Retrospective study of the impact of miniSTRs on forensic DNA profiling of touch DNA samples

The theoretical advantages of miniSTRs are undeniable. Several studies show that miniSTRs are more sensitive and robust in the analysis of low template and degraded DNA. In this study we want to show the overall benefit of using miniSTRs in real forensic casework samples and show the percentage of samples that benefit from analysis with additional miniSTR loci in terms of resulting in a useful profile. The considered samples were 3064 touch DNA samples, analyzed in our accredited routine forensic DNA profiling laboratory between mid 2009 and mid 2013. Of these 3064 samples, 618 samples were analyzed using 13 loci, 532 samples using 15 loci and 1914 samples using 20 loci of which 5 were the mini- and midi-STR loci that were added to the extended European Standard Set (ESS). The retrospective results show a small increased success rate after implementation of extra loci and an even smaller increase after the implementation of the mini- and midi-STR analysis. The percentage of touch DNA samples that benefit from the analysis of additional mini- and midi-STR loci is limited.