There has been a recent onslaught of data showing how gene editing can be used to delete and alter certain sequences of interest in the genome. The one tool that has received most attention is the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas system that was first discovered in bacteria and is now being used in a variety of cell types and models to silence genes and probe biological function. New studies show that CRISPR-Cas can also be used to achieve certain therapeutic endpoints. Zinc finger nucleases and recombinant adeno-associated virus (rAAV)-based gene editing have been around for many years as tools for gene editing. However the recent introduction of CRISPRs has made gene editing less laborious, less expensive, and easier to perform. These techniques have some similarities, but they differ in their mechanisms for bringing about gene editing and the specificity with which they achieve it, which lead to...