Targeted Next-Generation Sequencing in a Large Cohort of Genetically Undiagnosed Patients with Neuromuscular Disorders in Spain

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.

Utility of exome sequencing for the diagnosis of pediatric-onset neuromuscular diseases beyond diagnostic yield: a narrative review

Diagnosis of neuromuscular diseases (NMD) can be challenging because of the heterogeneity of this group of diseases. This review aimed to describe the diagnostic yield of whole exome sequencing (WES) for pediatric-onset neuromuscular disease diagnosis, as well as other benefits of this approach in patient management since WES can contribute to appropriate treatment selection in NMD patients. WES increases the possibility of reaching a conclusive genetic diagnosis when other technologies have failed and even exploring new genes not previously associated with a specific NMD. Moreover, this strategy can be useful when a dual diagnosis is suspected in complex congenital anomalies and undiagnosed cases.

Sodium Channel Gene Variants in Fetuses with Abnormal Sonographic Findings: Expanding the Prenatal Phenotypic Spectrum of Sodium Channelopathies

Voltage-gated sodium channels (VGSCs) are responsible for the initiation and propagation of action potentials in the brain and muscle. Pathogenic variants in genes encoding VGSCs have been associated with severe disorders including epileptic encephalopathies and congenital myopathies. In this study, we identified pathogenic variants in genes encoding the α subunit of VGSCs in the fetuses of two unrelated families with the use of trio-based whole exome sequencing, as part of a larger cohort study. Sanger sequencing was performed for variant confirmation as well as parental phasing. The fetus of the first family carried a known de novo heterozygous missense variant in the SCN2A gene (NM_001040143.2:c.751G>A p.(Val251Ile)) and presented intrauterine growth retardation, hand clenching and ventriculomegaly. Neonatally, the proband also exhibited refractory epilepsy, spasms and MRI abnormalities. The fetus of the second family was a compound heterozygote for two parentally inherited novel missense variants in the SCN4A gene (NM_000334.4:c.4340T>C, p.(Phe1447Ser), NM_000334.4:c.3798G>C, p.(Glu1266Asp)) and presented a severe prenatal phenotype including talipes, fetal hypokinesia, hypoplastic lungs, polyhydramnios, ear abnormalities and others. Both probands died soon after birth. In a subsequent pregnancy of the latter family, the fetus was also a compound heterozygote for the same parentally inherited variants. This pregnancy was terminated due to multiple ultrasound abnormalities similar to the first pregnancy. Our results suggest a potentially crucial role of the VGSC gene family in fetal development and early lethality.

Retrospective clinical and genetic analysis of COL6-RD patients with a long-term follow-up at a single French center

Collagen type VI-related dystrophies (COL6-RD) are rare diseases with a wide phenotypic spectrum ranging from severe Ullrich's congenital muscular dystrophy Ullrich congenital muscular dystrophy to much milder Bethlem myopathy Both dominant and recessive forms of COL6-RD are caused by pathogenic variants in three collagen VI genes (COL6A1, COL6A2 and COL6A3). The prognosis of these diseases is variable and difficult to predict during early disease stages, especially since the genotype-phenotype correlation is not always clear. For this reason, studies with long-term follow-up of patients with genetically confirmed COL6-RD are still needed. In this study, we present phenotypic and genetic data from 25 patients (22 families) diagnosed with COL6-RD and followed at a single French center, in both adult and pediatric neurology departments. We describe three novel pathogenic variants and identify COL6A2:c.1970-9G>A as the most frequent variant in our series (29%). We also observe an accelerated progression of the disease in a subgroup of patients. This large series of rare disease patients provides essential information on phenotypic variability of COL6-RD patients as well as on frequency of pathogenic COL6A gene variants in Southern France, thus contributing to the phenotypic and genetic description of Collagen type VI-related dystrophies.

Tropomyosin 3 (TPM3) function in skeletal muscle and in myopathy

The tropomyosin genes (TPM1-4) contribute to the functional diversity of skeletal muscle fibers. Since its discovery in 1988, the TPM3 gene has been recognized as an indispensable regulator of muscle contraction in slow muscle fibers. Recent advances suggest that TPM3 isoforms hold more extensive functions during skeletal muscle development and in postnatal muscle. Additionally, mutations in the TPM3 gene have been associated with the features of congenital myopathies. The use of different in vitro and in vivo model systems has leveraged the discovery of several disease mechanisms associated with TPM3-related myopathy. Yet, the precise mechanisms by which TPM3 mutations lead to muscle dysfunction remain unclear. This review consolidates over three decades of research about the role of TPM3 in skeletal muscle. Overall, the progress made has led to a better understanding of the phenotypic spectrum in patients affected by mutations in this gene. The comprehensive body of work generated over these decades has also laid robust groundwork for capturing the multiple functions this protein plays in muscle fibers.

Combined sequence and copy number analysis improves diagnosis of limb girdle and other myopathies

OBJECTIVE

Clinical and genetic heterogeneities make diagnosis of limb-girdle muscular dystrophy (LGMD) and other overlapping disorders of muscle weakness complicated and expensive. We aimed to develop a comprehensive next generation sequence-based multi-gene panel ("The Lantern Focused Neuromuscular Panel") to detect both sequence variants and copy number variants in one assay.

METHODS

Patients with clinical diagnosis of LGMD or other overlapping muscular dystrophies in the United States were tested by PerkinElmer Genomics in 2018-2021 via "The Lantern Project," a sponsored diagnostic testing program. Sixty-six genes related to LGMD subtypes- and other myopathies were investigated. Main outcomes were diagnostic yield, gene-variant spectrum, and LGMD subtypes' prevalence.

RESULTS

Molecular diagnosis was established in 19.6% (1266) of 6473 cases. Major genes contributing to LGMD were identified including CAPN3 (5.4%, 68), DYSF (4.0%, 51), GAA (3.7%, 47), ANO5 (3.6%, 45), and FKRP (2.7%, 34). Genes of other overlapping MD subtypes identified included PABPN1 (10.5%, 133), VCP (2.2%, 28), MYOT (1.2% 15), LDB3 (1.0%, 13), COL6A1 (1.5%, 19), FLNC (1.1%, 14), and DNAJB6 (0.8%, 10). Different sizes of copy number variants including single exon, multi-exon, and whole genes were identified in 7.5% (95) cases in genes including DMD, EMD, CAPN3, ANO5, SGCG, COL6A2, DOK7, and LAMA2.

INTERPRETATION

"The Lantern Focused Neuromuscular Panel" enables identification of LGMD subtypes and other myopathies with overlapping clinical features. Prevalence of some MD subtypes was higher than previously reported. Widespread deployment of this comprehensive NGS panel has the potential to ensure early, accurate diagnosis as well as re-define MD epidemiology.

Congenital Myasthenic Syndrome With Malignant Hyperthermia Susceptibility in a Child Undergoing Adenotonsillectomy for Obstructive Sleep Apnea: A Case Report

Congenital myasthenic syndromes are rare genetic diseases involving pathologic proteins in the neuromuscular junction. Malignant hyperthermia susceptibility is a genetic disorder involving a hypermetabolic response to volatile anesthetics and depolarizing neuromuscular blocking agents. We present the first reported case of a 3-year-old boy with both congenital myasthenic syndrome and malignant hyperthermia susceptibility, resulting from a mutation in the ryanodine receptor type 1 gene, who underwent an adenotonsillectomy for severe obstructive sleep apnea. We discuss the anesthetic challenges in navigating these 3 comorbidities in the setting of airway surgery.

Function of a mutant ryanodine receptor (T4709M) linked to congenital myopathy

Physiological muscle contraction requires an intact ligand gating mechanism of the ryanodine receptor 1 (RyR1), the Ca2+-release channel of the sarcoplasmic reticulum. Some mutations impair the gating and thus cause muscle disease. The RyR1 mutation T4706M is linked to a myopathy characterized by muscle weakness. Although, low expression of the T4706M RyR1 protein can explain in part the symptoms, little is known about the function RyR1 channels with this mutation. In order to learn whether this mutation alters channel function in a manner that can account for the observed symptoms, we examined RyR1 channels isolated from mice homozygous for the T4709M (TM) mutation at the single channel level. Ligands, including Ca2+, ATP, Mg2+ and the RyR inhibitor dantrolene were tested. The full conductance of the TM channel was the same as that of wild type (wt) channels and a population of partial open (subconductive) states were not observed. However, two unique sub-populations of TM RyRs were identified. One half of the TM channels exhibited high open probability at low (100 nM) and high (50 μM) cytoplasmic [Ca2+], resulting in Ca2+-insensitive, constitutively high Po channels. The rest of the TM channels exhibited significantly lower activity within the physiologically relevant range of cytoplasmic [Ca2+], compared to wt. TM channels retained normal Mg2+ block, modulation by ATP, and inhibition by dantrolene. Together, these results suggest that the TM mutation results in a combination of primary and secondary RyR1 dysfunctions that contribute to disease pathogenesis.

Using Cluster Analysis to Overcome the Limits of Traditional Phenotype-Genotype Correlations: The Example of RYR1-Related Myopathies

Thanks to advances in gene sequencing, RYR1-related myopathy (RYR1-RM) is now known to manifest itself in vastly heterogeneous forms, whose clinical interpretation is, therefore, highly challenging. We set out to develop a novel unsupervised cluster analysis method in a large patient population. The objective was to analyze the main RYR1-related characteristics to identify distinctive features of RYR1-RM and, thus, offer more precise genotype-phenotype correlations in a group of potentially life-threatening disorders. We studied 600 patients presenting with a suspicion of inherited myopathy, who were investigated using next-generation sequencing. Among them, 73 index cases harbored variants in RYR1. In an attempt to group genetic variants and fully exploit information derived from genetic, morphological, and clinical datasets, we performed unsupervised cluster analysis in 64 probands carrying monoallelic variants. Most of the 73 patients with positive molecular diagnoses were clinically asymptomatic or pauci-symptomatic. Multimodal integration of clinical and histological data, performed using a non-metric multi-dimensional scaling analysis with k-means clustering, grouped the 64 patients into 4 clusters with distinctive patterns of clinical and morphological findings. In addressing the need for more specific genotype-phenotype correlations, we found clustering to overcome the limits of the "single-dimension" paradigm traditionally used to describe genotype-phenotype relationships.

Miyoshi Muscular Dystrophy Type 1 with Mutated DYSF Gene Misdiagnosed as Becker Muscular Dystrophy: A Case Report and Literature Review

Dysferlinopathy covers a spectrum of muscle disorder categorized by two major phenotypes, namely Miyoshi muscular dystrophy type 1 (MMD1, OMIM #254130) and limb-girdle muscular dystrophy autosomal recessive 2 (LGMDR2, OMIM #253601), and two minor symptoms, including asymptomatic hyperCKemia and distal myopathy with anterior tibial onset (DMAT, OMIM #606768). We report the first Korean MMD1 misdiagnosed as Becker muscular dystrophy (BMD), which was caused by a combination of compound heterozygous c.663 + 1G > C and p.Trp992Arg of the DYSF gene. A 70-year-old male previously diagnosed with BMD was admitted for genetic counseling. Since he was clinically suspected to have dysferlinopathy but not BMD, targeted panel sequencing was performed to discover the potential hereditary cause of the suspected muscular dystrophy in the proband. Consequently, two pathogenic single nucleotide variants of the DYSF gene, c.663 + 1G > C (rs398123800) and p.Trp992Arg (rs750028300), associated with dysferlinopathy were identified. These variants were previously reported with variant allele frequencies of 0.000455 (c.663 + 1G > C) and 0.000455 (c.2974T > C; p.Trp992Arg) in the Korean population. This report emphasizes the need for common variant screening in the diagnostic algorithms of certain muscle disorders or gene panels with potential pathogenic effects and high rates of recurrent variants.

Copy-number analysis by base-level normalization: An intuitive visualization tool for evaluating copy number variations

Next-generation sequencing (NGS) facilitates comprehensive molecular analyses that help with diagnosing unsolved disorders. In addition to detecting single-nucleotide variations and small insertions/deletions, bioinformatics tools can identify copy number variations (CNVs) in NGS data, which improves the diagnostic yield. However, due to the possibility of false positives, subsequent confirmation tests are generally performed. Here, we introduce Copy-number Analysis by BAse-level NormAlization (CABANA), a visualization tool that allows users to intuitively identify candidate CNVs using the normalized single-base-level read depth calculated from NGS data. To demonstrate how CABANA works, NGS data were obtained from 474 patients with neuromuscular disorders. CNVs were screened using a conventional bioinformatics tool, ExomeDepth, and then we normalized and visualized those data at the single-base level using CABANA, followed by manual inspection by geneticists to filter out false positives and determine candidate CNVs. In doing so, we identified 31 candidate CNVs (7%) in 474 patients and subsequently confirmed all of them to be true using multiplex ligation-dependent probe amplification. The performance of CABANA was deemed acceptable by comparing its diagnostic yield with previous data about neuromuscular disorders. Despite some limitations, we expect CABANA to help researchers accurately identify CNVs and reduce the need for subsequent confirmation testing.

A Schematic Approach to Defining the Prevalence of COL VI Variants in Five Years of Next-Generation Sequencing

OBJECTIVE

To define the prevalence of variants in collagen VI genes through a next-generation sequencing (NGS) approach in undiagnosed patients with suspected neuromuscular disease and to propose a diagnostic flowchart to assess the real pathogenicity of those variants.

METHODS

In the past five years, we have collected clinical and molecular information on 512 patients with neuromuscular symptoms referred to our center. To pinpoint variants in COLVI genes and corroborate their real pathogenicity, we sketched a multistep flowchart, taking into consideration the bioinformatic weight of the gene variants, their correlation with clinical manifestations and possible effects on protein stability and expression.

RESULTS

In Step I, we identified variants in COLVI-related genes in 48 patients, of which three were homozygous variants (Group 1). Then, we sorted variants according to their CADD score, clinical data and complementary studies (such as muscle and skin biopsy, study of expression of COLVI on fibroblast or muscle and muscle magnetic resonance). We finally assessed how potentially pathogenic variants (two biallelic and 12 monoallelic) destabilize COL6A1-A2-A3 subunits. Overall, 15 out of 512 patients were prioritized according to this pipeline. In seven of them, we confirmed reduced or absent immunocytochemical expression of collagen VI in cultured skin fibroblasts or in muscle tissue.

CONCLUSIONS

In a real-world diagnostic scenario applied to heterogeneous neuromuscular conditions, a multistep integration of clinical and molecular data allowed the identification of about 3% of those patients harboring pathogenetic collagen VI variants.

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.

Investigating the Genetic Etiology of Pediatric Patients with Peripheral Hypotonia Using the Next-Generation Sequencing Method

Background  Hypotonia occurs as a result of neurological dysfunction in the brain, brainstem, spinal cord, motor neurons, anterior horn cells, peripheral nerves, and muscles. Although the genotype–phenotype correlation can be established in 15 to 30% of patients, it is difficult to obtain a correlation in most cases.

Aims  This study was aimed to investigate the genetic etiology in cases of peripheral hypotonia that could not be diagnosed using conventional methods.

Methods  A total of 18 pediatric patients with peripheral hypotonia were included. They were referred to our genetic disorders diagnosis center from the Pediatric Neurology Department with a prediagnosis of hypotonia. A custom designed multigene panel, including ACTA1 , CCDC78 , DYNC1H1 , GARS , RYR1 , COL6A1 , COL6A2 , COL6A3 , FKRP , FKTN , IGHMBP2 , LMNA , LAMA2 , LARGE1 , MTM1 , NEM , POMGnT1 , POMT1 , POMT2 , and SEPN1 , was used for genetic analysis using next-generation sequencing (NGS).

Results  In our study, we found 13 variants including pathogenic (two variants in LAMA2) and likely pathogenic variants (three variants in RYR1 and POMGnT1) and variants of uncertain clinical significance (eight variants in RYR1, COL6A3, COL6A2, POMGnT1 and POMT1) in 11 (61%) out of 18 patients. In one of our patients, a homozygous, likely pathogenic c.1649G > A, p.(Ser550Asn) variant was defined in the POMGnT1 gene which was associated with a muscle–eye–brain disease phenotype.

Conclusion  The contribution of an in-house designed gene panel in the etiology of peripheral hypotonia with a clinical diagnosis was 5.5%. An important contribution with the clinical diagnosis can be made using the targeted multigene panels in larger samples.

Diagnostic yield of multi-gene panel for muscular dystrophies and other hereditary myopathies

Genetic testing is being considered the first-step in the investigation of hereditary myopathies. However, the performance of the different testing approaches is little known. The aims of the present study were to evaluate the diagnostic yield of a next-generation sequencing panel comprising 39 genes as the first-tier test for genetic myopathies diagnosis and to characterize clinical and molecular findings of families from southern Brazil. Fifty-one consecutive index cases with clinical suspicion of genetic myopathies were recruited from October 2014 to March 2018 in a cross-sectional study. The overall diagnostic yield of the next-generation sequencing panel was 52.9%, increasing to 60.8% when including cases with candidate variants. Multi-gene panel solved the diagnosis of 12/25 (48%) probands with limb-girdle muscular dystrophies, of 7/14 (50%) with congenital muscular diseases, and of 7/10 (70%) with muscular dystrophy with prominent joint contractures. The most frequent diagnosis for limb-girdle muscular dystrophies were LGMD2A/LGMD-R1-calpain3-related and LGMD2B/LGMD-R2-dysferlin-related; for congenital muscular diseases, RYR1-related-disorders; and for muscular dystrophy with prominent joint contractures, Emery-Dreifuss-muscular-dystrophy-type-1 and COL6A1-related-disorders. In summary, the customized next-generation sequencing panel when applied in the initial investigation of genetic myopathies results in high diagnostic yield, likely reducing patient's diagnostic odyssey and providing important information for genetic counseling and participation in disease-specific clinical trials.

Genetic Profile of Patients with Limb-Girdle Muscle Weakness in the Chilean Population

Hereditary myopathies are a group of genetically determined muscle disorders comprising more than 300 entities. In Chile, there are no specific registries of the distinct forms of these myopathies. We now report the genetic findings of a series of Chilean patients presenting with limb-girdle muscle weakness of unknown etiology. Eighty-two patients were explored using high-throughput sequencing approaches with neuromuscular gene panels, establishing a definite genetic diagnosis in 49 patients (59.8%) and a highly probable genetic diagnosis in eight additional cases (9.8%). The most frequent causative genes identified were DYSF and CAPN3, accounting for 22% and 8.5% of the cases, respectively, followed by DMD (4.9%) and RYR1 (4.9%). The remaining 17 causative genes were present in one or two cases only. Twelve novel variants were identified. Five patients (6.1%) carried a variant of uncertain significance in genes partially matching the clinical phenotype. Twenty patients (24.4%) did not carry a pathogenic or likely pathogenic variant in the phenotypically related genes, including five patients (6.1%) presenting an autoimmune neuromuscular disorder. The relative frequency of the different forms of myopathy in Chile is like that of other series reported from different regions of the world with perhaps a relatively higher incidence of dysferlinopathy.

Rapid Molecular Diagnosis of Genetically Inherited Neuromuscular Disorders Using Next-Generation Sequencing Technologies

Neuromuscular diseases are genetically highly heterogeneous, and differential diagnosis can be challenging. Over a 3-year period, we prospectively analyzed 268 pediatric and adult patients with a suspected diagnosis of inherited neuromuscular disorder (INMD) using comprehensive gene-panel analysis and next-generation sequencing. The rate of diagnosis increased exponentially with the addition of genes to successive versions of the INMD panel, from 31% for the first iteration (278 genes) to 40% for the last (324 genes). The global mean diagnostic rate was 36% (97/268 patients), with a diagnostic turnaround time of 4–6 weeks. Most diagnoses corresponded to muscular dystrophies/myopathies (68.37%) and peripheral nerve diseases (22.45%). The most common causative genes, TTN, RYR1, and ANO5, accounted for almost 30% of the diagnosed cases. Finally, we evaluated the utility of the differential diagnosis tool Phenomizer, which established a correlation between the phenotype and molecular findings in 21% of the diagnosed patients. In summary, comprehensive gene-panel analysis of all genes implicated in neuromuscular diseases facilitates a rapid diagnosis and provides a high diagnostic yield.

Iron Deficiency Caused by Intestinal Iron Loss-Novel Candidate Genes for Severe Anemia

The adult human body contains about 4 g of iron. About 1-2 mg of iron is absorbed every day, and in healthy individuals, the same amount is excreted. We describe a patient who presents with severe iron deficiency anemia with hemoglobin levels below 6 g/dL and ferritin levels below 30 ng/mL. Although red blood cell concentrates and intravenous iron have been substituted every month for years, body iron stores remain depleted. Diagnostics have included several esophago-gastro-duodenoscopies, colonoscopies, MRI of the liver, repetitive bone marrow biopsies, psychological analysis, application of radioactive iron to determine intact erythropoiesis, and measurement of iron excretion in urine and feces. Typically, gastrointestinal bleeding is a major cause of iron loss. Surprisingly, intestinal iron excretion in stool in the patient was repetitively increased, without gastrointestinal bleeding. Furthermore, whole exome sequencing was performed in the patient and additional family members to identify potential causative genetic variants that may cause intestinal iron loss. Under different inheritance models, several rare mutations were identified, two of which (in CISD1 and KRI1) are likely to be functionally relevant. Intestinal iron loss in the current form has not yet been described and is, with high probability, the cause of the severe iron deficiency anemia in this patient.

An integrated approach to the evaluation of patients with asymptomatic or minimally symptomatic hyperCKemia

Introduction/Aims

Currently, there are no straightforward guidelines for the clinical and diagnostic management of hyperCKemia, a frequent and nonspecific presentation in muscle diseases. Therefore, we aimed to describe our diagnostic workflow for evaluating patients with this condition.

Methods

We selected 83 asymptomatic or minimally symptomatic patients with persistent hyperCKemia for participation in this Italian multicenter study. Patients with facial involvement and distal or congenital myopathies were excluded, as were patients with suspected inflammatory myopathies or predominant respiratory or cardiac involvement. All patients underwent a neurological examination and nerve conduction and electromyography studies. The first step of the investigation included a screening for Pompe disease. We then evaluated the patients for myotonic dystrophy type II–related CCTG expansion and excluded patients with copy number variations in the DMD gene. Subsequently, the undiagnosed patients were investigated using a target gene panel that included 20 genes associated with isolated hyperCKemia.

Results

Using this approach, we established a definitive diagnosis in one third of the patients. The detection rate was higher in patients with severe hyperCKemia and abnormal electromyographic findings.

Discussion

We have described our diagnostic workflow for isolated hyperCKemia, which is based on electrodiagnostic data, biochemical screening, and first‐line genetic investigations, followed by successive targeted sequencing panels. Both clinical signs and electromyographic abnormalities are associated with increased diagnostic yields.

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.

Pathogenic Mutations and Putative Phenotype-Affecting Variants in Polish Myofibrillar Myopathy Patients

Myofibrillar myopathies (MFM) are heterogeneous hereditary muscle diseases with characteristic myopathological features of Z-disk dissolution and aggregates of its degradation products. The onset and progression of the disease are variable, with an elusive genetic background, and around half of the cases lacking molecular diagnosis. Here, we attempted to establish possible genetic foundations of MFM by performing whole exome sequencing (WES) in eleven unrelated families of 13 patients clinically diagnosed as MFM spectrum. A filtering strategy aimed at identification of variants related to the disease was used and included integrative analysis of WES data and human phenotype ontology (HPO) terms, analysis of muscle-expressed genes, and analysis of the disease-associated interactome. Genetic diagnosis was possible in eight out of eleven cases. Putative causative mutations were found in the DES (two cases), CRYAB, TPM3, and SELENON (four cases) genes, the latter typically presenting with a rigid spine syndrome. Moreover, a variety of additional, possibly phenotype-affecting variants were found. These findings indicate a markedly heterogeneous genetic background of MFM and show the usefulness of next generation sequencing in the identification of disease-associated mutations. Finally, we discuss the emerging concept of variant load as the basis of phenotypic heterogeneity.