Neuropathophysiology of Duchenne muscular dystrophy: involvement of the dystrophin isoform Dp71 in cell migration and proliferation

Dystrophin Genotype and Risk of Neuropsychiatric Disorders in Dystrophinopathies: A Systematic Review and Meta-Analysis

BACKGROUND

Dystrophinopathies are associated with neuropsychiatric disorders due to alterations in dystrophin/DMD expression.

OBJECTIVE

The objective was to estimate the association of developmental disorders, autism spectrum disorders (ASD), attention deficit hyperactivity disorder (ADHD), depression, anxiety disorders, and obsessive-compulsive disorder with the dystrophin/DMD genotype in population with dystrophinopathies.

METHODS

Systematic searches of Medline, Scopus, Web of Science, and Cochrane Library were performed from inception to September 2022. We included observational studies in the population with Becker or Duchenne muscular dystrophies (BMD, DMD) that estimated the prevalence of these disorders according to Dp140 and/or Dp71 genotype. Meta-analysis of the prevalence ratio (PR) of genotype comparisons was conducted for each disorder.

RESULTS

Ten studies were included in the systematic review. In BMD, Dp140+ vs. Dp140- and Dp71+ vs. Dp71- were associated with developmental disorders with a PR of 0.11 (0.04, 0.34) and 0.22 (0.07, 0.67), respectively. In DMD, Dp140+/Dp71+ vs. Dp140- /Dp71- had a PR of 0.40 (0.28, 0.57), and Dp71+ vs. Dp71- had a PR of 0.47 (0.36, 0.63) for ADHD. However, there was no association of genotype with ASD, only a trend was observed for Dp71+ vs. Dp71-, with a PR of 0.61 (0.35, 1.06). Moreover, the data showed no association of these isoforms with emotional-related disorders.

CONCLUSIONS

In BMD, Dp140 and Dp71 could be associated with developmental disorders, while ADHD might be associated with the Dp71 genotype in DMD. Further research is needed regarding Dp140 and Dp71, especially in DMD for ASD.

Prevalence of Neuropsychiatric Disorders in Duchenne and Becker Muscular Dystrophies: A Systematic Review and Meta-analysis

OBJECTIVE

To estimate the prevalence of neuropsychiatric disorders, including autism spectrum disorders (ASDs), attention-deficit hyperactivity disorder (ADHD), depression, anxiety disorders, and obsessive-compulsive disorder (OCD), in populations with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD).

DATA SOURCES

MEDLINE (via PubMed), Scopus, Web of Science, and Cochrane Library from inception to November 2021.

STUDY SELECTION

Observational studies of individuals with DMD or BMD that estimated the prevalence of ASDs, ADHD, depression, anxiety disorders, and OCD in each population.

DATA EXTRACTION

A random-effects meta-analysis was performed on each outcome and each population (ie, DMD, BMD).

DATA SYNTHESIS

Twenty-three studies were included in the meta-analysis. In DMD, there was a prevalence of 7.0% of ASDs, 18.0% of ADHD, 11.0% of depression, 24.0% of anxiety disorders, and 12.0% of OCD. Furthermore, in BMD, there was a prevalence of 6.0% of ASDs, 28.0% of ADHD, 7.0% of depression, 25.0% of anxiety disorders, and 7.0% of OCD.

CONCLUSIONS

The prevalence of these neuropsychiatric disorders is higher among patients with DMD or BMD than among the general population, and the presence of these disorders may negatively influence optimal medical management.

Duchenne muscular dystrophy gene expression is an independent prognostic marker for IDH mutant low-grade glioma

Alterations in the expression of the Duchenne muscular dystrophy (DMD) gene have been associated with the development, progression and survival outcomes of numerous cancers including tumours of the central nervous system. We undertook a detailed bioinformatic analysis of low-grade glioma (LGG) bulk RNAseq data to characterise the association between DMD expression and LGG survival outcomes. High DMD expression was significantly associated with poor survival in LGG with a difference in median overall survival between high and low DMD groups of over 7 years (P = < 0.0001). In a multivariate model, DMD expression remained significant (P = 0.02) and was an independent prognostic marker for LGG. The effect of DMD expression on overall survival was only apparent in isocitrate dehydrogenase (IDH) mutant cases where non-1p/19q co-deleted LGG patients could be further stratified into high/low DMD groups. Patients in the high DMD group had a median overall survival time almost halve that of the low DMD group. The expression of the individual DMD gene products Dp71, Dp71ab and Dp427m were also significantly associated with overall survival in LGG which have differential biological effects relevant to the pathogenesis of LGG. Differential gene expression and pathway analysis identifies dysregulated biological processes relating to ribosome biogenesis, synaptic signalling, neurodevelopment, morphogenesis and immune pathways. Genes spanning almost the entirety of chromosome 1p are upregulated in patients with high overall DMD, Dp71 and Dp427m expression which worsens survival outcomes for these patients. We confirmed dystrophin protein is variably expressed in LGG tumour tissue by immunohistochemistry and, overall, demonstrate that DMD expression has potential utility as an independent prognostic marker which can further stratify IDH mutant LGG to identify those at risk of poor survival. This knowledge may improve risk stratification and management of LGG.

The Duchenne muscular dystrophy gene and cancer

BACKGROUND

Mutation of the Duchenne muscular dystrophy (DMD) gene causes Duchenne and Becker muscular dystrophy, degenerative neuromuscular disorders that primarily affect voluntary muscles. However, increasing evidence implicates DMD in the development of all major cancer types. DMD is a large gene with 79 exons that codes for the essential muscle protein dystrophin. Alternative promotor usage drives the production of several additional dystrophin protein products with roles that extend beyond skeletal muscle. The importance and function(s) of these gene products outside of muscle are not well understood.

CONCLUSIONS

We highlight a clear role for DMD in the pathogenesis of several cancers, including sarcomas, leukaemia's, lymphomas, nervous system tumours, melanomas and various carcinomas. We note that the normal balance of DMD gene products is often disrupted in cancer. The short dystrophin protein Dp71 is, for example, typically maintained in cancer whilst the full-length Dp427 gene product, a likely tumour suppressor, is frequently inactivated in cancer due to a recurrent loss of 5' exons. Therefore, the ratio of short and long gene products may be important in tumorigenesis. In this review, we summarise the tumours in which DMD is implicated and provide a hypothesis for possible mechanisms of tumorigenesis, although the question of cause or effect may remain. We hope to stimulate further study into the potential role of DMD gene products in cancer and the development of novel therapeutics that target DMD.

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.