PCR inhibition is a key challenge in forensic DNA analysis. Substances interfering with the amplification of PCR products can lower the success rate of Short Tandem Repeat (STR) analysis or generate ambiguous DNA profiles.
For forensic DNA laboratories it is therefore vital to have knowledge about how common inhibitory substances affect their STR analysis system. We have developed a broad-range panel of standardized PCR-inhibitory reference materials (RMs), representing the heterogeneous stains found at crime scenes. The panel, including solutions prepared from for example cigarette paper,
chewing gum, moist snuff and humic acid, is a tool for quality evaluation of STR systems. We applied the RMs to challenge PowerPlexÂ® ESX 16 Fast System (ESX Fast). Although ESX Fast tolerated high levels of some inhibitors, several RMs caused problems in different ways. Humic acid had a specific negative effect on amelogenin amplification, moist snuff hindered amplification of longer fragments, and chewing gum caused generally lowered allele peak heights. These different effects may provide information regarding the mechanisms of inhibition. For instance, our results indicate that one effect of humic acid on ESX Fast analysis is chelation of Mg2+ ions, thus altering the melting temperatures of the primers. In the developmental validation of STR systems, a limited evaluation of PCR inhibition involving only a few substances is generally performed. Applying a broad panel of RMs will ensure that a wider range of inhibitory substances from crime scene samples are included, giving a better understanding of inhibitor tolerance and effects.
2015. 226- p.