An evaluation of molecular and statistical methods for the attribution of body fluid sources to donors

Attributing mixed biological materials in crime stains to individual donors remains a challenge in forensic science. Characterisation of the messenger RNA (mRNA) transcripts in a biological material can be used for body fluid identification (BFID) purposes. Comparing coding region single nucleotide polymorphisms (cSNPs) in mRNA transcripts obtained from crime stains to reference cSNP profiles from known individuals presents a way to assign biological materials to donors. In this study, saliva, blood, skin, and vaginal samples were collected from eleven participants. Based on previous studies, a sequencing assay was designed targeting 23 cSNPs in single source gDNA and RNA samples to determine the potential of using Illumina MiSeq sequencing technology for BFID and donor association with cSNPs. Promising results were obtained from this preliminary study. The RNA samples displayed expression patterns typical of the biological materials they were sourced from. The expression results were investigated with principal component analysis (PCA) and incorporated into a Bayesian Network (BN) for statistical interpretation, with encouraging results. Variant calling of cSNPs had modest success. While the results showed potential for donor association, the discriminatory power and sequencing quality of some RNA transcripts limit donor attribution prospects, especially for the saliva and skin samples.