Lack of functional benefit with glutamine versus placebo in Duchenne muscular dystrophy: a randomized crossover trial

Navigating the uncommon: challenges in applying evidence-based medicine to rare diseases and the prospects of artificial intelligence solutions

The study of rare diseases has long been an area of challenge for medical researchers, with agonizingly slow movement towards improved understanding of pathophysiology and treatments compared with more common illnesses. The push towards evidence-based medicine (EBM), which prioritizes certain types of evidence over others, poses a particular issue when mapped onto rare diseases, which may not be feasibly investigated using the methodologies endorsed by EBM, due to a number of constraints. While other trial designs have been suggested to overcome these limitations (with varying success), perhaps the most recent and enthusiastically adopted is the application of artificial intelligence to rare disease data. This paper critically examines the pitfalls of EBM (and its trial design offshoots) as it pertains to rare diseases, exploring the current landscape of AI as a potential solution to these challenges. This discussion is also taken a step further, providing philosophical commentary on the weaknesses and dangers of AI algorithms applied to rare disease research. While not proposing a singular solution, this article does provide a thoughtful reminder that no 'one-size-fits-all' approach exists in the complex world of rare diseases. We must balance cautious optimism with critical evaluation of new research paradigms and technology, while at the same time not neglecting the ever-important aspect of patient values and preferences, which may be challenging to incorporate into computer-driven models.

What Nutraceuticals Can Do for Duchenne Muscular Dystrophy: Lessons Learned from Amino Acid Supplementation in Mouse Models

Duchenne muscular dystrophy (DMD), the severest form of muscular dystrophy, is characterized by progressive muscle weakness with fatal outcomes most often before the fourth decade of life. Despite the recent addition of molecular treatments, DMD remains a disease without a cure, and the need persists for the development of supportive therapies aiming to help improve patients' quality of life. This review focuses on the therapeutical potential of amino acid and derivative supplements, summarizing results obtained in preclinical studies in murine disease models. Several promising compounds have emerged, with L-arginine, N-acetylcysteine, and taurine featuring among the most intensively investigated. Their beneficial effects include reduced inflammatory, oxidative, fibrotic, and necrotic damage to skeletal muscle tissues. Improvement of muscle strength and endurance have been reported; however, mild side effects have also surfaced. More explorative, placebo-controlled and long-term clinical trials would need to be conducted in order to identify amino acid formulae that are safe and of true benefit to DMD patients.

Human Dystrophin Dp71ab Enhances the Proliferation of Myoblasts Across Species But Not Human Nonmyoblast Cells

Dystrophin Dp71 is an isoform produced from the Dp71 promoter in intron 62 of the DMD gene, mutations in which cause Duchenne muscular dystrophy. Dp71 is involved in various cellular processes and comprises more than 10 isoforms produced by alternative splicing. Dp71ab, in which both exons 71 and 78 are deleted, has a hydrophobic C-terminus that is hydrophilic in Dp71. Therefore, Dp71ab is believed to have different roles from Dp71. Previously, we reported that Dp71ab enhanced the proliferation of human myoblasts. Here, we further characterized Dp71ab, focusing on the activation of cell proliferation. Dp71ab increased the proliferation of immortalized human myoblasts in a dose-dependent manner. In contrast, Dp71 suppressed proliferation in a dose-dependent manner. Consistent with these opposite effects, eGFP-tagged Dp71ab and mCherry-tagged Dp71 showed different cellular distributions, with Dp71ab mostly in the nucleus. Notably, human Dp71ab enhanced the proliferation of rat and mouse myoblasts. Despite these findings, human Dp71ab did not enhance the proliferation of human nonmyoblast cells, including rhabdomyosarcoma cells. We concluded that Dp71ab is a myoblast-specific proliferation enhancer. In further studies, Dp71ab will be employed for the expansion of myoblasts in clinical settings.

Development of clinical practice guidelines for allied health and nursing assessment and management of Duchenne muscular dystrophy

PURPOSE

To provide evidence-based guidance specific to allied health and nursing practice for the assessment and management of individuals with Duchenne muscular dystrophy (DMD).

MATERIALS AND METHODS

Thirteen key focus areas were identified in consultation with health professionals and consumer advocacy groups. A series of systematic literature reviews were conducted to identify assessment and management strategies for each key focus area. A consensus process using modified Delphi methodology, including an Australia-New Zealand expert consensus meeting, was conducted. Recommendations underwent consultative review with key groups before being finalised and prepared for dissemination.

RESULTS

This clinical practice guideline (CPG) generated 19 evidence-based recommendations, 117 consensus-based recommendations and five research recommendations across the 13 focus areas to inform allied health assessment and management of individuals with DMD.

CONCLUSIONS

The resulting recommendations can be used in conjunction with existing medical CPGs to improve, standardise and advocate for allied health and rehabilitation care in DMD. The process used here may be useful for the development of CPGs in other rare diseases.Implications for rehabilitationImplementation-ready evidence-based statements to guide clinical care of individuals with DMD are provided with the potential to improve participation, function in the community and quality of life.A model for developing best practice statements for other rare neurological diseases is described.Allied health and nursing health professionals should focus research efforts to generate quality evidence to support rehabilitation practice.

Safety issues and harmful pharmacological interactions of nutritional supplements in Duchenne muscular dystrophy: considerations for Standard of Care and emerging virus outbreaks

At the moment, little treatment options are available for Duchenne muscular dystrophy (DMD). The absence of the dystrophin protein leads to a complex cascade of pathogenic events in myofibres, including chronic inflammation and oxidative stress as well as altered metabolism. The attention towards dietary supplements in DMD is rapidly increasing, with the aim to counteract pathology-related alteration in nutrient intake, the consequences of catabolic distress or to enhance the immunological response of patients as nowadays for the COVID-19 pandemic emergency. By definition, supplements do not exert therapeutic actions, although a great confusion may arise in daily life by the improper distinction between supplements and therapeutic compounds. For most supplements, little research has been done and little evidence is available concerning their effects in DMD as well as their preventing actions against infections. Often these are not prescribed by clinicians and patients/caregivers do not discuss the use with their clinical team. Then, little is known about the real extent of supplement use in DMD patients. It is mistakenly assumed that, since compounds are of natural origin, if a supplement is not effective, it will also do no harm. However, supplements can have serious side effects and also have harmful interactions, in terms of reducing efficacy or leading to toxicity, with other therapies. It is therefore pivotal to shed light on this unclear scenario for the sake of patients. This review discusses the supplements mostly used by DMD patients, focusing on their potential toxicity, due to a variety of mechanisms including pharmacodynamic or pharmacokinetic interactions and contaminations, as well as on reports of adverse events. This overview underlines the need for caution in uncontrolled use of dietary supplements in fragile populations such as DMD patients. A culture of appropriate use has to be implemented between clinicians and patients' groups.

Progressive Skeletal Muscle Atrophy in Muscular Dystrophies: A Role for Toll-like Receptor-Signaling in Disease Pathogenesis

Muscle atrophy is an active process controlled by specific transcriptional programs, in which muscle mass is lost by increased protein degradation and/or decreased protein synthesis. This review explores the involvement of Toll-like receptors (TLRs) in the muscle atrophy as it is observed in muscular dystrophies, disorders characterized by successive bouts of muscle fiber degeneration and regeneration in an attempt to repair contraction-induced damage. TLRs are defense receptors that detect infection and recognize self-molecules released from damaged cells. In muscular dystrophies, these receptors become over-active, and are firmly involved in the sustained chronic inflammation exhibited by the muscle tissue, via their induction of pro-inflammatory cytokine expression. Taming the exaggerated activation of TLR2/4 and TLR7/8/9, and their downstream effectors in particular, comes forward as a therapeutic strategy with potential to slow down disease progression.

A modified diet does not ameliorate muscle pathology in a mouse model for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by a lack of dystrophin protein. Next to direct effects on the muscles, this has also metabolic consequences. The influence of nutrition on disease progression becomes more and more recognized. Protein intake by DMD patients may be insufficient to meet the increased demand of the constantly regenerating muscle fibers. This led to the hypothesis that improving protein uptake by the muscles could have therapeutic effects. The present study examined the effects of a modified diet, which composition might stimulate muscle growth, on disease pathology in the D2-mdx mouse model. D2-mdx males were fed with either a control diet or modified diet, containing high amounts of branched-chain amino acids, vitamin D3 and ursolic acid, for six weeks. Our study indicates that the modified diet could not ameliorate the muscle pathology. No effects on bodyweight or weight of individual muscles were observed. Neither did the diet affect severity of fibrosis or calcification of the muscles.

Skeletal Muscle Metabolism in Duchenne and Becker Muscular Dystrophy-Implications for Therapies

The interactions between nutrition and metabolism and skeletal muscle have long been known. Muscle is the major metabolic organ—it consumes more calories than other organs—and therefore, there is a clear need to discuss these interactions and provide some direction for future research areas regarding muscle pathologies. In addition, new experiments and manuscripts continually reveal additional highly intricate, reciprocal interactions between metabolism and muscle. These reciprocal interactions include exercise, age, sex, diet, and pathologies including atrophy, hypoxia, obesity, diabetes, and muscle myopathies. Central to this review are the metabolic changes that occur in the skeletal muscle cells of muscular dystrophy patients and mouse models. Many of these metabolic changes are pathogenic (inappropriate body mass changes, mitochondrial dysfunction, reduced adenosine triphosphate (ATP) levels, and increased Ca²⁺) and others are compensatory (increased phosphorylated AMP activated protein kinase (pAMPK), increased slow fiber numbers, and increased utrophin). Therefore, reversing or enhancing these changes with therapies will aid the patients. The multiple therapeutic targets to reverse or enhance the metabolic pathways will be discussed. Among the therapeutic targets are increasing pAMPK, utrophin, mitochondrial number and slow fiber characteristics, and inhibiting reactive oxygen species. Because new data reveals many additional intricate levels of interactions, new questions are rapidly arising. How does muscular dystrophy alter metabolism, and are the changes compensatory or pathogenic? How does metabolism affect muscular dystrophy? Of course, the most profound question is whether clinicians can therapeutically target nutrition and metabolism for muscular dystrophy patient benefit? Obtaining the answers to these questions will greatly aid patients with muscular dystrophy.

Are mice good models for human neuromuscular disease? Comparing muscle excursions in walking between mice and humans

Background

The mouse is one of the most widely used animal models to study neuromuscular diseases and test new therapeutic strategies. However, findings from successful pre-clinical studies using mouse models frequently fail to translate to humans due to various factors. Differences in muscle function between the two species could be crucial but often have been overlooked. The purpose of this study was to evaluate and compare muscle excursions in walking between mice and humans.

Methods

Recently published musculoskeletal models of the mouse hindlimb and human lower limb were used to simulate muscle-tendon dynamics during mouse and human walking, a key daily activity. Muscle fiber length changes (fiber excursions) of 25 muscle homologs in the two species were calculated from these simulations and then compared. To understand potential causes of differences in fiber excursions in walking, joint excursions and muscle moment arms were also compared across one gait cycle.

Results

Most muscles (19 out of 25 muscles) of the mouse hindlimb had much smaller fiber excursions as compared to human lower limb muscles during walking. For these muscles, fiber excursions in mice were only 48 ± 19% of those in humans. The differences in fiber excursion between the two species were primarily due to the reduced joint excursions and smaller muscle moment arms in mice as compared to humans.

Conclusions

Since progressive neuromuscular diseases, such as Duchenne muscular dystrophy, are known to be accelerated by damage accumulated from active muscle lengthening, these results suggest that biomechanical differences in muscle function during walking between mice and humans may impede the translations of knowledge gained from mouse models to humans. This knowledge would add a fresh perspective on how pre-clinical studies on mice might be better designed to improve translation to human clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0143-9) contains supplementary material, which is available to authorized users.

Reliability, validity, and norms of the 2-min walk test in children with and without neuromuscular disorders aged 6-12

PURPOSE

The 2-min walk test may be more appropriate functional exercise test for young children. This study aimed to examine the 2-min walk test's reliability; validity; and minimal clinically important difference; and to establish norms for children aged 6-12.

METHODS

Sixty-one healthy children were recruited to examine the 2-min walk test's reliability. Forty-six children with neuromuscular disorders (63% cerebral palsy) were recruited to test the validity. The normative study involved 716 healthy children without neuromuscular disorders (male = 51%, female = 49%). They walked at a self-selected speed for 2 min along a smooth, flat path 15 m in length.

RESULTS

The mean distance covered in the 2-min walk test was 152.8 m (SD =27.5). No significant difference was found in the children's test-retest results (p > 0.05). The intra- and inter-rater reliability were high (all intra-class correlation coefficients >0.8). All children, except one with neuromuscular disorders, completed the 2-min walk test, of which the minimal clinically important difference at 95% confidence interval was 23.2 m for the entire group, 15.7 m for children walking with aids, and 16.6 m for those walking independently.

CONCLUSIONS

The 2-min walk test is a feasible, reliable, and valid exercise test for children with and without neuromuscular disorders aged 6-12. The first normative references and minimal clinically important difference for children with neuromuscular disorders were established for children of this age group. Implications for rehabilitation The 2-min walk test is a feasible, safe, reliable, and valid time-based walk test for children aged 6-12 years. Normative references have been established for healthy children aged 6-12 years. Minimal clinically important difference at 95% confidence interval were calculated for children with neuromuscular disorders who walked without aids (i.e., independent and stand-by supervision) and those who walked with aids equal to 16.6 and 15.7 m, respectively. Distance covered by the healthy children in the 2 min did not correlate with age, gender, height, and weight of the children.

Alternative designs for clinical trials in rare diseases

Evidence-based medicine requires strong scientific evidence upon which to base treatment. In rare diseases, study populations are often small, and thus this evidence is difficult to accrue. Investigators, though, should be creative and develop a flexible toolkit of methods to deal with the problems inherent in the study of rare disease. This narrative review presents alternative clinical trial designs for studying treatments of rare diseases, including cross-over and n-of-1 trials, randomized placebo-phase design, enriched enrollment, randomized withdrawal design, and classes of adaptive designs. Examples of applications of these designs are presented along with their advantages and disadvantages. Additional analytical considerations such as Bayesian analysis, internal pilots, and use of biomarkers as surrogate outcomes are further discussed. A framework for selecting appropriate clinical trial design is proposed to guide investigators in the process of selecting alternative designs for rare diseases. © 2016 Wiley Periodicals, Inc.

Metabogenic and Nutriceutical Approaches to Address Energy Dysregulation and Skeletal Muscle Wasting in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal genetic muscle wasting disease with no current cure. A prominent, yet poorly treated feature of dystrophic muscle is the dysregulation of energy homeostasis which may be associated with intrinsic defects in key energy systems and promote muscle wasting. As such, supplementative nutriceuticals that target and augment the bioenergetical expansion of the metabolic pathways involved in cellular energy production have been widely investigated for their therapeutic efficacy in the treatment of DMD. We describe the metabolic nuances of dystrophin-deficient skeletal muscle and review the potential of various metabogenic and nutriceutical compounds to ameliorate the pathological and clinical progression of the disease.

What has the mdx mouse model of Duchenne muscular dystrophy contributed to our understanding of this disease?

Duchenne muscular dystrophy (DMD) is a fatal X-chromosome linked recessive disorder caused by the truncation or deletion of the dystrophin gene. The most widely used animal model of this disease is the dystrophin-deficient mdx mouse which was first discovered 30 years ago. Despite its extensive use in DMD research, no effective treatment has yet been developed for this devastating disease. This review explores what we have learned from this mouse model regarding the pathophysiology of DMD and asks if it has a future in providing a better more thorough understanding of this disease or if it will bring us any closer to improving the outlook for DMD patients.

Autophagy is Impaired in the Tibialis Anterior of Dystrophin Null Mice

Background Duchenne muscular dystrophy is a lethal, progressive, muscle-wasting disease caused by mutations in the DMD gene. Structural remodelling processes are responsible for muscle atrophy and replacement of myofibers by fibrotic and adipose tissues. Molecular interventions modulating catabolic pathways, such as the ubiquitin-proteasome and the autophagy-lysosome systems, are under development for Duchenne and other muscular dystrophies. The Akt signaling cascade is one of the main pathways involved in protein synthesis and autophagy repression and is known to be up-regulated in dystrophin null mdx mice. Results We report that autophagy is triggered by fasting in the tibialis anterior muscle of control mice but not in mdx mice. Mdx mice show persistent Akt activation upon fasting and failure to increase the expression of FoxO3 regulated autophagy and atrophy genes, such as Bnip3 and Atrogin1. We also provide evidence that autophagy is differentially regulated in mdx tibialis anterior and diaphragm muscles. Conclusions Our data support the concept that autophagy is impaired in the tibialis anterior muscle of mdx mice and that the regulation of autophagy is muscle type dependent. Differences between muscle groups should be considered during the pre-clinical development of therapeutic strategies addressing muscle metabolism.

Recent advances in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), an allelic X-linked progressive muscle-wasting disease, is one of the most common single-gene disorders in the developed world. Despite knowledge of the underlying genetic causation and resultant pathophysiology from lack of dystrophin protein at the muscle sarcolemma, clinical intervention is currently restricted to symptom management. In recent years, however, unprecedented advances in strategies devised to correct the primary defect through gene- and cell-based therapeutics hold particular promise for treating dystrophic muscle. Conventional gene replacement and endogenous modification strategies have greatly benefited from continued improvements in encapsidation capacity, transduction efficiency, and systemic delivery. In particular, RNA-based modifying approaches such as exon skipping enable expression of a shorter but functional dystrophin protein and rapid progress toward clinical application. Emerging combined gene- and cell-therapy strategies also illustrate particular promise in enabling ex vivo genetic correction and autologous transplantation to circumvent a number of immune challenges. These approaches are complemented by a vast array of pharmacological approaches, in particular the successful identification of molecules that enable functional replacement or ameliorate secondary DMD pathology. Animal models have been instrumental in providing proof of principle for many of these strategies, leading to several recent trials that have investigated their efficacy in DMD patients. Although none has reached the point of clinical use, rapid improvements in experimental technology and design draw this goal ever closer. Here, we review therapeutic approaches to DMD, with particular emphasis on recent progress in strategic development, preclinical evaluation and establishment of clinical efficacy. Further, we discuss the numerous challenges faced and synergistic approaches being devised to combat dystrophic pathology effectively.

Effect of glutamine on glucose metabolism in children with Duchenne muscular dystrophy

BACKGROUND & AIMS

Glutamine is a potent gluconeogenic precursor and stimulates insulin secretion. Glutamine's effect on glucose metabolism in Duchenne muscular dystrophy (DMD) has never been studied. To determine plasma glucose and insulin concentrations measured during and after glutamine administration in DMD boys. We hypothesized that glutamine can modulate whole body glutamine-glucose metabolism in DMD, a genetically determined disease.

METHODS

As secondary endpoints of a randomized crossover trial in 30 prepubertal DMD boys, we measured fasting blood glucose, insulin and the Homeostasis Model Assessment (HOMA) index after daily oral glutamine (0.5 g kg(-1) d(-1)) for 4 months versus placebo. In a separate time series trial in 6 prepubertal DMD boys, we measured the same endpoints as well as plasma glutamine and whole body glucose turnover (Ra,glc) (primed continuous i.v. infusion of d-[6,6-(2)D]glucose), while participants received acute oral glutamine (0.5 g kg(-1) d(-1)) continuously for 5 h.

RESULTS

In the randomized trial, baseline measurements of HOMA correlated with age (r = 0,51, p = 0.007) and percent fat estimated by bioelectrical impedance analysis (BIA) (r = 0.39, p = 0.047). After 4 months glutamine supplementation, we observed no treatment or order effect on HOMA or insulin. During acute glutamine for 5 h (time series trial), plasma glutamine doubled and was associated with increased plasma insulin concentration (10.42 ± 2.54 vs 7.32 ± 1.86, p = 0.05) with no effect on plasma glucose, HOMA or Ra,glc.

CONCLUSIONS

Acute glutamine transiently stimulates insulin secretion in DMD boys, which could be mediated by plasma glutamine concentrations. Fasting insulin concentration and HOMA might provide quantifiable indices of disease progression.

Glutamine supplementation in sick children: is it beneficial?

The purpose of this review is to provide a critical appraisal of the literature on Glutamine (Gln) supplementation in various conditions or illnesses that affect children, from neonates to adolescents. First, a general overview of the proposed mechanisms for the beneficial effects of Gln is provided, and subsequently clinical studies are discussed. Despite safety, studies are conflicting, partly due to different effects of enteral and parenteral Gln supplementation. Further insufficient evidence is available on the benefits of Gln supplementation in pediatric patients. This includes premature infants, infants with gastrointestinal disease, children with Crohn's disease, short bowel syndrome, malnutrition/diarrhea, cancer, severe burns/trauma, Duchenne muscular dystrophy, sickle cell anemia, cystic fibrosis, and type 1 diabetes. Moreover, methodological issues have been noted in some studies. Further mechanistic data is needed along with large randomized controlled trials in select populations of sick children, who may eventually benefit from supplemental Gln.

Duchenne muscular dystrophy: Canadian paediatric neuromuscular physicians survey

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy in childhood.

METHOD

To assess the current care of paediatric DMD patients in Canada, a questionnaire was mailed to 17 physicians who were members of the Canadian paediatric neuromuscular group. Areas of enquiry included; 1) multidisciplinary team composition; 2) means of DMD diagnosis; 3) corticosteroid use; surveillance and management for: 4) orthopaedic, 5) respiratory and 6) cardiac complications and 7) health maintenance (nutrition & immunizations).

RESULTS

Completed surveys were returned by 14/17 (82%) of physicians. Twelve respondents followed DMD patients. All centres had multidisciplinary teams, including respirology (11/12), child neurology or physiatry (11), physiotherapy (9), occupational therapy (9) and orthopaedic surgery (7). Deflazacort 0.9 mg/kg/d was used at all centres, which was continued after loss of independent ambulation (11), along with routine calcium and vitamin D supplementation (10). Night splints were prescribed at all centres. Routine surveillance studies included pulmonary function testing (11), sleep studies (10), EKG/echocardiogram (10), bone density (DEXA) scans (10), spine radiography (9), and dietician referral (4).

CONCLUSION

Paediatric DMD patients are receiving relatively consistent care in multidisciplinary clinics across Canada, in accordance with recommended guidelines for DMD.

Assessing change in body composition in children with Duchenne muscular dystrophy: anthropometry and bioelectrical impedance analysis versus dual-energy X-ray absorptiometry

BACKGROUND & AIMS

To compare the ability of bioelectrical impedance analysis (BIA) and skinfold thickness (ST) measurements to estimate changes in body composition in Duchenne muscular dystrophy (DMD).

METHODS

A secondary analysis was performed on 26 ambulatory DMD boys aged 3-11 y selected for a randomised trial of glutamine supplementation. We assessed fat free mass (FFM) and percentage fat mass (%FM) by BIA (monofrequency (50kHz) unit), ST measurements and a criterion method, dual-energy X-ray absorptiometry (DXA), and repeated these measures 5 mo later at 3 outpatient clinical investigation centers in France.

RESULTS

When compared with DXA reference method, ST overestimated change in FFM (P<0.01), whereas BIA estimates did not differ from DXA. Concordance plots revealed that when compared with DXA, ST overestimated the increase in FFM (mean: 0.6 kg; 95% CI: 0.17 to 0.99) which led to an underestimation in %FM change (mean: -1.4%; 95% CI: -2.6 to -0.2), whereas BIA estimated change in FFM (mean: -0.05 kg; 95% CI: -0.39 to 0.29) and %FM (mean: 1.3%; 95% CI: -0.06 to 2.7) more accurately.

CONCLUSIONS

BIA method can be used to follow changes in nutritional status of ambulatory DMD children or to evaluate treatment efficacy.