhood or adult onset. These include dilated and/or hypertrophic cardiomyopathy, left ventricular non-compaction cardiomyopathy, congenital myopathies with multi-minicores and myofiber type disproportion, myosin storage myopathy, Laing distal myopathy and others (scapulo-peroneal or limb-girdle muscle forms). Here we report the results from molecular genetic analyses (NGS and Sanger sequencing) of 4 patients in two families with variable neuromuscular phenotypes with or without cardiac involvement. Interestingly, variants in MYH7 gene appeared to be the cause in all the cases. A novel nonsense variant c.5746C>T, p.(Gln1916Ter) was found in the patient in Family 1 who deceased at the age of 2 years 4 months with the clinical diagnosis of dilated cardiomyopathy, whose father died before the age of 40 years, due to cardiac failure with clinical diagnosis of suspected limb-girdle muscular dystrophy. A splice acceptor variant c.5560-2A>C in MYH7 was detected in the second proband and her sister, with late onset distal myopathy without cardiac involvement. These different phenotypes (muscular involvement with severe cardiomyopathy and pure late onset neuromuscular phenotype without heart involvement) may result from novel MYH7 variants, which most probably impact the LMM (light meromyosin) domain's function of the mature protein.

A study of the phenotypic variability and disease progression in Laing myopathy through the evaluation of muscle imaging

BACKGROUND

Laing myopathy is characterized by broad clinical and pathological variability. They are limited in number and protocol of study. We aimed to delineate muscle imaging profiles and validate imaging analysis as an outcome measure.

METHODS

This was a cross-sectional and longitudinal cohort study. Data from clinical, functional and semi-quantitative muscle imaging (60 magnetic resonance imaging [MRI] and six computed tomography scans) were studied. Hierarchical analysis, graphic heatmap representation and correlation between imaging and clinical data using Bayesian statistics were carried out.

RESULTS

The study cohort comprised 42 patients from 13 families harbouring five MYH7 mutations. The cohort had a wide range of ages, age at onset, disease duration, and myopathy extension and Gardner-Medwin and Walton (GMW) functional scores. Intramuscular fat was evident in all but two asymptomatic/pauci-symptomatic patients. Anterior leg compartment muscles were the only affected muscles in 12% of the patients. Widespread extension to the thigh, hip, paravertebral and calf muscles and, less frequently, the scapulohumeral muscles was commonly observed, depicting distinct patterns and rates of progression. Foot muscles were involved in 40% of patients, evolving in parallel to other regions with absence of a disto-proximal gradient. Whole cumulative imaging score, ranging from 0 to 2.9 out of 4, was associated with disease duration and with myopathy extension and GMW scales. Follow-up MRI studies in 24 patients showed significant score progression at a variable rate.

CONCLUSIONS

We confirmed that the anterior leg compartment is systematically affected in Laing myopathy and may represent the only manifestation of this disorder. However, widespread muscle involvement in preferential but variable and not distance-dependent patterns was frequently observed. Imaging score analysis is useful to categorize patients and to follow disease progression over time.

Role of RNA Binding Proteins with prion-like domains in muscle and neuromuscular diseases

A number of neuromuscular and muscular diseases, including amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA) and several myopathies, are associated to mutations in related RNA-binding proteins (RBPs), including TDP-43, FUS, MATR3 or hnRNPA1/B2. These proteins harbor similar modular primary sequence with RNA binding motifs and low complexity domains, that enables them to phase separate and create liquid microdomains. These RBPs have been shown to critically regulate multiple events of RNA lifecycle, including transcriptional events, splicing and RNA trafficking and sequestration. Here, we review the roles of these disease-related RBPs in muscle and motor neurons, and how their dysfunction in these cell types might contribute to disease.

Flexi-Myo Panel Strategy: Genomic Diagnoses of Myopathies and Muscular Dystrophies by Next-Generation Sequencing

Aims: Muscle disorders are clinically and genetically heterogeneous. Investigations, including plasma creatine kinase, electromyography, and nerve conduction velocity studies are often nonspecific, whereas muscle biopsy might be limited by sampling bias and variable histopathology. Next-generation sequencing is now generally considered an important diagnostic tool for muscle disorders, with decreased costs and improved diagnostic yield. Inclusion of a large number of genes in the analysis might, however, generate a large number of ambiguous results and create unnecessary confusion for clinicians and patients. Methods: An ethnic Chinese patient presented at age 10 with tip-toe walking. Upon examination the patient had a waddling gait, a tight Achilles tendon with pes cavus. A muscle biopsy showed the presence of minicores with disruption of the myofibrillary network and Z-bands. Sequencing was performed using the Flexi-Myo panel, which provides coverage for 85 myopathic genes. Reporting of sequencing results was decided by the responsible chemical pathologists based on the available clinical and genetic information. Results: A previously identified heterozygous in-frame deletion was detected in MYH7, which confirmed the diagnosis of Laing myopathy. No variants of uncertain significance required reporting. Conclusion: We describe the effectiveness of our Flexi-Myo panel approach for the diagnosis of muscle disorders, which confirmed diagnosis of Laing myopathy in what had been a clinically ambiguous presentation. This approach enables efficient genomic testing for muscle diseases in adults and children with satisfactory diagnostic yield and sufficient sensitivity, whereas avoiding the reporting of ambiguous results. Similar strategies might also be implemented for other groups of disorders.

Targeted sequencing with expanded gene profile enables high diagnostic yield in non-5q-spinal muscular atrophies

Spinal muscular atrophies (SMAs) are a heterogeneous group of disorders characterized by muscular atrophy, weakness, and hypotonia due to suspected lower motor neuron degeneration (LMND). In a large cohort of 3,465 individuals suspected with SMA submitted for SMN1 testing to our routine diagnostic laboratory, 48.8% carried a homozygous SMN1 deletion, 2.8% a subtle mutation, and an SMN1 deletion, whereas 48.4% remained undiagnosed. Recently, several other genes implicated in SMA/LMND have been reported. Despite several efforts to establish a diagnostic algorithm for non-5q-SMA (SMA without deletion or point mutations in SMN1 [5q13.2]), data from large-scale studies are not available. We tested the clinical utility of targeted sequencing in non-5q-SMA by developing two different gene panels. We first analyzed 30 individuals with a small panel including 62 genes associated with LMND using IonTorrent-AmpliSeq target enrichment. Then, additional 65 individuals were tested with a broader panel encompassing up to 479 genes implicated in neuromuscular diseases (NMDs) with Agilent-SureSelect target enrichment. The NMD panel provided a higher diagnostic yield (33%) than the restricted LMND panel (13%). Nondiagnosed cases were further subjected to exome or genome sequencing. Our experience supports the use of gene panels covering a broad disease spectrum for diseases that are highly heterogeneous and clinically difficult to differentiate.

Novel phenotypic variant in the MYH7 spectrum due to a stop-loss mutation in the C-terminal region: a case report

Background

Defects of the slow myosin heavy chain isoform coding MYH7 gene primarily cause skeletal myopathies including Laing Distal Myopathy, Myosin Storage Myopathy and are also responsible for cardiomyopathies. Scapuloperoneal and limb-girdle muscle weakness, congenital fiber type disproportion, multi-minicore disease were also reported in connection of MYH7. Pathogeneses of the defects in the head and proximal rod region of the protein are well described. However, the C-terminal mutations of the MYH7 gene are less known. Moreover, only two articles describe the phenotypic impact of the elongated mature protein product caused by termination signal loss.

Case presentation

Here we present a male patient with an unusual phenotypic variant of early-onset and predominant involvement of neck muscles with muscle biopsy indicating myopathy and sarcoplasmic storage material. Cardiomyopathic involvements could not be observed. Sequencing of MYH7 gene revealed a stop-loss mutation on the 3-prime end of the rod region, which causes the elongation of the mature protein.

Conclusions

The elongated protein likely disrupts the functions of the sarcomere by multiple functional abnormalities. This elongation could also affect the thick filament degradation leading to protein deposition and accumulation in the sarcomere, resulting in the severe myopathy of certain axial muscles. The phenotypic expression of the detected novel MYH7 genotype could strengthen and further expand our knowledge about mutations affecting the structure of MyHCI by termination signal loss in the MYH7 gene.

A Man With Distal Asymmetric Leg Weakness

EDUCATIONAL OBJECTIVES

To discuss a case of adult-onset asymmetric distal leg weakness in a patient who presented with weakness and atrophy of the posterior compartment of the left leg.

KEY QUESTIONS

1. What is the differential diagnosis of asymmetric distal leg weakness?2. How would a clinician approach diagnostic testing for such a patient?3. What is the final diagnosis for this patient?4. How to treat this patient?

De novo exonic mutation in MYH7 gene leading to exon skipping in a patient with early onset muscular weakness and fiber-type disproportion

Here we report on a case of MYH7-related myopathy in a boy with early onset of muscular weakness and delayed motor development in infancy. His most affected muscles were neck extensors showing a dropped head sign, proximal muscles of lower limbs with positive Gower's sign, and trunk muscles. Brain and spinal cord MRI scans, echocardiography, and laboratory analyses including creatine kinase and lactate did not reveal any abnormalities. Muscle histopathology showed fiber-type disproportion. Whole exome sequencing of the parents-offspring trio revealed a novel de novo c.5655G>A p.(Ala1885=) synonymous substitution of the last nucleotide in exon 38 of the MYH7 gene. Further RNA investigations proved the skipping of exon 38 (p.1854_1885del). This is a first report of an exon-skipping mutation in the MYH7 gene causing myopathy. This report broadens both the phenotypic and genotypic spectra of MYH7-related myopathies.

A de novo mutation of the MYH7 gene in a large Chinese family with autosomal dominant myopathy

Laing distal myopathy (LDM) is an autosomal dominant myopathy that is caused by mutations in the slow/beta cardiac myosin heavy-chain (MYH7) gene. It has been recently reported that LDM presents with a wide range of clinical manifestations. We herein report a large Chinese family with autosomal dominant myopathy. The affected individuals in the family presented with foot drop in early childhood, along with progressive distal and proximal limb weakness. Their characteristic symptoms include scapular winging and scoliosis in the early disease phase and impairment of ambulation in the advanced phase. Although limb-girdle muscle dystrophy (LGMD) was suspected initially, a definite diagnosis could not be reached. As such, we performed linkage analysis and detected four linkage regions, namely 1q23.2-24.1, 14q11.2-12, 15q26.2-26.3 and 17q24.3. Through subsequent whole exome sequencing, we found a de novo p.K1617del causative mutation in the MYH7 gene and diagnosed the disease as LDM. This is the first LDM case in China. Our patients have severe clinical manifestations that mimic LGMD in comparison with the patients with the same mutation reported elsewhere.

Clinical massively parallel sequencing for the diagnosis of myopathies

Massively parallel sequencing, otherwise known as high-throughput or next-generation sequencing, is rapidly gaining wide use in clinical practice due to possibility of simultaneous exploration of multiple genomic regions. More than 300 genes have been implicated in neuromuscular disorders, meaning that many genes need to be considered in a differential diagnosis for a patient affected with myopathy. By providing sequencing information for numerous genes at the same time, massively parallel sequencing greatly accelerates the diagnostic processes of myopathies compared to the classical "gene-after-gene" approach by Sanger sequencing. In this review, we describe multiple advantages of this powerful sequencing method for applications in myopathy diagnosis. We also outline recent studies that used this approach to discover new myopathy-causing genes and to diagnose cohorts of patients with muscular disorders. Finally, we highlight the key aspects and limitations of massively parallel sequencing that a neurologist considering this test needs to know in order to interpret the results of the test and to deal with other issues concerning the test.

Expanding the phenotype associated with the NEFL mutation: neuromuscular disease in a family with overlapping myopathic and neurogenic findings

IMPORTANCE

Newer sequencing technologies in combination with traditional gene mapping techniques, such as linkage analysis, can help identify the genetic basis of disease for patients with rare disorders of uncertain etiology. This approach may expand the phenotypic spectrum of disease associated with those genetic mutations.

OBJECTIVE

To elucidate the molecular cause of a neuromuscular disease among a family in which 4 members, a mother and her 3 sons, were affected.

DESIGN, SETTING, AND PARTICIPANTS

Two of 4 affected members manifested nemaline myopathy, a common subtype of congenital myopathy, while the other 2 had a nonspecific myopathy. Single-nucleotide polymorphism-based linkage analysis was performed on DNA samples from the 4 affected family members, and whole-genome sequencing was performed in the proband. Real-time quantitative reverse transcription-polymerase chain reaction, immunofluorescence, and Western blot analysis were performed on muscle biopsy specimens.

MAIN OUTCOMES AND MEASURES

Whole-genome sequencing and linkage analysis identified a variant in a gene that explains the phenotype.

RESULTS

We identified a novel neurofilament light polypeptide (NEFL) nonsense mutation in all affected members. NEFL mutations have been previously linked to Charcot-Marie-Tooth disease in humans. This led us to reevaluate the diagnosis, and we recognized that several of the findings, especially those related to the muscle biopsy specimens and electromyography, were consistent with a neurogenic disease.

CONCLUSIONS AND RELEVANCE

NEFL mutations are known to cause Charcot-Marie-Tooth disease in humans and motor neuron disease in mice. We report the identification of an NEFL mutation in a family clinically manifesting congenital myopathy. We also describe potential overlap between myopathic and neurogenic findings in this family. These findings expand the phenotypic spectrum of diseases associated with NEFL mutations. This study is an example of the power of genomic approaches to identify potentially pathogenic mutations in unsuspected genes responsible for heterogeneous neuromuscular diseases.