Genetic testing offer for inherited neuromuscular diseases within the EURO-NMD reference network: A European survey study

Next generation sequencing panel as an effective approach to genetic testing in patients with a highly variable phenotype of neuromuscular disorders

Neuromuscular disorders (NMDs) include a wide range of diseases affecting the peripheral nervous system. The genetic diagnoses are increasingly obtained with using the next generation sequencing (NGS). We applied the custom-design targeted NGS panel including 89 genes, together with genotyping and multiplex ligation-dependent probe amplification (MLPA) to identify a genetic spectrum of NMDs in 52 Polish patients. As a result, the genetic diagnosis was determined by NGS panel in 29 patients so its diagnostic utility is estimated at 55.8%. The most pathogenic variants were found in CLCN1, followed by CAPN3, SCN4A, and SGCA genes. Genotyping of myotonic dystrophy type 1 and 2 (DM1 and DM2) as a secondary approach has been performed. The co-occurrence of CAPN3 and CNBP mutations in one patient as well as DYSF and CNBP mutations in another suggests possibly more complex inheritance as well as expression of a phenotype. In 7 individuals with single nucleotide variant found in NGS testing, the MLPA of the CAPN3 gene was performed detecting the deletion encompassing exons 2-8 in the CAPN3 gene in one patient, confirming recessive limb-girdle muscular dystrophy type 1 (LGMDR1). Thirty patients obtained a genetic diagnosis (57.7%) after using NGS testing, genotyping and MLPA analysis. The study allowed for the identification of 27 known and 4 novel pathogenic/likely pathogenic variants and variants of uncertain significance (VUS) associated with NMDs.In conclusion, the diagnostic approach with diverse molecular techniques enables to broaden the mutational spectrum and maximizes the diagnostic yield. Furthermore, the co-occurrence of DM2 and LGMD has been detected in 2 individuals.

Understanding Challenges of Genetic Testing on Neuromuscular Disorders from the Parental Lens

Neuromuscular disorders, characterized by progressive muscle degeneration and weakness, present substantial challenges to both affected individuals and their families. Genetic testing assumes a pivotal role in facilitating early diagnosis, intervention, treatment, and informed family planning for these conditions. The objective of this qualitative study is to delve into the knowledge, awareness, and perceptions surrounding genetic testing within the cohort of parents caring for individuals with neuromuscular disorders in Malaysia. A semi-structured interview approach was employed to elicit data from parents of individuals diagnosed with neuromuscular disorders, encompassing those with clinical diagnoses and those diagnosed through genetic testing. Examination of the interview responses yielded nine overarching themes, which furnish invaluable insights into the perspectives of Malaysian parents concerning genetic testing. The study discerned several challenges associated with genetic testing, notably encompassing the limited awareness among parents, the financial constraints associated with genetic testing, and the perceived significance of genetic testing in the context of neuromuscular disorders. The findings suggest that the level of knowledge and awareness pertaining to genetic testing for neuromuscular disorders among parents in Malaysia varies, with initial levels of awareness ranging from relatively low to reasonably sufficient prior to and following the birth of an affected child. However, the investigation revealed that parents tended to cultivate more favorable perceptions regarding genetic testing subsequent to their experience with genetic counseling. This underscores the potential for heightened awareness and comprehension as a consequence of the personal experience of parenting an affected child confirmed through genetic testing and genetic counseling, ultimately influencing parental awareness.

The utility of whole-exome sequencing in accurate diagnosis of neuromuscular disorders in consanguineous families in Jordan

BACKGROUND

Neuromuscular disorders (NMDs) encompass a large group of genetic and acquired diseases affecting muscles, leading to progressive muscular weakness. These disorders are frequently inherited in an autosomal-recessive (AR) pattern with extreme heterogeneity and various clinical presentations. Consanguinity increases the likelihood of AR disorders, with high rates of cousin inbreeding in Jordan and other Arab countries. In Jordan, the implementation of genetic diagnosis is limited, with delayed or misdiagnosis of genetic disorders. Thus, the lack of genetic counselling and specialized treatment options is frequently encountered in the country.

METHODS

Whole-exome sequencing (WES) was conducted for eleven probands from ten Jordanian families who have been formerly diagnosed with limb-girdle dystrophy (LGMD) and Charcot-Marie-Tooth disease (CMT). The previous diagnoses were established principally on clinical examination in the absence of genetic testing. Additionally, Sanger sequencing and segregation analysis were used to validate the resulted pathogenic variants.

RESULTS

Multiple variants were identified using WES: For DYSF gene, a missense variant (c. 4076 T > C, p.Leu1359Pro) in exon 38; a nonsense variant (c. 4321C > T, p.Gln1441Ter) in exon 39; a single-nucleotide deletion (c. 5711delG, p.Gly1904AlafsTer101) in exon 51. Other variants included a missense variant (c. 122G > A, p.Arg41Gln) in exon 3 of MPV17 gene, a single-nucleotide deletion (c. 859 delC, p.Lue287Ser fs14*) in exon 6 of SGCB gene, a missense variant (c. 311G > A, p.Gly104Asp) in exon 2 of SLC25A46 gene, a nonsense variant (c. 496C > T, p.Arg166Ter) in exon 5 of SGCG gene, and a nonsense variant (c.3202C > T, p.Gln1068Ter) in exon 13 of SH3TC2 gene.

CONCLUSION

Utilization of WES is helpful to facilitate rapid and accurate NMDs diagnosis, complementing a thorough clinical evaluation. This approach can be invaluable to aid in the identification of genetic risks among consanguineous couples. Subsequently, well-informed genetic counselling and potential individualized treatment can be provided.

The Increasing Impact of Translational Research in the Molecular Diagnostics of Neuromuscular Diseases

The diagnosis of neuromuscular diseases (NMDs) has been progressively evolving from the grouping of clinical symptoms and signs towards the molecular definition. Optimal clinical, biochemical, electrophysiological, electrophysiological, and histopathological characterization is very helpful to achieve molecular diagnosis, which is essential for establishing prognosis, treatment and genetic counselling. Currently, the genetic approach includes both the gene-targeted analysis in specific clinically recognizable diseases, as well as genomic analysis based on next-generation sequencing, analyzing either the clinical exome/genome or the whole exome or genome. However, as of today, there are still many patients in whom the causative genetic variant cannot be definitely established and variants of uncertain significance are often found. In this review, we address these drawbacks by incorporating two additional biological omics approaches into the molecular diagnostic process of NMDs. First, functional genomics by introducing experimental cell and molecular biology to analyze and validate the variant for its biological effect in an in-house translational diagnostic program, and second, incorporating a multi-omics approach including RNA-seq, metabolomics, and proteomics in the molecular diagnosis of neuromuscular disease. Both translational diagnostics programs and omics are being implemented as part of the diagnostic process in academic centers and referral hospitals and, therefore, an increase in the proportion of neuromuscular patients with a molecular diagnosis is expected. This improvement in the process and diagnostic performance of patients will allow solving aspects of their health problems in a precise way and will allow them and their families to take a step forward in their lives.

Facilitations and Hurdles of Genetic Testing in Neuromuscular Disorders

Neuromuscular disorders (NMDs) comprise a heterogeneous group of disorders that affect about one in every thousand individuals worldwide. The vast majority of NMDs has a genetic cause, with about 600 genes already identified. Application of genetic testing in NMDs can be useful for several reasons: correct diagnostic definition of a proband, extensive familial counselling to identify subjects at risk, and prenatal diagnosis to prevent the recurrence of the disease; furthermore, identification of specific genetic mutations still remains mandatory in some cases for clinical trial enrollment where new gene therapies are now approaching. Even though genetic analysis is catching on in the neuromuscular field, pitfalls and hurdles still remain and they should be taken into account by clinicians, as for example the use of next generation sequencing (NGS) where many single nucleotide variants of “unknown significance” can emerge, complicating the correct interpretation of genotype-phenotype relationship. Finally, when all efforts in terms of molecular analysis have been carried on, a portion of patients affected by NMDs still remain “not genetically defined”. In the present review we analyze the evolution of genetic techniques, from Sanger sequencing to NGS, and we discuss “facilitations and hurdles” of genetic testing which must always be balanced by clinicians, in order to ensure a correct diagnostic definition, but taking always into account the benefit that the patient could obtain especially in terms of “therapeutic offer”.

Facilitations and Hurdles of Genetic Testing in Neuromuscular Disorders

Neuromuscular disorders (NMDs) comprise a heterogeneous group of disorders that affect about one in every thousand individuals worldwide. The vast majority of NMDs has a genetic cause, with about 600 genes already identified. Application of genetic testing in NMDs can be useful for several reasons: correct diagnostic definition of a proband, extensive familial counselling to identify subjects at risk, and prenatal diagnosis to prevent the recurrence of the disease; furthermore, identification of specific genetic mutations still remains mandatory in some cases for clinical trial enrollment where new gene therapies are now approaching. Even though genetic analysis is catching on in the neuromuscular field, pitfalls and hurdles still remain and they should be taken into account by clinicians, as for example the use of next generation sequencing (NGS) where many single nucleotide variants of "unknown significance" can emerge, complicating the correct interpretation of genotype-phenotype relationship. Finally, when all efforts in terms of molecular analysis have been carried on, a portion of patients affected by NMDs still remain "not genetically defined". In the present review we analyze the evolution of genetic techniques, from Sanger sequencing to NGS, and we discuss "facilitations and hurdles" of genetic testing which must always be balanced by clinicians, in order to ensure a correct diagnostic definition, but taking always into account the benefit that the patient could obtain especially in terms of "therapeutic offer".

Improving diagnostics of rare genetic diseases with NGS approaches

According to a rough estimate, one in fifteen people worldwide is affected by a rare disease. Rare diseases are therefore common in clinical practice; however, timely diagnosis of rare diseases is still challenging. Introduction of novel methods based on next-generation sequencing (NGS) technology offers a successful diagnosis of genetically heterogeneous disorders, even in case of unclear clinical diagnostic hypothesis. However, the application of novel technology differs among the centres and health systems significantly. Our goal is to discuss the impact of the implementation of NGS in the diagnosis of rare diseases and present advantages along with challenges of diagnostic approach. Systematic implementation of NGS in health systems can significantly improve the access of patients with rare diseases to diagnosis and reduce the dependence of national health systems for cross-border collaboration.

Panorama of the distal myopathies

Distal myopathies are genetic primary muscle disorders with a prominent weakness at onset in hands and/or feet. The age of onset (from early childhood to adulthood), the distribution of muscle weakness (upper versus lower limbs) and the histological findings (ranging from nonspecific myopathic changes to myofibrillar disarrays and rimmed vacuoles) are extremely variable. However, despite being characterized by a wide clinical and genetic heterogeneity, the distal myopathies are a category of muscular dystrophies: genetic diseases with progressive loss of muscle fibers. Myopathic congenital arthrogryposis is also a form of distal myopathy usually caused by focal amyoplasia. Massive parallel sequencing has further expanded the long list of genes associated with a distal myopathy, and contributed identifying as distal myopathy-causative rare variants in genes more often related with other skeletal or cardiac muscle diseases. Currently, almost 20 genes (ACTN2, CAV3, CRYAB, DNAJB6, DNM2, FLNC, HNRNPA1, HSPB8, KHLH9, LDB3, MATR3, MB, MYOT, PLIN4, TIA1, VCP, NOTCH2NLC, LRP12, GIPS1) have been associated with an autosomal dominant form of distal myopathy. Pathogenic changes in four genes (ADSSL, ANO5, DYSF, GNE) cause an autosomal recessive form; and disease-causing variants in five genes (DES, MYH7, NEB, RYR1 and TTN) result either in a dominant or in a recessive distal myopathy. Finally, a digenic mechanism, underlying a Welander-like form of distal myopathy, has been recently elucidated. Rare pathogenic mutations in SQSTM1, previously identified with a bone disease (Paget disease), unexpectedly cause a distal myopathy when combined with a common polymorphism in TIA1. The present review aims at describing the genetic basis of distal myopathy and at summarizing the clinical features of the different forms described so far.