Genetic Approaches for the Treatment of Facioscapulohumeral Muscular Dystrophy

Figures

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  FIGURE 1. Activation of DUX4 expression in FSHD. The DUX4 gene is located in the D4Z4 macrosatellite repeat array at chromosome 4q35. Each D4Z4 repeat (yellow triangles) contains DUX4 exons 1 and 2 (solid boxes; orange, open reading frame); exon three is found downstream of the last repeat in the array. The D4Z4 array is normally 11–100 repeats long and hypermethylated (purple line) in healthy individuals. Contractions of this array or mutations in genes coding for epigenetic regulators, in the 4qA haplotype, disrupt the silencing of DUX4 (dotted purple line) and lead to its aberrant expression in skeletal muscle.

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  FIGURE 2. Summary of genetic approaches for the treatment of FSHD. The approaches covered in this review are depicted above. Ultimately, all focus on reducing DUX4 expression, DUX4 protein activity, or the effects of DUX4-mediated toxicity. (1) Targeted gene repression with CRISPR/dCas9-KRAB; (2) correction of a SMCHD1 mutation with CRISPR/Cas9; (3) gene knockdown with antisense oligonucleotides; (4) gene knockdown/silencing with RNA interference; competing with DUX4 activity through (5) DNA aptamers, (6) introduction of proteins homologous or similar to DUX4, and (7) DNA decoys; (8) gene knockdown/silencing of DUX4 downstream targets; (9) gene knockdown/silencing of genetic modifiers of DUX4 expression or DUX4-mediated toxicity (10) delivery of genes coding for proteins that ameliorate DUX4-mediated toxicity or secondary features of FSHD pathology.

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  FIGURE 3. Overview of DUX4 regions that have been targeted by oligonucleotide therapies. The structure of the DUX4 gene is shown at the top (arrow indicates promoter region; boxes, exons; lines, introns; orange, open reading frame; red, polyadenylation signal), and the regions that have been targeted by antisense oligonucleotides (green) or RNA interference (purple) are shown at the bottom. Approximate locations are shown, and the figure is not to scale. Note that Ansseau et al. (2017) used the same oligonucleotides as Vanderplanck et al. (2011). DUX4 structure was based on information from Ensembl, transcript ID ENST00000569241.5.