Cognition of the mothers of patients with Duchenne muscular dystrophy

Quantitative ultrasonography reveals skeletal muscle abnormalities in carriers of DMD pathogenic variants

INTRODUCTION/AIMS

Carriers of DMD pathogenic variants may become symptomatic and develop muscle-related manifestations. Despite that, few studies have attempted to characterize changes in the muscles of these carriers using imaging tools, particularly muscle ultrasound (MUS). The aim of this study was to compare lower limb MUS findings in carriers of DMD pathogenic variants (cDMD) vs healthy controls.

METHODS

Twenty-eight women (15 cDMD and 13 controls) underwent clinical evaluation and MUS. We collected information about muscle-related symptoms and assessed muscle strength. MUS was performed by a single physician (blind to the genetic status of subjects). The following muscles were assessed: rectus femoris, sartorius, tibialis anterior, and medial gastrocnemius. For each site, we computed data on muscle thickness, cross-sectional area, sound attenuation index, and elastography. Between-group comparisons were assessed using nonparametric tests and p-values <.05 were deemed significant.

RESULTS

None of the subjects had objective muscle weakness, but exercise intolerance/fatigue was reported by four cDMDs and only one control. Regarding MUS, sound attenuation indices were significantly higher among carriers for all muscles tested. Longitudinal and axial deep echo intensities for the rectus femoris and tibialis anterior were also higher in the cDMD group compared with controls. No significant between-group differences were noted for elastography values, muscle area, or mean echo intensities.

DISCUSSION

cDMD have skeletal muscle abnormalities that can be detected using quantitative MUS. Further studies are needed to determine whether such abnormalities are related to muscle symptoms in these patients.

The unconditioned fear response in vertebrates deficient in dystrophin

Dystrophin loss due to mutations in the Duchenne muscular dystrophy (DMD) gene is associated with a wide spectrum of neurocognitive comorbidities, including an aberrant unconditioned fear response to stressful/threat stimuli. Dystrophin-deficient animal models of DMD demonstrate enhanced stress reactivity that manifests as sustained periods of immobility. When the threat is repetitive or severe in nature, dystrophinopathy phenotypes can be exacerbated and even cause sudden death. Thus, it is apparent that enhanced sensitivity to stressful/threat stimuli in dystrophin-deficient vertebrates is a legitimate cause of concern for patients with DMD that could impact neurocognition and pathophysiology. This review discusses our current understanding of the mechanisms and consequences of the hypersensitive fear response in preclinical models of DMD and the potential challenges facing clinical translatability.

267th ENMC International workshop: psychological interventions for improving quality of life in slowly progressive neuromuscular disorders

This workshop aimed to develop recommendations for psychological interventions to support people living with slowly progressive neuromuscular disorders (NMD). The workshop comprised clinicians, researchers, people living with NMD and their relatives. First, participants considered the key psychological challenges presented by NMD and the impact of NMD on relationships and mental health. Later, several psychological approaches for enhancing well-being in NMD were described. The results of randomised controlled trials of Cognitive Behaviour Therapy and Acceptance and Commitment Therapy for improving fatigue, quality of life, and mood in adults with NMD were examined. Then the group considered ways to adapt therapies for cognitive impairments or neurodevelopmental differences that occur in some NMD, alongside ways to support children and adolescents with NMD and their family members. Based on the evidence from randomised controlled trials, carefully conducted observational studies, and the coherence of these data with the experience of those living with NMD, the group recommends that psychological interventions should be embedded in the routine clinical care offered to people living with NMD.

The unconditioned fear response in dystrophin-deficient mice is associated with adrenal and vascular function

Loss of function mutations in the gene encoding dystrophin elicits a hypersensitive fear response in mice and humans. In the dystrophin-deficient mdx mouse, this behaviour is partially protected by oestrogen, but the mechanistic basis for this protection is unknown. Here, we show that female mdx mice remain normotensive during restraint stress compared to a hypotensive and hypertensive response in male mdx and male/female wildtype mice, respectively. Partial dystrophin expression in female mdx mice (heterozygous) also elicited a hypertensive response. Ovariectomized (OVX) female mdx mice were used to explain the normotensive response to stress. OVX lowered skeletal muscle mass and lowered the adrenal mass and zona glomerulosa area (aldosterone synthesis) in female mdx mice. During a restraint stress, OVX dampened aldosterone synthesis and lowered the corticosterone:11-dehydrocorticosterone. All OVX-induced changes were restored with replacement of oestradiol, except that oestradiol lowered the zona fasciculata area of the adrenal gland, dampened corticosterone synthesis but increased cortisol synthesis. These data suggest that oestrogen partially attenuates the unconditioned fear response in mdx mice via adrenal and vascular function. It also suggests that partial dystrophin restoration in a dystrophin-deficient vertebrate is an effective approach to develop an appropriate hypertensive response to stress.

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.

Sensitivity to behavioral stress impacts disease pathogenesis in dystrophin-deficient mice

Mutation to the gene encoding dystrophin can cause Duchenne muscular dystrophy (DMD) and increase the sensitivity to stress in vertebrate species, including the mdx mouse model of DMD. Behavioral stressors can exacerbate some dystrophinopathy phenotypes of mdx skeletal muscle and cause hypotension-induced death. However, we have discovered that a subpopulation of mdx mice present with a wildtype-like response to mild (forced downhill treadmill exercise) and moderate (scruff restraint) behavioral stressors. These "stress-resistant" mdx mice are more physically active, capable of super-activating the hypothalamic-pituitary-adrenal and renin-angiotensin-aldosterone pathways following behavioral stress and they express greater levels of mineralocorticoid and glucocorticoid receptors in striated muscle relative to "stress-sensitive" mdx mice. Stress-resistant mdx mice also presented with a less severe striated muscle histopathology and greater exercise and skeletal muscle oxidative capacity at rest. Most interestingly, female mdx mice were more physically active following behavioral stressors compared to male mdx mice; a response abolished after ovariectomy and rescued with estradiol. We demonstrate that the response to behavioral stress greatly impacts disease severity in mdx mice suggesting the management of stress in patients with DMD be considered as a therapeutic approach to ameliorate disease progression.