Are Dp71 and Dp140 brain dystrophin isoforms related to cognitive impairment in Duchenne muscular dystrophy?

Identifying inversions with breakpoints in the Dystrophin gene through long-read sequencing: report of two cases

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is an X-linked disorder caused by mutations in the DMD gene, with large deletions being the most common type of mutation. Inversions involving the DMD gene are a less frequent cause of the disorder, largely because they often evade detection by standard diagnostic methods such as multiplex ligation probe amplification (MLPA) and whole exome sequencing (WES).

CASE PRESENTATION

Our research identified two intrachromosomal inversions involving the dystrophin gene in two unrelated families through Long-read sequencing (LRS). These variants were subsequently confirmed via Sanger sequencing. The first case involved a pericentric inversion extending from DMD intron 47 to Xq27.3. The second case featured a paracentric inversion between DMD intron 42 and Xp21.1, inherited from the mother. In both cases, simple repeat sequences (SRS) were present at the breakpoints of these inversions.

CONCLUSIONS

Our findings demonstrate that LRS is an effective tool for detecting atypical mutations. The identification of SRS at the breakpoints in DMD patients enhances our understanding of the mechanisms underlying structural variations, thereby facilitating the exploration of potential treatments.

Duchenne Muscular Dystrophy from Brain to Muscle: The Role of Brain Dystrophin Isoforms in Motor Functions

Brain function and its effect on motor performance in Duchenne muscular dystrophy (DMD) is an emerging concept. The present study explored how cumulative dystrophin isoform loss, age, and a corticosteroid treatment affect DMD motor outcomes. A total of 133 genetically confirmed DMD patients from Sri Lanka were divided into two groups based on whether their shorter dystrophin isoforms (Dp140, Dp116, and Dp71) were affected: Group 1, containing patients with Dp140, Dp116, and Dp71 affected (n = 98), and Group 2, containing unaffected patients (n = 35). A subset of 52 patients (Group 1, n = 38; Group 2, n = 14) was followed for up to three follow-ups performed in an average of 28-month intervals. The effect of the cumulative loss of shorter dystrophin isoforms on the natural history of DMD was analyzed. A total of 74/133 (56%) patients encountered developmental delays, with 66/74 (89%) being in Group 1 and 8/74 (11%) being in Group 2 (p < 0.001). Motor developmental delays were predominant. The hip and knee muscular strength, according to the Medical Research Council (MRC) scale and the North Star Ambulatory Assessment (NSAA) activities, "standing on one leg R", "standing on one leg L", and "walk", declined rapidly in Group 1 (p < 0.001 In the follow-up analysis, Group 1 patients became wheelchair-bound at a younger age than those of Group 2 (p = 0.004). DMD motor dysfunction is linked to DMD mutations that affect shorter dystrophin isoforms. When stratifying individuals for clinical trials, considering the DMD mutation site and its impact on a shorter dystrophin isoform is crucial.

NGS-based targeted sequencing identified six novel variants in patients with Duchenne/Becker muscular dystrophy from southwestern China

BACKGROUND

At present, Multiplex ligation-dependent probe amplification (MLPA) and exome sequencing are common gene detection methods in patients with Duchenne muscular dystrophy or Becker muscular dystrophy (DMD/BMD), but they can not cover the whole-genome sequence of the DMD gene. In this study, the whole genome capture of the DMD gene and next-generation sequencing (NGS) technology were used to detect the patients with DMD/BMD in Southwest China, to clarify the application value of this technology and further study the gene variant spectrum.

METHODS

From 2017 to 2020, 51 unrelated patients with DMD/BMD in southwestern China were clinically diagnosed at West China Second University Hospital of Sichuan University (Chengdu, China). The whole-genome of the DMD gene was captured from the peripheral blood of all patients, and next-generation sequencing was performed. Large copy number variants (CNVs) in the exon regions of the DMD gene were verified through MLPA, and small variations (such as single nucleotide variation and < 50 bp fragment insertions/deletions) were validated using Sanger sequencing.

RESULTS

Among the 51 patients, 49 (96.1% [49/51]) had pathogenic or likely pathogenic variants in the DMD gene. Among the 49 positive samples, 17 patients (34.7% [17/49]) had CNVs in the exon regions and 32 patients (65.3% [32/49]) had small variations. A total of six novel variants were identified: c.10916_10917del, c.1790T>A, c.1842del, c.5015del, c.5791_5792insCA, and exons 38-50 duplication.

CONCLUSIONS

Pathogenic or likely pathogenic variants of the DMD gene were detected in 49 patients (96.1% [49/51]), of which 6 variants (12.2% [6/49]) had not been previously reported. This study confirmed the value of NGS-based targeted sequencing for the DMD gene expanding the spectrum of variants in DMD, which may provide effective genetic counseling and prenatal diagnosis for families.

Startle responses in Duchenne muscular dystrophy: a novel biomarker of brain dystrophin deficiency

Duchenne muscular dystrophy (DMD) is characterized by loss of dystrophin in muscle, however patients also have variable degree of intellectual disability and neurobehavioural co-morbidities. In contrast to muscle, in which a single full-length dystrophin isoform (Dp427) is produced, multiple isoforms are produced in the brain, and their deficiency accounts for the variability of CNS manifestations, with increased risk of comorbidities in patients carrying mutations affecting the 3' end of the gene, which disrupt expression of shorter Dp140 and Dp71 isoforms. A mouse model (mdx mouse) lacks Dp427 in muscle and CNS and exhibits exaggerated startle responses to threat, linked to the deficiency of dystrophin in limbic structures such as the amygdala, which normalize with postnatal brain dystrophin-restoration therapies. A pathological startle response is not a recognized feature of DMD, and its characterization has implications for improved clinical management and translational research. To investigate startle responses in DMD, we used a novel fear-conditioning task in an observational study of 56 males aged 7-12 years (31 affected boys, mean age 9.7 ± 1.8 years; 25 controls, mean age 9.6 ± 1.4 years). Trials of two neutral visual stimuli were presented to participants: one 'safe' cue presented alone; one 'threat' cue paired with an aversive noise to enable conditioning of physiological startle responses (skin conductance response and heart rate). Retention of conditioned physiological responses was subsequently tested by presenting both cues without the aversive noise in an 'Extinction' phase. Primary outcomes were the initial unconditioned skin conductance and change in heart rate responses to the aversive 'threat' and acquisition and retention of conditioned responses after conditioning. Secondary and exploratory outcomes were neuropsychological measures and genotype associations. The mean unconditioned skin conductance response was greater in the DMD group than controls [mean difference 3.0 µS (1.0, 5.1); P = 0.004], associated with a significant threat-induced bradycardia only in the patient group [mean difference -8.7 bpm (-16.9, -0.51); P = 0.04]. Participants with DMD found the task more aversive than controls, with increased early termination rates during the Extinction phase (26% of DMD group versus 0% of controls; P = 0.007). This study provides the first evidence that boys with DMD show similar increased unconditioned startle responses to threat to the mdx mouse, which in the mouse respond to brain dystrophin restoration. Our study provides new insights into the neurobiology underlying the complex neuropsychiatric co-morbidities in DMD and defines an objective measure of this CNS phenotype, which will be valuable for future CNS-targeted dystrophin-restoration studies.

Global prevalence of intellectual developmental disorder in dystrophinopathies: A systematic review and meta-analysis

AIM

To estimate the global prevalence of intellectual developmental disorder (IDD) and the IDD prevalence-genotype association in Becker muscular dystrophy (BMD) or Duchenne muscular dystrophy (DMD) according to the affected isoforms of the DMD gene: Dp427, Dp140, Dp71.

METHOD

Systematic searches in MEDLINE, Scopus, Web of Science, and the Cochrane Library were conducted from inception of each database to March 2022. Observational studies that determined the prevalence of IDD in the population with BMD or DMD were included. Meta-analyses of IDD prevalence and prevalence ratios of the IDD-genotype association were conducted.

RESULTS

Forty-nine studies were included. The prevalence of IDD in BMD was 8.0% (95% confidence interval 5.0-11.0), and in DMD it was 22.0% (18.0-27.0). Meta-analyses of IDD-genotype association showed a deleterious association between IDD and the number of isoforms affected in DMD, with a prevalence ratio = 0.43 (0.28-0.64) and 0.17 (0.09-0.34) for Dp140⁺ /Dp71⁺ versus Dp140^- /Dp71⁺ and Dp140⁺ /Dp71⁺ versus Dp140^- /Dp71^- comparisons respectively. However, in BMD, there was no association for Dp140⁺ /Dp71⁺ versus Dp140^- /Dp71⁺ .

INTERPRETATION

There is a high prevalence of IDD in BMD and DMD. Moreover, the number of isoforms affected is strongly and negatively associated with the prevalence of IDD in DMD.

Wechsler Scale Intelligence Testing in Males with Dystrophinopathies: A Review and Meta-Analysis

BACKGROUND

Intelligence scores in males with Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD) remain a major issue in clinical practice. We performed a literature review and meta-analysis to further delineate the intellectual functioning of dystrophinopathies.

METHOD

Published, peer-reviewed articles assessing intelligence, using Wechsler Scales, of males with DMD or BMD were searched from 1960 to 2022. Meta-analysis with random-effects models was conducted, assessing weighted, mean effect sizes of full-scale IQ (FSIQ) scores relative to normative data (Mean = 100, Standard Deviation = 15). Post hoc we analysed differences between performance and verbal intelligence scores.

RESULTS

43 studies were included, reporting data on 1472 males with dystrophinopathies; with FSIQ scores available for 1234 DMD (k = 32) and 101 BMD (k = 7). DMD males score, on average, one standard deviation below average (FSIQ = 84.76) and significantly lower than BMD (FSIQ = 92.11). Compared to a previous meta-analysis published in 2001, we find, on average, significantly higher FSIQ scores in DMD.

CONCLUSION

Males with Duchenne have, on average, significantly lower FSIQ scores than BMD males and the general population. Clinicians must consider lower intelligence in dystrophinopathies to ensure good clinical practice.

Associations Between Self-Reported Behavioral and Learning Concerns and DMD Isoforms in Duchenne Muscular Dystrophy

Background: Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder resulting from loss of dystrophin. In addition to its role in muscle, isoforms of dystrophin are expressed in different cell types of the brain, and DMD has been linked to language delays, behavioral abnormalities and learning disabilities. Objective: To determine whether disruption of specific DMD isoforms, age, corticosteroid use, ambulation status, or country are associated with behavioral and/or learning concerns in DMD. Methods: De-identified data were collected from the Duchenne Registry from 2007– 2019. Females, patients with BMD, and those without genetic testing reports were excluded from the cohort. For the genetic analysis, patients were divided into four subgroups based on the location of their mutation and the predicted isoforms affected. Bivariate analysis was conducted using chi-square for categorical variables. Two multivariate logistic regressions were used to assess independent associations with behavioral and learning concerns, respectively, and to estimate the effect size of each variable. Results: DMD mutations disrupting expression of Dp140 and Dp71 were associated with a higher likelihood of reported behavioral and learning concerns. Corticosteroid use, categorical age, and country were other factors associated with behavior and learning concerns. Conclusion: This data adds to our current understanding of DMD isoforms, their mutational consequence and impact on behavior and learning.

Age, corticosteroid treatment and site of mutations affect motor functional changes in young boys with Duchenne Muscular Dystrophy

The aim of this study was to establish the possible effect of age, corticosteroid treatment and brain dystrophin involvement on motor function in young boys affected by Duchenne Muscular Dystrophy who were assessed using the North Star Ambulatory Assessment between the age of 4 and 7 years. The study includes 951 North Star assessments from 226 patients. Patients were subdivided according to age, to the site of mutation and therefore to the involvement of different brain dystrophin isoforms and to corticosteroids duration. There was a difference in the maximum North Star score achieved among patients with different brain dystrophin isoforms (p = 0.007). Patients with the involvement of Dp427, Dp140 and Dp71, had lower maximum NSAA scores when compared to those with involvement of Dp427 and Dp140 or of Dp427 only. The difference in the age when the maximum score was achieved in the different subgroups did not reach statistical significance. Using a linear regression model on all assessments we found that each of the three variables, age, site of mutation and corticosteroid treatment had an influence on the NSAA values and their progression over time. A second analysis, looking at 12-month changes showed that within this time interval the magnitude of changes was related to corticosteroid treatment but not to site of mutation. Our findings suggest that each of the considered variables appear to play a role in the progression of North Star scores in patients between the age of 4 and 7 years and that these should be carefully considered in the trial design of boys in this age range.

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

BACKGROUND

Duchenne 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.

METHODS

Functional 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).

RESULTS

In 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.

CONCLUSIONS

Our 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.

Altered Gene Expression Profiles in Neural Stem Cells Derived from Duchenne Muscular Dystrophy Patients with Intellectual Disability

Intellectual disability (ID) is a neurodevelopmental disorder defined by below-average intelligence (intelligence quotient of <70) accompanied by adaptive behavior deficits. Defects in the functions of neural stem cells during brain development are closely linked to the pathogenesis of ID. To understand the molecular etiology of ID, we examined neural stem cells from individuals with Duchenne muscular dystrophy (DMD), a genetic disorder in which approximately one-third of the patients exhibit ID. In this study, we generated induced pluripotent stem cells from peripheral blood mononuclear cells from a normal individual and DMD patients with and without ID to identify ID-specific functional and molecular abnormalities. We found defects in neural ectoderm formation in the group of DMD patients with ID. Our transcriptome analysis of patient-derived neural stem cells revealed altered expression of genes related to the hippo signaling pathway and neuroactive ligand-receptor interaction, implicating these in the pathogenesis of ID in patients with DMD.

Neural substrates of neuropsychological profiles in dystrophynopathies: A pilot study of diffusion tractography imaging

Introduction

Cognitive difficulties and neuropsychological alterations in Duchenne and Becker muscular dystrophy (DMD, BMD) boys are not yet sufficiently explored, although this topic could have a relevant impact, finding novel biomarkers of disease both at genetics and neuroimaging point of view. The current study aims to: 1) analyze the neuropsychological profile of a group of DMD and BMD boys without cognitive impairment with an assessment of their executive functions; 2) explore the structural connectivity in DMD, BMD, and age-matched controls focusing on cortico-subcortical tracts that connect frontal cortex, basal ganglia, and cerebellum via the thalamus; 3) explore possible correlations between altered structural connectivity and clinical neuropsychological measures.

Materials and methods

This pilot study included 15 boys (5 DMD subjects, 5 BMD subjects, and 5 age-matched typically developing, TD). They were assessed using a neuropsychological assessment protocol including cognitive and executive functioning assessment and performed a 1.5T MRI brain exam including advance Diffusion Weighted Imaging (DWI) method for tractography. Structural connectivity measurements were extracted along three specific tracts: Cortico-Ponto-Cerebellar Tract (CPCT), Cerebellar-Thalamic Tract (CTT), and Superior Longitudinal Fasciculus (SLF). Cortical-Spinal Tract (CST) was selected for reference, as control tract.

Results

Regarding intellectual functioning, a major impairment in executive functions compared to the general intellectual functioning was observed both for DMD (mean score = 86.20; SD = 11.54) and for BMD children (mean score = 88; SD = 3.67). Mean FA resulted tendentially always lower in DMD compared to both BMD and TD groups for all the examined tracts. The differences in FA were statistically significant for the right CTT (DMD vs BMD, p = 0.002, and DMD vs TD, p = 0.0015) and the right CPCT (DMD vs TD, p = 0.008). Concerning DMD, significant correlations emerged between FA-R-CTT and intellectual quotients (FIQ, p = 0.044; ρs = 0.821), and executive functions (Denomination Total, p = 0.044, ρs = 0.821; Inhibition Total, p = 0.019, ρs = 0.900). BMD showed a significant correlation between FA-R-CPCT and working memory index (p = 0.007; ρs = 0.949).

Discussion and conclusion

In this pilot study, despite the limitation of sample size, the findings support the hypothesis of the involvement of a cerebellar-thalamo-cortical loop for the neuropsychological profile of DMD, as the CTT and the CPCT are involved in the network and the related brain structures are known to be implied in executive functions. Our results suggest that altered WM connectivity and reduced fibre organization in cerebellar tracts, probably due to the lack of dystrophin in the brain, may render less efficient some neuropsychological functions in children affected by dystrophinopathies. The wider multicentric study could help to better establish the role of cerebellar connectivity in neuropsychological profile for dystrophinopathies, identifying possible novel diagnostic and prognostic biomarkers.

Genetic identification of pathogenic variations of the DMD gene: a retrospective study from 10,481 neonatal patients based on next-generation sequencing data

Background

An elevated level of creatine kinase (CK) is usually the primary screening marker for Duchenne muscular dystrophy (DMD)/Becker muscular dystrophy (BMD). This study investigated the clinical application of next-generation sequencing (NGS) in newborns with a possible diagnosis of DMD/BMD in the neonatal intensive care unit (NICU).

Methods

NGS data from the NICU between June 1, 2016, and June 30, 2020, were reanalyzed by an in-house pipeline. Other methods confirmed the genetic findings, and clinical follow-up was performed until August 1, 2020.

Results

Of the 10,481 newborns, 19 (0.18%, 19/10,481) cases with pathogenic variations of the DMD gene were identified, including 13 (68.4%, 13/19) deletions, 4 (21.1%, 4/19) duplications, and 2 (10.5%, 2/19) nonsense mutations. Eight of the cases were diagnosed with DMD. Therapeutic strategies were modified for these patients. Six cases were diagnosed with BMD. Five patients except for 1 deceased patient were further followed-up, and clinical management was adjusted based on the clinical symptoms. The remaining 5 cases were indeterminate for DMD and BMD. Genetic counseling and further follow-up were performed or suggested.

Conclusions

Our study showed that DMD/BMD could be diagnosed earlier in the neonatal stage before the typical clinical symptoms appear. Early diagnosis may provide an opportunity for guiding the care and treatment of patients. However, ethical issues need to be kept in mind in the process of genetic counseling.

Computational cognitive modeling and validation of Dp140 induced alteration of working memory in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy has emerged as a model to assess cognitive domains. The DMD gene variant location and its association with variable degrees of cognitive impairment necessitate identification of a common denominator. Computer architectures provide a framework to delineate the mechanisms involved in the cognitive functioning of the human brain. Copy number variations in the 79 exons of DMD gene were screened in 84 DMD subjects by Multiplex Ligation-dependent Probe Amplification (MLPA). DMD subjects were categorized based on the presence or absence of DP140 isoform. The cognitive and neuropsychological assessments were carried out as per inclusion criteria using standard scales. Instance-based learning theory (IBLT) based on the partial matching process was developed to mimic Stroop Color and Word Task (SCWT) performance on Adaptive Control of Thought-Rational (ACT-R) cognitive architecture based on IBLT. Genotype-phenotype correlation was conducted based on the mutation location in DMD gene. Assessment of specific cognitive domains in DP140 - ve group corresponded to the involvement of multiple brain lobes including temporal (verbal and visual learning and memory), parietal (visuo-conceptual and visuo-constructive abilities) and frontal (sustained and focused attention, verbal fluency, cognitive control). Working memory axis was found to be the central domain through tasks including RAVLT trial 1, recency effect, digit span backward, working memory index, arithmetic subtests in the Dp140 - ve group. IBLT validated the non-reliance of DMD subjects on recency indicating affected working memory domain. Modeling strategy revealed altered working memory processes in DMD cases with affected Dp140 isoform. DMD brain was observed to rely on primacy than the recency suggesting alterations in working memory capacity. Modeling revealed lowered activation of DMD brain with Dp140 - ve in order to retrieve the instances.

Dystrophin Dp71 and the Neuropathophysiology of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by frameshift mutations in the DMD gene that prevent the body-wide translation of its protein product, dystrophin. Besides a severe muscle phenotype, cognitive impairment and neuropsychiatric symptoms are prevalent. Dystrophin protein 71 (Dp71) is the major DMD gene product expressed in the brain and mutations affecting its expression are associated with the DMD neuropsychiatric syndrome. As with dystrophin in muscle, Dp71 localises to dystrophin-associated protein complexes in the brain. However, unlike in skeletal muscle; in the brain, Dp71 is alternatively spliced to produce many isoforms with differential subcellular localisations and diverse cellular functions. These include neuronal differentiation, adhesion, cell division and excitatory synapse organisation as well as nuclear functions such as nuclear scaffolding and DNA repair. In this review, we first describe brain involvement in DMD and the abnormalities observed in the DMD brain. We then review the gene expression, RNA processing and functions of Dp71. We review genotype-phenotype correlations and discuss emerging cellular/tissue evidence for the involvement of Dp71 in the neuropathophysiology of DMD. The literature suggests changes observed in the DMD brain are neurodevelopmental in origin and that their risk and severity is associated with a cumulative loss of distal DMD gene products such as Dp71. The high risk of neuropsychiatric syndromes in Duchenne patients warrants early intervention to achieve the best possible quality of life. Unravelling the function and pathophysiological significance of dystrophin in the brain has become a high research priority to inform the development of brain-targeting treatments for Duchenne.

Neurodevelopmental, behavioral, and emotional symptoms common in Duchenne muscular dystrophy

INTRODUCTION

We studied neurodevelopmental and behavioral/emotional symptoms in patients with Duchenne muscular dystrophy (DMD).

METHODS

Retrospective case series of neurodevelopmental and behavioral/emotional symptoms obtained through review of systems of 700 DMD patients in relation to dystrophin gene mutations.

RESULTS

The most common symptoms encountered were emotional/behavioral dysregulation (38.7%), inattention/hyperactive features (31.4%), obsessive and compulsive features (25.0%), and language/speech delays (24.4%). Most patients (72.7%) had at least one symptom. Patients with mutations near the 3' end of the dystrophin gene were at higher risk for developing inattention/hyperactive features, language/speech delays, and global intellectual delays. Those with mutations between exon 31 and 79 had higher risk of clustering of symptoms when compared with those upstream of exon 30.

DISCUSSION

Neurodevelopmental, emotional, and behavioral symptoms are common comorbidities in DMD. There is higher prevalence of inattention/hyperactive features, language/speech delays, and global intellectual delays in genotypes affecting the 3' end of the dystrophin gene.

Towards Central Nervous System Involvement in Adults with Hereditary Myopathies

There is increasing evidence of central nervous system involvement in numerous neuromuscular disorders primarily considered diseases of skeletal muscle. Our knowledge on cerebral affection in myopathies is expanding continuously due to a better understanding of the genetic background and underlying pathophysiological mechanisms. Intriguingly, there is a remarkable overlap of brain pathology in muscular diseases with pathomechanisms involved in neurodegenerative or neurodevelopmental disorders. A rapid progress in advanced neuroimaging techniques results in further detailed insight into structural and functional cerebral abnormalities. The spectrum of clinical manifestations is broad and includes movement disorders, neurovascular complications, paroxysmal neurological symptoms like migraine and epileptic seizures, but also behavioural abnormalities and cognitive dysfunction. Cerebral involvement implies a high socio-economic and personal burden in adult patients sometimes exceeding the everyday challenges associated with muscle weakness. It is especially important to clarify the nature and natural history of brain affection against the background of upcoming specific treatment regimen in hereditary myopathies that should address the brain as a secondary target. This review aims to highlight the character and extent of central nervous system involvement in patients with hereditary myopathies manifesting in adulthood, however also includes some childhood-onset diseases with brain abnormalities that transfer into adult neurological care.

The expression of the distal dystrophin isoforms Dp140 and Dp71 in the human epileptic hippocampus in relation to cognitive functioning

Dystrophin is an important protein within the central nervous system. The absence of dystrophin, characterizing Duchenne muscular dystrophy (DMD), is associated with brain related comorbidities such as neurodevelopmental (e.g., cognitive and behavioural) deficits and epilepsy. Especially mutations in the downstream part of the DMD gene affecting the dystrophin isoforms Dp140 and Dp71 are found to be associated with cognitive deficits. However, the function of Dp140 is currently not well understood and its expression pattern has previously been implicated to be developmentally regulated. Therefore, we evaluated Dp140 and Dp71 expression in human hippocampi in relation to cognitive functioning in patients with drug-resistant temporal lobe epilepsy (TLE) and post-mortem controls. Hippocampal samples obtained as part of epilepsy surgery were quantitatively analyzed by Western blot and correlations with neuropsychological test results (i.e., memory and intelligence) were examined. First, we demonstrated that the expression of Dp140 does not appear to differ across different ages throughout adulthood. Second, we identified an inverse correlation between memory loss (i.e., verbal and visual memory), but not intelligence (i.e., neither verbal nor performance), and hippocampal Dp140 expression. Finally, patients with TLE appeared to have similar Dp140 expression levels compared to post-mortem controls without neurological disease. Dp140 may thus have a function in normal cognitive (i.e., episodic memory) processes.

Brain-related comorbidities in boys and men with Duchenne Muscular Dystrophy: A descriptive study

AIM

Duchenne Muscular Dystrophy (DMD) is more than a muscle disease since there is a higher prevalence of neuropsychological comorbidities. Similarly, the prevalence of epilepsy is increased. Given the nowadays-increasing interest in brain-related comorbidities in DMD, this study aimed to evaluate the relationship between DMD, epilepsy, and associated neurodevelopmental disorders in an international sample of DMD patients.

METHOD

Using a questionnaire-based study we investigated the occurrence of self/by-proxy reported brain-related comorbidities in a group of 228 DMD patients. We evaluated the presence of epilepsy and other brain-related comorbidities, but also the specific mutation in the dystrophin gene. With respect to epilepsy, all individually reported epilepsy cases as based on the questionnaire results including information provided on epilepsy treatment, EEG abnormalities, and a description of how a typical seizure would look like, were independently and blindly re-assessed by two external paediatric neurologists (Cohen's kappa of 0.85).

RESULTS

Based on the latter, 18 (7.9%) DMD patients were considered to have epilepsy. In patients with both DMD and epilepsy, certain other brain-related comorbidities (i.e. attention deficit hyperactivity disorder, obsessive compulsive disorder, anxiety disorders and sleep disorders) were significantly more prevalent.

CONCLUSION

This study is supportive of a high occurrence of epilepsy and other brain-related comorbidities in DMD. Furthermore this study shows for the first time that the frequency of some of these disorders appear to be further increased when epilepsy is present next to DMD. As this study is limited by the self/by proxy setup and the lack of response rates, future studies should elucidate the true incidence of the (triangular) cooccurrence between epilepsy, neurodevelopmental deficits, and DMD.

Implicit learning deficit in children with Duchenne muscular dystrophy: Evidence for a cerebellar cognitive impairment?

This study aimed at comparing implicit sequence learning in individuals affected by Duchenne Muscular Dystrophy without intellectual disability and age-matched typically developing children. A modified version of the Serial Reaction Time task was administered to 32 Duchenne children and 37 controls of comparable chronological age. The Duchenne group showed a reduced rate of implicit learning even if in the absence of global intellectual disability. This finding provides further evidence of the involvement of specific aspects of cognitive function in Duchenne muscular dystrophy and on its possible neurobiological substrate.

Proteomic Profiling of the Dystrophin-Deficient Brain

Duchenne muscular dystrophy is a highly progressive neuromuscular disorder caused by primary abnormalities in the Dmd gene encoding the membrane cytoskeletal protein dystrophin. Dystrophinopathies are multi-systems disorders that are characterized by severe skeletal muscle wasting, with loss of independent ambulation in the early teenage years, followed by cardio-respiratory complications and premature death. Nonprogressive cognitive impairments are estimated to affect approximately one-third of dystrophic children. To identify the molecular mechanisms behind the impaired brain function in dystrophinopathy, liquid chromatography-based mass spectrometry offers an unbiased and technology-driven approach. In this chapter, we give a detailed description of a label-free mass spectrometric method to investigate proteome-wide changes in the dystrophin-deficient brain from a genetic mouse model of Duchenne muscular dystrophy.

ECM-Related Myopathies and Muscular Dystrophies: Pros and Cons of Protein Therapies

Extracellular matrix (ECM) myopathies and muscular dystrophies are a group of genetic diseases caused by mutations in genes encoding proteins that provide critical links between muscle cells and the extracellular matrix. These include structural proteins of the ECM, muscle cell receptors, enzymes, and intracellular proteins. Loss of adhesion within the myomatrix results in progressive muscle weakness. For many ECM muscular dystrophies, symptoms can occur any time after birth and often result in reduced life expectancy. There are no cures for the ECM-related muscular dystrophies and treatment options are limited to palliative care. Several therapeutic approaches have been explored to treat muscular dystrophies including gene therapy, gene editing, exon skipping, embryonic, and adult stem cell therapy, targeting genetic modifiers, modulating inflammatory responses, or preventing muscle degeneration. Recently, protein therapies that replace components of the defective myomatrix or enhance muscle and/or extracellular matrix integrity and function have been explored. Preclinical studies for many of these biologics have been promising in animal models of these muscle diseases. This review aims to summarize the ECM muscular dystrophies for which protein therapies are being developed and discuss the exciting potential and possible limitations of this approach for treating this family of devastating genetic muscle diseases. © 2017 American Physiological Society. Compr Physiol 7:1519-1536, 2017.

Myelination is delayed during postnatal brain development in the mdx mouse model of Duchenne muscular dystrophy

BACKGROUND

In Duchenne muscular dystrophy (DMD), the loss of the dystrophin component of the dystrophin-glycoprotein complex (DGC) compromises plasma membrane integrity in skeletal muscle, resulting in extensive muscle degeneration. In addition, many DMD patients exhibit brain deficits in which the cellular etiology remains poorly understood. We recently found that dystroglycan, a receptor component of the DGC that binds intracellularly to dystrophin, regulates the development of oligodendrocytes, the myelinating glial cells of the brain.

RESULTS

We investigated whether dystrophin contributes to oligodendroglial function and brain myelination. We found that oligodendrocytes express up to three dystrophin isoforms, in conjunction with classic DGC components, which are developmentally regulated during differentiation and in response to extracellular matrix engagement. We found that mdx mice, a model of DMD lacking expression of the largest dystrophin isoform, have delayed myelination and inappropriate oligodendrocyte progenitor proliferation in the cerebral cortex. When we prevented the expression of all oligodendroglial dystrophin isoforms in cultured oligodendrocytes using RNA interference, we found that later stages of oligodendrocyte maturation were significantly delayed, similar to mdx phenotypes in the developing brain.

CONCLUSIONS

We find that dystrophin is expressed in oligodendrocytes and influences developmental myelination, which provides new insight into potential cellular contributors to brain dysfunction associated with DMD.

Cognitive flexibility deficits in a mouse model for the absence of full-length dystrophin

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder, caused by mutations in the DMD gene and the resulting lack of dystrophin. The DMD gene has seven promoters, giving rise to multiple full-length and shorter isoforms. Besides the expression of dystrophin in muscles, the majority of dystrophin isoforms is expressed in brain and dystrophinopathy can lead to cognitive deficits, including intellectual impairments and deficits in executive function. In contrast to the muscle pathology, the impact of the lack of dystrophin on the brain is not very well studied. Here, we study the behavioral consequences of a lack of full-length dystrophin isoforms in mdx mice, particularly with regard to domains of executive functions and anxiety. We observed a deficit in cognitive flexibility in mdx mice in the absence of motor dysfunction or general learning impairments using two independent behavioral tests. In addition, increased anxiety was observed, but its expression depended on the context. Overall, these results suggest that the absence of full-length dystrophin in mice has specific behavioral effects that compare well to deficits observed in DMD patients.

Language Disturbances in a Group of Participants Suffering from Duchenne Muscular Dystrophy: A Pilot Study

Results from several studies suggest that the process of language acquisition may be altered in patients suffering from Duchenne Muscular Dystrophy. In this study, a group of 8 male participants with Duchenne Muscular Dystrophy ( M age = 16 yr., SD = 4.7) underwent an extensive neuropsychological and language assessment. They also performed a discourse production task. Results showed mild mental retardation associated with a specific deficit in Verbal rather than Performance IQ. At the linguistic assessment, 7 of 8 participants showed moderate to severe difficulties on oral language processing with particularly impaired morphosyntactic competence.

A Novel Mutation in DMD (c.10797+5G>A) Causes Becker Muscular Dystrophy Associated with Intellectual Disability

BACKGROUND

Severe intellectual disability has been reported in a subgroup of patients with Duchenne muscular dystrophy but is not typically associated with Becker muscular dystrophy.

PATIENT

The authors report a 13-year-old boy, with severe intellectual disability (Wechsler Intelligence Scales for Children-IV, Full Scale IQ < 0.1 percentile), attention-deficit hyperactivity disorder, and mild muscle weakness. He had elevated serum creatine kinase and dystrophic changes on muscle biopsy. Dystrophin immunohistochemistry revealed decreased staining with the C-terminal and mid-rod antibodies and essentially absent staining of the N-terminal immunostain. Sequencing of muscle mRNA revealed aberrant splicing due to a c.10797+5G > A mutation in DMD.

CONCLUSION

Dystrophinopathy may be associated with predominantly cognitive impairment and neurobehavioral disorder, and should be considered in the differential diagnosis of unexplained cognitive or psychiatric disturbance in males.

Knocking down Dp71 expression in A549 cells reduces its malignancy in vivo and in vitro

Dp71 is one of the most ubiquitously expressed isoforms of dystrophin, the pathological genes of DMD. In order to find whether the alteration of Dp71 can affect the phenotypes of cell other than PC12, an A549 cell line with stably transfected Dp71 siRNA plasmids was set up and named A549-Dp71AS cell. It is demonstrated for the first time that the A549-Dp71AS cell line displayed decreased invasion capabilities, reduced migration ability, decreased proliferation rate, and lessened clonogenic formation. Cisplatin-induced apoptosis was also increased in A549-Dp71AS cell line via enhancing the Caspase 3, Caspase 8, and Caspase 9 activities. Knocking down Dp71 expression can significantly inhibit the A549 xenograft tumor growth in nude mice. The A549-Dp71AS cells and xenograft tumor tissues displayed reduced lamin B1, Bcl-2, and MMP2 protein expression, which accounts for the reduced malignancy of A549-Dp71AS cells in vivo and in vitro.

Animal models of Duchenne muscular dystrophy: from basic mechanisms to gene therapy

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder. It is caused by loss-of-function mutations in the dystrophin gene. Currently, there is no cure. A highly promising therapeutic strategy is to replace or repair the defective dystrophin gene by gene therapy. Numerous animal models of DMD have been developed over the last 30 years, ranging from invertebrate to large mammalian models. mdx mice are the most commonly employed models in DMD research and have been used to lay the groundwork for DMD gene therapy. After ~30 years of development, the field has reached the stage at which the results in mdx mice can be validated and scaled-up in symptomatic large animals. The canine DMD (cDMD) model will be excellent for these studies. In this article, we review the animal models for DMD, the pros and cons of each model system, and the history and progress of preclinical DMD gene therapy research in the animal models. We also discuss the current and emerging challenges in this field and ways to address these challenges using animal models, in particular cDMD dogs.

Cognitive and Neurobehavioral Profile in Boys With Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is a progressive neuromuscular condition that has a high rate of cognitive and learning disabilities as well as neurobehavioral disorders, some of which have been associated with disruption of dystrophin isoforms. Retrospective cohort of 59 boys investigated the cognitive and neurobehavioral profile of boys with Duchenne muscular dystrophy. Full-scale IQ of < 70 was seen in 27%; learning disability in 44%, intellectual disability in 19%; attention-deficit/hyperactivity disorder in 32%; autism spectrum disorders in 15%; and anxiety in 27%. Mutations affecting Dp260 isoform and 5'untranslated region of Dp140 were observed in 60% with learning disability, 50% intellectual disability, 77% with autism spectrum disorders, and 94% with anxiety. No statistically significant correlation was noted between comorbidities and dystrophin isoforms; however, there is a trend of cumulative loss of dystrophin isoforms with declining full-scale IQ. Enhanced psychology testing to include both cognitive and neurobehavioral disorders is recommended for all individuals with Duchenne muscular dystrophy.

Reading impairment in Duchenne muscular dystrophy: A pilot study to investigate similarities and differences with developmental dyslexia

Below-average reading performances have been reported in individuals with Duchenne muscular dystrophy (DMD), but literacy problems in these subjects have yet to be characterized. In this study, the presence and characteristics of literacy deficits in boys with DMD were investigated through a comparison with typically developing children and with children affected by developmental dyslexia, with the aim of clarifying whether DMD and developmental dyslexia have overlapping profiles of literacy deficits and whether these deficits are associated, as in children with dyslexia, with impairments in phonological processing and rapid lexical access. The results confirmed the high incidence of literacy problems in boys with DMD and revealed a profile less severe than, but qualitatively similar to, that of Italian children with developmental dyslexia. Both groups showed specific difficulties in reading and writing words and a reduced rapid automatized naming (RAN) speed. This is the first time that a RAN speed deficit has been documented in DMD. Moreover, the boys with DMD and the subgroup of dyslexic children with a previous language delay showed additional deficits in phonological processing. The impairments highlighted in this study could explain the reading difficulties observed in boys with DMD and suggest that there is a need for targeted preschool interventions.

Intellectual ability in the duchenne muscular dystrophy and dystrophin gene mutation location

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy during childhood. Mutations in dystrophin (DMD) gene are also recognized as a cause of cognitive impairment. We aimed to determine the association between intelligence level and mutation location in DMD genes in Serbian patients with DMD. Forty-one male patients with DMD, aged 3 to 16 years, were recruited at the Clinic for Neurology and Psychiatry for Children and Youth in Belgrade, Serbia. All patients had defined DMD gene deletions or duplications [multiplex ligation-dependent probe amplification (MLPA), polymerase chain reaction (PCR)] and cognitive status assessment (Wechsler Intelligence Scale for Children, Brunet-Lezine scale, Vineland-Doll scale). In 37 patients with an estimated full scale intelligence quotient (FSIQ), six (16.22%) had borderline intelligence (70<FSIQ ≤85), while seven (18.92%) were intellectually impaired (FSIQ <70). The FSIQ was not associated with proximal and distal mutations when boundaries were set at exons 30 and 45. However, FSIQ was statistically significantly associated with mutation location when we assumed their functional consequence on dystrophin isoforms and when mutations in the 5′-untranslated region (5′UTR) of Dp140 (exons 45–50) were assigned to affect only Dp427 and Dp260. Mutations affecting Dp140 and Dp71/Dp40 have been associated with more frequent and more severe cognitive impairment. Finally, the same classification of mutations explained the greater proportion of FSIQ variability associated with cumulative loss of dystrophin isoforms. In conclusion, cumulative loss of dystrophin isoforms increases the risk of intellectual impairment in DMD and characterizing the genotype can define necessity of early cognitive interventions in DMD patients.

Acetylcholine, GABA and neuronal networks: a working hypothesis for compensations in the dystrophic brain

Duchenne muscular dystrophy (DMD), a genetic disease arising from a mutation in the dystrophin gene, is characterized by muscle failure and is often associated with cognitive deficits. Studies of the dystrophic brain on the murine mdx model of DMD provide evidence of morphological and functional alterations in the central nervous system (CNS) possibly compatible with the cognitive impairment seen in DMD. However, while some of the alterations reported are a direct consequence of the absence of dystrophin, others seem to be associated only indirectly. In this review we reevaluate the literature in order to formulate a possible explanation for the cognitive impairments associated with DMD. We present a working hypothesis, demonstrated as an integrated neuronal network model, according to which within the cascade of events leading to cognitive impairments there are compensatory mechanisms aimed to maintain functional stability via perpetual adjustments of excitatory and inhibitory components. Such ongoing compensatory response creates continuous perturbations that disrupt neuronal functionality in terms of network efficiency. We have theorized that in this process acetylcholine and network oscillations play a central role. A better understating of these mechanisms could provide a useful diagnostic index of the disease's progression and, perhaps, the correct counterbalance of this process might help to prevent deterioration of the CNS in DMD. Furthermore, the involvement of compensatory mechanisms in the CNS could be extended beyond DMD and possibly help to clarify other physio-pathological processes of the CNS.

Psychological aspects in children affected by duchenne de boulogne muscular dystrophy

Impairment of intelligence in Duchenne muscular dystrophy (DMD) patients was described by Duchenne de Boulogne himself in 1868. Further studies report intelligence disorders with mayor impairment of memory. The aim of the present study was to assess the presence of affective and personality disorders in a group of children affected by DMD. Twenty six male DMD patients, mean age eleven and four months years old, were assessed for their affective and personality disorder. Only eight subjects had a total IQ below average with major difficulties in verbal and visual-spatial memory, comprehension, arithmetic and vocabulary. All the subjects presented some disorders: tendency to marginalization and isolation, self-depreciation, sense of insecurity, hypochondriac thoughts and marked state of anxiety. These disorders are often a dynamic prolongation of a psychological process which starts when the diagnosis is made and continues, in a slow and latent fashion, throughout the evolution of the disease.

Growth and psychomotor development of patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is one of the most common hereditary degenerative neuromuscular diseases and caused by mutations in the dystrophin gene. The objective of the retrospective study was to describe growth and psychomotor development of patients with DMD and to detect a possible genotype-phenotype correlation. Data from 263 patients with DMD (mean age 7.1 years) treated at the Departments of Pediatric Neurology in three German University Hospitals was assessed with respect to body measurements (length, weight, body mass index BMI, head circumference OFC), motor and cognitive development as well as genotype (site of mutation). Anthropometric measures and developmental data were compared to those of a reference population and deviations were analyzed for their frequency in the cohort as well as in relation to the genotypes. Corticosteroid therapy was implemented in 29 from 263 patients. Overall 30% of the patients exhibit a short statue (length < 3rd centile) with onset early in development at 2-5 years of age, and this is even more prevalent when steroid therapy is applied (45% of patients with steroid therapy). The BMI shows a rightwards shift (68% > 50th centile) and the OFC a leftwards shift (65% < 50th centile, 5% microcephaly). Gross motor development is delayed in a third of the patients (mean age at walking 18.3 months, 30% > 18 months, 8% > 24 months). Almost half of the patients show cognitive impairment (26% learning disability, 17% intellectual disability). Although there is no strict genotype-phenotype correlation, particularly mutations in the distal part of the dystrophin gene are frequently associated with short stature and a high rate of microcephaly as well as cognitive impairment.

Association between loss of dp140 and cognitive impairment in duchenne and becker dystrophies

The presence of variable degrees of non progressive cognitive impairment is recognized as a clinical feature of patients with Duchenne and Becker muscular dystrophies (DMD and BMD), but its pathogenesis still remains a matter of debate. A number of findings have proved that rearrangements located in the second part of the dystrophin ( DMD ) gene seem to be preferentially associated with cognitive impairment. Dp140 is a distal dystrophin isoform, mainly expressed during fetal brain development, whose role for neuropsychological functioning was suggested.

The aims of the current study were to explore the possible association between cognitive impairment and DNA mutations affecting the regulatory regions of Dp140, as well as to compare the neuropsychological functioning of patients affected with DMD and Intermediate muscular dystrophy (IMD) with those affected by Becker muscular dystrophy (BMD). Fiftythree patients genetically diagnosed with DMD, IMD and BMD, subdivided according to sites of mutations along the DMD gene, underwent a neuropsychological assessment, evaluating their general cognitive abilities, verbal memory, attention and executive functions. Twenty patients with mutations, terminating in exon 44 or starting at exon 45 were tested by polymerase chain reaction (PCR) amplification of microsatellites STR44, SK12, SK21 and P20 DXS269, in order to evaluate the integrity of the Dp140 promoter region.

According to our statistical results, there was not a significant difference in terms of general intelligence between the allelic forms of the disease, a higher frequency of mental retardation was observed in DMD patients. The patients with BMD had better results on tests, measuring long-term verbal learning memory and executive functions. We found that patients lacking Dp140 performed more poorly on all neuropsychological tests compared to those with preserved Dp140. Overall, our findings suggest that the loss of Dp140 is associated with a higher risk of intellectual impairment among patients with dystrophinopathies and highlights the possible role of this distal isoform in normal cognitive development.

A new look at cytoskeletal NOS-1 and β-dystroglycan changes in developing muscle and brain in control and mdx dystrophic mice

BACKGROUND

Loss of dystrophin profoundly affects muscle function and cognition. Changes in the dystrophin-glycoprotein complex (DGC) including disruption of nitric oxide synthase (NOS-1) may result from loss of dystrophin or secondarily after muscle damage. Disruptions in NOS-1 and beta-dystroglycan (bDG) were examined in developing diaphragm, quadriceps, and two brain regions between control and mdx mice at embryonic day E18 and postnatal days P1, P10, and P28. Age-dependent differential muscle loading allowed us to test the hypothesis that DGC changes are dependent on muscle use.

RESULTS

Muscle development, including loss of central nucleation and the localization of NOS-1 and bDG, was earlier in diaphragm than quadriceps; these features were differentially disrupted in dystrophic muscles. The NOS-1/bDG ratio, an index of DGC stability, was higher in dystrophic diaphragm (P10-P28) and quadriceps (P28) than controls. There were also distinct regional differences in NOS-1 and bDG in brain tissues with age and strain. NOS-1 increased with age in control forebrain and cerebellum, and in mdx cerebellum; NOS-1 and bDG were higher in control than mdx mouse forebrain.

CONCLUSIONS

Important developmental changes in structure and muscle DGC preceded the hallmarks of dystrophy, and are consistent with the impact of muscle-specific differential loading during maturation.

[Phenotypic heterogeneity and phenotype-genotype correlations in dystrophinopathies: Contribution of genetic and clinical databases]

The objective of this work was to study the natural history of dystrophinopathies and the genotype-phenotype correlations made possible by the development of the clinical part of the French DMD database. The collection of 70,000 clinical data for 600 patients with an average longitudinal follow-up of 12years enabled clarification of the natural history of Duchenne and Becker muscular dystrophies and clinical presentations in symptomatic females. We were able to specify the phenotypic heterogeneity of motor, orthopedic and respiratory involvements (severe, standard and intermediary form), of the cardiac disorder (severe, standard or absent cardiomyopathy, absence of correlation between motor and cardiac involvements), and of brain function (mental deficiency in the patients with Becker muscular dystrophy, psychopathological disorders in dystrophinopathies). Phenotypic variability did not correlate with a specific mutational spectrum. We propose a model of phenotypic analysis based on the presence or not of muscular and cardiac involvements (described by age at onset and rate of progression) and brain involvement (described by the type and the severity of the cognitive impairment and of the psychological disorders). The methodology developed for the DMD gene can be generalized and used for other databases dedicated to genetic diseases. Application of this model of phenotypic analysis for each patient and further development of the database should contribute substantially to clinical research providing useful tools for future clinical trials.

Dystrophin deletions and cognitive impairment in Duchenne/Becker muscular dystrophy

Analyses of deletions in the dystrophin gene and of cognitive status were performed on patients with Duchenne (DMD) or Becker (BMD) muscular dystrophy in order to find a correlation between both features. Molecular study by multiplex and simplex PCR of dystrophin exons led to the identification of 51 deletions in 126 unrelated patients. Most of them were frameshift, in full agreement with severe clinical symptoms, three patients with a BMD-like phenotype had in-frame mutations. Deletions were localized with reference to the different dystrophin isoform sequences and were clustered in two main areas, 5' and central+ 3' end of the gene. Cognitive abilities were tested in 47 out of 51 patients with identified mutations, 23 of them being mentally impaired. Comparison of molecular and neuropsychological features showed that deletions localized in central and 3' parts of the gene (18 out of 23) are preferentially associated with mental impairment. Fourteen of them were found in the regulatory and coding sequences for the three CNS specific carboxy terminal isoforms. Therefore, though mutations with variable locations may lead to cognitive impairment, our results show that deletions in the distal portion of the gene are basically related to mental retardation.

Neuropsychological and neurobehavioral functioning in Duchenne muscular dystrophy: a review

Duchenne muscular dystrophy (DMD) is a genetic condition affecting predominantly boys that is characterized by fatal muscle weakness. While there is no cure, recent therapeutic advances have extended the lifespan of those with DMD considerably. Although the physiological basis of muscle pathology is well-documented, less is known regarding the cognitive, behavioral, and psychosocial functioning of those afflicted. Several lines of evidence point to central nervous system involvement as an organic feature of DMD, challenging our view of the disorder as strictly neuromuscular. This report provides a review of the literature on neuropsychological and neurobehavioral functioning in DMD. Recent research identifying associations with DMD and neuropsychiatric disorders is also discussed. Lastly, the review presents implications of findings related to nonmotor aspects of DMD for improving the quality of life in those affected. While the literature is often contradictory in nature, this review highlights some key findings for consideration by clinicians, educators and parents when developing therapeutic interventions for this population.

Attention deficit hyperactivity disorder and cognitive function in Duchenne muscular dystrophy: phenotype-genotype correlation

OBJECTIVES

To assess attention deficit hyperactivity disorder (ADHD) in boys affected by Duchenne muscular dystrophy (DMD) and to explore the relationship with cognitive abilities and genetic findings.

STUDY DESIGN

Boys with DMD (n = 103; 4-17 years of age, mean: 12.6) were assessed using a cognitive test (Wechsler scales). Assessment of ADHD was based on the Diagnostic Statistical Manual, Fourth Edition, Text Revision criteria and on the long version of the Conners Parents and Teachers Rating Scales.

RESULTS

ADHD was found in 33 of the 103 boys with DMD. Attention problems together with hyperactivity (17/33) or in isolation (15/33) were more frequent than hyperactivity alone, which was found in 1 patient. Intellectual disability (ID) was found in 27/103 (24.6%). Sixty-two of the 103 boys had no ID and no ADHD, 9 had ID but no ADHD, 14 had ADHD but no ID, and 18 had both. ADHD occurred more frequently in association with mutations predicted to affect Dp140 expression (exon 45-55) and in those with mutations predicted to affect all dystrophin product, including Dp71 (ie, those that have promoter region and specific first exon between exons 62 and 63 but were also relatively frequent).

CONCLUSIONS

Our results suggest that ADHD is a frequent feature in DMD. The risk of ADHD appears to be higher in patients carrying mutations predicted to affect dystrophin isoforms expressed in the brain and are known to be associated with higher risk of cognitive impairment.

Specific profiles of neurocognitive and reading functions in a sample of 42 Italian boys with Duchenne Muscular Dystrophy

A group of 42 Italian boys with Duchenne Muscular Dystrophy was compared with a control group of 10 boys with Spinal Muscular Atrophy and Osteogenesis Imperfecta on tests assessing general intellectual ability, language, neuropsychological functions, and reading skills with the aim of describing a comprehensive profile of the various functions and investigating their interrelationships. The influence of general intellectual level on performance was analyzed. Further, correlations between various neuropsychological measures and language performances were computed for the group with Duchenne Muscular Dystrophy, as well as the correlations between reading scores and other cognitive and linguistic measures. A general lowering in VIQ, PIQ, and FSIQ scores was found to characterize the group with Duchenne Muscular Dystrophy. Expressive language skills were within the normal range, while syntactic and grammatical comprehension were significantly impaired. The presence of below-average reading performances was further confirmed. However, unlike previous studies on irregular orthographies, the present results show that (a) the mild reading difficulties found in the sample essentially concern speed rather than accuracy; (b) they concern word rather than nonword reading; (c) lower reading performances are related to lower scores in general IQ; (d) no correlations emerge with phonological abilities, verbal short-term memory, or working memory, but rather with long-term memory and lexical skills. This may suggest that language-specific effects modulate the cognitive expressions of Duchenne Muscular Dystrophy and raises the possibility that the dysfunctions underlying the reading difficulties observed in affected readers of regular orthographies involve different neurocognitive systems than the cortico-cerebellar circuits usually invoked.

The shortest isoform of dystrophin (Dp40) interacts with a group of presynaptic proteins to form a presumptive novel complex in the mouse brain

Duchenne muscular dystrophy (DMD) causes cognitive impairment in one third of the patients, although the underlying mechanisms remain to be elucidated. Recent studies showed that mutations in the distal part of the dystrophin gene correlate well with the cognitive impairment in DMD patients, which is attributed to Dp71. The study on the expression of the shortest isoform, Dp40, has not been possible due to the lack of an isoform specific antibody. Dp40 has the same promoter as that found in Dp71 and lacks the normal C-terminal end of Dp427. In the present study, we have raised polyclonal antibody against the N-terminal sequence common to short isoforms of dystrophin, including Dp40, and investigated the expression pattern of Dp40 in the mouse brain. Affinity chromatography with this antibody and the consecutive LC-MS/MS analysis on the interacting proteins revealed that Dp40 was abundantly expressed in synaptic vesicles and interacted with a group of presynaptic proteins, including syntaxin1A and SNAP25, which are involved in exocytosis of synaptic vesicles in neurons. We thus suggest that Dp40 may form a novel protein complex and play a crucial role in presynaptic function. Further studies on these aspects of Dp40 function might provide more insight into the molecular mechanisms of cognitive impairment found in patients with DMD.

Neurocognitive profiles in Duchenne muscular dystrophy and gene mutation site

The presence of nonprogressive cognitive impairment is recognized as a common feature in a substantial proportion of patients with Duchenne muscular dystrophy. To investigate the possible role of mutations along the dystrophin gene affecting different brain dystrophin isoforms and specific cognitive profiles, 42 school-age children affected with Duchenne muscular dystrophy, subdivided according to sites of mutations along the dystrophin gene, underwent a battery of tests tapping a wide range of intellectual, linguistic, and neuropsychologic functions. Full-scale intelligence quotient was approximately 1 S.D. below the population average in the whole group of dystrophic children. Patients with Duchenne muscular dystrophy and mutations located in the distal portion of the dystrophin gene (involving the 140-kDa brain protein isoform, called Dp140) were generally more severely affected and expressed different patterns of strengths and impairments, compared with patients with Duchenne muscular dystrophy and mutations located in the proximal portion of the dystrophin gene (not involving Dp140). Patients with Duchenne muscular dystrophy and distal mutations demonstrated specific impairments in visuospatial functions and visual memory (which seemed intact in proximally mutated patients) and greater impairment in syntactic processing.

Neuropsychological impairments and the impact of dystrophin mutations on general cognitive functioning of patients with Duchenne muscular dystrophy

Mutations in the dystrophin gene have long been recognised as a cause of mental retardation. However, for reasons that are unclear, some boys with dystrophin mutations do not show general cognitive deficits. To investigate the relationship between dystrophin mutations and cognition, the general intellectual abilities of a group of 25 boys with genetically confirmed Duchenne muscular dystrophy were evaluated. Furthermore, a subgroup underwent additional detailed neuropsychological assessment. The results showed a mean full scale intelligence quotient (IQ) of 88 (standard deviation 24). Patients performed very poorly on various neuropsychological tests, including arithmetics, digit span tests and verbal fluency. No simple relationship between dystrophin mutations and cognitive functioning could be detected. However, our analysis revealed that patients who lack the dystrophin isoform Dp140 have significantly greater cognitive problems.

Dystrophins, utrophins, and associated scaffolding complexes: role in mammalian brain and implications for therapeutic strategies

Two decades of molecular, cellular, and functional studies considerably increased our understanding of dystrophins function and unveiled the complex etiology of the cognitive deficits in Duchenne muscular dystrophy (DMD), which involves altered expression of several dystrophin-gene products in brain. Dystrophins are normally part of critical cytoskeleton-associated membrane-bound molecular scaffolds involved in the clustering of receptors, ion channels, and signaling proteins that contribute to synapse physiology and blood-brain barrier function. The utrophin gene also drives brain expression of several paralogs proteins, which cellular expression and biological roles remain to be elucidated. Here we review the structural and functional properties of dystrophins and utrophins in brain, the consequences of dystrophins loss-of-function as revealed by numerous studies in mouse models of DMD, and we discuss future challenges and putative therapeutic strategies that may compensate for the cognitive impairment in DMD based on experimental manipulation of dystrophins and/or utrophins brain expression.

The interaction with HMG20a/b proteins suggests a potential role for beta-dystrobrevin in neuronal differentiation

alpha and beta dystrobrevins are cytoplasmic components of the dystrophin-associated protein complex that are thought to play a role as scaffold proteins in signal transduction and intracellular transport. In the search of new insights into the functions of beta-dystrobrevin, the isoform restricted to non-muscle tissues, we performed a two-hybrid screen of a mouse cDNA library to look for interacting proteins. Among the positive clones, one encodes iBRAF/HMG20a, a high mobility group (HMG)-domain protein that activates REST (RE-1 silencing transcription factor)-responsive genes, playing a key role in the initiation of neuronal differentiation. We characterized the beta-dystrobrevin-iBRAF interaction by in vitro and in vivo association assays, localized the binding region of one protein to the other, and assessed the kinetics of the interaction as one of high affinity. We also found that beta-dystrobrevin directly binds to BRAF35/HMG20b, a close homologue of iBRAF and a member of a co-repressor complex required for the repression of neural specific genes in neuronal progenitors. In vitro assays indicated that beta-dystrobrevin binds to RE-1 and represses the promoter activity of synapsin I, a REST-responsive gene that is a marker for neuronal differentiation. Altogether, our data demonstrate a direct interaction of beta-dystrobrevin with the HMG20 proteins iBRAF and BRAF35 and suggest that beta-dystrobrevin may be involved in regulating chromatin dynamics, possibly playing a role in neuronal differentiation.