Enhancing the Sexual Assault Workflow: Testing of Next Generation Assessment and Y-STR Systems

<p>Sexual assault samples are among the most difficult samples types encountered by forensic laboratories. Typically a sexual assault sample has multiplex challenges including small quantity of male DNA, relatively high quantity of female DNA and the presence of PCR inhibitors. Therefore, there is a need for a more robust, highly sensitive and faster method for assessment (i.e. quality and quantity) of DNA extracts to determine optimal downstream processing methods, as well as an improved Y-STR amplification system for profiling these difficult samples.</p> <p>We tested newly developed tools, including a DNA quantification kit (Quantifiler® Trio) that exhibits high sensitivity, higher inhibitor tolerance and includes additional tools useful for the determination of DNA quality to inform downstream processing methodology. We also tested a new Y-STR kit (Yfiler® Plus) with enhanced capabilities. This 27-marker kit permits rapid amplification of single source and complex casework samples.</p> <p>These two next generation systems are intended to generate an improved workflow for obtaining interpretable profiles from sexual assault samples. Here, we present the utility of the new workflow in processing sexual assault samples. We have successfully used the Quantifiler® Trio quantitation and assessment kit and the Yfiler® Plus amplification kit to obtain informative Y-STR profiles from challenging sexual assault sample types, including extended interval post coital samples collected 4, 7 and 9 days after intercourse (28 sets), which contained extremely low quantities of male DNA and high amounts of female DNA (1:333 male:female DNA ratios or greater). Probative Y-STR profiles were obtained from these samples using the next generation quantification and amplification systems with mostly full profiles obtained if >100pg of male DNA was present. Additionally, a good correlation between male quantitation and profile recovery was observed, with a negative quantitation value indicating that a negative or unusable profile would be obtained.</p> <p>Since the examination of 4-9 day post coital samples is not routinely performed by operational crime laboratories, we also performed an analysis of one set of 1, 2 & 3 day samples. We report the use of Quantifiler® Trio, GlobalFilerTM and Yfiler® Plus to obtain full autosomal and Y-STR profiles.</p