The impact of illicit drugs on DNA extraction efficiency

The analysis of illicit drugs for the presence of human DNA provides an opportunity to gain greater information on 'who' is involved in the illicit drug supply chain, complementing the existing chemical profiling techniques to identify 'what' and 'where'. Given the known inhibitory effect of numerous illicit drugs and related compounds on PCR, it is crucial to understand the effectiveness of currently used DNA extraction kits to successfully remove these compounds while extracting sufficient DNA for downstream DNA profiling. To do this, four common illicit drugs (methamphetamine HCl, heroin HCl, MDMA HCl and GHB Na) in addition to two precursors of methamphetamine (pseudoephedrine HCl and phenyl-2-propanone) were spiked with saliva and DNA extracted. Two DNA extraction kits were selected to evaluate columns compared to beads, the QIAGEN QIAamp® DNA Investigator kit and the Promega DNA IQ™ system. DNA quantification of these samples yielded significantly more DNA recovery for each drug, except P2P, when extracted using DNA Investigator. Similarly, peak heights and heterozygous peak height balance were, on average, improved when samples were extracted with DNA Investigator compared to DNA IQ. Regardless of drug or extraction kit, no inhibition was detected during DNA quantification or profiling, indicating reduced DNA yields were caused by inefficient DNA extraction rather than inhibition of the PCR processes. All samples extracted using DNA Investigator yielded complete DNA profiles while DNA IQ yielded near-complete profiles, ultimately resulting in extremely strong likelihood ratio values from all samples. The generation of informative DNA profiles, despite the presence of illicit drugs, using two commercially available DNA extraction kits highlights the potential to implement these sample types into operational laboratories.