DMD mutation spectrum analysis in 613 Chinese patients with dystrophinopathy

Mutational spectrum and phenotypic variability of Duchenne muscular dystrophy and related disorders in a Bangladeshi population

Duchenne muscular dystrophy (DMD) is a severe rare neuromuscular disorder caused by mutations in the X-linked dystrophin gene. Several mutations have been identified, yet the full mutational spectrum, and their phenotypic consequences, will require genotyping across different populations. To this end, we undertook the first detailed genotype and phenotype characterization of DMD in the Bangladeshi population. We investigated the rare mutational and phenotypic spectrum of the DMD gene in 36 DMD-suspected Bangladeshi participants using an economically affordable diagnostic strategy involving initial screening for exonic deletions in the DMD gene via multiplex PCR, followed by testing PCR-negative patients for mutations using whole exome sequencing. The deletion mapping identified two critical DMD gene hotspot regions (near proximal and distal ends, spanning exons 8-17 and exons 45-53, respectively) that comprised 95% (21/22) of the deletions for this population cohort. From our exome analysis, we detected two novel pathogenic hemizygous mutations in exons 21 and 42 of the DMD gene, and novel pathogenic recessive and loss of function variants in four additional genes: SGCD, DYSF, COL6A3, and DOK7. Our phenotypic analysis showed that DMD suspected participants presented diverse phenotypes according to the location of the mutation and which gene was impacted. Our study provides ethnicity specific new insights into both clinical and genetic aspects of DMD.

Mutation spectrum analysis of DMD gene in Indonesian Duchenne and Becker muscular dystrophy patients

Background

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are allelic disorders caused by mutations in the DMD gene. The full mutation spectrum of the DMD gene in Indonesian patients is currently unknown. Mutation-specific therapies are currently being developed, such as exon skipping or stop codon read-through therapy. This study was conducted with the aim of identifying the mutation spectrum of the DMD gene in Indonesia to guide future development and application of feasible therapeutic strategies.

Methods

This study is a cross sectional study that enrolled 43 male patients with a clinical suspicion of DMD or BMD. Multiplex ligation-dependent probe amplification (MLPA) reaction was performed to screen for the common mutations in the DMD gene.

Results

Out of 43 subjects, deletions accounted for 69.77% (n=30) cases, while duplications were found in 11.63% (n=5) cases. One novel duplication spanning exons 2 to 62 was identified. Deletion mutations clustered around the distal (66.67%) and proximal (26.67%) hot spot regions of the DMD gene while duplication mutations were observed solely at the proximal region. Two false positive cases of single exon deletion detected through MLPA were attributed to sequence mutations affecting primer ligation sites, confirming the need to validate all single exon deletions when using this screening method. Analysis of available maternal DNA samples showed that the rate of de novo mutations (48.15%) appears higher than expected in this population. Out of 31 patients who were classified as DMD based on clinical and genotype characterizations, 60.47% (n=26) of cases were suitable for exon skipping therapy.

Conclusion

This is the first comprehensive study showing the feasibility of implementing the MLPA method for routine screening of DMD patients in Indonesia. This is also the first study showing the potential applicability of exon skipping therapy in the majority of DMD cases in the country.

NGS-based targeted sequencing identified six novel variants in patients with Duchenne/Becker muscular dystrophy from southwestern China

BACKGROUND

At present, Multiplex ligation-dependent probe amplification (MLPA) and exome sequencing are common gene detection methods in patients with Duchenne muscular dystrophy or Becker muscular dystrophy (DMD/BMD), but they can not cover the whole-genome sequence of the DMD gene. In this study, the whole genome capture of the DMD gene and next-generation sequencing (NGS) technology were used to detect the patients with DMD/BMD in Southwest China, to clarify the application value of this technology and further study the gene variant spectrum.

METHODS

From 2017 to 2020, 51 unrelated patients with DMD/BMD in southwestern China were clinically diagnosed at West China Second University Hospital of Sichuan University (Chengdu, China). The whole-genome of the DMD gene was captured from the peripheral blood of all patients, and next-generation sequencing was performed. Large copy number variants (CNVs) in the exon regions of the DMD gene were verified through MLPA, and small variations (such as single nucleotide variation and < 50 bp fragment insertions/deletions) were validated using Sanger sequencing.

RESULTS

Among the 51 patients, 49 (96.1% [49/51]) had pathogenic or likely pathogenic variants in the DMD gene. Among the 49 positive samples, 17 patients (34.7% [17/49]) had CNVs in the exon regions and 32 patients (65.3% [32/49]) had small variations. A total of six novel variants were identified: c.10916_10917del, c.1790T>A, c.1842del, c.5015del, c.5791_5792insCA, and exons 38-50 duplication.

CONCLUSIONS

Pathogenic or likely pathogenic variants of the DMD gene were detected in 49 patients (96.1% [49/51]), of which 6 variants (12.2% [6/49]) had not been previously reported. This study confirmed the value of NGS-based targeted sequencing for the DMD gene expanding the spectrum of variants in DMD, which may provide effective genetic counseling and prenatal diagnosis for families.

New advancements in CRISPR based gene therapy of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by the dystrophin gene mutations and is one of the most common and lethal human hereditary disorders. A novel therapeutic approach using CRISPR technology has gained attention in the treatment of DMD. Gene replacement strategies are being proposed as a promising therapeutic option to compensate the loss of function mutations. Although, the large size of the dystrophin gene and the limitations of the existing gene replacement approach, could mean the gene delivery of shortened versions of dystrophin such as midystrophin and microdystrophins. There are also other approaches: including Targeted removal of dystrophin exons to restore the reading-frame; Dual sgRNA-directed DMD exon deletion, CRISPR-SKIP strategy; reframing of dystrophin using Prime Editing technology; exon removal using twin prime technology; TransCRISTI technology to targeted exon integration into dystrophin gene. Here we provide an overview of recent progresses in dystrophin gene editing using updated versions of CRISPR to introduce novel opportunities in DMD gene therapy. Overall, the novel CRISPR based technologies are improving and expanding to allow the application of more precise gene editing for the treatment of DMD.

Clinical, muscle imaging, and genetic characteristics of dystrophinopathies with deep-intronic DMD variants

BACKGROUND

Phenotypic heterogeneity within or between families with a same deep-intronic splice-altering variant in the DMD gene has never been systematically analyzed. This study aimed to determine the phenotypic and genetic characteristics of patients with deep-intronic DMD variants.

METHODS

Of 1338 male patients with a suspected dystrophinopathy, 38 were confirmed to have atypical pathogenic DMD variants via our comprehensive genetic testing approach. Of the 38 patients, 30 patients from 22 unrelated families with deep-intronic DMD variants underwent a detailed clinical and imaging assessment.

RESULTS

Nineteen different deep-intronic DMD variants were identified in the 30 patients, including 15 with Duchenne muscular dystrophy (DMD), 14 with Becker muscular dystrophy (BMD), and one with X-linked dilated cardiomyopathy. Of the 19 variants, 15 were single-nucleotide variants, 2 were structural variants (SVs), and 2 were pure-intronic large-scale SVs causing aberrant inclusion of other protein-coding genes sequences into the mature DMD transcripts. The trefoil with single fruit sign was observed in 18 patients and the concentric fatty infiltration pattern was observed in 2 patients. Remarkable phenotypic heterogeneity was observed not only in skeletal but also cardiac muscle involvement in 2 families harboring a same deep-intronic variant. Different skeletal muscle involvement between families with a same variant was observed in 4 families. High inter-individual phenotypic heterogeneity was observed within two BMD families and one DMD family.

CONCLUSIONS

Our study first highlights the variable phenotypic expressivity of deep-intronic DMD variants and demonstrates a new class of deep-intronic DMD variants, i.e., pure-intronic SVs involving other protein-coding genes.

Spectrum of Genetic Variants in the Dystrophin Gene: A Single Centre Retrospective Analysis of 750 Duchenne and Becker Patients from Southern Italy

Dystrophinopathies are X-linked recessive muscle disorders caused by mutations in the dystrophin (DMD) gene that include deletions, duplications, and point mutations. Correct diagnosis is important for providing adequate patient care and family planning, especially at this time when mutation-specific therapies are available. We report a large single-centre study on the spectrum of DMD gene variants observed in 750 patients analyzed for suspected Duchenne (DMD) or Becker (BMD) muscular dystrophy, over the past 30 years, at the Cardiomyology and Medical Genetics of the University of Campania. We found 534 (71.21%) large deletions, 73 (9.73%) large duplications, and 112 (14.93%) point mutations, of which 44 (5.9%) were small ins/del causing frame-shifts, 57 (7.6%) nonsense mutations, 8 (1.1%) splice site and 3 (0.4%) intronic mutations, and 31 (4.13%) non mutations. Moreover, we report the prevalence of the different types of mutations in patients with DMD and BMD according to their decade of birth, from 1930 to 2020, and correlate the data to the different techniques used over the years. In the most recent decades, we observed an apparent increase in the prevalence of point mutations, probably due to the use of Next-Generation Sequencing (NGS). In conclusion, in southern Italy, deletions are the most frequent variation observed in DMD and BMD patients followed by point mutations and duplications, as elsewhere in the world. NGS was useful to identify point mutations in cases of strong suspicion of DMD/BMD negative on deletions/duplications analyses. In the era of personalized medicine and availability of new causative therapies, a collective effort is necessary to enable DMD and BMD patients to have timely genetic diagnoses and avoid late implementation of standard of care and late initiation of appropriate treatment.

Duchenne Muscular Dystrophy in Kazakhstan: A Journey from Diagnosis to the Treatment, the Biases and Achievements

BACKGROUND

Neuro-muscular disorders constitutes a group of rare but heterogeneous conditions. The onset of these diseases ranges widely from birth to elderly. Many of them are life threatening and progressive. Neuromuscular science is a very specialised medical field for which specific knowledge and expertise are necessary. Such an expertise is available only partially in Kazakhstan where underdiagnosis, misdiagnosis and mismanagement of patients with muscle diseases are commonplace. Hopefully, times are changing. With the implementation of international guidelines for the diagnosis and treatment of Duchenne Muscular Dystrophy (DMD), patients are now given better care including pharmacological interventions (including steroids in DMD), respiratory and nutritional support.

OBJECTIVES

To report on clinical data and genetic variants in a nationwide cohort of DMD patients. To describe and analyse management strategies applied in Kazakhstan in these patients.

METHODS

The medical records of 84 patients recruited by the national expert-consulting board based at the national multidisciplinary centre of reference in neuro-muscular disorders in Astana, Kazakhstan, have been ascertained for the study. The national expert committee meets monthly to decide over the prescription of disease-modifying therapies in paediatric neuromuscular disorders. Data on the age of disease onset, the age at genetic testing, spectrum of genetic variants, the stage of disease and the serum CK levels have been collected.ResultsThe mean age of 84 examined patients was 10 years. In Kazakhstan, the average age of disease manifestation was 3 years and 3 months. The vast majority of patients passed through genetic test due to the clinical manifestations. The average age of genetic confirmation was 7 years and 6 months. There were 58,33%of gross variations, of which 55,95%were deletions and 2,38%were duplications. Nonsense mutations were identified in 29,7%.

CONCLUSION

The authors contend that strictly keeping the clinical guides in the diagnosis of DMD is essential, as the genetic variations may affect the stage and feasibility of novel therapies. The way of management of neuro-muscular diseases used in Kazakhstan is strictly recommended for implementation in developing countries.

Identification of Biallelic dystrophin gene variants during maternal carrier testing for Becker muscular dystrophy and review of the DMD exon 49-51 deletion phenotype

BACKGROUND

Dystrophinopathies are X-linked recessive conditions caused by pathogenic variants in the dystrophin (DMD) gene. In a family that included two boys with Becker muscular dystrophy (BMD) due to a DMD deletion of exons 45-47, maternal carrier testing unexpectedly identified biallelic DMD deletions of exons 45-47 and 49-51.

METHODS

The patient's mild phenotype in the setting of biallelic DMD variants prompted further investigation of the exon 49-51 deletion in particular, via literature review and retrospective chart review of patients who have been evaluated in our institution's comprehensive neuromuscular center and/or diagnosed in our clinical genetic testing laboratory.

RESULTS

To our knowledge, this is only the fifth case of confirmed biallelic DMD variants in a female. In males, the DMD exon 49-51 deletion appears to result in a mild BMD phenotype with low or normal creatine kinase levels. This deletion comprised 19% (4/21) of dystrophinopathies diagnosed by chromosomal microarray (CMA) in males during the past ten years in our clinical laboratory. Most individuals identified by chart review were diagnosed through CMA, despite the fact that microarray was genome-wide and not DMD-specific. This case raised important genetic counseling issues.

CONCLUSION

The DMD exon 49-51 deletion appears to cause a variable but generally mild BMD phenotype. Its relatively frequent detection by CMA suggests it may be underdiagnosed.

Walking alone milestone combined reading-frame rule improves early prediction of Duchenne muscular dystrophy

OBJECTIVE

To explore the potential of walking alone milestone combined reading-frame rule to improve the early diagnosis of Duchenne muscular dystrophy (DMD).

METHOD

To retrospectively describe the genotype and phenotype of Duchenne and Becker muscular dystrophies (BMD) patients with deletions and duplicates in the dystrophin gene. The sensitivity and specificity of the reading frame rule were calculated and compared to that of the combined reading frame rule and walking alone milestone. The diagnostic coincidence rate of two different methods was analyzed.

RESULT

One hundred sixty-nine male DMD/BMD patients were enrolled, including 17 cases of BMD and 152 cases of DMD. The diagnostic coincidence rate, diagnostic sensitivity, and specificity of the reading-frame rule for DMD/BMD were 85.2, 86.8, and 70.59%, respectively. The sensitivity and specificity of the reading frame principle combined with the walking alone milestone for DMD/BMD were 96.05 and 70.59%, respectively. The diagnostic coincidence rate increased to 93.49%, significantly different from that predicted by reading- frame rule (P < 0.05).

CONCLUSION

The reading-frame rule combined with the walking alone milestone significantly improved the early diagnosis rate of DMD.

Noninvasive prenatal diagnosis of duchenne muscular dystrophy in five Chinese families based on relative mutation dosage approach

Background

Relative haplotype dosage (RHDO) approach has been applied in noninvasive prenatal diagnosis (NIPD) of Duchenne muscular dystrophy (DMD). However, the RHDO procedure is relatively complicated and the parental haplotypes need to be constructed. Furthermore, it is not suitable for the diagnosis of de novo mutations or mosaicism in germ cells. Here, we investigated NIPD of DMD using a relative mutation dosage (RMD)-based approach—cell-free DNA Barcode-Enabled Single-Molecule Test (cfBEST), which has not previously been applied in the diagnosis of exon deletion.

Methods

Five DMD families caused by DMD gene point mutations or exon deletion were recruited for this study. After the breakpoints of exon deletion were precisely mapped with multiple PCR, the genotypes of the fetuses from the five DMD families were inferred using cfBEST, and were further validated by invasive prenatal diagnosis.

Results

The cfBEST results of the five families indicated that one fetus was female and did not carry the familial molecular alteration, three fetuses were carriers and one was male without the familial mutation. The invasive prenatal diagnosis results were consistent with those of the cfBEST procedure.

Conclusion

This is the first report of NIPD of DMD using the RMD-based approach. We extended the application of cfBEST from point mutation to exon deletion mutation. The results showed that cfBEST would be suitable for NIPD of DMD caused by different kinds of mutation types.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01128-1.

Becker muscular dystrophy: case report, review of the literature, and analysis of differentially expressed hub genes

INTRODUCTION

Becker muscular dystrophy (BMD) is a genetic and progressive neuromuscular disease caused by mutations in the dystrophin gene with no available cure. A case report and comprehensive review of BMD cases aim to provide important clues for early diagnosis and implications for clinical practice. Genes and pathways identified from microarray data of muscle samples from patients with BMD help uncover the potential mechanism and provide novel therapeutic targets for dystrophin-deficient muscular dystrophies.

METHODS

We describe a BMD family with a 10-year-old boy as the proband and reviewed BMD cases from PubMed. Datasets from the Gene Expression Omnibus database were downloaded and integrated with the online software.

RESULTS

The systematic review revealed the clinical manifestations and mutation points of the dystrophin gene. Gene ontology analysis showed that extracellular matrix organization and extracellular structure organization with enrichment of upregulated genes coexist in three datasets. We present the first report of TUBA1A involvement in the development of BMD/Duchenne muscular dystrophy (DMD).

DISCUSSION

This study provides important implications for clinical practice, uncovering the potential mechanism of the progress of BMD/DMD, and provided new therapeutic targets.

Comparison of The Carrier Frequency of Pathogenic Variants of DMD Gene in an Indian Cohort

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked disorder caused due to large deletions, duplications,and small pathogenic variants. This article compares the carrier frequency of different pathogenic variants in the DMD gene for the first time in an Indian cohort.

METHODS

Ninety-one mothers of genetically confirmed DMD probands are included in this study. Pathogenic variants in the DMD gene in probands were detected by multiplex ligation-dependent probe amplification (MLPA) or next-generation sequencing (NGS). Maternal blood samples were evaluated either by MLPA or Sanger sequencing. The demographic and clinical details for screening of muscle weakness and cardiomyopathy were collected from the confirmed carriers.

RESULTS

Out of 91 probands, large deletions and duplications were identified in 46 and 6 respectively, while 39 had small variants. Among the small variants, substitutions predicted to cause nonsense mutations were the most common (61.5%), followed by frameshift causing small insertion/deletions (25.6%) and splice affecting intronic variants (12.8%). Notably, 19 novel small variants predicted to be disease-causing were identified. Of the 91 mothers, 53 (58.7%) were confirmed to be carriers. Exonic deletions had a significantly lower carrier frequency of 47.8% as compared to small variants (64.1%). The mean age of the carriers at evaluation was 30 years. Among the carriers, two were symptomatic with onset in the 4th decade, manifesting with progressive proximal muscle weakness and dilated cardiomyopathy.

CONCLUSION

Carrier frequency of small pathogenic variants differs significantly from large deletions. Small pathogenic variants are more commonly inherited, whereas large deletions arise de novo.

Prenatal diagnosis of de novo DMD duplication by multiplex ligation-dependent probe amplification (MLPA) after noninvasive prenatal screening (NIPS) at 11 gestational weeks

OBJECTIVE

Dystrophinopathy is an X-linked recessive muscular dystrophy caused by mutations in the DMD gene. Herein we describe the prenatal detection of DMD gene mutations in a patient with no family history, by multiplex ligation-dependent probe amplification (MLPA) after noninvasive prenatal screening (NIPS).

CASE REPORT

A 41-year-old woman underwent NIPS owing to an advanced maternal age. A copy number variation was detected in the maternal X chromosome, and uninformative results were obtained for the fetal sex chromosomes. Following amniocentesis, a duplication was identified in exons 1-29 of the dystrophin gene by MLPA. After interviewing her family members it was confirmed that the patient is a de novo carrier of DMD duplications, and her daughter is a carrier of the same mutation.

CONCLUSION

his is the first case report to describe the prenatal diagnosis of duplications in the DMD gene by MLPA following NIPS in a patient with no family history.

Small mutations in Duchenne/Becker muscular dystrophy in 164 unrelated Polish patients

In the 164 patients with Duchenne/Becker muscular dystrophy, we found 142 different small mutations including 51 novel mutations not listed in the LOVD, the UMD-DMD, the ClinVar, and the HGMD databases. Among all mutations, nonsense mutations occurred in 45.7%, frameshift mutations in 32.9%, and splicing mutations in 19.5%. Small mutations were distributed throughout the whole dystrophin gene. Splicing mutations were twice more common in BMD patients than in DMD patients. Eighty-two percent of mothers of the males affected with DMD/BMD were found to be carriers of small mutations.

Practical approach to the genetic diagnosis of unsolved dystrophinopathies: a stepwise strategy in the genomic era

OBJECTIVE

To investigate the diagnostic value of implementing a stepwise genetic testing strategy (SGTS) in genetically unsolved cases with dystrophinopathies.

METHODS

After routine genetic testing in 872 male patients with highly suspected dystrophinopathies, we identified 715 patients with a pathogenic DMD variant. Of the 157 patients who had no pathogenic DMD variants and underwent a muscle biopsy, 142 patients were confirmed to have other myopathies, and 15 suspected dystrophinopathies remained genetically undiagnosed. These 15 patients underwent a more comprehensive evaluation as part of the SGTS pipeline, which included the stepwise analysis of dystrophin mRNA, short-read whole-gene DMD sequencing, long-read whole-gene DMD sequencing and in silico bioinformatic analyses.

RESULTS

SGTS successfully yielded a molecular diagnosis of dystrophinopathy in 11 of the 15 genetically unsolved cases. We identified 8 intronic and 2 complex structural variants (SVs) leading to aberrant splicing in 10 of 11 patients, of which 9 variants were novel. In one case, a molecular defect was detected on mRNA and protein level only. Aberrant splicing mechanisms included 6 pseudoexon inclusions and 4 alterations of splice sites and splicing regulatory elements. We showed for the first time the exonisation of a MER48 element as a novel pathogenic mechanism in dystrophinopathies.

CONCLUSION

Our study highlights the high diagnostic utility of implementing a SGTS pipeline in dystrophinopathies with intronic variants and complex SVs.

The position of nonsense mutations can predict the phenotype severity: A survey on the DMD gene

A nonsense mutation adds a premature stop signal that hinders any further translation of a protein-coding gene, usually resulting in a null allele. To investigate the possible exceptions, we used the DMD gene as an ideal model. First, because dystrophin absence causes Duchenne muscular dystrophy (DMD), while its reduction causes Becker muscular dystrophy (BMD). Second, the DMD gene is X-linked and there is no second allele that can interfere in males. Third, databases are accumulating reports on many mutations and phenotypic data. Finally, because DMD mutations may have important therapeutic implications. For our study, we analyzed large databases (LOVD, HGMD and ClinVar) and literature and revised critically all data, together with data from our internal patients. We totally collected 2593 patients. Positioning these mutations along the dystrophin transcript, we observed a nonrandom distribution of BMD-associated mutations within selected exons and concluded that the position can be predictive of the phenotype. Nonsense mutations always cause DMD when occurring at any point in fifty-one exons. In the remaining exons, we found milder BMD cases due to early 5’ nonsense mutations, if reinitiation can occur, or due to late 3’ nonsense when the shortened product retains functionality. In the central part of the gene, all mutations in some in-frame exons, such as in exons 25, 31, 37 and 38 cause BMD, while mutations in exons 30, 32, 34 and 36 cause DMD. This may have important implication in predicting the natural history and the efficacy of therapeutic use of drug-stimulated translational readthrough of premature termination codons, also considering the action of internal natural rescuers. More in general, our survey confirm that a nonsense mutation should be not necessarily classified as a null allele and this should be considered in genetic counselling.

Effective generation of maternal genome point mutated porcine embryos by injection of cytosine base editor into germinal vesicle oocytes

Cytosine and adenine base editors are promising new tools for introducing precise genetic modifications that are required to generate disease models and to improve traits in pigs. Base editors can catalyze the conversion of C→T (C>T) or A→G (A>G) in the target site through a single guide RNA. Injection of base editors into the zygote cytoplasm can result in the production of offspring with precise point mutations, but most F0 are mosaic, and breeding of F1 heterozygous pigs is time-intensive. Here, we developed a method called germinal vesicle oocyte base editing (GVBE) to produce point mutant F0 porcine embryos by editing the maternal alleles during the GV to MII transition. Injection of cytosine base editor 3 (BE3) mRNA and X-linked Dmd-specific guide RNAs into GVoocytes efficiently edited maternal Dmd during in vitro maturation and did not affect the maturation potential of the oocytes. The edited MII oocytes developed into blastocysts after parthenogenetic activation (PA) or in vitro fertilization (IVF). However, BE3 may reduce the developmental potential of IVF blastocysts from 31.5%±0.8% to 20.4% ±2.1%. There 40%-78.3% diploid PA blastocysts had no more than two different alleles, including up to 10% embryos that had only C>T mutation alleles. Genotyping of IVF blastocysts indicated that over 70% of the edited embryos had one allele or two different alleles of Dmd. Since the male embryos had only a copy of Dmd allele, all five (5/19) F0 male embryos are homozygous and three of them were Dmd precise C>T mutation. Nine (9/19) female IVF embryos had two different alleles including a WT and a C>T mutation. DNA sequencing showed that some of them might be heterozygous embryos. In conclusion, the GVBE method is a valuable method for generating F0 embryos with maternal point mutated alleles in a single step.

Gene therapeutic strategies and relevant clinical trials in neuromuscular disorder in China

Neuromuscular disorder is a diverse group of genetic disease, among which Duchenne muscular dystrophy and Spinal muscular atrophy are most common. Recently, the great breakthroughs of gene targeted therapeutic strategies are leading a profound revolution in the standard care of neuromuscular disorders over the world including China. This review will offer an outline of the molecular pathogenesis, clinical progress, critical trials, as well as the challenges of new gene therapy in the treatment of Spinal muscular atrophy and Duchenne muscular dystrophy in China, mainly includes mRNA splicing modulators and adeno-associated virus mediated gene replacement. We hope to highlight some important findings about the critical development of gene therapy in this field, which might be helpful for suggesting potential therapeutic treatment for neuromuscular disease in China.

Severe cardiac involvement with preserved truncated dystrophin expression in Becker muscular dystrophy by +1G>A DMD splice-site mutation: a case report

Becker muscular dystrophy (BMD) is caused by specific mutations in the DMD gene that causes progressive muscle weakness and primarily affects skeletal and cardiac muscle. Although cardiac involvement is a significant cause of mortality in BMD, the genetic–phenotype correlation for skeletal and cardiac muscles has not been elucidated. Here, we described a 39-year-old man with BMD, who presented with subtle skeletal muscle weakness in the right leg in his 20s and underwent left ventricular restoration for severe dilated cardiomyopathy at the age of 29. He had difficulty climbing stairs after the age of 35. Neither duplication nor deletion of exons was detected by multiplex ligation-dependent probe amplification. A hemizygous c.264 + 1G>A mutation in intron 4 of the DMD was identified by next-generation sequencing. Furthermore, exon 4 skipping of the DMD was confirmed in both skeletal and cardiac muscles evaluated by reverse transcriptase PCR. Endomyocardial and skeletal muscle biopsies revealed dystrophic pathology characterized by muscle fiber atrophy and hypertrophy with a mild degree of interstitial fibrosis. Interestingly, dystrophin immunohistochemistry demonstrated patchy and faint staining of the skeletal muscle membranes but almost normal staining of the cardiac muscle membranes. Western blot analysis revealed a decreased amount of truncated dystrophin in skeletal muscle but surprisingly almost normal amount in cardiac muscle. This case indicates that BMD patients may have severe cardiac dysfunction despite preserved cardiac truncated dystrophin expression.

Molecular diagnosis of dystrophinopathies in Morocco and report of six novel mutations

Dystrophinopathies are the most common genetic neuromuscular disorders during childhood, with an X-linked recessive inheritance pattern. Because of clinical and genetic heterogeneity of dystrophinopathies, genetic testing of dystrophin gene at Xp21.2 is constantly evolving. Multiplex Polymerase Chain Reaction (MPCR) is used in the first line to detect common exon deletions of dystrophin gene (accounting for 65% of mutations), followed by the Multiplex Ligation-dependent Probe Amplification (MLPA) technique to reveal deletions of exons outside the usual hotspot and duplications in male and female carriers. (MLPA adds another 10-15% positive cases to MPCR). Recently, Next Generation Sequencing allows to screen for rare large and point mutations. We report here, molecular analysis results of dystrophin gene during 27 years in a large Moroccan cohort of 356 patients, using the multiplex polymerase chain reaction (MPCR) to screen for hot-spot exon deletions. First applications of whole dystrophin gene sequencing in our lab lead to the identification of six novel mutations.

The Genetic Landscape of Dystrophin Mutations in Italy: A Nationwide Study

Dystrophinopathies are inherited diseases caused by mutations in the dystrophin (DMD) gene for which testing is mandatory for genetic diagnosis, reproductive choices and eligibility for personalized trials. We genotyped the DMD gene in our Italian cohort of 1902 patients (BMD n = 740, 39%; DMD n =1162, 61%) within a nationwide study involving 11 diagnostic centers in a 10-year window (2008–2017). In DMD patients, we found deletions in 57%, duplications in 11% and small mutations in 32%. In BMD, we found deletions in 78%, duplications in 9% and small mutations in 13%. In BMD, there are a higher number of deletions, and small mutations are more frequent than duplications. Among small mutations that are generally frequent in both phenotypes, 44% of DMD and 36% of BMD are nonsense, thus, eligible for stop codon read-through therapy; 63% of all out-of-frame deletions are eligible for single exon skipping. Patients were also assigned to Italian regions and showed interesting regional differences in mutation distribution. The full genetic characterization in this large, nationwide cohort has allowed us to draw several correlations between DMD/BMD genotype landscapes and mutation frequency, mutation types, mutation locations along the gene, exon/intron architecture, and relevant protein domain, with effects on population genetic characteristics and new personalized therapies.

Genetic analysis of 62 Chinese families with Duchenne muscular dystrophy and strategies of prenatal diagnosis in a single center

Background

Duchenne muscular dystrophy (DMD) is a severe X-linked recessive neuromuscular disorder. Patients with DMD usually have severe and fatal symptoms, including progressive irreversible muscle weakness and atrophy complicated with gastrocnemius muscle pseudohypertrophy. DMD is caused by mutations in the dystrophin-encoding DMD gene, including large rearrangements and point mutations. This retrospective study was aimed at supplying information on our 4-year clinical experience of DMD genetic and prenatal diagnosis at the Department of Prenatal Diagnosis in Women’s Hospital of Nanjing Medical University.

Methods

Multiplex ligation-dependent probe amplification (MLPA) was used to detect the exon deletions or duplications. And Ion AmpliSeq™ panel for inherited disease was used as the next-generation sequencing (NGS) method to identify the point mutations in exons of DMD gene, but the introns were not sequenced.

Results

In this study, the large deletions and duplications of DMD gene were detected in 32 (51.6%) of the 62 families, while point mutations were detected in 20 families (32.3%). The remaining 10 families with a negative genetic diagnosis need to be reevaluated for clinical symptoms or be detected by other molecular methods. Notably, six novel mutations were identified, including c.412A > T(p.Lys138*), c.2962delT(p.Ser988Leufs*16), c.6850dupA (p.Ser2284Lysfs*7), c.5139dupA (p.Glu 1714Argfs*5), c.6201_6203delGCCins CCCA(p.Val2069Cysfs*14) and c.10705A > T (p.Lys3569*). In 52 families with positive results, 45 mothers (86.5%) showed positive results during carrier testing and de novo mutations arose in 7 probands. The prenatal diagnosis was offered to 34 fetuses whether the pregnant mother was a carrier or not. As a result, eight male fetuses were affected, three female fetuses were carriers, and the remaining fetuses had no pathogenic mutation.

Conclusions

This study reported that MLPA and NGS could be used for screening the DMD gene mutations. Furthermore, the stepwise procedure of prenatal diagnosis of DMD gene was shown in our study, which is important for assessing the mutation type of fetuses and providing perinatal care in DMD high-risk families.

Distrofia muscular de Becker con duplicación en el exón 5del gen DMD

Las distrofinopatías son un grupo de enfermedades ligadas al cromosoma X que abarcan diferentes entidades, siendo las más importantes la distrofia muscular de Duchenne (DMD) y la de Becker (DMB). Están causadas por mutaciones en el gen de la distrofina (gen DMD) localizado en el cromosoma X, locus Xp21.1. En relación con el tipo de mutaciones reportadas en el gen DMD, las delecciones  y las mutaciones puntuales son las más comunes,  mientras que las duplicaciones corresponden a 10-12%. Aunque las duplicaciones que abarcan el exón 5 ya han sido reportadas en la literatura, a la fecha no existen informes de casos que establezcan una relación genotipo fenotipo clara.  Presentamos el caso de un paciente con distrofia muscular de Becker con un fenotipo no tan severo, en quien se encontró una duplicación en el exón 5.  Con este caso pretendemos profundizar en la relación genotipo-fenotipo de la DMB, reportando las características clínicas en relación con la duplicación del exón 5 encontrada.

CRISPR-Cas9 corrects Duchenne muscular dystrophy exon 44 deletion mutations in mice and human cells

Mutations in the dystrophin gene cause Duchenne muscular dystrophy (DMD), which is characterized by lethal degeneration of cardiac and skeletal muscles. Mutations that delete exon 44 of the dystrophin gene represent one of the most common causes of DMD and can be corrected in ~12% of patients by editing surrounding exons, which restores the dystrophin open reading frame. Here, we present a simple and efficient strategy for correction of exon 44 deletion mutations by CRISPR-Cas9 gene editing in cardiomyocytes obtained from patient-derived induced pluripotent stem cells and in a new mouse model harboring the same deletion mutation. Using AAV9 encoding Cas9 and single guide RNAs, we also demonstrate the importance of the dosages of these gene editing components for optimal gene correction in vivo. Our findings represent a significant step toward possible clinical application of gene editing for correction of DMD.

Genotypes and Phenotypes of DMD Small Mutations in Chinese Patients With Dystrophinopathies

Dystrophinopathies are a group of neuromuscular disorders resulting from mutations in DMD, including Duchenne muscular dystrophy (DMD), intermediate muscular dystrophy (IMD), and Becker muscular dystrophy (BMD). Herein, we present the characteristics of small mutations in Chinese patients with dystrophinopathies, and explore genotype–phenotype correlations. In our cohort, 115 patients with small mutations (18.49% of all patients) were included and DMD mutations were detected by either Sanger (53.91%) or next generation sequencing (46.09%). In total, 106 small mutations were detected, 28 of which (26.42%) had not been reported previously. The most common mutations were nonsense mutations (52.17%), followed by splicing (24.35%), frameshift (17.39%), and missense mutations (5.22%), in addition to a single untranslated region mutation (0.87%). We discovered distinct mutation characteristics in our patients, such as different positional distributions, indicating different exon skipping therapy strategies for small mutations in Chinese patients. Almost all patients (96.51%) with truncating or missense mutations, were covered by triple/double/single-exon skipping therapy; the most frequent single-exon skipping strategy was skipping exon 32, applicable for 8.51% of patients. Furthermore, splicing classification grades were correlated with phenotypes in nonsense mutations (P < 0.001), and serum creatinine levels differed significantly between DMD/IMD and BMD for patients ≤ 16 years old (P = 0.002). These observations can further aid prognostic judgment and guide treatment. In conclusion, the mutation characteristics and genotype–phenotype correlations in Chinese patients with dystrophinopathies and small mutations could provide insights into the molecular mechanisms of pathogenesis, diagnosis, and treatment designs.

Mutation spectrum analysis of Duchenne/Becker muscular dystrophy in 68 families in Kuwait: The era of personalized medicine

Duchenne and Becker muscular dystrophies (DMD/BMD) are X-linked recessive neuromuscular disorders characterized by progressive irreversible muscle weakness and atrophy that affect both skeletal and cardiac muscles. DMD/BMD is caused by mutations in the Dystrophin gene on the X chromosome, leading to the absence of the essential muscle protein Dystrophin in DMD. In BMD, Dystrophin is partially functioning with a shorter protein product. Recent advances in molecular therapies for DMD require precise genetic diagnoses because most therapeutic strategies are mutation-specific. Hence, early diagnosis is crucial to allow appropriate planning for patient care and treatment. In this study, data from DMD/BMD patients who attended the Kuwait Medical Genetic Center during the last 20 years was retrieved from a Kuwait neuromuscular registry and analyzed. We combined multiplex PCR and multiplex ligation-dependent probe amplification (MLPA) with Sanger sequencing to detect Dystrophin gene mutations. A total of 35 different large rearrangements, 2 deletion-insertions (Indels) and 4 substitution mutations were identified in the 68 unrelated families. The deletion and duplication rates were 66.2% and 4.4%, respectively. The analyzed data from our registry revealed that 11 (16%) of the DMD families will benefit from newly introduced therapies (Ataluren and exon 51 skipping). At the time of submitting this paper, two cases have already enrolled in Ataluren (Tranlsarna™) therapy, and one case has been enrolled in exon 51 skipping therapy.

Identification of a novel DMD duplication identified by a combination of MLPA and targeted exome sequencing

Background

Duchenne muscular dystrophy (DMD) is an X-linked recessive muscle-wasting disease caused by a mutation in the DMD gene. The aim of this study was to identify a de novo mutation of the DMD gene in the family of a 9-month-old Chinese male patient, as well as to describe the phenotypic characteristics of this patient.

Results

The patient was suspected to suffer from DMD according to physical examination, biochemical analyses, and electromyogram. We identified a duplication of exons 4–42 in DMD gene with targeted exome sequencing and multiplex ligation-dependent probe amplification (MLPA). In addition, the patient’s mother was a carrier of the same mutation.

Conclusions

We identified a de novo duplication of exons 4–42 in a patient with early stage DMD. The discovery of this mutation may provide insights into future investigations.

Clinical and mutational characteristics of Duchenne muscular dystrophy patients based on a comprehensive database in South China

The development of clinical trials for Duchenne muscular dystrophy (DMD) in China faces many challenges due to limited information about epidemiological data, natural history and clinical management. To provide these detailed data, we developed a comprehensive database based on registered DMD patients from South China and analysed their clinical and mutational characteristics. The database included DMD registrants confirmed by clinical presentation, family history, genetic detection, prognostic outcome, and/or muscle biopsy. Clinical data were collected by a registry form. Mutations of dystrophin were detected by multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. Currently, 132 DMD patients from 128 families in South China have been registered, and 91.7% of them were below 10 years old. In mutational detection, large deletions were the most frequent type (57.8%), followed by small deletion/insertion mutations (14.1%), nonsense mutations (13.3%), large duplications (10.9%), and splice site mutations (3.1%). Clinical analysis revealed that most patients reported initial symptoms between 1 and 3 years of age, but the diagnostic age was more frequently between 6 and 8 years. 81.4% of patients were ambulatory. Baseline cardiac assessments at diagnosis were conducted in 39.4% and 29.5% of patients by echocardiograms and electrocardiograms, respectively. Only 22.7% of registrants performed baseline respiratory assessments. A small numbers of patients (20.5%) were treated with glucocorticoids. 13.3% of patients were eligible for stop codon read-through therapy, and 48.4% of patients would potentially benefit from exon skipping. The top five exon skips applicable to the largest group of registrants were skipping of exons 51 (14.8% of total mutations), 53 (12.5%), 45 (7.0%), 55 (4.7%), and 44 (3.9%). In conclusion, our database provided information on the natural history, diagnosis and management status of DMD in South China, as well as potential molecular therapies suitable for these patients. This comprehensive database will promote future experimental therapies in China.

MLPA analysis of an Argentine cohort of patients with dystrophinopathy: Association of intron breakpoints hot spots with STR abundance in DMD gene

Dystrophinopathies are X-linked recessive diseases caused by mutations in the DMD gene. Our objective was to identify mutations in this gene by Multiplex Ligation Probe Amplification (MLPA), to confirm the clinical diagnosis and determine the carrier status of at-risk relatives. Also, we aimed to characterize the Dystrophinopathies argentine population and the DMD gene. We analyzed a cohort of 121 individuals (70 affected boys, 11 symptomatic women, 37 at-risk women and 3 male villus samples). The MLPA technique identified 56 mutations (45 deletions, 9 duplications and 2 point mutations). These results allowed confirming the clinical diagnosis in 63% (51/81) of patients and symptomatic females. We established the carrier status of 54% (20/37) of females at-risk and 3 male villus samples. We could establish an association between the most frequent deletion intron breakpoints and the abundance of dinucleotide microsatellites loci, despite the underlying mutational molecular mechanism remains to be elucidated. The MLPA demonstrate, again, to be the appropriate first mutation screening methodology for molecular diagnosis of Dystrophinopathies. The reported results permitted to characterize the Dystrophinopathies argentine population and lead to better understanding of the genetic and molecular basis of rearrangements in the DMD gene, useful information for the gene therapies being developed.

Mutational spectrum of Duchenne muscular dystrophy in Spain: Study of 284 cases

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a severe X-linked recessive neuromuscular disease that affects one in 3500 live-born males. The total absence of dystrophin observed in DMD patients is generally caused by mutations that disrupt the reading frame of the DMD gene, and about 80% of cases harbour deletions or duplications of one or more exons.

METHODS

We reviewed 284 cases of males with a genetic diagnosis of DMD between 2007 and 2014. These patients were selected from 8 Spanish reference hospitals representing most areas of Spain. Multiplex PCR, MLPA, and sequencing were performed to identify mutations.

RESULTS

Most of these DMD patients present large deletions (46.1%) or large duplications (19.7%) in the dystrophin gene. The remaining 34.2% correspond to point mutations, and half of these correspond to nonsense mutations. In this study we identified 23 new mutations in DMD: 7 large deletions and 16 point mutations.

CONCLUSIONS

The algorithm for genetic diagnosis applied by the participating centres is the most appropriate for genotyping patients with DMD. The genetic specificity of different therapies currently being developed emphasises the importance of identifying the mutation appearing in each patient; 38.7% of the cases in this series are eligible to participate in current clinical trials.

Distribution of dystrophin gene deletions in a Chinese population

Objective

To describe the deletion patterns and distribution characteristics of the dystrophin gene in a Chinese population of patients with Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD).

Methods

Patients with DMD/BMD were recruited. Deletions in 19 exons of the dystrophin gene were evaluated using accurate multiplex polymerase chain reaction (PCR).

Result

Multiplex PCR identified deletions in 238/401 (59.4%) patients with DMD/BMD. Of these, 196 (82.4%) were in the distal hotspot, 32 (13.4%) were in the proximal hotspot, five (2.1%) were in both regions and five (2.1%) were in neither hotspot. Deletions were classified into 54 patterns. Exon 49 was the most frequently deleted. The reading frame rule was upheld for 91.9% of cases.

Conclusion

Accurate multiplex PCR for 19 exons is an effective diagnostic tool.