Delayed onset of ambulation in boys with Duchenne muscular dystrophy: Potential use as an endpoint in clinical trials

Early motor, cognitive, language, behavioural and social emotional development in infants and young boys with Duchenne Muscular Dystrophy- A systematic review

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin gene. Deficiency of the dystrophin protein causes not only motor, but also cognitive, language, behavioural and social emotional problems. This is the first systematic review investigating five early developmental domains in boys with DMD between 0 and 6 years old. Interactions between different domains and links with mutation types and sites were explored. A systematic search was performed in PubMed, Web of Science and Scopus. An adapted version of the Scottish Intercollegiate Guidelines Network (SIGN) Checklists for case-control and cohort studies was used to evaluate quality. Fifty-five studies of high or acceptable quality were included. One was an RCT of level 1b; 50 were cohort studies of level 2b; and four were an aggregation of case-control and cohort studies receiving levels 2b and 3b. We found that young boys with DMD experienced problems in all five developmental domains, with significant interactions between these. Several studies also showed relationships between mutation sites and outcomes. We conclude that DMD is not only characterised by motor problems but by a more global developmental delay with a large variability between boys. Our results emphasise the need for harmonisation in evaluation and follow-up of young boys with DMD. More high-quality research is needed on the different early developmental domains in young DMD to facilitate early detection of difficulties and identification of associated early intervention strategies.

Detecting early signs in Duchenne muscular dystrophy: comprehensive review and diagnostic implications

Despite the early onset of clinical signs suggestive of Duchenne muscular dystrophy (DMD), a diagnosis is often not made until four years of age or older, with a diagnostic delay of up to two years from the appearance of the first symptoms. As disease-modifying therapies for DMD become available that are ideally started early before irreversible muscle damage occurs, the importance of avoiding diagnostic delay increases. Shortening the time to a definite diagnosis in DMD allows timely genetic counseling and assessment of carrier status, initiation of multidisciplinary standard care, timely initiation of appropriate treatments, and precise genetic mutation characterization to assess suitability for access to drugs targeted at specific mutations while reducing the emotional and psychological family burden of the disease. This comprehensive literature review describes the early signs of impairment in DMD and highlights the bottlenecks related to the different diagnostic steps. In summary, the evidence suggests that the best mitigation strategy for improving the age at diagnosis is to increase awareness of the early symptoms of DMD and encourage early clinical screening with an inexpensive and sensitive serum creatine kinase test in all boys who present signs of developmental delay and specific motor test abnormality at routine pediatrician visits.

Duchenne expert physician perspectives on Duchenne newborn screening and early Duchenne care

Duchenne muscular dystrophy (DMD) is a progressive, fatal neuromuscular disorder typically diagnosed between 4 and 5 years of age. DMD currently has five FDA approved therapies, which has led to increased interest in newborn screening (NBS) for DMD. Our objective was to explore the perspectives and predicted practices of physicians (primarily neurologists) who will likely be responsible for the follow-up of infants identified with DMD through NBS. A short survey was developed and distributed to physicians who are responsible for providing care for patients with Duchenne at Certified Duchenne Care Centers across the USA. Twenty-seven physicians responded to statements about benefit and readiness for dystrophinopathy NBS, which care recommendations they would make at initial infant visits, and when they would recommend initiating approved therapies. Most DMD physicians indicated they see benefit in NBS (82%) and believe the DMD care community is ready for NBS in dystrophinopathies (74%). The majority of physicians would recommend multiple interventions, including genetic counseling, maternal carrier testing, referral to early intervention services, screening siblings, discussion of clinical trials, exon skipping therapies, and assessment of social and language development at initial visits. The majority of physicians also indicated they would recommend initiating approved therapies much earlier than the typical age of diagnosis.

Clinical and Genetic Characteristics in Young, Glucocorticoid-Naive Boys With Duchenne Muscular Dystrophy

BACKGROUND AND OBJECTIVES

Duchenne muscular dystrophy (DMD) is a pediatric neuromuscular disorder caused by mutations in the dystrophin gene. Genotype-phenotype associations have been examined in glucocorticoid-treated boys, but there are few data on the young glucocorticoid-naive DMD population. A sample of young glucocorticoid-naive DMD boys is described, and genotype-phenotype associations are investigated.

METHODS

Screening and baseline data were collected for all the participants in the Finding the Optimum Corticosteroid Regime for Duchenne Muscular Dystrophy (FOR-DMD) study, an international, multicenter, randomized, double-blind, clinical trial comparing 3 glucocorticoid regimens in glucocorticoid-naive, genetically confirmed boys with DMD between 4 and <8 years of age.

RESULTS

One hundred ninety-six boys were recruited. The mean ± SD age at randomization was 5.8 ± 1.0 years. The predominant mutation type was out-of-frame deletions (67.4%, 130 of 193), of which 68.5% (89 of 130) were amenable to exon skipping. The most frequent mutations were deletions amenable to exon 51 skipping (13.0%, 25 of 193). Stop codon mutations accounted for 10.4% (20 of 193). The mean age at first parental concerns was 29.8 ± 18.7 months; the mean age at genetic diagnosis was 53.9 ± 21.9 months; and the mean diagnostic delay was 25.9 ± 18.2 months. The mean diagnostic delay for boys diagnosed after an incidental finding of isolated hyperCKemia (n = 19) was 6.4 ± 7.4 months. The mean ages at independent walking and talking in sentences were 17.1 ± 4.2 and 29.0 ± 10.7 months, respectively. Median height percentiles were below the 25th percentile regardless of age group. No genotype-phenotype associations were identified expect for boys with exon 8 skippable deletions, who had better performance on time to walk/run 10 m (p = 0.02) compared to boys with deletions not amenable to skipping.

DISCUSSION

This study describes clinical and genetic characteristics of a sample of young glucocorticoid-naive boys with DMD. A low threshold for creatine kinase testing can lead to an earlier diagnosis. Motor and speech delays were common presenting symptoms. The effects of low pretreatment height on growth and adult height require further study. These findings may promote earlier recognition of DMD and inform study design for future clinical trials. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov Identifier: NCT01603407.

Striated muscle activator of Rho signalling (STARS) overexpression in the mdx mouse enhances muscle functional capacity and regulates the actin cytoskeleton and oxidative phosphorylation pathways

NEW FINDINGS

What is the central question of this study? Striated muscle activator of rho signalling (STARS) is an actin-binding protein that regulates transcriptional pathways controlling muscle function, growth and myogenesis, processes that are impaired in dystrophic muscle: what is the regulation of the STARS pathway in Duchenne muscular dystrophy (DMD)? What is the main finding and its importance? Members of the STARS signalling pathway are reduced in the quadriceps of patients with DMD and in mouse models of muscular dystrophy. Overexpression of STARS in the dystrophic deficient mdx mouse model increased maximal isometric specific force and upregulated members of the actin cytoskeleton and oxidative phosphorylation pathways. Regulating STARS may be a therapeutic approach to enhance muscle health.

ABSTRACT

Duchenne muscular dystrophy (DMD) is characterised by impaired cytoskeleton organisation, cytosolic calcium handling, oxidative stress and mitochondrial dysfunction. This results in progressive muscle damage, wasting and weakness and premature death. The striated muscle activator of rho signalling (STARS) is an actin-binding protein that activates the myocardin-related transcription factor-A (MRTFA)/serum response factor (SRF) transcriptional pathway, a pathway regulating cytoskeletal structure and muscle function, growth and repair. We investigated the regulation of the STARS pathway in the quadriceps muscle from patients with DMD and in the tibialis anterior (TA) muscle from the dystrophin-deficient mdx and dko (utrophin and dystrophin null) mice. Protein levels of STARS, SRF and RHOA were reduced in patients with DMD. STARS, SRF and MRTFA mRNA levels were also decreased in DMD muscle, while Stars mRNA levels were decreased in the mdx mice and Srf and Mrtfa mRNAs decreased in the dko mice. Overexpressing human STARS (hSTARS) in the TA muscles of mdx mice increased maximal isometric specific force by 13% (P < 0.05). This was not associated with changes in muscle mass, fibre cross-sectional area, fibre type, centralised nuclei or collagen deposition. Proteomics screening followed by pathway enrichment analysis identified that hSTARS overexpression resulted in 31 upregulated and 22 downregulated proteins belonging to the actin cytoskeleton and oxidative phosphorylation pathways. These pathways are impaired in dystrophic muscle and regulate processes that are vital for muscle function. Increasing the STARS protein in dystrophic muscle improves muscle force production, potentially via synergistic regulation of cytoskeletal structure and energy production.

Rehabilitation Following Fracture in Dystrophinopathy, A Case Series

BACKGROUND

Boys with dystrophinopathies (DMD) are at increased risk of low bone mineral density and fracture. Femoral fracture is the most common extremity fracture and is accompanied by significant risk of functional loss. Care considerations for DMD have stressed that aggressive management may be needed to maintain ambulation and that surgical fixation allows early mobilization.

OBJECTIVES

Describe 5 cases of femoral fracture in ambulatory boys with DMD and the course of care undertaken to optimize function.

PATIENTS

Five boys with DMD median age 15y (12-16) who were independently ambulatory. Median 10m walk speed prior to their first fracture was 8 sec (7-17.37) and 4 of 5 were less than the 9 seconds predictive of 2 year ambulation retention. Three of the cases had a single incident causing fracture; the remaining cases had 2 and 3 incidents respectively representing a total of 8 fractures 6 of which were surgically stabilized.

RESULTS

Following the first fracture, all 5 subjects regained some form of ambulation. Three patients regained independent ambulation and 2 with hand held support or contact guard. Two subjects went on to have additional falls with associated fracture. No patient regained the ability to rise from the floor and only one of the 5 regained the ability to climb steps and all demonstrated a decline in walking speed.

CONCLUSION

Prompt orthopedic intervention, early mobility, and intensive rehabilitation even in the end stage ambulatory patient, were factors in helping preserve function in these patients with dystrophinopathies.

A Review of MD STAR net's Research Contributions to Pediatric-Onset Dystrophinopathy in the United States; 2002-2017

Population studies of rare disorders, such as Duchenne and Becker muscular dystrophies (dystrophinopathies), are challenging due to diagnostic delay and heterogeneity in disorder milestones. To address these challenges, the Centers for Disease Control and Prevention established the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STAR net) in 2002 in the United States. From 2002 to 2012, MD STAR net longitudinally tracked the prevalence, clinical, and health care outcomes of 1054 individuals born from 1982 to 2011 with pediatric-onset dystrophinopathy through medical record abstraction and survey data collection. This article summarizes 31 MD STAR net peer-reviewed publications. MD STAR net provided the first population-based prevalence estimates of childhood-onset dystrophinopathy in the United States. Additional publications provided insights into diagnostic delay, dystrophinopathy-specific growth charts, and health services use. Ongoing population-based surveillance continually improves our understanding of clinical and diagnostic outcomes of rare disorders.