The Casework Direct System

Efficiently Process Sexual Assault Evidence and Property Crime Evidence

Ann MacPhetridge, Promega

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In recent years, the overwhelming number of property crime and sexual assault evidentiary samples submitted to forensic laboratories has resulted in a significant need for improved solutions for processing these challenging sample types. The Casework Direct System is designed to rapidly process swabs from casework samples or cuttings of sexual assault swabs and stained fabric prior to quantification of human DNA using the PowerQuant® System, and amplification of normalized template using PowerPlex® Systems for STR analyses. For casework samples, no further purification of the Casework Direct lysate is required prior to STR amplification unless data from the quantification step suggests that PCR inhibitors may be present.

  • Generates amplification-ready lysates in less than 1 hour
  • Improves efficiency for Y-screening and selection of evidentiary samples for STR testing
  • Optimized for use with PowerQuant®, Plexor® HY and PowerPlex® Systems

When used specifically with the PowerQuant® System, additional valuable information on the quality and integrity of the DNA can also be obtained, helping laboratories to quickly determine which samples may be the most optimal for moving on to STR analysis.

With a brief incubation step followed by centrifugation, the protocol is straightforward. The resulting lysate is ready for use in a quantification assay and STR amplification.

How it Works: Y-Screening Application

Sexual Assault Kits (SAK) account for a substantial percentage of backlogged cases in forensic laboratories. However, traditional methods require hours to complete and are often laborious, while providing insufficient sensitivity when compared to male DNA detection by amplification. Additionally, conventional screening results offer analysts little predictive power as to what DNA profile may result. Recognizing the limitations and challenges associated with traditional serology methods, SWGDAM recommendations are now instructing the use of a “direct to DNA” approach, where DNA analysis is performed before serology to maximize the chances of obtaining CODIS eligible profiles. The Casework Direct System is highly sensitive, enabling detection of male DNA in the presence of high amounts of female DNA (see Table 1).

By using Casework Direct System to perform this “direct to DNA” amplification, laboratories can reduce the overall turnaround time for SAK sample processing in addition to minimizing the potential DNA loss typically seen in the DNA extraction step.

How it Works: Touch DNA Samples

When DNA is found at a property crime scene, laboratories may be able to match the evidence to a known offender’s sample in CODIS, and these profiles could be connected to other types of offenses. Because of these successes, crime investigators will submit numerous “touch DNA” samples to their forensic laboratories, causing the laboratory to use significant resources for property crime cases by testing evidence for “touch DNA”. These samples tend to contain very little DNA, so running them through a typical DNA extraction protocol can also result in further loss of DNA, which can lead to an unusable profile.

Integration of the Casework Direct System into a laboratory’s workflow provides a rapid and cost-effective means to generate high-quality STR profiles from precious, low-abundance DNA samples with minimal hands-on time.

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Figure 2. The Casework Direct System generates high-quality STR profiles from touch DNA samples. Cotton swabs were used to collect touch DNA samples from steering wheel, computer mouse and cell phone surfaces. For each sample, 400µl of Casework Direct Solution was added to the swab placed in a spin basket assembly, incubated at 70ºC for 30 minutes and centrifuged at 16,000 × g for 5 minutes to recover the lysate. The amount of human amplifiable DNA was quantified from 2µl of lysate using the PowerQuant® System, and 0.5ng or the maximum volume of lysate was used for STR amplification using the PowerPlex® Fusion and PowerPlex® Y23 Systems. The amplified products were electrophoresed on the Applied Biosystems® 3500xL Genetic Analyzer using POP4 with 3kV, 5 second injection and analyzed on GeneMapper® IDv3.2 with an analysis threshold of 50 RFU.

In conclusion, with the ever-increasing workloads seen by forensic casework laboratories, solutions such as the Casework Direct System, which can provide a more efficient method to triage samples to ensure that the samples processed have a high probability of providing a usable profile, are a welcome answer to the challenge of finding ways to work smarter, not harder.