Abstract: Disclosed herein are methods for systemically editing a gene in a subject and for systemically treating a genetic condition in a subject using a dual-vector CRISPR-Cas therapy. The methods comprise administering to the subject, via systemic administration, a gene editing AAV vector encoding a CRISPR effector protein (e.g., a Cas protein) and a targeting AAV vector providing one or more gRNAs targeted to the gene. In the methods, the ratio of the targeting AAV vector to the gene editing vector is greater than or equal to 2. Also provided are dual-vector systems for editing a gene or treating a genetic disease in a subject.