Adeno-associated virus (AAV)-derived vectors are among the most promising gene therapy tools because of their safety and ability to mediate long-term transgene expression. The quantification of viral nucleic acid by quantitative polymerase chain reaction are widely employed to study the biodistribution of AAV products. The procedure by Betroff et al is described below as an example. Collection and Preparation of Animal Tissues: Homogenize the frozen animal organs by applying mechanical force using liquid nitrogen and a pestle to obtain a fine dry powder. Extraction of Genomic DNA extraction Perform the extraction of DNA using using the protocol of the DNeasy Blood & Tissue Kit (“Purification of Total DNA from Animal Tissues (Spin-Column Protocol)” in the DNeasy Blood & Tissue Handbook; QIAGEN, Hilden, Germany). Add 20 µl Proteinase K to the tissue homogenate. Mix thoroughly by vortexing, and incubate at 56°C until the tissue is completely lysed. Vortex occasio...