Use of skeletal muscle MRI in diagnosis and monitoring disease progression in Duchenne muscular dystrophy

Patterns of decline in upper limb function of boys and men with DMD: an international survey

With increasing life expectancy, upper extremity (UE) function becomes more and more important in boys with Duchenne muscular dystrophy (DMD). Knowledge of UE function in these children is, however, limited. The aim of this study was to gain insight into the changing patterns of UE function during the course of DMD. A Web-based questionnaire on UE function, covering all domains of the International Classification of Functioning Disability and Health, was distributed worldwide. Primary domains of the questionnaire were: participant characteristics, UE pain and stiffness, UE activities, and social participation. Data were described per disease stage and analyzed using descriptive analysis. A total of 213 boys/men with DMD (1-35 years) were included in this study. UE pain, stiffness, and activity limitations increased with disease stage. UE activity limitations already occurred in the early ambulatory stage. Compared to the healthy population, social participation was restricted in DMD patients and about 70% of the respondents experienced UE limitations when performing social activities. Despite the existence of UE impairments, only 9% of the respondents used supportive aids. Functional capacities and activities of the UE are limited already in the early ambulatory stage of patients with DMD affecting their social participation. Therefore, clinicians should pay attention to UE limitations before DMD patients lose their capacity to walk. Effective and adequate aids as well as attention for pain and stiffness in the therapeutic management could help to reduce UE activity limitations and related restrictions in social participation.

Chemical shift-based MRI to measure fat fractions in dystrophic skeletal muscle

PURPOSE

The relationship between fat fractions (FFs) determined based on multiple TE, unipolar gradient echo images and (1) H magnetic resonance spectroscopy (MRS) was evaluated using different models for fat-water decomposition, signal-to-noise ratios, and excitation flip angles.

METHODS

A combination of single-voxel proton spectroscopy ((1) H-MRS) and gradient echo imaging was used to determine muscle FFs in both normal and dystrophic muscles. In order to cover a large range of FFs, the soleus and vastus lateralis muscles of 22 unaffected control subjects, 16 subjects with collagen VI deficiency (COL6), and 71 subjects with Duchenne muscular dystrophy (DMD) were studied. (1) H-MRS-based FF were corrected for the increased muscle (1) H2 O T1 and T2 values observed in dystrophic muscles.

RESULTS

Excellent agreement was found between coregistered FFs derived from gradient echo images fit to a multipeak model with noise bias correction and the relaxation-corrected (1) H-MRS FFs (y = 0.93x + 0.003; R(2)  = 0.96) across the full range of FFs. Relaxation-corrected (1) H-MRS FFs and imaging-based FFs were significantly elevated (P < 0.01) in the muscles of COL6 and DMD subjects.

CONCLUSION

FFs, T2 , and T1 were all sensitive to muscle involvement in dystrophic muscle. MRI offered an additional advantage over single-voxel spectroscopy in that the tissue heterogeneity in FFs could be readily determined.

Multimodal MRI and (31)P-MRS investigations of the ACTA1(Asp286Gly) mouse model of nemaline myopathy provide evidence of impaired in vivo muscle function, altered muscle structure and disturbed energy metabolism

Nemaline myopathy (NM), the most common non-dystrophic congenital disease of skeletal muscle, can be caused by mutations in the skeletal muscle α-actin gene (ACTA1) (~25% of all NM cases and up to 50% of severe forms of NM). Muscle function of the recently generated transgenic mouse model carrying the human Asp286Gly mutation in the ACTA1 gene (Tg(ACTA1)(Asp286Gly)) has been mainly investigated in vitro. Therefore, we aimed at providing a comprehensive picture of the in vivo hindlimb muscle function of Tg(ACTA1)(Asp286Gly) mice by combining strictly noninvasive investigations. Skeletal muscle anatomy (hindlimb muscles, intramuscular fat volumes) and microstructure were studied using multimodal magnetic resonance imaging (Dixon, T2, Diffusion Tensor Imaging [DTI]). Energy metabolism was studied using 31-phosphorus Magnetic Resonance Spectroscopy ((31)P-MRS). Skeletal muscle contractile performance was investigated while applying a force-frequency protocol (1-150 Hz) and a fatigue protocol (6 min-1.7 Hz). Tg(ACTA1)(Asp286Gly) mice showed a mild muscle weakness as illustrated by the reduction of both absolute (30%) and specific (15%) maximal force production. Dixon MRI did not show discernable fatty infiltration in Tg(ACTA1)(Asp286Gly) mice indicating that this mouse model does not reproduce human MRI findings. Increased T2 values were observed in Tg(ACTA1)(Asp286Gly) mice and might reflect the occurrence of muscle degeneration/regeneration process. Interestingly, T2 values were linearly related to muscle weakness. DTI experiments indicated lower λ2 and λ3 values in Tg(ACTA1)(Asp286Gly) mice, which might be associated to muscle atrophy and/or the presence of histological anomalies. Finally (31)P-MRS investigations illustrated an increased anaerobic energy cost of contraction in Tg(ACTA1)(Asp286Gly) mice, which might be ascribed to contractile and non-contractile processes. Overall, we provide a unique set of information about the anatomic, metabolic and functional consequences of the Asp286Gly mutation that might be considered as relevant biomarkers for monitoring the severity and/or the progression of NM and for assessing the efficacy of potential therapeutic interventions.

Muscular dystrophies

Muscular dystrophies are a heterogeneous group of inherited disorders that share similar clinical features and dystrophic changes on muscle biopsy. An improved understanding of their molecular bases has led to more accurate definitions of the clinical features associated with known subtypes. Knowledge of disease-specific complications, implementation of anticipatory care, and medical advances have changed the standard of care, with an overall improvement in the clinical course, survival, and quality of life of affected people. A better understanding of the mechanisms underlying the molecular pathogenesis of several disorders and the availability of preclinical models are leading to several new experimental approaches, some of which are already in clinical trials. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, and therapeutic developments.

Gene therapy for Duchenne muscular dystrophy

PURPOSE OF REVIEW

Duchenne muscular dystrophy is a severe neuromuscular disorder for which there is currently no cure. Years of research have come to fruition during the past 18 months with publications on clinical trials for several gene therapy approaches for Duchenne muscular dystrophy. This review covers the present status of these approaches.

RECENT FINDINGS

The exon skipping approach is most advanced in the process of clinical application. Encouraging results have been obtained in two systemic clinical trials and further optimization has increased delivery to the heart in animal models. Limitations of the approach are the mutation-specificity and the anticipated requirement for lifelong treatment. Gene therapy by means of gene transfer holds the promise of more long-lasting effects. Results of a first, early-stage gene therapy trial, using viral vectors to deliver a minidystrophin gene, were reported. Animal studies suggest that it may be possible to overcome the main challenges currently facing gene therapy (immunogenicity of the vector and systemic body-wide delivery).

SUMMARY

Significant steps have been made in the development of gene therapy approaches for Duchenne muscular dystrophy. These approaches aim to slow down disease progression, requiring robust outcome measures to assess efficacy.

Clinical approach to the diagnostic evaluation of hereditary and acquired neuromuscular diseases

For diagnostic evaluation of a neuromuscular disease, the clinician must be able to obtain a relevant patient and family history and perform focused general, musculoskeletal, neurologic, and functional physical examinations to direct further diagnostic evaluations. Laboratory studies for hereditary neuromuscular diseases include the relevant molecular genetic studies. The electromyogram and nerve-conduction studies remain an extension of the physical examination, and help to guide further diagnostic studies such as molecular genetics and muscle and nerve biopsies. All diagnostic information needs are to be interpreted within the context of relevant historical information, family history, physical examination, laboratory data, electrophysiology, pathology, and molecular genetics.