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Dryad

Improving results from touch DNA evidence with optimized direct PCR methods

Abstract

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 purification 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 3-year study was to generate data in support of a reevaluation of QAS 9.4.

In two phases, this study examined 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 were stored at room temperature for up to six months after collection with the optimum methods identified in Phase I, and direct PCR of touch DNA samples that were re-sampled after initial processing. Nine collection methods and various substrates were examined in Phase I, and three time points were examined in Phase II. In both phases, two processing methods were used: standard processing samples were extracted, quantified, and amplified in accordance with the QAS; and direct PCR samples were directly amplified. All STR profiles were assessed for overall profile quality.

This project was supported by Award No. 2019-DU-BX-0009, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect those of the Department of Justice.