The authors previously performed proof-of-concept studies using a prototype Illumina MiSeq MPS cSNP assay to demonstrate the usefulness of this approach, and the current article reports on their continuation of this work and introducing an MPS assay on the Ion S5 system comprising a set of 21 cSNPs in body fluid specific mRNA transcripts [7 blood (3 genes), 8 semen (4 genes), and 6 saliva (4 genes)].
Biological traces found at crime scenes can be analyzed to genetically identify the donor(s) but also to determine the body fluid composition of the stain. The latter can be accomplished with high specificity by mRNA profiling. In some mixed body fluid samples, it might be of probative value to directly associate each body fluid with each of the DNA donors. Associating a DNA profile to the contributing body fluid is often not possible, with the exception of simple binary mixtures that contain male and female specific body fluids; however, genomic information is transferred from DNA to mRNA, and RNA-cSNPs (coding region SNPs) should be identifiable by MPS methods. The current study found that combined with optimized primer sets for body fluid identification, the assay can identify all forensically relevant body fluids and skin as well as differentiating blood, semen, and saliva transcripts from different individuals. The assay has been evaluated with numerous donors of each body fluid to evaluate the specificity and the discriminatory power of the cSNPs. The findings are promising, since donors could be associated with body fluids in mixtures of body fluids; however, more cSNPs are needed to improve the discriminatory power, particularly for vaginal secretions and menstrual blood transcripts. Assigning body fluids to DNA donors is a realistic possibility with the continued development of MPS cSNP assays. (publisher abstract modified)