A collaborative European exercise on mRNA-based body fluid/skin typing and interpretation of DNA and RNA results.

The European Forensic Genetics Network of Excellence (EUROFORGEN-NoE) undertook a collaborative project on mRNA-based body fluid/skin typing and the interpretation of the resulting RNA and DNA data. Although both body fluids and skin are composed of a variety of cell types with different functions and gene expression profiles, we refer to the procedure as 'cell type inference'. Nine laboratories participated in the project and used a 20-marker multiplex to analyse samples that were centrally prepared and thoroughly tested prior to shipment. Specimens of increasing complexity were assessed that ranged from reference PCR products, cDNAs of indicated or unnamed cell type source(s), to challenging mock casework stains. From this specimen set, information on the overall sensitivity and specificity of the various markers was obtained. In addition, the reliability of a scoring system for inference of cell types was assessed. This scoring system builds on replicate RNA analyses and the ratio observed/possible peaks for each cell type [1]. The results of the exercise support the usefulness of this scoring system. When interpreting the data obtained from the analysis of the mock casework stains, the participating laboratories were asked to integrate the DNA and RNA results and associate donor and cell type where possible. A large variation for the integrated interpretations of the DNA and RNA data was obtained including correct interpretations. We infer that with expertise in analysing RNA profiles, clear guidelines for data interpretation and awareness regarding potential pitfalls in associating donors and cell types, mRNA-based cell type inference can be implemented for forensic casework.