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

Abstract

Successful forensic DNA profiling from handled items is increasingly routine in casework. This "touch DNA" is thought to contain both cellular and acellular nucleic acid sources. However, there is little clarity on the origins or characteristics of this material. The cellular component consists of anucleate, terminally differentiated corneocytes (assumed to lack DNA), and the occasional nucleated cell. The acellular DNA source is fragmentary, presumably cell breakdown products. This study examines the relative contributions each component makes to the hand-secretions (endogenous) and hand-accumulations (exogenous) by recovering rinses from the inside and outside of worn gloves. Additionally, cellular and acellular DNA was measured at timepoints up to 2 h after hand washing, both with and without interim contact. Microscopic examination confirmed cell morphology and presence of nucleic acids. Following the novel application of a hair keratinocyte lysis method and plasma-DNA fragment purification to hand rinse samples, DNA profiles were generated from both fractions. Exogenous cell-free DNA is shown to be a significant source of touch DNA, which reaccumulates quickly, although its amplifiable nuclear alleles are limited. Endogenous DNA is mostly cellular in origin and provides more allelic information consistently over time.

Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022

“…Other recent studies on DNA-TPPR include examining prevalence and persistence of DNA or saliva from car drivers and passengers [ [310] , [311] , [312] ], evaluation of DNA from regularly-used knives after a brief use by someone else [ 313 ], studying the accumulation of endogenous and exogenous DNA on hands [ 314 ] and non-self-DNA on the neck [ 315 ], considering the potential of DNA transfer via work gloves [ 316 , 317 ] or during lock picking [ 318 ], and investigating whether DNA can be recovered from illicit drug capsules [ 319 , 320 ] or packaging [ 321 ] to identify those individuals preparing or handling the drugs.…”

High‐resolution melt analysis for the detection of skin/sweat via DNA methylation

“…"Touch DNA" (tDNA) refers to the small amount of DNA transferred via skin cells to an object when it has been handled or touched [3,4]. Previous research has suggested that these deposits are a combination of nucleated cells (secreted through pores), anucleate corneocytes (from the outermost skin layer), and possibly fragmented cell debris [5][6][7][8]. In addition, DNA recovered from touched surfaces may contain cell-free nucleic acids (CNAs) that are also present in sweat [9].…”