Twgdam Validation of Ampf_str•: PCR Amplification Kits for Forensic DNA Casework

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Abstract
Laboratory procedures used in short tandem repeat (STR) analysis were subjected to various scenarios that assessed reliability and identified potential limitations. These validation studies were designed as recommended by the Technical Working Group on DNA Analysis Methods (TWGDAM) and the DNA Advisory Board (DAB) (17,18). Various DNA samples were amplified by the polymerase chain reaction (PCR) using AmpF_STR• PCR Amplification Kits (i.e., AmpF_STR Green I, Profiler•, Profiler Plus•, and COfiler• kits), detected with ABI Prism instrumentation, and analyzed using GeneScan and Genotyper software. Data acquired in these studies reinforced an existing body of knowledge and expertise regarding application and interpretation of STR typing in the forensic science community. Consistent STR genotypes were detected in various body tissues and fluids. Inter-laboratory comparisons produced concordant genotype results. Quantitative interpretational aids for DNA mixtures were characterized. Ability of the typing systems to type potentially compromised samples reliably was evaluated. Nonprobative case evidentiary DNA was successfully amplified, genotyped, and interpreted. Potential limitations or cautionary factors in the interpretation of minimal fluorescence intensity were demonstrated. Differential amplification between loci was observed when PCR was inhibited; preferential amplification typically was not. Single AmpF_STR locus amplification did not offer consistent benefit over AmpF_STR multiplexing, even in cases of DNA degradation or PCR inhibition. During rigorous evaluation, AmpF_STR PCR Amplification Kits reproducibly yielded sensitive and locusspecific results, as required in routine forensic analyses.