The relative frequency of common neuromuscular diagnoses in a reference center

Application of whole exome sequencing in the diagnosis of muscular disorders: a study of Taiwanese pediatric patients

Background

Muscular dystrophies and congenital myopathies encompass various inherited muscular disorders that present diagnostic challenges due to clinical complexity and genetic heterogeneity.

Methods

This study aimed to investigate the use of whole exome sequencing (WES) in diagnosing muscular disorders in pediatric patients in Taiwan. Out of 161 pediatric patients suspected to have genetic/inherited myopathies, 115 received a molecular diagnosis through conventional tests, single gene testing, and gene panels. The remaining 46 patients were divided into three groups: Group 1 (multiplex ligation-dependent probe amplification-negative Duchenne muscular dystrophy) with three patients (6.5%), Group 2 (various forms of muscular dystrophies) with 21 patients (45.7%), and Group 3 (congenital myopathies) with 22 patients (47.8%).

Results

WES analysis of these groups found pathogenic variants in 100.0% (3/3), 57.1% (12/21), and 68.2% (15/22) of patients in Groups 1 to 3, respectively. WES had a diagnostic yield of 65.2% (30 patients out of 46), detecting 30 pathogenic or potentially pathogenic variants across 28 genes.

Conclusion

WES enables the diagnosis of rare diseases with symptoms and characteristics similar to congenital myopathies and muscular dystrophies, such as muscle weakness. Consequently, this approach facilitates targeted therapy implementation and appropriate genetic counseling.

High Prevalence of a c.5979dupA Variant in the Dysferlin Gene (DYSF) in Individuals from a Semiarid Region of Brazil

Background

Dysferlinopathies represent a group of limb girdle or distal muscular dystrophies with an autosomal-recessive inheritance pattern resulting from the presence of pathogenic variants in the dysferlin gene (DYSF).

Objective

In this work, we describe a population from a small city in Brazil carrying the c.5979dupA pathogenic variant of DYSF responsible for limb girdle muscular dystrophy type 2R and distal muscular dystrophy.

Methods

Genotyping analyses were performed by qPCR using customized probe complementary to the region with the duplication under analysis in the DYSF.

Results

A total of 104 individuals were examined. c.5979dupA was identified in 48 (46.15%) individuals. Twenty-three (22%) were homozygotes, among whom 13 (56.5%) were female. A total of 91.3% (21) of homozygous individuals had a positive family history, and seven (30.4%) reported consanguineous marriages. Twenty-five (24%) individuals were heterozygous (25.8±16 years) for the same variant, among whom 15 (60%) were female. The mean CK level was 697 IU for homozygotes, 140.5 IU for heterozygotes and 176 IU for wild-type homo-zygotes. The weakness distribution pattern showed 17.3% of individuals with a proximal pattern, 13% with a distal pattern and 69.6% with a mixed pattern. Fatigue was present in 15 homozygotes and one heterozygote.

Conclusion

The high prevalence of this variant in individuals from this small community can be explained by a possible founder effect associated with historical, geographical and cultural aspects.

Utilisation of exome sequencing for muscular disorders in Thai paediatric patients: diagnostic yield and mutational spectrum

Muscular dystrophies and congenital myopathies are heterogeneous groups of inherited muscular disorders. An accurate diagnosis is challenging due to their complex clinical presentations and genetic heterogeneity. This study aimed to determine the utilisation of exome sequencing (ES) for Thai paediatric patients with muscular disorders. Of 176 paediatric patients suspected of genetic/inherited myopathies, 133 patients received a molecular diagnosis after performing conventional investigations, single gene testing, and gene panels. The remaining 43 patients from 42 families could be classified into three groups: Group 1, MLPA-negative Duchenne muscular dystrophy (DMD) with 9 patients (9/43; 21%), Group 2, other muscular dystrophies (MD) with 18 patients (18/43; 42%) and Group 3, congenital myopathies (CM) with 16 patients (16/43; 37%). All underwent exome sequencing which could identify pathogenic variants in 8/9 (89%), 14/18 (78%), and 8/16 (50%), for each Group, respectively. Overall, the diagnostic yield of ES was 70% (30/43) and 36 pathogenic/likely pathogenic variants in 14 genes were identified. 18 variants have never been previously reported. Molecular diagnoses provided by ES changed management in 22/30 (73%) of the patients. Our study demonstrates the clinical utility and implications of ES in inherited myopathies.

Central Core Disease: Facial Weakness Differentiating Biallelic from Monoallelic Forms

Central Core Disease (CCD) is a genetic neuromuscular disorder characterized by the presence of cores in muscle biopsy. The inheritance has been described as predominantly autosomal dominant (AD), and the disease may present as severe neonatal or mild adult forms. Here we report clinical and molecular data on a large cohort of Brazilian CCD patients, including a retrospective clinical analysis and molecular screening for RYR1 variants using Next-Generation Sequencing (NGS). We analyzed 27 patients from 19 unrelated families: four families (11 patients) with autosomal dominant inheritance (AD), two families (3 patients) with autosomal recessive (AR), and 13 sporadic cases. Biallelic RYR1 variants were found in six families (two AR and four sporadic cases) of the 14 molecularly analyzed families (~43%), suggesting a higher frequency of AR inheritance than expected. None of these cases presented a severe phenotype. Facial weakness was more common in biallelic than in monoallelic patients (p = 0.0043) and might be a marker for AR forms. NGS is highly effective for the identification of RYR1 variants in CCD patients, allowing the discovery of a higher proportion of AR cases with biallelic mutations. These data have important implications for the genetic counseling of the families.

Muscle biopsy essential diagnostic advice for pathologists

Background

Muscle biopsies are important diagnostic procedures in neuromuscular practice. Recent advances in genetic analysis have profoundly modified Myopathology diagnosis.

Main body

The main goals of this review are: (1) to describe muscle biopsy techniques for non specialists; (2) to provide practical information for the team involved in the diagnosis of muscle diseases; (3) to report fundamental rules for muscle biopsy site choice and adequacy; (4) to highlight the importance of liquid nitrogen in diagnostic workup. Routine techniques include: (1) histochemical stains and reactions; (2) immunohistochemistry and immunofluorescence; (3) electron microscopy; (4) mitochondrial respiratory chain enzymatic studies; and (5) molecular studies. The diagnosis of muscle disease is a challenge, as it should integrate data from different techniques.

Conclusion

Formalin-fixed paraffin embedded muscle samples alone almost always lead to inconclusive or unspecific results. Liquid nitrogen frozen muscle sections are imperative for neuromuscular diagnosis. Muscle biopsy interpretation is possible in the context of detailed clinical, neurophysiological, and serum muscle enzymes data. Muscle imaging studies are strongly recommended in the diagnostic workup. Muscle biopsy is useful for the differential diagnosis of immune mediated myopathies, muscular dystrophies, congenital myopathies, and mitochondrial myopathies. Muscle biopsy may confirm the pathogenicity of new gene variants, guide cost-effective molecular studies, and provide phenotypic diagnosis in doubtful cases. For some patients with mitochondrial myopathies, a definite molecular diagnosis may be achieved only if performed in DNA extracted from muscle tissue due to organ specific mutation load.