[DNA amplification on chemically structured chips in forensic STR analysis]. / Amplifikation von DNA auf chemisch strukturierten Chips in der forensischen STR-analyse.

The present study deals with low-volume amplification of short tandem repeats (STRs) for forensic DNA analysis. A chemically structured chip in microscopic slide format was used to amplify standard forensic casework samples in a 1-microL reaction volume primarily with the well-known and widely used PowerPlex kit and with other commercially available STR kits. Tests regarding sensitivity, mixture analysis, robustness, reproducibility, buffer composition and technical performance were carried out to check the usefulness of this amplification strategy. The results obtained show that low-volume amplification is a promising option in the forensic DNA typing toolbox. Restrictions to this method, which are strictly related to the kit and the respective buffer used, were found in low copy number (LCN) DNA typing, mixture analysis and technical performance. Problematic typing results included artefact alleles, increase in locus and heterozygote imbalance, allelic and locus dropout as well as increase of stutters, especially when amplifying less than 200-300 pg of DNA. In contrast, convincing advantages are a higher sensitivity, better amplification efficiency and the low cost factor of this method.

Forensic validation of the SNPforID 52-plex assay.

The advantages of single nucleotide polymorphism (SNP) typing in forensic genetics are well known and include a wider choice of high-throughput typing platforms, lower mutation rates, and improved analysis of degraded samples. However, if SNPs are to become a realistic supplement to current short tandem repeat (STR) typing methods, they must be shown to successfully and reliably analyse the challenging samples commonly encountered in casework situations. The European SNPforID consortium, supported by the EU GROWTH programme, has developed a multiplex of 52 SNPs for forensic analysis, with the amplification of all 52 loci in a single reaction followed by two single base extension (SBE) reactions which are detected with capillary electrophoresis. In order to validate this assay, a variety of DNA extracts were chosen to represent problems such as low copy number and degradation that are commonly seen in forensic casework. A total of 40 extracts were used in the study, each of which was sent to two of the five participating laboratories for typing in duplicate or triplicate. Laboratories were instructed to carry out their analyses as if they were dealing with normal casework samples. Results were reported back to the coordinating laboratory and compared with those obtained from traditional STR typing of the same extracts using Powerplex 16 (Promega). These results indicate that, although the ability to successfully type good quality, low copy number extracts is lower, the 52-plex SNP assay performed better than STR typing on degraded samples, and also on samples that were both degraded and of limited quantity, suggesting that SNP analysis can provide advantages over STR analysis in forensically relevant circumstances. However, there were also additional problems arising from contamination and primer quality issues and these are discussed.