Correction of muscular dystrophies by CRISPR gene editing
Francesco Chemello, Rhonda Bassel-Duby, Eric N. Olson
Francesco Chemello, Rhonda Bassel-Duby, Eric N. Olson
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Review

Correction of muscular dystrophies by CRISPR gene editing

Abstract

Muscular dystrophies are debilitating disorders that result in progressive weakness and degeneration of skeletal muscle. Although the genetic mutations and clinical abnormalities of a variety of neuromuscular diseases are well known, no curative therapies have been developed to date. The advent of genome editing technology provides new opportunities to correct the underlying mutations responsible for many monogenic neuromuscular diseases. For example, Duchenne muscular dystrophy, which is caused by mutations in the dystrophin gene, has been successfully corrected in mice, dogs, and human cells through CRISPR/Cas9 editing. In this Review, we focus on the potential for, and challenges of, correcting muscular dystrophies by editing disease-causing mutations at the genomic level. Ideally, because muscle tissues are extremely long-lived, CRISPR technology could offer a one-time treatment for muscular dystrophies by correcting the culprit genomic mutations and enabling normal expression of the repaired gene.

Authors

Francesco Chemello, Rhonda Bassel-Duby, Eric N. Olson

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Figure 2

Components and outcomes of CRISPR genome editing.

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Components and outcomes of CRISPR genome editing. (A) DNA double-strand ...
(A) DNA double-strand breaks generated by CRISPR/Cas9 and sgRNA are repaired by nonhomologous end joining (NHEJ) or, in the presence of a donor template, by homology-directed repair (HDR). The Cas protein recognizes the DNA by the protospacer adjacent motif (PAM). Base editors are generated by fusion of nCas9 or dCas9 with the cytidine deaminase APOBEC1 for cytidine base editors (CBEs) to convert nucleotide C/G to T/A within a 5-bp activity window located in the spacer sequence (108). Similarly, fusion with adenosine deaminase TadA produces adenine base editors (ABEs) to convert nucleotide A/T to G/C (109). Prime editors (PEs) are generated by fusion of nCas9 or dCas9 with reverse transcriptase to perform targeted small insertions, deletions, and base changing in a precise way (28). (B) DMD patients with deletion of exon 50 in the DMD gene have an out-of-frame mutation. (i) Double-cut myoediting results in single- or multi-exon deletion. (ii) Single-cut sgRNA myoediting precisely designed at splice sites (e.g., splice acceptor site [SAS]) restores the correct ORF by both exon skipping and exon reframing events. (iii) Nucleotide editing can be accomplished by BEs or PEs, correcting nonsense mutations. Shaded area highlights different myoediting approaches. Exons encoding ORF are shown in blue. Exons with stop codon are shown in red. The corrected exon is shown in green.