AVI-4225

**AVI-4225** is a mouse-specific phosphorodiamidate morpholino oligomer (PMO) designed to induce **exon 23 skipping** in the dystrophin gene in the mdx mouse model of Duchenne muscular dystrophy (DMD). By binding to exon 23 during pre-mRNA splicing, it restores the dystrophin reading frame, leading to production of truncated but partially functional dystrophin protein, which improves muscle pathology, function, and serum biomarkers like ALT and CK in skeletal muscles such as tibialis anterior, quadriceps, diaphragm, and others. Developed by **Sarepta Therapeutics** (formerly AVI BioPharma), it was well-tolerated in preclinical studies with weekly IV or SC dosing up to 960 mg/kg for 12 weeks, showing reversible mild renal findings (basophilic granules/tubules) but no significant toxicity or impacts on cardiac muscle.