Phosphorodiamidate morpholino oligomers (PMOs; figure 1) are non-toxic, and in the mdx mouse model of DMD they were the most effective oligomer chemistry for inducing exon skipping and restoring long-lasting (weeks) dystrophin expression after intravenous or intramuscular injection.21, 22, 23, 24 PMOs, unlike other antisense oligonucleotides, are uncharged, not metabolised, and in preclinical or clinical studies were not associated with activation of the immune system, anaphylaxis, hypotension, or anti-arrhythmias.25 The gene discussed is DMD; the disease is Duchenne muscular dystrophy.