Restoration of dystrophin expression and correction of Duchenne muscular dystrophy by genome editing

ABSTRACT

Introduction: Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder that affects approximately one in 3500–5000 male births. Patients experience muscle degeneration, loss of ambulation, and eventual death from cardiac or respiratory failure in early adulthood due to a lack of functional dystrophin protein, which is required to maintain the integrity of muscle cell membranes. Out-of-frame mutations in the DMD gene generally lead to no dystrophin protein expression and a more severe phenotype (DMD). Conversely, in-frame mutations are often associated with milder Becker muscular dystrophy (BMD) with a truncated dystrophin expression.

Areas covered: Genome editing via the clustered regularly interspaced short palindromic repeats (CRISPR) system can induce permanent corrections of the DMD gene, thus becoming an increasingly popular potential therapeutic method. In this review, we outline recent developments in CRISPR/Cas9 genome editing for the correction of DMD, both in vitro and in vivo, as well as novel delivery methods.

Expert opinion: Despite recent advances, many limitations to CRISPR/Cas9 therapy are still prevalent such as off-target editing and immunogenicity. Specifically, for DMD, intervention time and efficient delivery to cardiac and skeletal muscles also present inherent challenges. Research needs to focus on the therapeutic safety and efficacy of this approach.

KEYWORDS:

• Duchenne muscular dystrophy (DMD)
• CRISPR/Cas9
• genome editing
• exon skipping
• dystrophin
• mdx mice
• deltaE50-MD dog model

Article highlights

• Genome editing mediated by CRISPR/Cas9 system has been successful in rectifying mutations associated with DMD models

• CRISPR works alongside the host cell’s endogenous repair machinery (such as non-homologous end joining) to facilitate the removal of an exon(s)

• Several in vitro studies using CRISPR-mediated exon skipping and deletion strategies have been summarized in this review, ranging from murine to DMD patient cell lines

• Additional genome editing approaches such as base editing and transcription activator-like effector nucleases (TALENs) are discussed

• Recent developments in in vivo studies of genome editing in murine, canine, and porcine models are summarized in this review

• Novel delivery techniques like lipid nanoparticles may serve as future candidates for delivering the CRISPR proteins in vivo and bypass issues associated with immune responses

This box summarizes key points contained in the article.

Declaration of interest

The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial relationships or otherwise to disclose.

Additional information

Funding

The work is supported by the University of Alberta Faculty of Medicine and Dentistry, the Canadian Institutes of Health Research, the Friends of Garrett Cumming Research Funds, HM Toupin Neurological Science Research Funds, Muscular Dystrophy Canada, the Canada Foundation for Innovation, the Women and Children’s Health Research Institute.