Really the best of both? Application of an mRNA/miRNA multiplex assay to casework samples, animal samples, and a storage study

The identification of body fluids is an important area of forensic genetics. In particular, the susceptibility to degradation of casework samples is of crucial importance, as the traces can often be exposed to different environmental conditions over a long period of time. RNAs especially are used as molecular markers for the identification of body fluids in forensics. Messenger RNAs (mRNAs) show an increased susceptibility to degradation, e.g. under humidity and UV radiation but are highly body fluid-specific. The shorter micro RNAs (miRNAs), however, are less susceptible to degradation, but only a few body fluid-specific markers could be investigated. In this study, a self-developed mRNA/miRNA multiplex assay for capillary electrophoresis from a preliminary study was further adapted and validated. The approach was applied to casework samples, animal samples, and a storage study. The advantages and disadvantages of the mRNA/miRNA assay were investigated in order to review a possible application for forensic casework. Some miRNA markers were also detected in animal samples, which once again underlines the possible non-specificity of miRNAs. In the storage study, the different markers were detected for different lengths of time depending on the body fluid examined. For almost all body fluids, the miRNA markers were still detectable after a period of 35 days under environmental conditions compared to the mRNA markers. The mRNA peaks were often already clearly reduced or no longer detectable after 14 days. The results show the advantage of the new mRNA/miRNA assay compared to established mRNA approaches, especially for older and degraded samples, but the assay has its limitations due to the limited number of specific miRNA markers.