Improving Results from Touch DNA Evidence with Optimized Direct PCR Methods

Improved methods to generate high-quality DNA profiles from touch DNA samples are of considerable interest to forensic DNA laboratories. Direct polymerase chain reaction (PCR) amplification, a sample processing method in which samples are added directly to amplification reactions without prior extraction or quantification, has been identified as a method that may improve the generation of genotyping data from such samples; however, laboratories in the United States are required to use standard DNA processing methods to process low-level sample types. In part, this is due to FBI Quality Assurance Standard (QAS) 9.4, which requires all unknown forensic samples to undergo human-specific DNA quantification prior to amplification of short tandem repeat (STR) loci. The goal of this 2-year study is to generate data in support of a reevaluation of QAS 9.4.

In two phases, this study will examine the following: direct PCR-compatible collection methods in conjunction with mock touch DNA evidence samples on a variety of substrates (Phase I), direct PCR of touch DNA samples that have been stored at room temperature for up to six months after collection with the optimum method identified in Phase I, and direct PCR of touch DNA samples that have been re-sampled after initial direct PCR analysis. Nine collection methods and ten substrates (including cartridge casings) will be examined in Phase I, and three time points will be examined in Phase II. In both phases, two replicate sample groups will be processed: Group 1 samples will be extracted, quantified, and amplified in accordance with the QAS; and Group 2 samples will be directly amplified. All STR profiles will be assessed for overall profile quality, and statistical analyses for both phases will be performed using f-tests for variance, two-tailed t-tests, and multivariate analyses as appropriate.

Dissemination of the results of this study may assist the Scientific Working Group on DNA Analysis Methods (SWGDAM) in their reevaluation of QAS 9.4. For submitting agencies and forensic laboratory personnel, the results may also facilitate improvements to sample collection and submission guidelines, evaluations of the efficacy of current touch DNA processing techniques, and evaluations/validations of direct PCR for touch DNA samples. Additional benefits include the ability to maximize the information that can be obtained from touch DNA samples and decreased processing time and costs per sample. Study results will be disseminated to the forensic community through publications in peer-reviewed journals and presentations at scientific meetings.

Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

CA/NCF