Evaluation of mRNA specific markers using a pentaplex system for the identification of skin and saliva from contact trace evidence

Abstract

A vast number of mRNA markers have been proposed for the identification of the source of biological stains recovered from crime scenes. Blood, semen, saliva, menstrual blood, vaginal secretions, urine and skin represent the majority of sample types in body fluid identification. However, certain sample types, such as blood, may not be considered as main targets for identification in comparison to “non-coloured” and contact trace evidence given the high sensitivity of the currently available STR typing kits and which are frequently found at crime scenes. Skin and saliva are examples of such evidentiary material and are often present as single sources or mixture, representing a greater challenge for identification. In this work, a pentaplex mRNA identification system was developed and optimised for the analysis of three skin genes LCE1C, LOR and CDSN and two saliva genes, HTN3 and STATH in one single end-point PCR reaction. The specificity of the selected mRNA transcripts was evaluated through the analysis of several saliva and skin samples (cross-reactivity testing) and in addition, sensitivity was analysed by testing common objects of contact trace evidence such as telephone mouthpiece, keyboards, bottles, computer mouse, pens, etc. Results supported the high specificity of these markers for a straightforward discrimination of skin and saliva and demonstrated LCE1C as the most sensitive skin mRNA marker in the low trace evidence samples. The five skin and saliva mRNA markers optimised in a pentaplex system revealed to be highly specific, sensitive and a useful tool to distinguish between skin and saliva body fluid/tissue types.