![]() It has previously been observed that thermostable DNA polymerases of different origins may have different abilities to withstand the effects of various PCR inhibitors ( 10). Simple dilution of the extract may be applied ( 8, 9), but only if the DNA concentration is sufficiently high. In special cases, isolation of single cells using laser-capture microdissection can be used ( 7). The common approach to overcoming PCR inhibition is extensive DNA purification ( 3–5). As an illustration, a police force in the UK reported that 57% of swabs from bottles and cans failed to produce acceptable DNA profiles ( 6), which could be explained by a lack of sufficient amounts of DNA or the presence of PCR inhibitors. Failure to produce a DNA profile from a crime scene stain may leave a case unsolved or a person wrongly accused. The consequences of PCR inhibition in forensic casework may be severe. The problem of inhibition is especially prominent in forensic DNA analysis, due to the nature of the sampling environment at crime scenes ( 3–5). Several substances have been identified as PCR inhibitors, and some have been characterized with respect to their PCR-inhibitory mechanism(s) ( 2). Diagnostic DNA analysis, including forensic applications, is often limited by components that interfere with the amplification, so-called PCR inhibitors ( 1). Physical evidence, especially DNA, is increasingly important in the investigation of criminal cases and in the court of law in today's society. Our study demonstrates the importance of adjusting the chemistry of the PCR to enhance forensic DNA analysis and diagnostic PCR, providing an alternative to laborious sample preparation protocols. A statistical model for unbiased quality control of forensic DNA profiles was developed to quantify the results. DNA profiles from 20 of 32 totally or partially inhibited crime scene saliva samples were significantly improved using Bio-X-Act Short, Ex Taq Hot Start, or PicoMaxx High Fidelity instead of Ampli Taq Gold. Here, we show that alternative DNA polymerase–buffer systems can improve the quality of forensic DNA analysis and efficiently circumvent PCR inhibition in crime scene samples, without additional sample preparation. Most forensic laboratories use commercial DNA amplification kits (e.g., Amp FlSTR SGM Plus) with the DNA polymerase Ampli Taq Gold as the gold standard. Extensive DNA purification can be required to rid the sample of these inhibitors, although these procedures increase the risk of DNA loss. However, DNA samples from crime scenes often contain PCR-inhibitory substances, which may generate blank or incomplete DNA profiles. DNA evidence, linking perpetrators to crime scenes, is central to many legal proceedings. ![]()
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