Being able to identify not only from whom, but also from which specific tissue, a body fluid sample collected at a crime scene is derived could help forensic investigators fine-tune their efforts to reconstruct criminal acts. And that, say researchers at Yonsei University in Seoul, is where recent advances in DNA methylation profiling come in.
"Determining the cellular source of a forensic sample is crucial because it can provide a link between sample donors who have been identified by DNA profiling and actual criminal acts," Yonsei's Hwan Young Lee says. "We expect DNA methylation will be widely applicable to forensic investigations."
In an April International Journal of Legal Medicine paper, Lee and her colleagues describe their selection of five previously reported tissue-specific differentially methylated regions, or tDMRs, for which they produced methylation profiles using bisulfite sequencing on pooled DNA from venous blood, menstrual blood, vaginal fluid, saliva, and semen. Then, using those five tDMRs as candidate markers of tissue-of-origin, the team sought to evaluate the potential of methylation profiling to accurately identify the cellular sources of body fluid samples collected from 16 study participants — 10 male, six female.
The team found that when combined, four of the tDMRs it tested — those for DACT1, USP49, PRMT2, and PFN3 — can be used to identify semen and vaginal fluid. However, the team says the fifth candidate marker it tested — a tDMR for HOX4 — is not suitable for body fluid identification, as it showed sex-specific differences in saliva sample profiles. In their paper, Lee et al. note that while they chose to interrogate five, there are nearly two dozen reported mammalian tDMRs. They also suggest that future genome-wide DNA methylation analyses using a variety of samples could be useful to identify additional body fluid-specific markers for forensic use.
Of more immediate interest to her team, Lee says, is the looming possibility of "identifying body fluid-specific epigenetic markers that would enable age-estimation of sample donors," among other predictions, which could help forensic investigators pinpoint otherwise unidentifiable sources as potential suspects. "We are planning to do research on identifying more body fluid-specific epigenetic markers and on applying ... [them] to forensic investigations," she adds.
The team also plans to streamline its approach to testing tDMRs and other epigenetic markers. "After selecting tDMRs or selecting a small set of CpG loci for forensic application, we may be able to use other methods, such as methylation-sensitive restriction enzymes ... allele-specific PCR, or single-base primer extension after bisulfite treatment" as cost-effective alternatives to traditional bisulfite sequencing, Lee says.