Genetic and clinical specificity of 26 symptomatic carriers for dystrophinopathies at pediatric age

Treatment with ataluren in four symptomatic Duchenne carriers. A pilot study

Duchenne muscular dystrophy (DMD) is a devastating X-linked neuromuscular disorder caused by dystrophin gene deletions (75%), duplications (15-20%) and point mutations (5-10%), a small portion of which are nonsense mutations. Women carrying dystrophin gene mutations are commonly unaffected because the wild X allele may produce a sufficient amount of the dystrophin protein. However, approximately 8-10% of them may experience muscle symptoms and 50% of those over 40 years develop cardiomyopathy. The presence of symptoms defines the individual as an affected "symptomatic or manifesting carrier". Though there is no effective cure for DMD, therapies are available to slow the decline of muscle strength and delay the onset and progression of cardiac and respiratory impairment. These include ataluren for patients with nonsense mutations, and antisense oligonucleotides therapies, for patients with specific deletions. Symptomatic DMD female carriers are not included in these indications and little data documenting their management, often entrusted to the discretion of individual doctors, is present in the literature. In this article, we report the clinical and instrumental outcomes of four symptomatic DMD carriers, aged between 26 and 45 years, who were treated with ataluren for 21 to 73 months (average 47.3), and annually evaluated for muscle strength, respiratory and cardiological function. Two patients retain independent ambulation at ages 33 and 45, respectively. None of them developed respiratory involvement or cardiomyopathy. No clinical adverse effects or relevant abnormalities in routine laboratory values, were observed.

Diagnosis and management of Becker muscular dystrophy: the French guidelines

Becker muscular dystrophy (BMD) is one of the most frequent among neuromuscular diseases, affecting approximately 1 in 18,000 male births. It is linked to a genetic mutation on the X chromosome. In contrast to Duchenne muscular dystrophy, for which improved care and management have changed the prognosis and life expectancy of patients, few guidelines have been published for management of BMD. Many clinicians are inexperienced in managing the complications of this disease. In France, a committee of experts from a wide range of disciplines met in 2019 to establish recommendations, with the goal of improving care of patients with BMD. Here, we present the tools to provide diagnosis of BMD as quickly as possible and for differential diagnoses. Then, we describe the multidisciplinary approach essential for optimum management of BMD. We give recommendations for the initial assessment and follow-up of the neurological, respiratory, cardiac, and orthopedic consequences of males who present with BMD. Finally, we describe the optimal therapeutic management of these complications. We also provide guidance on cardiac management for female carriers.

Clinical, pathological, and genetic characterization in a large Chinese cohort with female dystrophinopathy

We aimed to investigate the clinical, pathological, and genetic characteristics of Chinese female dystrophinopathy and to identify possible correlations among them. One hundred forty genetically and/or pathologically confirmed female DMD variant carriers were enrolled, including 104 asymptomatic carriers and 36 symptomatic carriers. Twenty of 36 symptomatic and 16 of 104 asymptomatic carriers were sporadic with no family history. Muscle pathological analysis was performed in 53 carriers and X chromosome inactivation (XCI) analysis in 19 carriers. In asymptomatic carriers, the median age was 35.0 (range 2.0-58.0) years, and the serum creatine kinase (CK) level was 131 (range 60-15,745) IU/L. The median age, age of onset, and CK level of symptomatic carriers were 15.5 (range 1.8-62.0) years, 6.3 (range 1.0-54.0) years, and 6,659 (range 337-58,340) IU/L, respectively. Four female carriers with X-autosome translocation presented with a Duchenne muscular dystrophy (DMD) phenotype. Skewed XCI was present in 70.0% of symptomatic carriers. Compared to Becker muscular dystrophy (BMD)-like carriers, DMD-like carriers were more likely to have an early onset age, rapidly progressive muscle weakness, delayed walking, elevated CK levels, severe reduction of dystrophin, and skewed XCI. Our study reports the largest series of symptomatic female DMD carriers and suggests that delayed walking, elevated CK levels, severe reduction of dystrophin, X-autosome translocation, and skewed XCI pattern are associated with a severe phenotype in female dystrophinopathy.

Cognitive function in DMD carriers: personal case series and literature review

Improvement in clinical conditions allowed physicians to pay more attention to the cognitive function in DMD patients, leading to description of a cognitive impairment not only in affected males, but in female carriers as well. This study aimed to investigate the cognitive involvement in a cohort of DMD carriers and to summarize the current knowledge about the intellectual involvement and neuropsychological profile in DMD/BMD carriers. Our case series consisted of 22 carrier patients from two different centers (IRCCS Mondino, Pavia and Policlinico Gemelli, Rome), for whom we retrospectively collected cognitive, clinical and genetic data. For literature review, we selected 9 studies published in English language from 2011 to 2023 and cited in PubMed. We found that the average IQ of DMD carriers was lower (74; very low) than the average score on normal curve (100 as average standard score). Furthermore, about 50% of them fell in the "extremely low IQ" range, compared with 2-3% of general population. A higher incidence of intellectual disability was confirmed in symptomatic DMD carriers (mean IQ 66; extremely low) from IRCCS Mondino, but not in the asymptomatic ones (mean IQ 99; average), when compared to the general population. Current literature, albeit limited, seems to confirm the presence of a cognitive impairment in carriers, although milder than in affected males but with a similar neuropsychological profile. However, further studies are necessary to delve deeper into this issue and provide adequate educational support.

Identification of Two Novel Variants of the DMD Gene in Chinese Families with Duchenne Muscular Dystrophy

Background

Duchenne muscular dystrophy (DMD), an X-linked recessive neuromuscular disorder, is caused by pathogenic variants in the DMD gene encoding a large structural protein in muscle cells.

Methods

Two probands, a 6-year old boy and a 1-month old infant, respectively, were clinically diagnosed with DMD based on elevated levels of creatine kinase and creatine kinase isoenzyme. CNVplex and whole exome sequencing (WES) were performed for causal variants, and Sanger sequencing was used for verification.

Results

CNVplex found no large deletions or duplications in the DMD gene in both patients, but WES discovered a single-nucleotide deletion in exon 48 (NM_004006.2:c.6963del, p.Asp2322ThrfsTer16) in the proband of pedigree 1, and a nonsense mutation in exon 27 (NM_004006.2:c.3637A>T, p.K1213Ter) in the proband of pedigree 2.

Conclusion

The results of our study expand the mutation spectrum of DMD and enrich our understanding of the clinical characteristics of DMD. Genetic counseling was provided for the two families involved in this study.

Long-term outcomes for females with early-onset dystrophinopathy

AIM

To study long-term disease course for females with early-onset dystrophinopathy, including common (female) symptoms, challenges in social participation, the need for care, and current healthcare management to support guideline development.

METHOD

Twelve females with early-onset dystrophinopathy were followed for a median period of more than 17 years (range 1-36).

RESULTS

One patient died owing to end-stage cardiac failure. Cardiac abnormalities were observed in three of the remaining 11 participants. Respiratory function was reduced in seven of 10 participants. Fatigue, myalgia, lower back pain, and arthralgia were reported in more than six of the participants. Functional status varied from exercise intolerance to wheelchair dependency. Most or all of the 10 participants reported restrictions in participation in work (n = 10), household duties (n = 10), sports (n = 9), and education (n = 8). Only a few participants received followed-up pulmonary (n = 2) or rehabilitation (n = 3) care.

INTERPRETATION

Females with early-onset dystrophinopathy experience a wide range of impairments, comorbidities, limitations in activities, and restrictions in social participation. The whole spectrum should be acknowledged in the healthcare setting. Neuromuscular and cardiac follow-up are indispensable. Additional respiratory assessment and rehabilitation care are expected to improve health status and support daily activities and participation.

WHAT THIS PAPER ADDS

No standard diagnostic procedures seem to exist for female patients suspected for dystrophinopathy. Female participants with early-onset dystrophinopathy experienced a broad scope of burdening symptoms, such as fatigue, myalgia, lower back pain, and arthralgia. None of participants worked full time, all felt restricted in paid work, and most felt restricted in education. Most participants showed decreased lung function, while only one was symptomatic. Availability of rehabilitation care may improve support for daily activities and participation for females with early-onset dystrophinopathy.

Factors Influencing Creatine Kinase-MM Concentrations in Newborns and Implications for Newborn Screening for Duchenne Muscular Dystrophy

INTRODUCTION

Newborn screening for Duchenne muscular dystrophy can be performed via a first-tier creatine kinase-MM measurement followed by reflex testing to second-tier molecular analysis of the DMD gene. In order to establish appropriate cut-offs for the creatine kinase-MM screen, factors that influence creatine kinase-MM in newborns were investigated.

MATERIALS AND METHODS

Creatine kinase-MM data from a consented pilot study in New York State were collected over a two-year period and combined with de-identified validation data and analyzed. Univariate analysis and multiple linear regression analysis were performed.

RESULTS

The analysis indicated that age of newborn at specimen collection, gestational age and birth weight were significant influencers of CK-MM levels in newborns. In addition, to a lesser extent, sex, race/ethnicity and seasonal temperature also affect CK-MM levels in newborns.

CONCLUSIONS

To reduce false positive and false negative cases, newborn screening programs should be cognizant of factors that influence CK-MM when determining cut-offs for the assay. Variability based on age at specimen collection and birth weight are primarily observed within the first week of life. Therefore, particularly during this time period, multi-tiered cut-offs based on age of collection and lower cut-offs for premature and low birth weight babies are recommended. Other cut-off determinants may include sex, race/ethnicity and seasonal temperature.

Porta J, Nascimento A, Jou C. Innovative Computerized Dystrophin Quantification Method Based on Spectral Confocal Microscopy

Several clinical trials are working on drug development for Duchenne and Becker muscular dystrophy (DMD and BMD) treatment, and, since the expected increase in dystrophin is relatively subtle, high-sensitivity quantification methods are necessary. There is also a need to quantify dystrophin to reach a definitive diagnosis in individuals with mild BMD, and in female carriers. We developed a method for the quantification of dystrophin in DMD and BMD patients using spectral confocal microscopy. It offers the possibility to capture the whole emission spectrum for any antibody, ensuring the selection of the emission peak and allowing the detection of fluorescent emissions of very low intensities. Fluorescence was evaluated first on manually selected regions of interest (ROIs), proving the usefulness of the methodology. Later, ROI selection was automated to make it operator-independent. The proposed methodology correctly classified patients according to their diagnosis, detected even minimal traces of dystrophin, and the results obtained automatically were statistically comparable to the manual ones. Thus, spectral imaging could be implemented to measure dystrophin expression and it could pave the way for detailed analysis of how its expression relates to the clinical course. Studies could be further expanded to better understand the expression of dystrophin-associated protein complexes (DAPCs).

Highly asymmetrical distribution of muscle wasting correlates to the heteroplasmy in a patient carrying a large-scale mitochondrial DNA deletion: a novel pathophysiological mechanism for explaining asymmetry in mitochondrial myopathies

Mitochondrial diseases are a heterogeneous group of pathologies, caused by missense mutations, sporadic large-scale deletions of mitochondrial DNA (mtDNA) or mutations of nuclear maintenance genes. We report the case of a patient in whom extended muscle pathology, biochemical and genetic mtDNA analyses have proven to be essential to elucidate a unique asymmetrical myopathic presentation. From the age of 34 years on, the patient has presented with oculomotor disorders, right facial peripheral palsy and predominantly left upper limb muscle weakness and atrophy. By contrast, he displayed no motor weakness on the right hemi-body, and no sensory symptoms, cerebellar syndrome, hypoacusis, or parkinsonism. Cardiac function was normal. CK levels were elevated (671 UI/L). Electroneuromyography (ENMG) and muscle MRI showed diffuse myogenic alterations, more pronounced on the left side muscles. Biopsy of the left deltoid muscle showed multiple mitochondrial defects, whereas in the right deltoid, mitochondrial defects were much less marked. Extended mitochondrial biochemical and molecular workup revealed a unique mtDNA deletion, with a 63.4% heteroplasmy load in the left deltoid, versus 8.1% in the right one. This case demonstrates that, in mitochondrial myopathies, heteroplasmy levels may drastically vary for the same type of muscle, rising the hypothesis of a new pathophysiological mechanism explaining asymmetry in hereditary myopathies.

X-chromosomal inactivation patterns in women with Fabry disease

BACKGROUND

Although Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the α-galactosidase A gene (GLA), women may develop severe symptoms. We investigated X-chromosomal inactivation patterns (XCI) as a potential determinant of symptom severity in FD women.

PATIENTS AND METHODS

We included 95 women with mutations in GLA (n = 18 with variants of unknown pathogenicity) and 50 related men, and collected mouth epithelial cells, venous blood, and skin fibroblasts for XCI analysis using the methylation status of the androgen receptor gene. The mutated X-chromosome was identified by comparison of samples from relatives. Patients underwent genotype categorization and deep clinical phenotyping of symptom severity.

RESULTS

43/95 (45%) women carried mutations categorized as classic. The XCI pattern was skewed (i.e., ≥75:25% distribution) in 6/87 (7%) mouth epithelial cell samples, 31/88 (35%) blood samples, and 9/27 (33%) skin fibroblast samples. Clinical phenotype, α-galactosidase A (GAL) activity, and lyso-Gb3 levels did not show intergroup differences when stratified for X-chromosomal skewing and activity status of the mutated X-chromosome.

CONCLUSIONS

X-inactivation patterns alone do not reliably reflect the clinical phenotype of women with FD when investigated in biomaterial not directly affected by FD. However, while XCI patterns may vary between tissues, blood frequently shows skewing of XCI patterns.

Characteristics of disease progression and genetic correlation in ambulatory Iranian boys with Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy in the pediatric population. The manifestations of this disease include progressive muscle weakness, gait dysfunction, and motor impairment, leading to a loss of ambulation by the age of 13 years. Molecular diagnosis is the standard diagnostic tool for DMD. This study aimed to investigate disease progression and genetic patterns in Iranian ambulant boys and to find the correlation between genotypes and motor function phenotypes.

METHODS

This study was performed on 152 DMD patients. Clinical history, including the disease phenotype, steroid therapy, and the North Star Ambulatory Assessment (NSAA) score, was taken for all the patients. Molecular diagnoses were confirmed by multiplex ligation-dependent probe amplification and next-generation sequencing tests.

RESULTS

A total of 152 Iranian DMD patients were examined in this study. The mean age at the time of disease onset was 4.04 ± 2.00 years, and the mean age at diagnosis was 5.05 ± 2.08 years. The mean age of ambulation loss was 10.9 years. Contracture was reported in 38.9% of cases. In terms of age, the mean total NSAA score showed a peak at 4 years of age, with a mean NSAA score of 24. Annual changes in the NSAA score were determined for all cases, based on the mutation type and exon site. Deletion mutation was found in 79.1% of cases, duplication in 6.8%, nonsense in 12.8%, and splice site in 1.4%. The most common single exon deletion was exon 44 (5.3%), and the most common multiexon deletions were attributed to exons 45-50 and exons 45-52 (4.6%). The results did not indicate any correlation between the mutation type and age at the time of disease onset, loss of ambulation age, and wheelchair dependence; however, a significant association was found between contracture and mutation type. The results showed a significant difference in the NSAA score between the deletion and nonsense groups at the age of 3 years (P = 0.04). No significant correlation was found between the phenotype and exon site. Overall, 91.1% of the study population had a history of corticosteroid use, and 54.1% showed compliance with rehabilitation therapy.

CONCLUSION

This study demonstrated the phenotypes and mutational features of Iranian DMD boys and provided information regarding the natural motor history of the disease, disease progression, diagnosis, and status of DMD management in Iran. The present findings can promote the development of clinical trials and future advanced molecular therapies in Iran.

Dystrophin genetic variants and autism

Loss-of-function variants in the dystrophin gene, a well-known cause of muscular dystrophies, have emerged as a mutational risk mechanism for autism spectrum disorder (ASD), which in turn is a highly prevalent (~ 1%) genetically heterogeneous neurodevelopmental disorder. Although the association of intellectual disability with the dystrophinopathies Duchenne (DMD) and Becker muscular dystrophy (BMD) has been long established, their association with ASD is more recent, and the dystrophin genotype-ASD phenotype correlation is unclear. We therefore present a review of the literature focused on the ASD prevalence among dystrophinopathies, the relevance of the dystrophin isoforms, and most particularly the relevance of the genetic background to the etiology of ASD in these patients. Four families with ASD-DMD/BMD patients are also reported here for the first time. These include a single ASD individual, ASD-discordant and ASD-concordant monozygotic twins, and non-identical ASD triplets. Notably, two unrelated individuals, which were first ascertained because of the ASD phenotype at ages 15 and 5 years respectively, present rare dystrophin variants still poorly characterized, suggesting that some dystrophin variants may compromise the brain more prominently. Whole exome sequencing in these ASD-DMD/BMD individuals together with the literature suggest, although based on preliminary data, a complex and heterogeneous genetic architecture underlying ASD in dystrophinopathies, that include rare variants of large and medium effect. The need for the establishment of a consortia for genomic investigation of ASD-DMD/BMD patients, which may shed light on the genetic architecture of ASD, is discussed.

Can symptomatic nmDuchenne carriers benefit from treatment with ataluren? Results of 193-month follow-up

Duchenne's muscular dystrophy (DMD) is an X-linked neuromuscular disorder caused by deletions (75%), duplications (15-20%) and point mutations (5-10%) in the dystrophin gene. Among the latter, stop-codon point mutations are rare. Female carriers of dystrophin gene mutations are usually asymptomatic as they are "protected" by the second X-chromosome, which produces a normal dystrophin protein. However, about 8-10% of them can present symptoms that set the clinical picture of the manifesting or symptomatic carrier. Although no causative cure there is for DMD, therapies are available to slow the decline of muscle weakness and delay the onset of heart and respiratory involvement. However, there is limited data in the literature documenting the treatment of symptomatic carriers, often entrusted to the sensitivity of individual doctors. In this paper, we report the follow-up outcomes of four European symptomatic nmDMD carriers treated with ataluren, overall followed for 193 months. Annual assessment of muscle strength, pulmonary lung function tests, and echocardiography, indicate a mild attenuation of disease progression under treatment.. There were no adverse clinical effects or relevant abnormalities in routine laboratory tests. We can conclude that ataluren appears to stabilize, if not slightly improve, the clinical course of patients with a good safety profile, especially if we consider that the treatment was late for 3/4 patients, at a mean age of 36.6 ± 10.6 years.

Intellectual disability in paediatric patients with genetic muscle diseases

The differential diagnosis of genetic muscle disease has become increasingly difficult due to the rapid progress in genetic medicine in recent years. Where classifications based on the clinical picture were attributed to one gene only a few years ago, today we know that a variety of clinical presentations can result from the same mutation and, conversely, various genes are associated with a similar phenotype. A significant consideration in assessing a patient with muscle weakness is the presence or absence of intellectual disability, thus narrowing the differential diagnostic approach in any child with an as yet undiagnosed muscle disease. Intellectual disability in neuromuscular diseases is often associated with behavioural disorders and may be correlated with abnormal brain imaging. Conversely, brain involvement can sometimes be seen without intellectual disability, but may be associated with an epilepsy risk and is helpful for the differential diagnosis. This review focuses on the three most common causes of paediatric muscle diseases with intellectual disability, dystrophinopathies, myotonic dystrophy type 1 and dystroglycanopathies. It also summarises differential diagnostic considerations when assessing a child with a genetic muscle disease and intellectual disability. The recent scientific literature on this topic is reviewed, the frequency of intellectual disability assessed, and specific clinical features are described. Where available, data on disease onset, progression and serum creatine kinase levels are presented and the pattern of muscle involvement described in an algorithm. Central nervous involvement and brain imaging analysis was reviewed and included.

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.

DMD/BMD prenatal diagnosis and treatment expectation in a single centre in China for 15 years

OBJECTIVE

DMD/BMD prenatal diagnosis for 931 foetuses.

BACKGROUND

DMD is the most common fatal X-linked recessive muscular disease. There is no effective clinical treatment method at present. Accurate gene diagnosis and prenatal diagnosis technology are important ways for early detection, early prevention and early treatment.

METHODS

A total of 931 prenatal diagnoses were performed for pregnant women with a definite family history of DMD or a history of DMD childbirth between 2005 and 2019. This report may be considered the largest DMD prenatal diagnosis report in a single centre worldwide. Multiple ligation-dependent probe amplification (MLPA) and next-generation sequencing were used in combination. Techniques and short tandem repeat (STR) linkage analysis were used to determine the location of the DMD gene mutation in the pregnant woman and then to detect the DMD gene in the foetuses.

RESULTS

There were 872 families in our study. Among all 931 foetuses, 20.73% (193/931) were males expected to develop DMD and 16.33% (152/931) were female carriers. In addition, gonadal mosaicism was observed in 5 mothers, and gene recombination was identified in three foetuses. The results of the prenatal diagnosis were consistent with the results of the CPK analysis, and the results of the prenatal diagnosis were 100% accurate.

CONCLUSIONS

MLPA and Sanger sequencing, when combined with STR linkage analyses, can provide an accurate and rapid prenatal diagnosis. Due to the high de novo rate, prenatal diagnosis and genetic counselling should be given great attention.

A female carrier of a novel DMD mutation with slightly skewed X-chromosome inactivation shows a suspected case of Becker muscular dystrophy in a Chinese family

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are both caused by mutations in DMD gene effecting the expression of dystrophin. Generally female carriers are asymptomatic; however, it has been suggested that carriers may exhibit symptoms. We investigated a 6-year-old Chinese girl exhibiting a suspected BMD phenotype, including persistently elevated creatine kinase and creatine kinase isoenzyme levels. The proband harbored a novel heterozygous mutation, c.3458_3459insAA, within exon 26 of the DMD gene inherited from her mother who had a completely normal phenotype and presented with mosaicism in her lymphocytes with 45, X [17%]/46, XX [83%]. In addition, X-chromosome inactivation (XCI) patterns in the peripheral blood of the child were slightly skewed: proband with 62% (mutant allele)/38% (normal allele) when compared with her mother with 32/68%. Amplification of regions of the cDNA revealed different ratios for the expression of these alleles: proband with 50/50% and her mother with 20/80%. Real-time PCR showed that mRNA expression was significantly decreased in both. We proposed that a frameshift or nonsense mutation may contribute to the development of symptoms in carriers. These phenotypes correlate with nonrandom XCI patterns and are compounded by the locus of the mutation. For incompletely skewed XCI patterns, although the mutant allele could suppress the expression of a normal allele, carriers would remain asymptomatic as long as there was adequate compensation from the normal allele. We also proposed a mechanism where mRNA from the mutant allele may be unstable and easily degraded, allowing for phenotypic compensation by the wildtype allele.

Targeting Nrf2 for the treatment of Duchenne Muscular Dystrophy

Imbalances in redox homeostasis can result in oxidative stress, which is implicated in various pathological conditions including the fatal neuromuscular disease Duchenne Muscular Dystrophy (DMD). DMD is a complicated disease, with many druggable targets at the cellular and molecular level including calcium-mediated muscle degeneration; mitochondrial dysfunction; oxidative stress; inflammation; insufficient muscle regeneration and dysregulated protein and organelle maintenance. Previous investigative therapeutics tended to isolate and focus on just one of these targets and, consequently, therapeutic activity has been limited. Nuclear erythroid 2-related factor 2 (Nrf2) is a transcription factor that upregulates many cytoprotective gene products in response to oxidants and other toxic stressors. Unlike other strategies, targeted Nrf2 activation has the potential to simultaneously modulate separate pathological features of DMD to amplify therapeutic benefits. Here, we review the literature providing theoretical context for targeting Nrf2 as a disease modifying treatment against DMD.

Serum MyomiRs as Biomarkers for Female Carriers of Duchenne/Becker Muscular Dystrophy

Background: Duchenne/Becker muscular dystrophy (DMD/BMD) is an X-linked recessive lethal neuromuscular disease. MicroRNAs expressed in striated muscle, myomiRs, have been proposed as its potential biomarkers. Serum creatine kinase (CK) is commonly used as a biomarker in clinical practice, but it is not reliable. The aim of this study was to assess whether serum levels of myomiRs has diagnostic value for detection of female DMD/BMD carriers with normal or elevated CK.

Methods: Thirty four female carriers and 33 age-matched healthy female controls were enrolled. Peripheral blood samples were collected and serum miRNAs were extracted for measurement of miR-1, miR-133a, miR-133b, miR-206, miR-208a, miR-208b, and miR-499 by quantitative real-time polymerase chain reaction.

Results: MiR-1, miR-133a, miR-133b, miR-206, miR-208a, miR-208b, and miR-499 were upregulated in all female carriers in comparison to healthy controls. MiR-1 (Spearman's rho = +0.406, p = 0.017) was correlated with CK in the female carrier group. Receiver operating characteristic curve analysis of all seven myomiRs showed that the area under the curve (AUC) for miR-499, miR-133b, miR-1, miR-208b, and miR-133a exceeded 70.0%, and for miR-206 and miR-208a exceeded 60.0%. MiR-133b and miR-499 were significantly increased in all female carriers, even those with normal CK. AUC for the combination of all seven miRNAs was 87.2%. CK (OR 0.406, 95% CI 0.000–0.001, p < 0.0001) and miR-499 (OR 0.323, 95% CI 0.023–0.106, p = 0.003) were considered to be independent predictors for female carriers presence in the multivariable regression analysis model.

Conclusions: MiR-133b and miR-499 are potentially useful biomarkers for female carriers with DMD/BMD (including those with normal CK). The combination of all seven serum miRNAs and their respective combinations with CK have better diagnostic value for female carriers than either CK or any separate miRNA.

Cognition of the mothers of patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) has been found to be associated with cognitive impairment. However, few studies have addressed cognitive impairment among mothers of children with DMD. In the present study, the neuropsychological profiles of both carrier mothers (C-Ms) and noncarrier mothers (NC-Ms) were examined, and the findings were compared with healthy control mothers (HC-Ms). There were 90 participants, consisting of 31 C-Ms, 24 NC-Ms, and 35 HC-Ms, each of whom completed a neuropsychological test battery. C-Ms had poorer cognition performance in attention, working memory, immediate verbal memory, visuospatial skills, and executive functions than NC-Ms, and HC-Ms. This study provides evidence that there may be cognitive impairment in mothers of patients with DMD. The cognitive impairment of C-Ms has similarities to that seen in children with DMD.

Connexin-43 reduction prevents muscle defects in a mouse model of manifesting Duchenne muscular dystrophy female carriers

Duchenne muscular dystrophy (DMD) is a severe X-linked neuromuscular disorder that affects males. However, 8% of female carriers are symptomatic and underrepresented in research due to the lack of animal models. We generated a symptomatic mouse model of DMD carriers via injection of mdx (murine DMD) embryonic stem cells (ESCs) into wild-type (WT) blastocysts (mdx/WT chimera). mdx/WT chimeras developed cardiomyopathic features and dystrophic skeletal muscle phenotypes including elevated mononuclear invasion, central nucleation, fibrosis and declined forelimb grip strength. The disease was accompanied by connexin-43 (Cx43) aberrantly enhanced in both cardiac and skeletal muscles and remodeled in the heart. Genetic reduction of Cx43-copy number in mdx/WT-Cx43(+/-) chimeras protected them from both cardiac and skeletal muscle fiber damage. In dystrophic skeletal muscle, Cx43 expression was not seen in the fibers but in adjacent F4/80+ mononuclear cells. Ethidium Bromide uptake in purified F4/80+/CD11b+ mdx macrophages revealed functional activity of Cx43, which was inhibited by administration of Gap19 peptide mimetic, a Cx43 hemichannel-specific inhibitor. Thus, we suggest that Cx43 reduction in symptomatic DMD carrier mice leads to prevention of Cx43 remodeling in the heart and prevention of aberrant Cx43 hemichannel activity in the skeletal muscle macrophages neighboring Cx43 non-expressing fibers.

Functional performance and muscular strength in symptomatic female carriers of Duchenne muscular dystrophy

Abstract Duchenne muscular dystrophy (DMD) usually affects men. However, women are also affected in rare instances. Approximately 8% of female DMD carriers have muscle weakness and cardiomyopathy. The early identification of functional and motor impairments can support clinical decision making. Objective: To investigate the motor and functional impairments of 10 female patients with dystrophinopathy diagnosed with clinical, pathological, genetic and immunohistochemical studies. Methods: A descriptive study of a sample of symptomatic female carriers of DMD mutations. The studied variables were muscular strength and functional performance. Results: The prevalence was 10/118 (8.4%) symptomatic female carriers. Deletions were found in seven patients. The age of onset of symptoms in female carriers of DMD was quite variable. Pseudohypertrophy of calf muscles, muscular weakness, compensatory movements and longer timed performance on functional tasks were observed in most of the cases. Differently from males with DMD, seven female patients showed asymmetrical muscular weakness. The asymmetric presentation of muscle weakness was frequent and affected posture and functionality in some cases. The functional performance presents greater number of compensatory movements. Time of execution of activities was not a good biomarker of functionality for this population, because it does not change in the same proportion as the number of movement compensations. Conclusion: Clinical manifestation of asymmetrical muscle weakness and compensatory movements, or both can be found in female carriers of DMD mutations, which can adversely affect posture and functional performance of these patients.

Report of a TREAT-NMD/World Duchenne Organisation Meeting on Dystrophin Quantification Methodology

Representatives of academia, patient organisations, industry and the United States Food and Drug Administration attended a workshop on dystrophin quantification methodology. The aims of the workshop were to provide an overview of methods used to quantify dystrophin levels in human skeletal muscle and their applicability to clinical trial samples, outline the gaps with regards to validating the methods for robust clinical applications prior to regulatory agency review, and to align future efforts towards further optimizing these methods. The workshop facilitated a constructive but also critical discussion on the potential and limitations of techniques currently used in the field of translational research (western blot and immunofluorescence analysis) and emerging techniques (mass spectrometry and capillary western immunoassay). Notably, all participants reported variation in dystrophin levels between muscle biopsies from different healthy individuals and agreed on the need for a common reference sample.

In vivo cerebellar circuit function is disrupted in an mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a debilitating and ultimately lethal disease involving progressive muscle degeneration and neurological dysfunction. DMD is caused by mutations in the dystrophin gene, which result in extremely low or total loss of dystrophin protein expression. In the brain, dystrophin is heavily localized to cerebellar Purkinje cells, which control motor and non-motor functions. In vitro experiments in mouse Purkinje cells revealed that loss of dystrophin leads to low firing rates and high spiking variability. However, it is still unclear how the loss of dystrophin affects cerebellar function in the intact brain. Here, we used in vivo electrophysiology to record Purkinje cells and cerebellar nuclear neurons in awake and anesthetized female mdx (also known as Dmd) mice. Purkinje cell simple spike firing rate is significantly lower in mdx mice compared to controls. Although simple spike firing regularity is not affected, complex spike regularity is increased in mdx mutants. Mean firing rate in cerebellar nuclear neurons is not altered in mdx mice, but their local firing pattern is irregular. Based on the relatively well-preserved cytoarchitecture in the mdx cerebellum, our data suggest that faulty signals across the circuit between Purkinje cells and cerebellar nuclei drive the abnormal firing activity. The in vivo requirements of dystrophin during cerebellar circuit communication could help explain the motor and cognitive anomalies seen in individuals with DMD.This article has an associated First Person interview with the first author of the paper.

Value of muscle magnetic resonance imaging in the differential diagnosis of muscular dystrophies related to the dystrophin-glycoprotein complex

BACKGROUND

Dystrophin-glycoprotein complex (DGC)-related muscular dystrophies may present similar clinical and pathological features as well as undetectable mutations thus being sometimes difficult to distinguish. We investigated the value of muscle magnetic resonance imaging (MRI) in the differential diagnosis of DGC-related muscular dystrophies and reported the largest series of Chinese patients with sarcoglycanopathies studied by muscle MRI.

RESULTS

Fifty-five patients with DGC-related muscular dystrophies, including 22 with confirmed sarcoglycanopathies, 11 with limb-girdle muscular dystrophy 2I (LGMD2I, FKRP-associated dystroglycanopathy), and 22 with dystrophinopathies underwent extensive clinical evaluation, muscle biopsies, genetic analysis, and muscle MRI examinations. Hierarchical clustering of patients according to the clinical characteristics showed that patients did not cluster according to the genotypes. No statistically significant differences were observed between sarcoglycanopathies and LGMD2I in terms of thigh muscle involvement. The concentric fatty infiltration pattern was observed not only in different sarcoglycanopathies (14/22) but also in LGMD2I (9/11). The trefoil with single fruit sign was observed in most patients with dystrophinopathies (21/22), and a few patients with sarcoglycanopathies (4/22) or LGMD2I (2/11). Hierarchical clustering showed that most patients with sarcoglycanopathies or LGMD2I can be distinguished from dystrophinopathies based on the concentric fatty infiltration pattern and trefoil with single fruit sign at the thigh level on muscle MRI.

CONCLUSIONS

Muscle MRI at the thigh level potentially allows distinction of sarcoglycanopathies or FKRP-associated dystroglycanopathy from dystrophinopathies.

Duchenne Muscular Dystrophy Newborn Screening: Evaluation of a New GSP® Neonatal Creatine Kinase-MM Kit in a US and Danish Population

Duchenne muscular dystrophy (DMD/Duchenne) is a progressive X-linked disease and is the most common pediatric-onset form of muscular dystrophy, affecting approximately 1:5000 live male births. DNA testing for mutations in the dystrophin gene confirms the diagnosis of this disorder. This study involves assessment of screening newborns for DMD using an immunoassay for muscle-type (MM) creatine kinase (CK) isoform-the GSP Neonatal CK-MM kit. Comparisons were made with CK activity determination by fluorescence measurement. In addition, the study evaluated the effect of gestational age, age of infant at time of sampling and how stable the CK-MM was over time. This assay discriminates well between normal, unaffected and Duchenne affected populations and is suitable for Duchenne newborn screening.

Clinical and genetic characteristics of female dystrophinopathy carriers

The present study aimed to determine the genetic status of manifesting carriers (MCs) of Duchenne muscular dystrophy (DMD)/Becker muscular dystrophy (BMD) and asymptomatic carriers with a family history of DMD/BMD, and identify potential simple and reliable methods for screening dystrophinopathy carriers. Clinical data from probable carriers and MCs were collected and analyzed. MCs underwent multiplex ligation‑dependent probe amplification (MLPA) for dystrophin gene exons combined with muscle disease panel test based on a next‑generation sequencing (NGS) platform. In addition, the status of probable carriers was determined by MLPA or Sanger sequencing, according to the mutations of probands. A total of 154 female were enrolled, among which 78 cases were found to be carriers, including 4 MCs and 74 asymptomatic female carriers. The 4 MCs exhibited duplication mutations. Among the 74 asymptomatic carriers, 41.89% harbored deletion mutations, including 2 cases with suspected germline mosaicism and no mutation in the dystrophin gene, while 44.59% harbored point mutations in exons and only 10 cases (13.51%) carried duplication mutations. The area under the receiver operating characteristic (ROC) curve of creatine kinase (CK) was 0.822, with a sensitivity of 65.38% and specificity of 92.1%. In addition, DMD was positively correlated with the CK, alanine transaminase and aspartate transaminase levels of the carriers. MLPA for exons of the dystrophin gene, along with NGS and Sanger sequencing, was effective for the diagnosis of MCs and for determining the status of probable carriers. The ROC curve analysis also demonstrated that CK level was an excellent predictor for distinguishing DMD/BMD carriers.

Psychosocial Management of the Patient With Duchenne Muscular Dystrophy

In this article, we outline a comprehensive plan for the psychosocial management of patients with Duchenne muscular dystrophy (DMD) across the life span. In 2010, the Centers for Disease Control and Prevention sponsored the development of multidisciplinary management guidance for DMD, and in 2018, that guidance was updated. In the intervening years, a new emphasis was placed on studying and addressing the psychosocial issues that affect patients with DMD, driven in part by improved patient survival. Once viewed as ancillary to managing the significant medical needs of patients with DMD, it is now standard practice to integrate psychosocial management into the multidisciplinary management of the disease. It is also increasingly recognized that neurodevelopmental disorders in DMD occur at a higher rate than what was previously understood and that these disorders warrant early and intensive intervention. In this article, we expand on the content found in the 2018 DMD Care Considerations.

Female dystrophinopathy: Review of current literature

Skeletal muscle or cardiac symptoms are known to appear in a certain proportion of female patients carrying the dystrophin gene mutation. There is limited high-quality evidence to guide the treatment of female carriers of Duchenne muscular dystrophy/Becker muscular dystrophy (DMD/BMD). The available evidence is mainly based on expert opinions and clinical experience. To improve this situation, we reviewed 1002 reports published from 1967 to 2017 to assess the following themes: epidemiology, clinical symptoms, cardiomyopathy, burdens on parents or caregivers, pregnancy or delivery, and prognosis. We aimed to provide guidance for the provision of support, care, and education for patients, caregivers, and health care professionals. There were 271 reports before 1987, and 731 reports after 1987 when dystrophin was first recognized. In this review, we mainly selected 37 papers that were reported after 1987. In seven large research papers, the incidence of skeletal muscle damage among female carriers, including asymptomatic carriers, was reported as 2.5%-19%, and the incidence of dilated cardiomyopathy was 7.3%-16.7% for DMD and 0%-13.3% for BMD. We integrated and summarized the genetically definite manifesting carriers with skeletal muscle symptoms from 10 case series. In combined data, among 93 manifesting carriers, 16 (17.2%) presented with cardiac abnormalities. The frequency of manifesting carriers complicated by cardiomyopathy increased with age. Reports on cardiac magnetic resonance in female carriers and the burden on caregivers are increasing, whereas literatures concerning pregnancy, delivery, and prognosis in female carriers are limited. This represents a future direction for research.

Outside in: The matrix as a modifier of muscular dystrophy

Muscular dystrophies are genetic conditions leading to muscle degeneration and often, impaired regeneration. Duchenne Muscular Dystrophy is a prototypical form of muscular dystrophy, and like other forms of genetically inherited muscle diseases, pathological progression is variable. Variability in muscular dystrophy can arise from differences in the manner in which the primary mutation impacts the affected protein's function; however, clinical heterogeneity also derives from secondary mutations in other genes that can enhance or reduce pathogenic features of disease. These genes, called genetic modifiers, regulate the pathophysiological context of dystrophic degeneration and regeneration. Understanding the mechanistic links between genetic modifiers and dystrophic progression sheds light on pathologic remodeling, and provides novel avenues to therapeutically intervene to reduce muscle degeneration. Based on targeted genetic approaches and unbiased genomewide screens, several modifiers have been identified for muscular dystrophy, including extracellular agonists of signaling cascades. This review will focus on identification and possible mechanisms of recently identified modifiers for muscular dystrophy, including osteopontin, latent TGFβ binding protein 4 (LTBP4) and Jagged1. Moreover, we will review the investigational approaches that aim to target modifier pathways and thereby counteract dystrophic muscle wasting.

[Central manifestations of dystrophinopathies]

The dystrophin gene involved in Duchenne and Becker muscular dystrophy is expressed in three main tissues resulting in clinical manifestations: skeletal muscle, heart and central nervous system. The 6 different existing dystrophins in the brain may play a role in the maturation and plasticity of neuronal synapses in particular by their functions in clustering and stabilization of different receptors at the post synaptic membrane. The possibility of an intellectual deficiency in Duchenne muscular dystrophy is known from the original description by Duchenne himself. Current data are in line with a constant cognitive impairment with a Gaussian curve shifted intellectual quotient (IQ) at -1 standard deviation from the standard population with an average IQ around 80. Clinical manifestations suggestive of a central nervous system involvement can affect all dystrophinopathies, including isolated central presentations without myopathic sign. The phenotypic spectrum appears broader and more subtle than non specific intellectual deficiency. The isolated or shared involvement of specific cognitive functions is possible (memory functions, executive functions, attention) with or without intellectual deficiency. Autism spectrum disorders are also among the encountered events. In clinical practice, it seems worth to ask for a measurement of serum creatine kinase (CK) in these different situations, keeping in mind that pure forms of central dystrophinopathies with a normal CK level have been recently reported.

Serum Levels of MicroRNA-206 and Novel Mini-STR Assays for Carrier Detection in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is an X-linked neuromuscular disorder in which the detection of female carriers is of the utmost importance for genetic counseling. Haplotyping with polymorphic markers and quantitation of creatine kinase levels (CK) allow tracking of the at-risk haplotype and evidence muscle damage, respectively. Such approaches are useful for carrier detection in cases of unknown mutations. The lack of informative markers and the inaccuracy of CK affect carrier detection. Therefore, herein we designed novel mini-STR (Short Tandem Repeats) assays to amplify 10 loci within the DMD gene and estimated allele frequencies and the polymorphism information content among other parameters in 337 unrelated individuals from three Mexican populations. In addition, we tested the utility of the assays for carrier detection in three families. Moreover, given that serum levels of miR-206 discern between DMD patients and controls with a high area under the curve (AUC), the potential applicability for carrier detection was assessed. The serum levels of miR-206 of non-carriers (n = 24) and carriers (n = 23) were compared by relative quantitation using real-time PCR (p < 0.05), which resulted in an AUC = 0.80 in the Receiver Operating Characteristic curve analysis. In conclusion, miR-206 has potential as a "liquid biopsy" for carrier detection and genetic counseling in DMD.

Determining the role of skewed X-chromosome inactivation in developing muscle symptoms in carriers of Duchenne muscular dystrophy

Duchenne and Becker dystrophinopathies (DMD and BMD) are X-linked recessive disorders caused by mutations in the dystrophin gene that lead to absent or reduced expression of dystrophin in both skeletal and heart muscles. DMD/BMD female carriers are usually asymptomatic, although about 8 % may exhibit muscle or cardiac symptoms. Several mechanisms leading to a reduced dystrophin have been hypothesized to explain the clinical manifestations and, in particular, the role of the skewed XCI is questioned. In this review, the mechanism of XCI and its involvement in the phenotype of BMD/DMD carriers with both a normal karyotype or with X;autosome translocations with breakpoints at Xp21 (locus of the DMD gene) will be analyzed. We have previously observed that DMD carriers with moderate/severe muscle involvement, exhibit a moderate or extremely skewed XCI, in particular if presenting with an early onset of symptoms, while DMD carriers with mild muscle involvement present a random XCI. Moreover, we found that among 87.1 % of the carriers with X;autosome translocations involving the locus Xp21 who developed signs and symptoms of dystrophinopathy such as proximal muscle weakness, difficulty to run, jump and climb stairs, 95.2 % had a skewed XCI pattern in lymphocytes. These data support the hypothesis that skewed XCI is involved in the onset of phenotype in DMD carriers, the X chromosome carrying the normal DMD gene being preferentially inactivated and leading to a moderate-severe muscle involvement.

Diagnosis of late-onset Pompe disease and other muscle disorders by next-generation sequencing

Background

Late-onset Pompe disease (LOPD) is a rare treatable lysosomal storage disorder characterized by progressive lysosomal glycogen accumulation and muscle weakness, with often a limb-girdle pattern. Despite published guidelines, testing for LOPD is often overlooked or delayed in adults, owing to its low frequency compared to other muscle disorders with similar muscle patterns. Next-generation sequencing has the capability to test concurrently for several muscle disorders. This could potentially lead to increased diagnosis of LOPD, disorders with non-specific muscle weakness or atypical patients.

Methods

We developed a gene panel to further study its clinical utility in a cohort of patients with suspected muscle disorders. We designed a gene panel to analyze the coding sequences and splice site junctions of GAA causing LOPD, along with 77 other genes causing muscle disorders with overlapping phenotypes.

Results

At a median coverage of ~200X (sequences per base), all GAA exons were successfully covered with >20X and only 0.3 % of exons across all genes were <20X. The panel showed an excellent sensitivity (100 %) and specificity (98 %) across all selected genes, using known variations in Pompe patients and controls. We determined its clinical utility by analyzing 34 patients with suspected muscle disorders of undetermined etiology and various muscle patterns, who were referred or followed in neuromuscular and genetics clinics. A putative diagnosis was found in up to 32 % of patients. The gene panel was instrumental in reaching a diagnosis in atypical patients, including one LOPD case. Acid alpha-glucosidase activity was used to confirm the molecular results in all patients.

Conclusion

This work highlights the high clinical utility of gene panels in patients with suspected muscle disorders and its potential to facilitate the diagnosis of patients showing non-specific muscle weakness or atypical phenotypes. We propose that gene panels should be used as a first-tier test in patients with suspected muscle disorders of undetermined etiology, which could further increase overall diagnosis of muscle conditions, and potentially reduce diagnostic delay. Further studies are necessary to determine the impact of first-tier gene panels on diagnostic delay and on treatment outcome for LOPD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0390-6) contains supplementary material, which is available to authorized users.

[Specific features of Becker Muscular Dystrophy patients and female carriers of Duchenne Muscular Dystrophy]

Becker muscular dystrophy (BMD) was first described in 1955 and linked to the DMD gene in 1987. Compared to Duchenne muscular dystrophy (DMD), clinical onset of BMD usually occurs after the age of 12 and wheelchair is required after the age of 16. BMD is characterized by generalized weakness first affecting limb girdle muscles, hypertrophy of the calves and cardiomyopathy in males. Some patients have only mild symptoms such as cramps or elevated serum creatine kinases (SCK) throughout all their lives. SCK levels are usually elevated. Muscle biopsy (immunohistochemistry or immunoblotting) shows a dystrophic pattern with abnormal dystrophin staining. Diagnosis is confirmed by DMD gene sequencing. Deletions or duplications of one or several exons are identified in the majority of cases. A multidisciplinary approach is recommended for the care management of these patients with a particular attention to the cardiomyopathy, which is typically responsible for death but can be prevented by specific treatment. X-linked dilated cardiomyopathies linked to DMD gene are a phenotypic continuum of BMD. Some female carriers of DMD mutations exhibit clinical symptoms of variable severity, often milder and beginning later than in males. The cardiomyopathy is the most frequent feature that should be especially monitored in these patients. Genetic counselling should be systematically proposed.

Non-Invasive Biomarkers for Duchenne Muscular Dystrophy and Carrier Detection

Non-invasive biological indicators of the absence/presence or progress of the disease that could be used to support diagnosis and to evaluate the effectiveness of treatment are of utmost importance in Duchenne Muscular Dystrophy (DMD). This neuromuscular disorder affects male children, causing weakness and disability, whereas female relatives are at risk of being carriers of the disease. A biomarker with both high sensitivity and specificity for accurate prediction is preferred. Until now creatine kinase (CK) levels have been used for DMD diagnosis but these fail to assess disease progression. Herein we examined the potential applicability of serum levels of matrix metalloproteinase 9 (MMP-9) and matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinases 1 (TIMP-1), myostatin (GDF-8) and follistatin (FSTN) as non-invasive biomarkers to distinguish between DMD steroid naïve patients and healthy controls of similar age and also for carrier detection. Our data suggest that serum levels of MMP-9, GDF-8 and FSTN are useful to discriminate DMD from controls (p < 0.05), to correlate with some neuromuscular assessments for DMD, and also to differentiate between Becker muscular dystrophy (BMD) and Limb-girdle muscular dystrophy (LGMD) patients. In DMD individuals under steroid treatment, GDF-8 levels increased as FSTN levels decreased, resembling the proportions of these proteins in healthy controls and also the baseline ratio of patients without steroids. GDF-8 and FSTN serum levels were also useful for carrier detection (p < 0.05). Longitudinal studies with larger cohorts are necessary to confirm that these molecules correlate with disease progression. The biomarkers presented herein could potentially outperform CK levels for carrier detection and also harbor potential for monitoring disease progression.