Adeno-Associated Virus serotype 9 (AAV9) is one of the most promising serotypes for gene therapy applications. AAV9 transduces a wide range of tissue types, including cardiac and skeletal muscle, and liver, pancreas, and eye tissue. AAV8 and AAV9 have recently been used to correct disease-causing mutations and improve muscle function in mouse models of Duchenne muscular dystrophy. AAV9 has significantly lower seroprevalence in the human population than other AAV serotypes, making AAV9 a desirable candidate for therapeutic applications.Cas9 is an endonuclease enzyme that introduces a double stranded break into the DNA when recruited to a specific DNA sequence by the sgRNA (single guide RNA). This double stranded break is repaired in mammalian cells either through Non-Homologous End Joining or Homologous Recombination. Non-Homologous End Joining often results in the deletion or insertion of several base pairs at the cut site, which, when resulting in a frameshift, causes the functional inactivation of the gene.SaCas9 (Staphylococcus aureus CRISPR-associated protein 9) has demonstrated high cutting efficiency in mammalian cells, and its smaller size makes it ideal for packaging into AAV. SaCas9 recognizes a longer protospacer adjacent motif (PAM) site, 5'-NNGRRT-3', than the more traditional SpCas9 (Streptococcus pyogenes CRISPR-associated protein 9). These AAV particles constitutively express SaCas9 under the control of a CMV promoter.