STR Profiles from DNA Samples with “Undetected” or Low Quantifiler™ Results

Abstract

Screening methods capable of identifying DNA samples that will not yield short tandem repeat (STR) profiles are desired. In the past, quantitation methods have not been sensitive enough for this purpose. In this study, low level DNA samples were used to assess whether Quantifiler has a minimum quantitation value below which STR profiles would consistently fail to be detected. Buccal swabs were obtained and the DNA extracted, quantified, and serially diluted to concentrations ranging from 0.002 to 0.250 ng/microL. Samples were analyzed once with Quantifiler, followed by Profiler Plus amplification and capillary electrophoresis analysis. An absolute minimum value below which STR results were unobtainable could not be defined. From the 96 low level samples tested, STR loci (including one full profile) were successfully amplified and detected from 27% of the samples "undetected" by Quantifiler. However, no STR alleles were detected in 73% of these "undetected" samples, indicating that Quantifiler data may be useful for predicting STR typing success.

The effects of metal ion PCR inhibitors on results obtained with the Quantifiler ® Human DNA Quantification Kit

“…Samples with negative human DNA results and normal IPC Cq values may still produce full STR profiles without additional purification of the sample [34]. Another study reported 27% of low-quantity samples with "undetermined" quantification values tested produced at least partial STR profiles [35]. These observations are important to relate to samples that may contain PCR inhibitors, as inhibition effectively decreases the amplifiable concentration of a DNA sample.…”

Leading-edge forensic DNA analyses and the necessity of including crime scene investigators, police officers and technicians in a DNA elimination database

“…The very first technique (i.e. restriction fragment length polymorphism (RFLP) analysis) required large amounts of DNA to create individual genetic profiles [2], however the advent of highly sensitive PCR multiplex assays has markedly reduced that amount, insomuch that DNA deemed "undetectable" during quantification may still yield complete genetic profiles [3].…”

An Information Gap in DNA Evidence Interpretation

“…When using qualitative threshold-based methods, they seek criteria for processing only those samples having enough DNA to elevate data peaks above threshold [18], [56]. Another strategy is to report only genotype matches for major contributors to a mixture [12].…”