Body fluid mixtures; resolution using forensic microRNA analysis

Body fluid identification is a crucial aspect of forensic biology; particularly in sexual assaults which is usually characterised as a mixture of body fluids. Whilst there are considerable efforts to identify single source body fluids using genetic markers; no substantial research appears to have been carried out on mixed body fluids. This is a potentially complex area and before such genetic based body fluid identification can be utilised, an understanding of the effects of mixtures on the results is required. Can body fluid mixtures be identified and if so, what is the value of the information gained?
Samples of blood and saliva were acquired from volunteers with informed consent. The samples underwent total RNA extraction. A range of mixtures were then prepared in the mixing ratios of 1:1, 5:1, and 10:1 (both with blood and then with saliva as the major contributor). Single source controls were included. All samples then underwent stem-loop reverse transcription and quantitative PCR analysis targeting blood and saliva specific microRNA markers using commercially available kits.
When compared with the single source controls, the mixed body fluid samples could be easily identified. By comparing the samples with the 1:1 blood/saliva mixture, the major and minor contributor for each body fluid mixture could be correctly identified. Finally, when compared with the mixed DNA results, the major body fluid could be correctly associated with the major DNA contributor and vice versa.