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Feb 1, 2009 (Vol. 29, No. 3)

Uncovering Applications for DNA Forensics

It Is Not Just Law-Enforcement Agencies Who Are Finding a Panoply of Uses for New Tools

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    Samples taken from a crime scene can be of great value in identifying a perpetrator or ruling suspects out of an investigation (Forensic Science Service).

    What began as a community workshop nearly 20 years has grown exponentially, as has the field it addresses. In 1989, Promega hosted its first symposium on human identification. “The original goal of the meeting was to facilitate the exchange of ideas between scientists working on methods for DNA analysis,” said Len Goren, global director of Promega’s genetic identity business. “The annual symposium now has an international reputation for providing the forensic community with a forum to learn about new technologies and applications.”

    The “International Symposium on Human Identification” held late last year, highlighted advances and applications in the field. Recent advances in technology are driving increased sample throughput and speed. “This is a very exciting time to be in the field,” explained Lenny Klevan, Ph.D., head of forensics at Life Technologies. “DNA forensics is taking hold in the global market—it’s a growing field as law enforcement agencies around the world are using DNA testing as a way to keep their citizens safe.”

    DNA forensics is not the sole property of murder and rape cases anymore. “People are now more interested in using DNA to solve less serious crimes,” noted  Steven Hofstadler, Ph.D., vp research at Ibis Biosciences. “Using DNA forensics to solve burglaries now enables law enforcement to cast a larger net. After all, there is a correlation—if someone breaks into houses, they are more likely to commit other crimes. And now we have the capability to catch those people.”

  • Quantitative Studies

    Dr. Hofstadler noted that, as technology evolves, the applications broaden. He presented his group’s recent results on a DNA forensics platform based on fully automated high-throughput electrospray ionization mass spectrometry (ESI-MS). “The approach is based on using ESI-MS to weigh DNA forensic markers with enough accuracy to yield an unambiguous base composition, or the number of As, Gs, Ts, and Cs,” said Dr. Hofstadler. “This, in turn, can be used to derive a DNA profile for an individual.”

    This is important, according to Dr. Hofstadler, because base composition profiles can be referenced in existing forensics databases derived from a mitochondrial DNA (mtDNA) sequence or short tandem repeat (STR) profiles. “With mtDNA typing, the ESI-MS approach facilitates the analysis of samples containing sequence and length heteroplasmy in the HV1, HV2, and HV3 regions without degradation of information,” he added. “In fact, the method captures the extent and type of heteroplasmy in situations that are not amenable to sequencing.”

    Using the base compositions derived from a 24-primer pair tiling panel that covers nucleotide positions 15924-16428 and 31-576 as a basis, Dr. Hofstadler demonstrated that this approach has better resolution than traditional sequencing methods. “Because of the quantitative nature of ESI-MS, mixtures of different mtDNA types can be detected and resolved into distinctive components,” he pointed out. “Sometimes mixtures of mtDNA types analyzed by sequencing lead to uninterpretable results; analysis through ESI-MS yields quantitative data that maximizes the informative value of evidence.”

    According to Dr. Hofstadler, this platform has a number of other applications, which include clinical and epidemiology work, as well as work on biodefense. “It’s all about amplifying DNA, weighing it, and using it to get base pair signatures, and it’s not limited to forensics work. We’ve performed a number of blinded validation studies with FBI and National Institute of Standards and Technology to evaluate the platform for mtDNA and STR typing. And it offers distinct advantages over the conventional approach.”

    On the STR side, the MS-based method picks up single nucleotide polymorphisms (SNPs) with STR regions that conventional electrophoretic analyses won’t detect. “SNPs show great promise as a next generation of forensic markers,” said Dr. Hofstadler. “One of the drawbacks right now is that the fragments are not large enough to measure markers. On the up side, they are easy markers to amplify.”


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