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
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, 2:1,
5:1, 10:1 and 20:1 (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.