An Assessment of in vitro DNA Repair Mechanisms as Related to Damaged Forensic Specimens

Forensic samples submitted as evidence for DNA testing are often damaged. Enzymatic “cocktails” have been developed that mirror the in vivo repair mechanisms associated with cellular DNA damage repair. One such cocktail has been developed with an eye toward developing a treatment kit that will repair damaged regions of interest, and allow for their successful STR analysis.DNA from extracted buccal samples were subjected to various UV exposure times prior to their STR analysis. Profiles were obtained using the Promega PowerPlex® amplification kit with subsequent capillary electrophoresis on the ABI 3130xl instrument. The results were directly compared to the known buccal sample profiles of the donors that were obtained prior to damage. Specific mechanisms of damage were assessed as well.The damaged samples were subjected to enzymatic repair treatment and retested to assess the amount of repair. By comparing the profile information from the damaged samples, to profiles obtained from the repair treated damaged material, we were able to determine the amount of repair taking place, the repair system’s accuracy, and any possible inhibitory effects. Repair treatment was assessed as it relates to certain kinds of forensic samples, for example mixtures. Were repair treated samples allowing for accurate mixture interpretation and deconvolution when compared to mixture ratios of more pristine samples? Samples with stochastic levels of DNA were also examined in order to assess the impact of low quantities of amplifiable material, in addition to damage.Results of these studies indicated an application of the repair process for evidentiary material. Data showed that there is fidelity associated with the application; there is profile concordance after its use, and there an increase in the amount of recovered profile alleles after inflicted damage.