Duchenne Muscular Dystrophy Boys Research Articles

Muscle Ultrasonography in Relation to Motor Function in Children with Duchenne Muscular Dystrophy

Abstract Background and Aim Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood and affects 1 per 3600 male births. Electromyography and muscle biopsy were a commonly ordered invasive diagnostic procedure, used to evaluate children with weakness suspected to be caused by muscle disease. Recently, neuromuscular imaging is used as non-invasive diagnostic tool for various muscle diseases. Muscle ultrasonography is increasingly used for the diagnosis and follow up of children with DMD. Aim of the Work The aim of this study was to describe the pattern of ultrasonographic thigh muscles involvement, and to correlate the US findings with motor functional status. Patients and Methods Functional motor assessment was the functional performance protocol (GSGC score) Gait (G), Climbing stairs (S), Gower's maneuver (G), and Arising from a chair (C). Sonographic assessment of quadriceps rectus femoris muscles. Results Twenty-four genetically confirmed ambulatory DMD children were enrolled in this cross- sectional study. Their mean age of 7.46 ± 1.82 (4.5–11 years). The Rt and Lt Quadriceps muscles positively correlated with the age. The Rt. and Lt. Quadriceps muscle assessment significantly related to the scores for gait, stairs, chair arising, GSGC total score, time to walk 10 m, Time to rise from the floor. Conclusion Ultrasonography could be used as a non-invasive method to assess progressive muscle hypertrophy in boys with Duchenne muscular dystrophy. Furthermore, Quadriceps muscle US correlates with the motor functions in ambulant DMD boys below the age of 12 years.

Association Between Myocardial Oxygenation and Fibrosis in Duchenne Muscular Dystrophy: Analysis by Rest Oxygenation-Sensitive Magnetic Resonance Imaging.

Myocardial hypoxia has been demonstrated in many cardiomyopathies and is related to development of myocardial fibrosis. However, myocardial hypoxia and its association with myocardial fibrosis are understudied in Duchenne muscular dystrophy (DMD)-associated cardiomyopathy. To evaluate myocardial hypoxia by oxygenation-sensitive (OS) cardiac magnetic resonance imaging, and further explore its association with fibrosis. Prospective. Ninety-one DMD boys (8.78 ± 2.32) and 30 healthy boys (9.07 ± 2.30). 3 T, Balanced steady-state free procession, Modified Look-Locker inversion recovery sequence and Single-shot phase-sensitive inversion recovery sequence. Cardiac MRI data, including left ventricular functional, segmental native T1, and oxygenation signal-intensity (SI) according to AHA 17-segment model, were acquired. Patients were divided into LGE+ and LGE- groups. In patients with LGE, all segments were further classified as positive or negative segments by segmentally presence/absence of LGE. Variables were compared using Student's t, Wilcoxon, Kruskal-Wallis test and one-way analysis of variance. Bivariate Pearson or Spearman correlation were calculated to determine association between oxygenation SI and native T1. Variables with P < 0.10 in the univariable analysis were included in multivariable model. Receiver operating characteristic analysis was used to assess the performance of OS in diagnosing myocardial hypoxia. The myocardial oxygenation SI of DMD was significantly decreased in all segments compared with normal controls, and more obvious in the LGE+ segments (0.46 ± 0.03 vs. 0.52 ± 0.03). For patients with and without LGE, myocardial oxygenation SI were significantly negatively correlated with native T1 in all segments (r = -0.23 to -0.42). The inferolateral oxygenation SI was a significant independent associator of LGE presence (adjusted OR = 0.900). Myocardial hypoxia evaluated by the OS-Cardiac-MRI indeed occurs in DMD and associate with myocardial fibrosis, which might be used as a biomarker in assessing myocardial damage in DMD. 1 TECHNICAL EFFICACY: Stage 1.

Different bone health progression patterns and early-stage risk marker in glucocorticoid-treated ambulatory Duchenne muscular dystrophy.

Most Duchenne muscular dystrophy (DMD) children suffer bone loss after long-term glucocorticoid (GC) exposure, which induces scoliosis and fragility fractures. To assess the BMD progression pattern and individual medical risk markers for these phenotypes in young ambulatory boys with DMD, and provide evidence-based suggestions for clinical management of bone health. A retrospective longitudinal cohort study of 153 boys with DMD in West China Second University Hospital (2016-2023) was performed. Group-based trajectory modeling was used to study the BMD progression pattern, and potential predictors were further analyzed by logistic regression and survival analysis. One hundred and fifty-three participants were included, 71 of which had more than 3 BMD records. Three BMD trajectories were identified. Baseline BMD and age-started GC and were independent predictors of trajectory attribution. The median survival time of the first observation of low BMD in GC-treated DMD boys was 5.32 (95% CI 4.05-6.59) years, and a significant difference was tested (P < 0.001) among the three trajectory groups. BMD may serve as a novel early indicating marker for monitoring bone fragility for DMD. We proposed a bone health risk stratification through BMD progression trajectory that allows us to adapt the osteoporosis warning sign in DMD from a fixed threshold approach to a more individualized strategy, where baseline BMD and age of glucocorticoid initiation can provide an earlier prediction of bone loss. Better management of primary BMD may be able to delay or avoid the onset of adverse bone health outcomes in the fifth year in children with DMD.

Patient reported outcome measure for upper limb in Duchenne muscular dystrophy: correlation with PUL2.0.

The increasing pressure to include non ambulant Duchenne muscular dystrophy (DMD) boys in clinical trials has highlighted the need for outcome measures that could address the impact of upper limb function on activities of daily living. The aim of the present study was to establish the correlation between the recently developed Patient Reported Outcome Measure for the upper limb (PROM UL) and the observer rated functional scale Performance of Upper Limb (PUL 2.0) in a large cohort of DMD boys and young adults. As part of a larger natural history study, non ambulant DMD patients were assessed using PUL2.0 and PROM UL. One hundred and twenty-five concurrent PUL 2.0 and PROM UL evaluations from 60 non ambulant DMD boys were taken into consideration. The total PROM UL scores showed a strong correlation with both PUL 2.0 total scores and with PUL 2.0 entry item score. The strong correlation between the two tools confirms the clinical meaningfulness of the PUL2.0 and that the PROM UL can help to detect the gradient of progression of upper limb involvement.

Microdystrophin Gene Addition Significantly Improves Muscle Functionality and Diaphragm Muscle Histopathology in a Fibrotic Mouse Model of Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a rare neuromuscular disease affecting 1:5000 newborn males. No cure is currently available, but gene addition therapy, based on the adeno-associated viral (AAV) vector-mediated delivery of microdystrophin transgenes, is currently being tested in clinical trials. The muscles of DMD boys present significant fibrotic and adipogenic tissue deposition at the time the treatment starts. The presence of fibrosis not only worsens the disease pathology, but also diminishes the efficacy of gene therapy treatments. To gain an understanding of the efficacy of AAV-based microdystrophin gene addition in a relevant, fibrotic animal model of DMD, we conducted a systemic study in juvenile D2.mdx mice using the single intravenous administration of an AAV8 system expressing a sequence-optimized murine microdystrophin, named MD1 (AAV8-MD1). We mainly focused our study on the diaphragm, a respiratory muscle that is crucial for DMD pathology and that has never been analyzed after treatment with AAV-microdystrophin in this mouse model. We provide strong evidence here that the delivery of AAV8-MD1 provides significant improvement in body-wide muscle function. This is associated with the protection of the hindlimb muscle from contraction-induced damage and the prevention of fibrosis deposition in the diaphragm muscle. Our work corroborates the observation that the administration of gene therapy in DMD is beneficial in preventing muscle fibrosis.

Neuro-Cardio-Autonomic Modulations in Children with Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a degenerative X-linked muscle disease. Death frequently results from complications in cardiopulmonary systems. Preclinical/early diagnosis of cardiac autonomic abnormalities may aid initiate cardioprotective therapy and enhance prognosis. A cross sectional, prospective study of 38 DMD boys compared with 37 age-matched healthy controls was conducted. Lead II electrocardiography and beat-to-beat blood pressure were recorded to assess heart rate variability (HRV), blood pressure variability (BPV), and baroreceptor sensitivity (BRS) in a standardized environment. Data were analysed and correlated with disease severity and genotype. In the DMD group, the median age at assessment was 8 years [IQR 7-9 years], the median age at disease onset was 3 years [IQR, 2-6 years], and the mean duration of illness was 4 years [IQR, 2.5-5]. DNA sequencing showed deletions in 34/38 (89.5 %) and duplications in 4/38 (10.5%) patients. The median heart rate in DMD children was significantly higher [101.19 (Range, 94.71-108.49)] /min compared to controls [81 (Range, 76.2-92.76)] /min (p < 0.05). All the assessed HRV and BPV parameters were significantly impaired in DMD cases except for the coefficient of variance of systolic blood pressure. Further, BRS parameters were also significantly reduced in DMD, excluding alpha-LF. A positive correlation was found between alpha HF with age at onset and duration of illness. This study demonstrates a distinct early impairment of neuro-cardio-autonomic regulation in DMD. Simple yet effective non-invasive techniques such as HRV, BPV, and BRS may help identify cardiac dysfunction in a pre-clinical state, paving the way for early cardio-protective therapies and limiting disease progression in DMD patients.

High-Speed T2 -Corrected Multiecho Magnetic Resonance Spectroscopy for Quantitatively Detecting Skeletal Muscle Fatty Infiltration and Predicting the Loss of Ambulation in Patients With Duchenne Muscular Dystrophy.

High-speed T2 -corrected multiecho MRS (HISTO-MRS) is emerging as a quantitative modality for detecting muscle fat infiltration (MFF). However, the predictive value of HISTO-MRS for the loss of ambulation (LoA) in Duchenne muscular dystrophy (DMD) is unknown. To determine the feasibility of HISTO-MRS for assessing MFF in DMD and further identify the predictive value of HISTO-MRS for the LoA. Prospective. A total of 134 DMD boys (9.20 ± 2.43 years old) and 21 healthy boys (9.25 ± 2.10 years old). A 3 T, fast spin echo T1 -weighted imaging (T1 WI), two-point-Dixon gradient echo sequence (2-pt-Dixon) and HISTO-MRS. Subjective T1 WI fat grades by three radiologists, ROI analysis for MFF on 2pt-Dixon (Dixon MFF) and MFF on HISTO-MRS (HISTO MFF) by two radiologists. Clinical motor function: North Star Ambulatory Assessment, 10-m run/walk time, Gowers maneuver, and time to four-stairs climb and descend. Spearman rank correlation was used to assess the relation of fat filtration assessments and motor ability. Bland-Altman plots was performed to determine the agreement of HISTO MFF and Dixon MFF. Receiver operating characteristic (ROC) curves were analyzed to determine the discriminating ability of above MRI modalities for ambulatory and nonambulatory DMD. Logistic regression was used to identify the predictor of LoA. Variables with P < 0.05 in univariate logistic regression analysis were entered into the multivariate logistic regression model. HISTO MFF was significantly correlated with Dixon MFF. Bland-Altman plots show good agreement of HISTO MFF and Dixon MFF. ROC curves indicated that HISTO MFF show similar discrimination of LoA for DMD with Dixon MFF but better value than T1WI fat grades. Logistic regression showed that HISTO MFF was an independent predictor for LoA. HISTO-MRS is a potential quantitative method for assessing fat infiltration and shows predictive value for LoA in DMD patients. Stage 5.

DUCHENNE MUSCULAR DYSTROPHY RESPIRATORY PROFILES FROM REAL-WORLD REGISTRY DATA: A RETROSPECTIVE LONGITUDINAL STUDY

DUCHENNE MUSCULAR DYSTROPHY RESPIRATORY PROFILES FROM REAL-WORLD REGISTRY DATA: A RETROSPECTIVE LONGITUDINAL STUDY

P.81 Nutritional status and bone health in pediatric patients with low skeletal muscle mass

Children with low skeletal muscle mass caused by neuromuscular disorders (NMDs) or cerebral palsy (CP) have altered body composition and many are wheelchair dependent. Feeding and swallowing issues are frequently reported, and they are at increased risk of malnutrition and nutrient deficiencies. Poor nutrition, physical inactivity or use of glucocorticoids also increase the risk of osteoporosis in the patient group. The aim of the study was to conduct a vitamin-, nutritional, and bone health screening in children with low skeletal muscle mass due to CP and NMDs followed in our clinic. In an observational study, a total of 66 patients < 18 years were included with: spinal muscular atrophy (11), Duchenne muscular dystrophy (DMD) (23), Merosin-deficient-muscular dystrophy (5), other myopathies (3), Charcot-Marie-Tooth neuropathy (2), and CP (22). The majority of participants were moderately or severely affected by their disease, 46/66 were wheelchair dependent. The vitamin-, nutrition and bone health were assessed by dual X-ray absorptiometry scan, blood samples (vitamins, minerals, hormones, lipids), anthropometric measurements, and a three-day diet registration. The prevalence of severe underweight (BMI z-score <-3) and underweight (BMI z-score <-2) were 13% (n=9) and 6% (n=4). Furthermore, 12% (n=8) were obese (BMI z-score > 3), and 15% (n=10) were overweight (BMI z-score 2-3). The majority of overweight patients had DMD (13/18). Decreased bone mineral density (BMD) was found in 29 patients (44%) (BMD z-score <-2). Moreover, vitamin D insufficiency (vitamin D <50 nmol/L) and deficiency (vitamin D <25 nmol/L) were found in 18% (N=12) and 4.5% (N=3), respectively. Otherwise, calcium, phosphate and parathyroid hormone were in the normal range in most of the patients. Total-cholesterol and LDL-cholesterol were elevated in 8 patients (n=12%). These findings suggest that children with low skeletal muscle mass should be systemically and thoroughly assessed for malnutrition and overweight, to offer early nutritional support. As DMD boys are regularly assessed for decreased BMD, these findings suggest a need for expanding the assessment of BMD and vitamins in other NMDs and CP patients.

P.63 Comparison of brain volume reduction in boys with Duchenne muscular dystrophy treated with different corticosteroid regimes

Recent studies show lower gray matter volumes and altered white matter networks in boys with Duchenne Muscular Dystrophy (DMD) compared with healthy controls, suggesting a lack of dystrophin impacts brain structures. However, the majority of boys with DMD are chronically treated with corticosteroids (CS), which are known to cross the blood-brain barrier and cause brain atrophy. Unraveling the impact of CS treatment on the brain of boys with DMD is key to understand brain involvement in this disease. This study compared two groups of DMD boys treated with a different CS regimen with 2 healthy control groups. 3D T1-weighted images were obtained on a 3T Philips system at two different sites. Scans from 20 DMD patients (13.0±3.1y) on a 10 days on/10 days off prednisolone schedule and 20 age-matched controls (13.2±1.8y) were obtained at the LUMC Leiden, the Netherlands. Additionally scans of 20 age-matched DMD patients (12.8±3.0y) on a daily deflazacort regime and 20 age-matched controls (13.1±3.2y) were acquired at the UZ Leuven, Belgium. All 80 scans were processed using FSL software to calculate intracranial (ICV), total brain (TBV), grey matter (GMV), white matter (WMV) and CSF volumes. In addition, volumes of the hippocampus, amygdala, thalamus, nucleus accumbens, caudate nucleus, globus pallidus and putamen were calculated. To control for intracranial volume differences, relative volumes were compared between controls and DMD per center using univariate analyses of variances in SPSS and considered significant at p<0.05. Both DMD groups showed a significant lower relative GMV, and higher relative CSF volume compared to their control groups. Interestingly, a significantly lower relative WMV (33.81% vs 35.45%, p=.002) and relative volume of the globus pallidus (0.25% vs 0.22%, p<.001) was found in the deflazacort group compared with their control group, but not in the prednisolone group. This study suggest that different CS regimes lead to different regional brain volume reductions in patients with DMD.

Language Development in Preschool Duchenne Muscular Dystrophy Boys.

Background: the present study aims to assess language in preschool-aged Duchenne muscular dystrophy (DMD) boys with normal cognitive quotients, and to establish whether language difficulties are related to attentional aspects or to the involvement of brain dystrophin isoforms. Methods: 20 children aged between 48 and 72 months were assessed with language and attention assessments for preschool children. Nine had a mutation upstream of exon 44, five between 44 and 51, four between 51 and 63, and two after exon 63. A control group comprising 20 age-matched boys with a speech language disorder and normal IQ were also used. Results: lexical and syntactic comprehension and denomination were normal in 90% of the boys with Duchenne, while the articulation and repetition of long words, and sentence repetition frequently showed abnormal results (80%). Abnormal results were also found in tests assessing selective and sustained auditory attention. Language difficulties were less frequent in patients with mutations not involving isoforms Dp140 and Dp71. The profile in Duchenne boys was different form the one observed in SLI with no cognitive impairment. Conclusion: The results of our observational cross-sectional study suggest that early language abilities are frequently abnormal in preschool Duchenne boys and should be assessed regardless of their global neurodevelopmental quotient.

Evaluating the Feasibility and Reliability of Remotely Delivering and Scoring the North Star Ambulatory Assessment in Ambulant Patients with Duchenne Muscular Dystrophy.

Objective: The North Star Ambulatory Assessment (NSAA) is a validated 17-item functional rating scale and widely used to assess motor function in boys with Duchenne muscular dystrophy (DMD). The SARS-CoV-2 pandemic and subsequent Government ‘lockdown’ resulted in no face-to-face clinic visits hence the motor abilities were not monitored. The aim was to investigate whether the NSAA was feasible and reliable by video assessment. Method: Ten ambulant DMD boys were selected from the electronic hospital records. Two physiotherapists scored the boys’ NSAA independently and the intraclass correlation coefficient was used to assess agreement. The video scores were compared to two previous NSAA in-clinic scores. Results: Mean scores (SD) for clinic visit one were 22.6 (4.19) and clinic visit two 21.8 (5.3). The two physiotherapists video mean scores were 20.6 (5.66) for physiotherapist 1 and 20.6 (6.53) for physiotherapist 2. The intraclass correlation coefficient was 0.98 (95% CI 0.93–1.00) for the total NSAA and 1.00 (95% CI 1.00 to 1.00) for the rise time. The mean decline in score from clinic visit one (−12 months) to video assessment was 2.0 (2.8SD). Conclusion: The results from the study suggest that video NSAA is partially feasible and reliable.

Determinants of epigenetic resistance to HDAC inhibitors in dystrophic fibro-adipogenic progenitors.

Pharmacological treatment of Duchenne muscular dystrophy (DMD) with histone deacetylase inhibitors (HDACi) is currently being tested in clinical trials; however, pre‐clinical studies indicated that the beneficial effects of HDACi are restricted to early stages of disease. We show that FAPs from late‐stage mdx mice exhibit aberrant HDAC activity and genome‐wide alterations of histone acetylation that are not fully reversed by HDACi. In particular, combinatorial H3K27 and/or H3K9/14 hypo‐acetylation at promoters of genes required for cell cycle activation and progression, as well as glycolysis, are associated with their downregulation in late‐stage mdx FAPs. These alterations could not be reversed by HDACi, due to a general resistance to HDACi‐induced H3K9/14 hyperacetylation. Conversely, H3K9/14 hyper‐acetylation at promoters of Senescence Associated Secretory Phenotype (SASP) genes is associated with their upregulation in late‐stage mdx FAPs; however, HDACi could reduce promoter acetylation and blunt SASP gene activation. These data reveal that during DMD progression FAPs develop disease‐associated features reminiscent of cellular senescence, through epigenetically distinct and pharmacologically dissociable events. They also indicate that HDACi might retain anti‐fibrotic effects at late stages of DMD.

Functional outcome measures in young, steroid-naïve boys with Duchenne muscular dystrophy

The purpose of this study was to quantitate motor performance in 196 genetically confirmed steroid-naïve boys with Duchenne muscular dystrophy (DMD), to evaluate the test-retest reliability of measures of motor performance in young DMD boys, and to assess correlations among the different functional outcomes including timed tests. Boys aged 4–7 years were recruited in the FOR-DMD study, a comparative effectiveness study of different steroid regimens in DMD. Eligible boys had to be able to rise from the floor independently and to perform pulmonary function testing consistently. The boys were evaluated with standardized assessments at the screening and baseline visits at 32 sites in 5 countries (US, UK, Canada, Italy, Germany). Assessments included timed rise from floor, timed 10 m walk/run, six-minute walk distance, North Star Ambulatory Assessment (NSAA) and forced vital capacity (FVC). Mean age at baseline was 5.9 years (range 4.1–8.1 years). Test-retest reliability was high for functional assessments, regardless of time lag between assessments (up to 90 days) and for the majority of age groups. Correlations were strong among the functional measures and timed tests, less so with FVC. Physiotherapy measures are reliable in a young, steroid-naïve population and rise from floor velocity appears to be a sensitive measure of strength in this population.

Investigating the role of dystrophin isoform deficiency in motor function in Duchenne muscular dystrophy.

BackgroundDuchenne muscular dystrophy (DMD) is caused by DMD mutations leading to dystrophin loss. Full‐length Dp427 is the primary dystrophin isoform expressed in muscle and is also expressed in the central nervous system (CNS). Two shorter isoforms, Dp140 and Dp71, are highly expressed in the CNS. While a role for Dp140 and Dp71 on DMD CNS comorbidities is well known, relationships between mutations expected to disrupt Dp140 and Dp71 and motor outcomes are not.MethodsFunctional outcome data from 387 DMD boys aged 4–15 years were subdivided by DMD mutation expected effects on dystrophin isoform expression; Group 1 (Dp427 absent, Dp140/Dp71 present, n = 201); Group 2 (Dp427/Dp140 absent, Dp71 present, n = 152); and Group 3 (Dp427/Dp140/Dp71 absent, n = 34). Relationships between isoform group and North Star ambulatory assessment (NSAA) scores, 10 m walk/run velocities and rise time velocities were explored using regression analysis.Western blot analysis was used to study Dp427, Dp140 and Dp71 production in myogenic cells (control and DMD human), control skeletal muscle, DMD skeletal muscle from the three isoform groups and cerebral cortex from mice (wild‐type and DMD models). Grip strength and rotarod running test were studied in wild‐type mice and DMD mouse models. DMD mouse models were mdx (Dp427 absent, Dp140/Dp71 present), mdx52 (Dp427/Dp140 absent, Dp71 present) and DMD‐null (lacking all isoforms).ResultsIn DMD boys, mean NSAA scores at 5 years of age were 6.1 points lower in Group 3 than Group 1 (P < 0.01) and 4.9 points lower in Group 3 than Group 2 (P = 0.05). Mean peak NSAA scores were 4.0 points lower in Group 3 than Group 1 (P < 0.01) and 1.6 points lower in Group 2 than Group 1 (P = 0.04).Mean four‐limb grip strength was 1.5 g/g lower in mdx52 than mdx mice (P = 0.003) and 1.5 g/g lower in DMD‐null than mdx mice (P = 0.002).Dp71 was produced in myogenic cells (control and DMD human) and skeletal muscle from humans in Groups 1 and 2 and mdx mice, but not skeletal muscle from human controls, myogenic cells and skeletal muscle from humans in Group 3 or skeletal muscle from wild‐type, mdx52 or DMD‐null mice.ConclusionsOur results highlight the importance of considering expected effects of DMD mutations on dystrophin isoform production when considering patterns of DMD motor impairment and the implications for clinical practice and clinical trials. Our results suggest a complex relationship between dystrophin isoforms expressed in the brain and DMD motor function.

Cessation of ambulation results in a dramatic loss of trabecular bone density in boys with Duchenne muscular dystrophy (DMD).

Glucocorticoids are currently used to improve muscle strength and prolong ambulation in boys with DMD although the effect on bone health is still unclear. The aim of this study was to compare bone strength in healthy children and boys with DMD and investigate the interaction between diminished muscle function, loss of ambulation and high dose oral steroids, over a two year time frame. Fifty children were studied, 14 healthy boys (HB), 13 boys with DMD who remained ambulant (DMD-RA) and 23 boys with DMD who lost ambulation (DMD-LA). All boys with DMD had taken oral glucocorticoids. Peripheral quantitative computed tomography was used to measure bone geometry, density, strength and muscle mass of the non-dominant tibia and radius. Measurements were made at baseline, 12 and 24months at the distal metaphysis and mid diaphysis sites. Differences between the three groups were evaluated using ANOVA and a repeated measures model. There were no significant differences in age between the groups: mean age was 9.4, 8.7 and 8.8years for HB, DMD-RA and DMD-LA, respectively. There was no significant difference in steroid exposure between the DMD groups. However, boys who lost ambulation had significantly lower muscle function at baseline (North Star Ambulatory Assessment DMD-RA 23.6 vs. DMD-LA 18.8; p<0.05). At baseline, healthy boys had significantly greater trabecular bone density at the distal radius /ulna (23%/27%) and distal tibia/fibula (30%/46%) than boys with DMD (p<0.05). They also had significantly larger diaphyseal tibiae/fibulae (74%/36%) and radii/ulnae (49%/31%) with thicker corticies and consequently greater bone strength. In contrast, boys with DMD had greater cortical density (4%). Over time, there were small significant differences in the rate of change of both muscle and bone parameters between healthy boys and boys with DMD. For both ambulant and non-ambulant boys with DMD the greatest changes in cortical bone were evident at the tibia. After two years boys with DMD had on average, 63% less bone strength than healthy boys. However, the most strikingly significant difference was in trabecular bone density for boys who became non-ambulant. By 2years non-ambulant DMD boys had 53% less trabecular bone density at distal tibia than their healthy age matched peers compared with boys who remained ambulant who had 27% less trabecular bone density. In conclusion, bone and muscle strength is reduced for all boys with DMD even while they remain ambulant. However, tibia trabecular bone density loss is significantly accelerated in DMD boys who lose independent ambulation compared to DMD boys who remain ambulant despite equivalent levels of corticosteroid exposure.

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

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. 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. 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. 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.

Effects of Chronic, Maximal Phosphorodiamidate Morpholino Oligomer (PMO) Dosing on Muscle Function and Dystrophin Restoration in a Mouse Model of Duchenne Muscular Dystrophy.

Phosphorodiamidate morpholino oligomer (PMO)-mediated exon skipping is currently used in clinical development to treat Duchenne muscular dystrophy (DMD), with four exon-skipping drugs achieving regulatory approval. Exon skipping elicits a truncated, but semi-functional dystrophin protein, similar to the truncated dystrophin expressed in patients with Becker Muscular dystrophy (BMD) where the disease phenotype is less severe than DMD. Despite promising results in both dystrophic animal models and DMD boys, restoration of dystrophin by exon skipping is highly variable, leading to contradictory functional outcomes in clinical trials. To develop optimal PMO dosing protocols that result in increased dystrophin and improved outcome measures in preclinical models of DMD. Tested effectiveness of multiple chronic, high dose PMO regimens using biochemical, histological, molecular, and imaging techniques in mdx mice. A chronic, monthly regimen of high dose PMO increased dystrophin rescue in mdx mice and improved specific force in the extensor digitorum longus (EDL) muscle. However, monthly high dose PMO administration still results in variable dystrophin expression localized throughout various muscles. High dose monthly PMO administration restores dystrophin expression and increases muscle force; however, the variability of dystrophin expression at both the inter-and intramuscular level remains. Additional strategies to optimize PMO uptake including increased dosing frequencies or combination treatments with other yet-to-be-defined therapies may be necessary to achieve uniform dystrophin restoration and increases in muscle function.

DMD/BMD - GENETICS: EP.116 Establishing clinical and genetic characteristics in young, glucocorticoid-naïve boys with Duchenne muscular dystrophy: the FOR DMD study

We describe the clinical characteristics and genetic profile of a large sample of young glucocorticoid-naïve boys with Duchenne muscular dystrophy (DMD). Screening and baseline data were collected for participants in the FOR-DMD study, an international, multi-centre, randomized, double-blind clinical trial comparing 3 commonly prescribed glucocorticoid regimens in untreated DMD boys with a confirmed genetic diagnosis of DMD between 4 and < 8 years of age. One hundred ninety-six boys were recruited in the study. The mean age at randomization was 5.9 (standard deviation, SD 1 year). The most frequent mutation type was out of frame deletions (130/193, 67.3%) of which 68.5% (89/130) were amenable to exon skipping. Mutations amenable to exon 51 skipping were the most frequent (n=25). Stop codon mutations were reported in 19/193 boys (10%). The mean age of parental concern was 29.8 months (SD 18.7); the mean age of genetic diagnosis was 50.3 months (SD 23.8). The mean ages at independent walking and talking in sentences were 17.1 (SD 4.2) and 29.0 (SD 10.7) months, respectively. Pre-steroid median height and weight were below the 50th percentiles regardless of age group. Boys with exon 8 skippable deletions performed better in time to walk/run 10 meters compared to boys carrying other out of frame deletions not amenable to skipping (4.8±0.7 vs 6.3±4 seconds, p 0.001). Boys with exon 53 skippable deletions showed a lower baseline performance in the 6-minute walk test compared to boys with other out of frame deletions not amenable to skipping (308.9±61 vs 342±46 metres, p 0.003). In conclusion, this study describes clinical, genetic, and anthropometric characteristics of a sample of young glucocorticoid-naïve boys with DMD. Some genotype-phenotype associations were identified. These findings characterise a baseline pre-steroid cohort and, with the longitudinal data to follow, will help to inform eligibility criteria and outcome measures for future clinical trials in DMD.

Right Ventricular Function and T1-Mapping in Boys With Duchenne Muscular Dystrophy.

Clinical management of boys with Duchenne muscular dystrophy (DMD) relies on in-depth understanding of cardiac involvement, but right ventricular (RV) structural and functional remodeling remains understudied. To evaluate several analysis methods and identify the most reliable one to measure RV pre- and postcontrast T1 (RV-T1) and to characterize myocardial remodeling in the RV of boys with DMD. Prospective. Boys with DMD (N=27) and age-/sex-matched healthy controls (N=17) from two sites. 3.0 T using balanced steady state free precession, motion-corrected phase sensitive inversion recovery and modified Look-Locker inversion recovery sequences. Biventricular mass (Mi), end-diastolic volume (EDVi) and ejection fraction (EF) assessment, tricuspid annular excursion (TAE), late gadolinium enhancement (LGE), pre- and postcontrast myocardial T1 maps. The RV-T1 reliability was assessed by three observers in four different RV regions of interest (ROI) using intraclass correlation (ICC). The Wilcoxon rank sum test was used to compare RV-T1 differences between DMD boys with negative LGE(-) or positive LGE(+) and healthy controls. Additionally, correlation of precontrast RV-T1 with functional measures was performed. A P-value <0.05 was considered statistically significant. A 1-pixel thick RV circumferential ROI proved most reliable (ICC > 0.91) for assessing RV-T1. Precontrast RV-T1 was significantly higher in boys with DMD compared to controls. Both LGE(-) and LGE(+) boys had significantly elevated precontrast RV-T1 compared to controls (1543 [1489-1597] msec and 1550 [1402-1699] msec vs. 1436 [1399-1473] msec, respectively). Compared to healthy controls, boys with DMD had preserved RVEF (51.8 [9.9]% vs. 54.2 [7.2]%, P=0.31) and significantly reduced RVMi (29.8 [9.7]g vs. 48.0 [15.7]g), RVEDVi (69.8 [29.7]mL/m2 vs. 89.1 [21.9]mL/m2 ), and TAE (22.0 [3.2]cm vs. 26.0 [4.7]cm). Significant correlations were found between precontrast RV-T1 and RVEF (β=-0.48%/msec) and between LV-T1 and LVEF (β=-0.51%/msec). Precontrast RV-T1 is elevated in boys with DMD compared to healthy controls and is negatively correlated with RVEF. 1 TECHNICAL EFFICACY: Stage 2.