Corneocyte lysis and fragmented DNA considerations for the cellular component of forensic touch DNA

Accumulation of endogenous and exogenous nucleic acids in “Touch DNA” components on hands

“…While the outside OV DNA level may reflect predominantly cfDNA, the OV allele total is better accounted for by PL alleles than by CF in both inside and outside (Figure 3C), likely due to relative amplification dropout levels. This is in line with authors' previous reports of fragmented DNA in anucleate corneocytes [30], although the mechanism remains obscure [56]. Mean PC was consistent across outside fractions.…”

“…Ten volunteer donors (five females, five males) were asked to wash and air‐dry their hands without interim contact as described previously [30]. UV‐sterilized nitrile gloves were placed onto the donor's hands and worn for 4 h outside the laboratory while conducting normal activities.…”

“…PL samples were resuspended in 500 μL SDW. All PL and OV samples were combined with 500 μL keratinocyte lysis buffer (described previously [30,45]) and incubated at 56°C overnight. Samples were then centrifuged (5 min, 12 000 × g) and supernatants processed as described in section 2.4.…”

“…When hand rinses were separated using flow cytometry, corneocyte cells indicated much higher levels of nucleic acid fluorescence than the subcellular fragment population [29]. Some studies report negligible DNA from these shed cells, while some yield useable DNA levels or full profiles, leaving ambiguity and variability [14,30,31].…”

“…Lysis buffers with reductants, such as DTT or β‐mercaptoethanol, and longer incubations are used for hair shaft DNA extraction [45–48]. Similar lysis methods have been reported as beneficial for improving corneocyte DNA recovery from hand rinses [30]. Both cfDNA and corneocyte DNA are likely highly fragmented, and thus, genomic DNA purification methods may limit their recovery [38] (see Supporting Information).…”