Touch DNA is widely used in forensic casework and observed to be of low quantity and degraded quality. Research collecting touch DNA following established activity often fails to consider resolving how much of one’s own DNA is accumulated through endogenous secretion versus exogenous handling. The material from donors’ hands must be parsed appropriately into constituent parts and examined.
They have isolated material accumulated from the hands themselves, versus external contact and they further separated cells from cfDNA to assess accumulation at timepoints after washing. This knowledge has implications for our fundamental understanding of transfer DNA. It may inform best practices for collection and recovery as well as aid DNA profile evaluation from touched samples.
The data from this study indicated that more DNA accumulated on their hands from the environmental contact than those from the hands of themselves. A large proportion of this externally derived DNA was one’s own DNA and was acellular, yet it’s provenance was not their hands themselves, underscoring the ubiquity of DNA transfer.
Corneocytes may be the primary DNA contributor in the endogenously accumulated deposits, when lysis and purification methods enhancing their DNA recovery were used. DNA accumulated quickly on hands, within 15 min following washing, but as a result of regular activity rather than secretion. “Shedder status,” if assessed following contact, might reflect accumulation of one’s DNA from elsewhere on the body, possibly a behavioral variable as much as an intrinsic status; or a “good shedder” may reflect an individual with a higher secretion of the rarely observed but highly impactful nucleated cells.
If DNA from the hands is minimal compared to DNA accumulated through contact, then most “touch DNA” may be “transfer DNA,” even if it is one’s own. Given the meaning attached to DNA profiles that have transferred onto incriminating items, it is significant to understand that transfer may be the origin of most touch DNA, occurring more frequently and at higher levels than was previously understood.
This is critical as forensic scientists are increasingly asked to report and explain touch DNA and DNA transfer in a courtroom. Most key at this juncture is further exploration of touch deposit contents, whether cfDNA or cellular, whether endogenously or exogenously accumulated.