Exploring the recovery and detection of messenger RNA and DNA from enhanced finger-marks in blood

Abstract

Often in the examination of bloodstained evidence discussion occurs around whether to prioritise the fingerprint evidence, or focus on the biological evidence. Collecting a sample for DNA profiling could result in the loss of ridge detail that could have been used for fingerprint comparison. When the finger-marks are not clearly visible, chemical enhancement techniques are applied to the surface which could reduce or degrade the cellular material obtained. Previous forensic casework has highlighted circumstances where, after enhancement had been performed, it would be extremely valuable to both identify the body fluid present in a fingermark, and generate a DNA profile from the same sample, after enhancement procedures have been applied. This project further develops a novel body fluid identification technique by assessing the effects of chemical enhancement on the ability to detect a specific messenger RNA (mRNA) marker, Glycophorin A, which indicates the presence of blood. We treated several series of visible and latent finger-marks made in blood, using the most common blood-enhancement methods employed in New Zealand, including aqueous amido black, methanol-based amido black, acid yellow and leucocrystal violet. The treated finger-marks were collected, and using a modified DNA IQ™ system, DNA and RNA were co-isolated from the same sample. The mRNA was analysed using CellTyper, the PCR multiplex developed by ESR. DNA profiling was generally successful, even after those treatments which are often considered detrimental to DNA recovery from trace samples. Consistent with previously documented impacts of enhancement procedures on DNA profiling, it appears that even with visible fingermarks, leucocrystal violet can reduce the effectiveness of subsequent mRNA profiling. Aqueous amido black and acid yellow may also have adverse effects on mRNA profiling of depleted finger-marks with low levels of cellular material. While we have shown that mRNA profiling of finger-marks can be successful even after being enhanced for fingerprint analysis, it may still be necessary to prioritise evidence types in certain circumstances. These results should help with forensic decision-making by expanding knowledge of the extent of the detrimental effects of blood-enhancement reagents on DNA profiling and body fluid identification using mRNA profiling.