Progress toward Gene Therapy for Duchenne Muscular Dystrophy

Abstract

Duchenne muscular dystrophy (DMD) has been a major target for gene therapy development for nearly 30 years. DMD is among the most common genetic diseases, and isolation of the defective gene (DMD, or dystrophin) was a landmark discovery, as it was the first time a human disease gene had been cloned without knowledge of the protein product. Despite tremendous obstacles, including the enormous size of the gene and the large volume of muscle tissue in the human body, efforts to devise a treatment based on gene replacement have advanced steadily through the combined efforts of dozens of labs and patient advocacy groups. Progress in the development of DMD gene therapy has been well documented in Molecular Therapy over the past 20 years and will be reviewed here to highlight prospects for success in the imminent human clinical trials planned by several groups.

Keywords: AAV; dystrophin; gene therapy; mdx mice; microdystrophin; muscular dystrophy.

Figure 1

Domain Structure of Dystrophin Comparative domain structures of full-length dystrophin (top), the mini-dystrophin expressed in a very mildly affected Becker muscular dystrophy (BMD) patient carrying a genomic deletion that removed exons 17–48 (middle) and the structure of a micro-dystrophin protein (bottom). Domains within dystrophin are abbreviated as follows: ABD, actin-binding domain; R, spectrin-like repeats; H, hinge domains; CR, cysteine-rich domain; CT, carboxy-terminal domain. Note that the exon 17–48 genomic deletion removes approximately two-thirds of the spectrin-like repeat 19 coding region. Numerous variants of micro-dystrophin structures have been described by different labs.

Figure 2

Systemic Delivery of AAV/Micro-dystrophin to Adult Mouse Muscles Shown are images of muscle cryosections immunostained using an N-terminal antibody against dystrophin. Control quadriceps cryosections from wild-type (C57BL/6) or mdx^4cv mice (top). Representative cryosections (heart, quadriceps, and diaphragm muscle) from mdx^4cv mice infused with 4 × 10¹⁴ vector genomes per kilogram of AAV6/CK8-microdystrophin (bottom). Vector was administered via retro-orbital injection at ∼2 months of age, and mice were analyzed at 6 months.