Treatment of a severe vascular disease using a bespoke CRISPR-Cas9 base editor in mice

Pathogenic missense mutations in the alpha actin isotype 2 gene (ACTA2) cause multisystemic smooth muscle dysfunction syndrome (MSMDS), a genetic vasculopathy that is associated with stroke, aortic dissection, and death in childhood. Here, we correct the most common MSMDS-causative mutation ACTA2 R179H using genome editing. We perform mutation-specific protein engineering to develop a bespoke CRISPR-Cas9 enzyme with enhanced on-target activity against the R179H sequence. To directly correct the R179H mutation, we screened dozens of configurations of base editors to develop a highly precise corrective A-to-G edit with minimal deleterious bystander editing that is otherwise prevalent when using wild-type SpCas9 base editors.