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Braun. J Transl Genet Genom. 2025;9:35-47 https://dx.doi.org/10.20517/jtgg.2024.79 Page 43

risk of inducing an anti-transgene immune response, which must be prevented.

Non-dystrophin genes

To bypass any anti-transgene immune response, genes that are constitutively expressed are being
investigated. Utrophin, a functional paralog of dystrophin that is naturally expressed in muscles, has been
proposed as an immunologically safer therapeutic gene alternative. Utrophin is a ubiquitous protein,
expressed at the sarcolemma of embryonic muscles and progressively replaced by dystrophin at the muscle
membrane after birth. In adult skeletal muscle, utrophin is confined to the neuromuscular and
myotendinous junctions, as well as blood vessels, and is only expressed at the sarcolemma of regenerated
myofibers. Utrophin is highly homologous to dystrophin and can recruit most of the components of the
[64]
dystrophin-associated protein complex . Despite efforts, pharmaceutical stimulation of utrophin to
compensate for the absence of dystrophin has not yet been successful. Therefore, utrophin gene therapy
remains a promising alternative. Given the size of its coding sequence, truncated versions of micro-utrophin
are being designed, with consideration given to the differential binding capacity and suitable folding of
utrophin and dystrophin .
[65]
Another potential candidate is Cytotoxic T cell GalNAc transferase (GALGT2), an enzyme normally
distributed, like utrophin, at the neuromuscular junctions of myofibers postnatally. GALGT2 glycosylates
the dystrophin-associated glycoprotein a-dystroglycan. The delivery ofrAAVrh74-GALGT2 has been shown
[66]
[67]
to successfully treat DMD mice and, to a lesser extent, DMD dogs . Encouraging functional data were
obtained in a phase 1/2 clinical trial assessing the safety and efficacy of GALGT2 gene therapy
[69]
[68]
(NCT03333590) . However, the clinical development of this program was discontinued by the sponsor .
AAV-microdystrophin, utrophin, or GALGT2 gene therapy would be potentially applicable to all DMD
patients regardless of their mutation. Active clinical development programs and approved gene-based drugs
are shown in Figure 1.

A range of challenges remain in fully optimizing AAV dosage, immune control and large-scale
manufacturing. A more potent expression cassette could reduce the required viral dose to achieve the
therapeutic effect. However, according to the nuclear domain theory, stronger expression cassettes with
lower vector amounts would not align with the need to transduce a maximum of nuclei along the muscle
fibers. Natural variant-based AAVs lack specificity and often accumulate in the liver, with the concomitant
[70]
risks of hepatotoxicity and general toxicity due to high dosage . One potential solution is lowering the dose
by enhancing vector specificity through capsid modification. High-throughput screened or computationally
designed AAV capsids that more specifically target skeletal muscle to lower treatment doses are being
developed . A recent variant, LICA1, demonstrates comparable muscle transduction to other myotropic
[71]
AAVs, with significantly reduced liver targeting and, not to underestimate, large-scale production yield
capacity , which could help reduce the heavy burden of manufacturing costs. Nevertheless, while
[72]
myotropic AAVs represent attractive second-generation vectors, they still require careful safety assessment.

CONCLUSION
The perfect molecular therapy, administered in very low doses and targeting motor function, circulation,
and digestive tracks, as well as cognitive skills, does not exist yet. Nevertheless, emerging combination
therapies show promise in addressing the specific needs of each organ. The remaining hurdles
(immunological issues, persistence and optimization of therapeutic effects for complete disease remission)
are being investigated separately and possible solutions are under consideration. Another key obstacle